**4. Conclusions**

In anticipation of COVID-19 demands upon nursing staff and subsequent potential weakening of care levels in the provision of patient care, specifically in the ICU setting, a panel was formed to raise and answer critical concerns. The nursing surge capacity of critically ill patients with COVID-19 in the ICU was addressed through searching available evidence. Substantiation was retrieved from a variety of databases inclusive of published and unpublished studies. The retrieved studies were then reviewed by a minimum of two reviewers independently using JBI critical appraisal tools. The recommendations in the recent guidelines covered ICU nursing surge capacity strategies. We recommend that hospitals implement the evidence-based strategies that have been shown to be effective such as a team-based approach, and to establish other innovative strategies for ICU nursing staff surge capacity in the COVID-19 pandemic. As new evidence presents itself, further updates of the guideline will be issued.

**Author Contributions:** A.A.M.–Conception, manuscript preparation; A.A.–Conception; Z.A.–Manuscript preparation; K.A.S.–Manuscript preparation; D.S.–Manuscript preparation. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** Authors acknowledge Sulaiman Al Habib Research Center that supported this research.

**Conflicts of Interest:** The authors declare no conflict of interest.


**2.5 Nanocrystal and nanosuspension**

Aggregated structures are formed through the combination of various particles in crystalline form coated with surfactant combinations which impart static and electrostatic surface stabilization. Such nanocrystal and nanosuspension aggregated materials lessen bioavailability and absorption issues due to its resolved formulation. Nanocrystal size permits safe and effective passage via the capillaries. Reconfigurated solid lipid nanoparticles owe discrete reward of unique carrier systems over liposomes and polymeric nanoparticles due to solid lipid matrix owing to 1 μm diameter where drug gets easily incorporated. Such nanoparticle/nanosystems for clinical usage are obtained by high-pressure homogenization that uses varied surfactants to avoid aggregation and imparts dispersion stability. Reconfigurated cationic solid lipid colloidal nanoparticles are prepared and used for liposomal transfection agents besides gene transferring dominant for in vitro [1, 3, 15–18].

**121**

*Nanomaterials via Reconfiguration of Skeletal Matrix DOI: http://dx.doi.org/10.5772/intechopen.86818*

preferred in micro-electromechanical usage [1–3].

Silicon-based nanostructures are reconfigured by means of assorted techniques

including etching, photolithography and deposition. Materials like porous silicon, silica and silicon dioxide are facile to reconfigure as the calcified nanopores, nanoparticles and nanoneedles. Assorted porous hollow silica nanoparticle suspensions owing sacrificial nanoscale templates mostly involved the usage of sodium silicate as a precursor. Such reconfigurated silicon-derived materials can offer effective delivery of drugs like porous silicon-embedded platinum which is applied for many usages like antitumour drug release and carrier for antibody, antibiotic, enzyme and DNA. These materials also act as good semiconductors and thus

Polymeric micelle assemblies are reconfigured through amphiphilic block copolymers which impart nanoscopic supramolecular core shells as aggregates in solutions. In such micelles, the reconfigured components get ordered as spheroidal owing to hydrophobic core shells that are water secured due to hydrophilicity. Many components owing to hydrophobic and hydrophilic portions are reconfigured like amphiphilic AB, or ABA kind of block copolymeric units yield polymeric micelles as nanoscopic supramolecular core shells as aggregates in solutions [1–3]. Nanoscience technology has reconfigurated assorted supramolecular architectures as a result of self-assemblage of amphiphilic block polymers through hydrophobic/hydrophilic effects, electrostatic interactions, hydrogen bonding and metal complexation which proffer sharp structures and precise functionalities for their usages in biomedical purpose. Such polymeric micelles fascinated special attention in drug/gene release by virtue of outstanding biocompatibility, less toxicity, more blood circulation and enhanced solubility in its innate micellar core shells. Polymeric micelles act as 'smart drug carriers' due to binding of specific ligand onto proactive surfaces which aids targeted/formulated stimuli sensitivity found devoid in their counterparts. Selfassemblage in block/graft copolymers occurs in selective solvents spontaneously reconfigured as supramolecular assemblies owing to cylindric and vesicular core shells of 10–100 nm shape/size nanomaterials called polymeric micelles. Spherical reconfigured core-shell size/morphology gets crucially varied with chemical structures and compositions of constituent block copolymers besides exhibited elevated thermodynamic/kinetic stabilities over surfactant micelles. Polymeric micelle yields through advanced reconfigurations own an external hydrophilic nanoshell that assists in prolonged residency in blood, besides gathering in tumor-specific zone due to more permeation, and thus acts as a novel vehicle for sparingly soluble (hydrophobic) drugs. Polymeric micelles have shown adaptability to various ligands which aids active targeted delivery by virtue of better solubility and improved pharmacokinetics besides no adverse effects. Great interest is generated by these micelles in technological advancements due to remarkably stable and bendable

physicochemical features exhibited with various stimuli [1–3, 19].

Nano-array of polymer-based nano-conjugates obtained from different natural sources own modern functions besides specific and targeted drug delivery. The natural polymeric reconfigured nanoparticles are biocompatible, less toxic across many bio-membranes against various pH and non-immunogenic and appear to be extra stable to volatile pharmaceutical agents besides offering low-cost fabrication at

**2.8 Biopolymeric nanoparticles**

**2.6 Silicon-based nanomaterials**

**2.7 Nano-micelles**

*Nano-dendrimer synthetic route: block polymerization and chemical cross-linking.*


**2.1 Economy, agriculture and social development**

Although the agricultural sector continues to dominate Kenya's economy, only 15–20% of Kenya's total land area has sufficient fertility and rainfall to be farmed, but only 7–8% of the land can be classified as first-class agricultural land. A considerable number of Kenyans make their living off the land, but this trend has continued to decline from the 1980s for various reasons including: rural–urban migration, the low economic gains from the sector, population growth and conversion of agricultural land to residential land, and, sub-division for purposes of inheritance, etc.

Agriculture is the second largest contributor to Kenya's gross domestic product (GDP) after the service sector and fundamentally drives the country's economy, as about 75% of Kenyans earn all or part of their income from the sector. Agriculture generally accounts for 33% of the nation's GDP, but its contribution to the country's GDP has continued to fluctuate over the years as agricultural productivity has either stagnated or declined. This has been observed for major food crops such as wheat and rice. Furthermore, the 15–20% of Kenya's land area that is regarded as suitable for farming is not also utilized efficiently.

Recurrent crises such as drought add to the agriculture-related challenges which largely contribute to the high malnutrition levels in the country. In 2005, agriculture, including forestry and fishing, accounted for 18% of wage employment and 50% of revenue from exports. For decades, the principal cash crops have remained tea, horticultural produce and coffee, with horticultural produce and tea being the major earners of foreign exchange. Horticultural produce and tea accounted for 23% and 22% of total export earnings, respectively. Coffee which has declined in importance due in part to depressed world prices and the decline of land under the crop, accounted for just 5% of export receipts in 2005. The production of major food staples such as maize is subject to sharp weather-related fluctuations. Declines in maize production often times leads to the need for Government to appeal for food aid, as was witnessed in 2004, and even lately in 2016–2017, when as many as 1.8–2.0 million people needed food relief. The expansion of credit to the agricultural sector by the financial sector has enabled farmers to better deal with the large risk of agriculture based on seasonal rainfall and dramatic fluctuations of the prices of agricultural commodities. The expansion of the area under irrigation is another major food policy issue for government as it works to find ways of increasing food production.

**97**

*Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges…*

Tea, coffee, sisal, pyrethrum, maize, and wheat are grown in the fertile Kenya highlands, which is one of the most successful agricultural production regions in Africa. However, the production of sisal and pyrethrum is declining to levels where there may be no production of these two crops in the near future for various reasons

Local livestock breeds (Boran and Zebu) predominate in the semi-arid savanna

Kenya Vision 2030, the development blue print for the country, was initiated in 2013 by Emilio Mwai Kibaki, the 3rd President of Kenya. It has the economic, social and political pillars as its anchors; the economic pillar aims at improving the prosperity of all Kenyans through an economic development programme, covering all the regions of Kenya. It aimed to achieve a GDP growth rate of 10% per annum beginning in 2004, but the country has consistently fallen short of the target every subsequent financial year. However, to work towards achieving the target, Kenya is continuing with the tradition of macro-economic stability that has been established since 2002. The New Administration of President Uhuru M. Kenyatta has picked up some key economic deliverables in the Vision, in what in 2018, it has characterized

Through the economic pillar and strategy, Kenya aims to build a just and cohesive society with social equity available to all its citizens and enable them live in a clean and secure environment. The vision presents comprehensive social interventions for improving the quality of life of all Kenyans and Kenyan residents. The strategy contains special provisions to help persons living with various disabilities and previously marginalized communities, who may lack a good education, are unemployed and experience poor nutritional status due to high poverty prevalence among them. These policies (and those in the economic pillar) are equally anchored on an all-round strategy of adopting science, technology and innovation (STI) as the implementation tool. The STI concentrates in certain areas for it to contribute to

to the north and east of the country, but exotic dairy breeds such as Friesian, Ayrshire, Sahiwal and crosses of the exotic and local Zebu cattle are kept in the highlands and mid altitudes, with the latter region sustaining the beef breeds. Cash and food crops including coconuts, pineapples, cashew nuts, sugarcane, and maize

*DOI: http://dx.doi.org/10.5772/intechopen.95036*

are grown in most parts of the country.

as "The Big Four." These are:

1.Universal Healthcare,

3.Affordable Housing and

the success of the initiative, including:

• Education and vocational/technical training

2.Manufacturing,

4.Food Security,

• Healthcare

• Water and sanitation

• Housing and urbanization

• The environment

which are outside the realm of the current discussion.

*Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges… DOI: http://dx.doi.org/10.5772/intechopen.95036*

Tea, coffee, sisal, pyrethrum, maize, and wheat are grown in the fertile Kenya highlands, which is one of the most successful agricultural production regions in Africa. However, the production of sisal and pyrethrum is declining to levels where there may be no production of these two crops in the near future for various reasons which are outside the realm of the current discussion.

Local livestock breeds (Boran and Zebu) predominate in the semi-arid savanna to the north and east of the country, but exotic dairy breeds such as Friesian, Ayrshire, Sahiwal and crosses of the exotic and local Zebu cattle are kept in the highlands and mid altitudes, with the latter region sustaining the beef breeds. Cash and food crops including coconuts, pineapples, cashew nuts, sugarcane, and maize are grown in most parts of the country.

Kenya Vision 2030, the development blue print for the country, was initiated in 2013 by Emilio Mwai Kibaki, the 3rd President of Kenya. It has the economic, social and political pillars as its anchors; the economic pillar aims at improving the prosperity of all Kenyans through an economic development programme, covering all the regions of Kenya. It aimed to achieve a GDP growth rate of 10% per annum beginning in 2004, but the country has consistently fallen short of the target every subsequent financial year. However, to work towards achieving the target, Kenya is continuing with the tradition of macro-economic stability that has been established since 2002. The New Administration of President Uhuru M. Kenyatta has picked up some key economic deliverables in the Vision, in what in 2018, it has characterized as "The Big Four."

These are:

*Food Security in Africa*

Sudan.

**2. Kenya**

inheritance, etc.

potential and are associated with high poverty indices and therefore poor food and nutrition security. Nomadic pastoralism based on livestock keeping is the major mode of production and livelihood in these semi-arid areas. The region's vegetation is composed of thick woodlands and grassland in the high and wetter elevations, to scanty, thorny shrub and vegetation to desert terrain in the arid and semi-arid plains, respectively. South Sudan is hot with seasonal rainfall as influenced by the annual shift of the Inter-tropical Convergence Zone. Rainfall is heaviest in the southern highlands and reduces towards the north as it merges into the Republic of

This chapter examines the economic, food and nutrition security situation in Kenya, Uganda and Tanzania. For each country, some recommendations that are likely to improve food and nutrition security in the long-term are provided.

Although the agricultural sector continues to dominate Kenya's economy, only 15–20% of Kenya's total land area has sufficient fertility and rainfall to be farmed, but only 7–8% of the land can be classified as first-class agricultural land. A considerable number of Kenyans make their living off the land, but this trend has continued to decline from the 1980s for various reasons including: rural–urban migration, the low economic gains from the sector, population growth and conversion of agricultural land to residential land, and, sub-division for purposes of

Agriculture is the second largest contributor to Kenya's gross domestic product (GDP) after the service sector and fundamentally drives the country's economy, as about 75% of Kenyans earn all or part of their income from the sector. Agriculture generally accounts for 33% of the nation's GDP, but its contribution to the country's GDP has continued to fluctuate over the years as agricultural productivity has either stagnated or declined. This has been observed for major food crops such as wheat and rice. Furthermore, the 15–20% of Kenya's land area that is regarded as suitable

Recurrent crises such as drought add to the agriculture-related challenges which largely contribute to the high malnutrition levels in the country. In 2005, agriculture, including forestry and fishing, accounted for 18% of wage employment and 50% of revenue from exports. For decades, the principal cash crops have remained tea, horticultural produce and coffee, with horticultural produce and tea being the major earners of foreign exchange. Horticultural produce and tea accounted for 23% and 22% of total export earnings, respectively. Coffee which has declined in importance due in part to depressed world prices and the decline of land under the crop, accounted for just 5% of export receipts in 2005. The production of major food staples such as maize is subject to sharp weather-related fluctuations. Declines in maize production often times leads to the need for Government to appeal for food aid, as was witnessed in 2004, and even lately in 2016–2017, when as many as 1.8–2.0 million people needed food relief. The expansion of credit to the agricultural sector by the financial sector has enabled farmers to better deal with the large risk of agriculture based on seasonal rainfall and dramatic fluctuations of the prices of agricultural commodities. The expansion of the area under irrigation is another major food policy issue for government as it works to find ways of increasing food

**2.1 Economy, agriculture and social development**

for farming is not also utilized efficiently.

**96**

production.

Through the economic pillar and strategy, Kenya aims to build a just and cohesive society with social equity available to all its citizens and enable them live in a clean and secure environment. The vision presents comprehensive social interventions for improving the quality of life of all Kenyans and Kenyan residents. The strategy contains special provisions to help persons living with various disabilities and previously marginalized communities, who may lack a good education, are unemployed and experience poor nutritional status due to high poverty prevalence among them. These policies (and those in the economic pillar) are equally anchored on an all-round strategy of adopting science, technology and innovation (STI) as the implementation tool. The STI concentrates in certain areas for it to contribute to the success of the initiative, including:

### **2.2 Food and nutrition security**

Kenya has a current population of 47.6 million [4] and is generally regarded as water-deficient and food and nutrition insecure. It suffers from frequent droughts and famines with as many as 2–3 million people affected every time a famine or drought occurs, and, about 10 million suffering from chronic food insecurity and poor nutrition. Most of those affected live in the pastoral, semi-arid and arid areas of the country located in the North, Northeast and Northwest of the country, although parts of the Upper Eastern that include the Counties of Kitui, Makueni and Tana River County in the Coastal Region (**Figure 2**), are often also affected. Some of these arid and semi-arid zones receive as little 5–30 inches or more of rain annually. The other category of consumers that is often affected by food and nutrition insecurity is the slum dwellers, who constitute a considerable percentage of the country's population, and, live in the inner cities of the major urban settlements. The Cities of Nairobi, Mombasa, Kisumu, Nakuru and Eldoret hold about 20% of the country's population and will therefore require significant attention in the effort to reduce food and nutrition insecurity in the country. Malnutrition is a public concern and is the single most important contributor to child mortality which stood at 30.6% in every 1000 births by 2018 down from 33.3% in 2015. Malnutrition is mainly due to inadequate food intake and disease, with the underlying factors being poor child care practices, household food insecurity, and inadequate sanitation and health care services, among others. Most of the indicators on food availability, access and affordability, poverty levels and nutritional status are obtained through statistics generated from the Integrated Household Budget Surveys (IHBS) and the Kenya Household and Dietary Surveys (KHDS). The latest IHBS and KHDS were done in 2011 and 2014, respectively. The IHBS surveys show different levels of food poverty across the former eight Kenyan Administrative Provinces, which were abolished after the promulgation of the new Kenya Constitution in 2010 [5].

**99**

businesses.

*Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges…*

They were replaced by 47 Counties, which came into being in March 2013. The IHBS of 2011 showed food poverty levels of 31, 45, 46, 50, 51, 64 and 66% for the then Central, Eastern, Nyanza, Rift Valley, Western, Coast and Northeastern Provinces, respectively. It is likely that the indicators have declined in some of the regions between then and now. Low indicators are normally apparent in the Provinces where nomadic pastoralists are a significant percentage of the population. The pastoralist, semi-arid and arid areas that compose about 70% of the country's land mass and hold about 30% of the human population, are some of the poorest regions of the country, with the worst food poverty, nourishment, health and sanitation indicators. In the counties where nomadic pastoralism dominates as a form of resource use and production, the factors that seem to be major drivers of food and nutrition insecurity include weather anomalies, water scarcity, ethnic resource-based conflicts and displacements, high food prices, depressed livestock sales prices, hardships associated with migration in search of water and pasture for livestock herds by the nomads, cross-border conflicts and livestock pest and disease outbreaks. Climate variability is an ongoing phenomenon that is affecting food production. The rest of the country falls under the agrarian belt, where arable farming is practised. In the agrarian belt, the major drivers for food and nutrition insecurity include poor transport infrastructure, poor market access for farm produce, climate variability, late arrival of government subsidized fertilizer and agro-chemicals, late payments to farmers for crop delivered to depots of the National Cereals and Produce Board, poor management of farmers' cooperatives, depressed food sales prices and crop pests and livestock diseases. Grossly inadequate storage facilities and poor handling and storage practices for cereal grain, pulses and oil seeds, also contribute to food and nutrition insecurity as considerable amounts of produce is lost through microbially-mediated deterioration and pest infestation. Poor purchase prices, delayed payments of deliveries to National Government grain depots, often encourage sales of surplus harvest to middlemen, who despite offering modest prices compared to government agencies have the advantage of on-the-spot cash payments for produce bought. It is envisaged that the provision of storage facilities through the National Cereals and Produce Board, Co-operatives, improvement in road infrastructure, the expansion of rural electrification programmes, adoption of climate-smart agriculture, diversification of the food supply and diets, especially an increase in consumption of fruits and vegetables will lower food and nutrition

security indicators and improve consumer nutritional status and health.

The mortality rate of Kenyan children under age five has fallen steadily since 2000 [6], but remains of grave concern. On the positive side, the level of undernourishment among Kenya's children fell in 2001–2003 and again in 2013–2015, but recurring droughts have led to a noticeable rise in levels. A decline was also recently observed after the 2016–2017 drought which affected Kenya and her neighbors, and which resulted in drops in agricultural production, increases in food prices [7, 8], and the consumption of inadequate food of low calorie and protein content. The impact of the current COVID-19 pandemic is expected to be disastrous as agricultural production is expected to fall arising from the lengthy lockdowns and restrictions of movement of goods, people, the imposed curfews and the closing down of

Kenya's child stunting and child wasting levels have also fallen considerably,

with the stunting rate dropping from 35.2–26.0%, and the wasting rate falling from 7.0–4.0% in 2008–2009 and in 2014 [9, 10]. Levels vary substantially between regions and counties, with some having values significantly higher than the national averages. The highest child stunting percentages were found in Kitui County and West Pokot at 45.8% and 45.9%, respectively [10]. Although these Counties have high poverty levels (48 and 57%, respectively, based on national

*DOI: http://dx.doi.org/10.5772/intechopen.95036*

**Figure 2.** *GHI for Kenya's regions.*

#### *Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges… DOI: http://dx.doi.org/10.5772/intechopen.95036*

They were replaced by 47 Counties, which came into being in March 2013. The IHBS of 2011 showed food poverty levels of 31, 45, 46, 50, 51, 64 and 66% for the then Central, Eastern, Nyanza, Rift Valley, Western, Coast and Northeastern Provinces, respectively. It is likely that the indicators have declined in some of the regions between then and now. Low indicators are normally apparent in the Provinces where nomadic pastoralists are a significant percentage of the population. The pastoralist, semi-arid and arid areas that compose about 70% of the country's land mass and hold about 30% of the human population, are some of the poorest regions of the country, with the worst food poverty, nourishment, health and sanitation indicators. In the counties where nomadic pastoralism dominates as a form of resource use and production, the factors that seem to be major drivers of food and nutrition insecurity include weather anomalies, water scarcity, ethnic resource-based conflicts and displacements, high food prices, depressed livestock sales prices, hardships associated with migration in search of water and pasture for livestock herds by the nomads, cross-border conflicts and livestock pest and disease outbreaks. Climate variability is an ongoing phenomenon that is affecting food production. The rest of the country falls under the agrarian belt, where arable farming is practised. In the agrarian belt, the major drivers for food and nutrition insecurity include poor transport infrastructure, poor market access for farm produce, climate variability, late arrival of government subsidized fertilizer and agro-chemicals, late payments to farmers for crop delivered to depots of the National Cereals and Produce Board, poor management of farmers' cooperatives, depressed food sales prices and crop pests and livestock diseases. Grossly inadequate storage facilities and poor handling and storage practices for cereal grain, pulses and oil seeds, also contribute to food and nutrition insecurity as considerable amounts of produce is lost through microbially-mediated deterioration and pest infestation. Poor purchase prices, delayed payments of deliveries to National Government grain depots, often encourage sales of surplus harvest to middlemen, who despite offering modest prices compared to government agencies have the advantage of on-the-spot cash payments for produce bought. It is envisaged that the provision of storage facilities through the National Cereals and Produce Board, Co-operatives, improvement in road infrastructure, the expansion of rural electrification programmes, adoption of climate-smart agriculture, diversification of the food supply and diets, especially an increase in consumption of fruits and vegetables will lower food and nutrition security indicators and improve consumer nutritional status and health.

The mortality rate of Kenyan children under age five has fallen steadily since 2000 [6], but remains of grave concern. On the positive side, the level of undernourishment among Kenya's children fell in 2001–2003 and again in 2013–2015, but recurring droughts have led to a noticeable rise in levels. A decline was also recently observed after the 2016–2017 drought which affected Kenya and her neighbors, and which resulted in drops in agricultural production, increases in food prices [7, 8], and the consumption of inadequate food of low calorie and protein content. The impact of the current COVID-19 pandemic is expected to be disastrous as agricultural production is expected to fall arising from the lengthy lockdowns and restrictions of movement of goods, people, the imposed curfews and the closing down of businesses.

Kenya's child stunting and child wasting levels have also fallen considerably, with the stunting rate dropping from 35.2–26.0%, and the wasting rate falling from 7.0–4.0% in 2008–2009 and in 2014 [9, 10]. Levels vary substantially between regions and counties, with some having values significantly higher than the national averages. The highest child stunting percentages were found in Kitui County and West Pokot at 45.8% and 45.9%, respectively [10]. Although these Counties have high poverty levels (48 and 57%, respectively, based on national

*Food Security in Africa*

• Gender, youth and vulnerable groups

• Equity and poverty elimination, and,

**2.2 Food and nutrition security**

• National reconciliation, integration and cohesion

Kenya has a current population of 47.6 million [4] and is generally regarded as water-deficient and food and nutrition insecure. It suffers from frequent droughts and famines with as many as 2–3 million people affected every time a famine or drought occurs, and, about 10 million suffering from chronic food insecurity and poor nutrition. Most of those affected live in the pastoral, semi-arid and arid areas of the country located in the North, Northeast and Northwest of the country, although parts of the Upper Eastern that include the Counties of Kitui, Makueni and Tana River County in the Coastal Region (**Figure 2**), are often also affected. Some of these arid and semi-arid zones receive as little 5–30 inches or more of rain annually. The other category of consumers that is often affected by food and nutrition insecurity is the slum dwellers, who constitute a considerable percentage of the country's population, and, live in the inner cities of the major urban settlements. The Cities of Nairobi, Mombasa, Kisumu, Nakuru and Eldoret hold about 20% of the country's population and will therefore require significant attention in the effort to reduce food and nutrition insecurity in the country. Malnutrition is a public concern and is the single most important contributor to child mortality which stood at 30.6% in every 1000 births by 2018 down from 33.3% in 2015. Malnutrition is mainly due to inadequate food intake and disease, with the underlying factors being poor child care practices, household food insecurity, and inadequate sanitation and health care services, among others. Most of the indicators on food availability, access and affordability, poverty levels and nutritional status are obtained through statistics generated from the Integrated Household Budget Surveys (IHBS) and the Kenya Household and Dietary Surveys (KHDS). The latest IHBS and KHDS were done in 2011 and 2014, respectively. The IHBS surveys show different levels of food poverty across the former eight Kenyan Administrative Provinces, which were abolished after the promulgation of the new Kenya Constitution in 2010 [5].

**98**

**Figure 2.**

*GHI for Kenya's regions.*

poverty indicators), stunting in Kenya is not perfectly associated with poverty levels. Rather, it seems to be influenced by a complex set of factors that include dietary diversity, feeding and caregiving practices, access to appropriate sanitation and disease prevalence [11, 12]. Wasting is highest in Kenya's northernmost counties: with a value of 22.9% in Turkana, 16.3% in Marsabit, 14.8% in Mandera, 14.3% in West Pokot, and 14.2% in Wajir [10]. These Counties are arid or semi-arid, and are dominated by pastoralism as a form of livelihood and production and therefore have high poverty levels [13, 14]. Moreover, rates of contraception use and women's education levels in these counties are low and fertility rates are high [10]. It has been observed that children's nutritional status is associated with mothers' education and literacy rates [15], both globally and in Kenya, specifically. A study from urban settlements of Nairobi found that maternal education strongly predicts children's nutritional status, when controlling for other socio-economic and demographic factors [16]. Some recent data from Kenya shows that the stunting rate of children whose mothers had no formal education was 31%, while that of children whose mothers had secondary education or higher was 17% [10]. Children's nutrition is also associated with mothers' nutritional status and therefore income. A study from rural Kenya showed a positive correlation between maternal nutrition and children's nutritional status in terms of anthropometric measures [17]. As Kenya attempts to further reduce child undernutrition, albeit with persistent challenges, any gains will be achieved if it addresses infant and young child feeding practices in the Counties. Breastfeeding practices have improved substantially in Kenya, with 61% of children under 6 months exclusively breastfed in 2014, compared with just 32% in 2008–2009 [10, 9]. Meanwhile, in 2014, just 22% of children between 6 and 23 months of age received a minimum acceptable diet [10]. **Figure 2** gives global hunger indicators (GHI) for Kenya's regions.

Although most food and nutrition analyses of Kenya have traditionally focused on rural areas, where rates of child undernutrition tend to be higher than in urban areas, Kenya's population is increasingly urbanizing, and urban food insecurity and undernutrition, are emerging concerns [10, 18, 19]. Urban dwellers are highly vulnerable to food price spikes, which affect their access to affordable food, especially the unemployed, casual labourers who mainly live in the sprawling informal settlements of Nairobi, Kisumu, Nakuru, Mombasa and Eldoret, and increasingly in every major urban centre in the country. Moreover, urban populations live in crowded, poor accommodation, and often lack adequate water, sanitation and therefore live in unhygienic conditions are subject to illness and disease [18, 19]. Child mortality declined much more slowly in urban than in rural areas of Kenya between 1993 and 2008, perhaps because of the deplorable living conditions in urban settlements [20]. In 2014, Nairobi had the second highest child mortality rate among Kenya's regions (**Figure 2**).

Agriculture is considered to have considerable potential to increase household food security and nutrition. Although evidence of the impact of agricultural technologies on relevant outcomes is limited, some studies have shown promising results in Kenya [21]. Dairying and pastoralism play important economic roles among Kenyan smallholder farmers, with significant implications for nutrition. Roughly a quarter of Kenyan households engage in small-scale dairy activities. Studies of pastoralism in four of Kenya's northern, and arid counties–Mandera, Marsabit, Turkana, and Wajir (**Figure 3**) showed that livestock is the main source of livelihood for not less than 57% of households [13, 22]. For pastoralist households, the animals provide the milk consumed by families, and as livestock assets decrease, so does milk consumption affecting children's nutritional status and well-being. Milk consumption at the household level was found to be positively associated with higher body mass index among Samburu youth [23]. Consumption

**101**

**Figure 3.**

*The counties of Kenya.*

the current Counties of Kenya.

*Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges…*

of animal-source foods by Kenyan schoolchildren has also been shown to be positively associated with height and weight gains. A school-feeding programme that tested the effect of different types of snacks given to children found that meat and milk snacks contributed the most to children's arm muscle growth. **Figure 3** shows

Kenya is engaged in cash transfer initiatives as a way to lift the poor out of food and nutrition insecurity. The unconditional cash transfer programme for Orphans and Vulnerable Children increased households' food expenditures and dietary diversity, and the consumption of food produced by households themselves. The unconditional cash transfer programme in rural Kenya also increased households' food security and food expenditures, particularly when the transfers are made monthly rather than in a lump sum [24]. Kenya's Hunger Safety Net Programme, an

*DOI: http://dx.doi.org/10.5772/intechopen.95036*

*Food and Nutrition Security in East Africa (Kenya, Uganda and Tanzania): Status, Challenges… DOI: http://dx.doi.org/10.5772/intechopen.95036*

*Food Security in Africa*

hunger indicators (GHI) for Kenya's regions.

among Kenya's regions (**Figure 2**).

poverty indicators), stunting in Kenya is not perfectly associated with poverty levels. Rather, it seems to be influenced by a complex set of factors that include dietary diversity, feeding and caregiving practices, access to appropriate sanitation and disease prevalence [11, 12]. Wasting is highest in Kenya's northernmost counties: with a value of 22.9% in Turkana, 16.3% in Marsabit, 14.8% in Mandera, 14.3% in West Pokot, and 14.2% in Wajir [10]. These Counties are arid or semi-arid, and are dominated by pastoralism as a form of livelihood and production and therefore have high poverty levels [13, 14]. Moreover, rates of contraception use and women's education levels in these counties are low and fertility rates are high [10]. It has been observed that children's nutritional status is associated with mothers' education and literacy rates [15], both globally and in Kenya, specifically. A study from urban settlements of Nairobi found that maternal education strongly predicts children's nutritional status, when controlling for other socio-economic and demographic factors [16]. Some recent data from Kenya shows that the stunting rate of children whose mothers had no formal education was 31%, while that of children whose mothers had secondary education or higher was 17% [10]. Children's nutrition is also associated with mothers' nutritional status and therefore income. A study from rural Kenya showed a positive correlation between maternal nutrition and children's nutritional status in terms of anthropometric measures [17]. As Kenya attempts to further reduce child undernutrition, albeit with persistent challenges, any gains will be achieved if it addresses infant and young child feeding practices in the Counties. Breastfeeding practices have improved substantially in Kenya, with 61% of children under 6 months exclusively breastfed in 2014, compared with just 32% in 2008–2009 [10, 9]. Meanwhile, in 2014, just 22% of children between 6 and 23 months of age received a minimum acceptable diet [10]. **Figure 2** gives global

Although most food and nutrition analyses of Kenya have traditionally focused on rural areas, where rates of child undernutrition tend to be higher than in urban areas, Kenya's population is increasingly urbanizing, and urban food insecurity and undernutrition, are emerging concerns [10, 18, 19]. Urban dwellers are highly vulnerable to food price spikes, which affect their access to affordable food, especially the unemployed, casual labourers who mainly live in the sprawling informal settlements of Nairobi, Kisumu, Nakuru, Mombasa and Eldoret, and increasingly in every major urban centre in the country. Moreover, urban populations live in crowded, poor accommodation, and often lack adequate water, sanitation and therefore live in unhygienic conditions are subject to illness and disease [18, 19]. Child mortality declined much more slowly in urban than in rural areas of Kenya between 1993 and 2008, perhaps because of the deplorable living conditions in urban settlements [20]. In 2014, Nairobi had the second highest child mortality rate

Agriculture is considered to have considerable potential to increase household

food security and nutrition. Although evidence of the impact of agricultural technologies on relevant outcomes is limited, some studies have shown promising results in Kenya [21]. Dairying and pastoralism play important economic roles among Kenyan smallholder farmers, with significant implications for nutrition. Roughly a quarter of Kenyan households engage in small-scale dairy activities. Studies of pastoralism in four of Kenya's northern, and arid counties–Mandera, Marsabit, Turkana, and Wajir (**Figure 3**) showed that livestock is the main source of livelihood for not less than 57% of households [13, 22]. For pastoralist households, the animals provide the milk consumed by families, and as livestock assets decrease, so does milk consumption affecting children's nutritional status and well-being. Milk consumption at the household level was found to be positively associated with higher body mass index among Samburu youth [23]. Consumption

**100**

of animal-source foods by Kenyan schoolchildren has also been shown to be positively associated with height and weight gains. A school-feeding programme that tested the effect of different types of snacks given to children found that meat and milk snacks contributed the most to children's arm muscle growth. **Figure 3** shows the current Counties of Kenya.

Kenya is engaged in cash transfer initiatives as a way to lift the poor out of food and nutrition insecurity. The unconditional cash transfer programme for Orphans and Vulnerable Children increased households' food expenditures and dietary diversity, and the consumption of food produced by households themselves. The unconditional cash transfer programme in rural Kenya also increased households' food security and food expenditures, particularly when the transfers are made monthly rather than in a lump sum [24]. Kenya's Hunger Safety Net Programme, an unconditional cash transfer programme, boosted beneficiaries' food consumption relative to controls and increased dietary diversity for poorer households in the project [25, 26].

Nutrition education can also help improve diet quality for children and adults in Kenya. A pilot study in western Kenya showed that providing nutrition education to fathers and grandmothers on proper complementary feeding practices for children raised social support for mothers, and, resulted in the adoption of beneficial child feeding practices [27]. Despite the need to continue addressing malnutrition in the country, micronutrient deficiencies of Vitamin A, Folic acid, Iron, Zinc and Iodine are widespread, with the re-emerging rise in rickets. However, the iodization of salt and fortification of many processed foods, especially the staples with most of the above micronutrients will alleviate the problem. Emerging issues include child obesity, where female children appear more obese and overweight than their male counterparts.


*Article* **A Hybrid Tool for Visual Pollution Assessment in Urban Environments**

### **Khydija Wakil 1,\*, Malik Asghar Naeem 1, Ghulam Abbas Anjum 2, Abdul Waheed 1, Muhammad Jamaluddin Thaheem 3, Muhammad Qadeer ul Hussnain 1 and Raheel Nawaz 4**

Received: 3 January 2019; Accepted: 24 February 2019; Published: 12 April 2019

**Abstract:** With increasing focus on more nuanced aspects of quality of life, the phenomenon of urban visual pollution has been progressively gaining attention from researchers and policy makers, especially in the developed world. However, the subjectivity and complexity of assessing visual pollution in urban settings remain a challenge, especially given the lack of robust and reliable methods for quantification of visual pollution. This paper presents a novel systematic approach for the development of a robust Visual Pollution Assessment (VPA) tool. A key feature of our methodology is explicit and systematic incorporation of expert and public opinion for listing and ranking Visual Pollution Objects (VPOs). Moreover, our methodology deploys established empirical complex decision-making techniques to address the challenge of subjectivity in weighting the impact of individual VPOs. The resultant VPA tool uses close-ended options to capture the presence and characteristics of various VPOs on a given node. Based on these inputs, it calculates a point based visual pollution scorecard for the observation point. The performance of the VPA tool has been extensively tested and verified at various locations in Pakistan. To the best of our knowledge, this is the first such tool, both in terms of quantitative robustness and broad coverage of VPOs. Our VPA tool will help regulators in assessing and charting visual pollution in a consistent and objective manner. It will also help policy makers by providing an empirical basis for gathering evidence; hence facilitating evidence-based and evidence-driven policy strategies, which are likely to have significant impact, especially in the developing countries.

**Keywords:** Visual Pollution Assessment (VPA); Visual Pollution Objects (VPOs); Analytical Hierarchy Process (AHP); urban visual pollution; urban areas; evidence based policy; urban planning

### **1. Introduction to Visual Pollution**

Recent decades have witnessed an exponential growth in urbanization demands, especially for improved governance in response to an ever-increasing urban complexity in a global and multi-level context [1]. In the developing countries, economic development, urban growth and dynamic economic transformation are accompanied by many other phenomena [2]. Usually, amenities are provided to the citizens without a well-managed plan of service provision; this results in the visual deterioration of the urban fabric. For example, marketing agencies install various kinds of outdoor advertisements

particularly hoardings and billboards, which in the absence of strict enforcement policies, often emerge as eye-sores and visual blights [3]. Similarly, provision of other services without strong management result in solid waste dumps, cluttered hanging communication wires, encroachments, slums, bad road infrastructures, dilapidation of historical buildings, etc. Resultantly, urban life has come across as a disaster of aesthetic deterioration, transportation issues, air pollution, fumes, smog, and land and water pollution. However, in contrast to other types of pollutions, visual pollution has remained the most neglected aspect of urban life, both in policy and enforcement.

From the definitional evolution aspect, the term 'visual pollution' has been primarily recognized and researched in the mid of 20th century. Although earlier references to air and water pollution can still be found in the literature [4]. During the 19th century, recognition of types of pollution started from the laws on air and water pollution due to their harmful influences on the human environment. The era of the 1970s yielded a number of laws and treaties on 'noise pollution' that denotes the beginning of accepting other types of pollution. During the same period, the visual and light pollution was acknowledged in general, particularly in legal documents, and their management was mandated to local authorities, state agencies, and municipalities [4].

Parallel to that, since the 1960s, visual pollution has been discussed in the developed part of the world resulting in the emergence of di fferent acts, rules and policies for the protection, preservation and enhancement of the urban visual environment [5]. A school of thought defined visual pollution as the type of pollution which o ffends human vision, spatial orientation, physical, mental health, or has psychological and economic e ffects on a community [6–8]. All those elements which a community finds unattractive, ugly, intrusive, disturbing come under visual pollution [9]. While, Nami et al and Jana describe visual pollution as "unbridled and uncoordinated diversity" of form, color, light, materials and accumulation of heterogeneous visual elements which make the manmade environment and urban landscape ugly and unattractive [3,7]. Chmielewski et al quote the term as compound and the resultant e ffect of "clutter, disorder and excess of various objects and graphics in urban landscape" [10]. Jurat ¯ e et al define visual pollution as "negative visual impact of Visual Pollution Object (VPO) on ˙ landscape" [11]. Additionally, the Supreme Court of the USA declared that "pollution is not limited to the air we breathe and the water we drink, it can equally o ffend the eye and ear" [12,13]. The scholars engaged in the visual impact assessments of natural landscapes have used the term visual pollution objects (VPOs) to refer to the physical components that have the ability to decrease the landscape's visual quality, may contribute to diminish visual significance, or may obstruct the view of valuable natural complexes [11]. A similar analogy is valid for urban visual pollution. In an urban context, we define the term 'VPOs' to refer to all the manmade features along with their physical characteristics (placement, appearance, size, color, view and functional hindrance etc.) that a ffect the visual quality of urban surroundings from a human's eye view.

Urban visual pollution is the negative physical condition of a number of objects which have a direct as well as an indirect relation with the quality of the built environment which ultimately has implications for humans living in that place [14–18]. It has been reported that visual pollution objects (together or individually) impact human health [19,20], distract drivers particularly along main highways [3,14,21,22], reduce property values, deface public places, spread annoyance, encourage needless consumption, or a ffect the identity of places [5,13,23]. It has been argued that better visual quality of a space has a relation to the safe and good behavior of residents and so as with better communities at a larger scale [24,25].

Furthermore, it is important to mention that the term visual pollution must not be confused with the concept of neighborhood disorder. As discussed earlier, visual pollution is the compound e ffect of disorder, excess of a number of physical elements while neighborhood disorder can be defined as "observed or perceived physical and social features of neighborhoods that may signal the breakdown of order and social control, and that can undermine the quality of life" [26]. The examples of neighborhood disorder may be adult loitering, drug dealing, crime, fighting in the streets and prostitution, and physical characteristics such as abandoned cars, dilapidated buildings, or litter in the streets [26,27]. Visual pollution is very much linked with the visual quality of public and community spaces [25] which includes regularity, order, beauty, symmetry, and simplicity, etc.

In previous studies, the subject of visual pollution has been explored from the dimensions of concept development, the listing of visual pollution objects and mitigation strategies [28]. However, the quantification and measurement have not been explored su fficiently. We have synthesized the previous work on the measurement of visual pollution and have provided a systematic approach to the development of a visual pollution assessment tool.

### **2. Approaches to Assessing Visual Pollution**

Although visual pollution is recognized as a type of pollution, most of the city governments find it hard to regulate it since they do not have any systematic way of quantifying its presence and measuring its level of intensity vis-a-vis its local impacts [10]. Various scholars have used di fferent techniques to measure visual pollution in their respective contexts, and at various scales ranging from a single street to a city. Table 1 presents a list of the relevant studies and highlights their respective scale, VPO coverage and methods.

**Table 1.** List of studies containing components similar to visual pollution assessment.

### *The Challenges of Measuring Visual Pollution*

It is evident from the literature review that the quantification of visual pollution at any point has always been challenging because of its subjective nature [28] and there doesn't seem to exist any standard set of guidelines for systematic assessment of visual pollution [7]. This further highlights the need for the development of a unified quantitative assessment tool. Although, researchers all around the globe have contributed to the assessment of visual pollution, they have had a certain set of limitations which are discussed below:

*Micro vs. Macro-level research:* Previous studies on visual pollution can be broadly categorized into two extremes of micro and macro scale. Some of the previous studies have on a small case study area like a commercial street, public buildings in a residential area, or a neighborhood with maybe one or two VPOs (billboards, commercial signs). In contrast, other groups of researches adopted a bigger working scale like a city, with multiple VPOs. Consequently, two (somewhat opposite) strategies with narrow and broad classes of indicators are found in the literature to assess the visual pollution of any area.

*Lack of quantification:* Since visual pollution is intrinsically sensitive, subjective and a complex type of pollution, no specific tool or instrument is available to measure the scale of visual pollution at any node [29].

*Dependency on subjective variables:* Most of the available research has used a mix of subjective and objective indicators where the proportion of subjective indicators has been considerably high. Hence, the results can be potentially influenced either by the respondent or the researchers' interpretation, expertise, interest and prevailing literature concepts. So, they may not be agreed upon or adopted in a di fferent context.

*Narrow coverage of VPOs:* Visual pollution has a broad area of knowledge of built and aesthetic environments comprising multiple objects. However, most previous work has focused on the measurement of visual pollution by means of single VPOs, which has resulted in single-object assessment approaches.

*The absence of structured tools:* Unlike other types of pollution, structured instruments and tools are not available for the measurement of visual pollution. Moreover, in some cases a combination of di fferent kinds of methodologies like public surveys [2,7], inter-visibility analysis, triangulation method, focus group discussions, photo comparisons [28,38], visual comparisons and experimentation, etc. [3] has been explored to assess a few (or often a single) VPO, which again indicates the need of a composite VPA tool. In most cases, statistical validity or reliability of the methods has not been assessed and discussed thoroughly.

From the above discussion, it is evident that there is a strong need to develop a comprehensive visual pollution assessment tool that can cover a wider variety of VPOs and can be used at various scales to calculate the visual pollution level at a certain point.

When it comes to subjective ranking and weighting, expert evaluation is preferred as they use their knowledge and experience for comparing objects or phenomena under study [39–41]. The relevant literature contains several weighing methods and techniques (e.g. Delphie method, ordering method [42–44]) that have experts evaluation at their core but possess respective pros and cons. In contrast, an Analytical Hierarchy Process (AHP) is considered comprehensive as it is a multi-criteria decision-making approach to deal with subjective and multiple conflicting criteria. The most prominent feature of the AHP method is the ability to compare both the quantitative and qualitative variables (verbal, graphics or numerical) on the same preference scale [45]. From the psychological point of view, it is also e fficient and consistent to compare two alternatives at a time rather than comparing them all at once. It is based on a ratio scale instead of an interval scale unlike other methods [27,45–47]. The other advantages of using AHP include its ability to handle multi-fold subjects, higher consistency among choices and the ability to evaluate the composite and compound scores of alternatives [48].


**3.3 Optical properties**

*Solar Cells - Theory, Materials and Recent Advances*

molecular configurations of P-CPDTBT3 and SM-CPDTDPP.

The simultaneous interactions of donor and acceptor groups are the responsible of the electron delocalization and thus producing the electronic charge distribution within the HOMOs and LUMOs. As it can be seen from **Figure 4**, there is considerable discrepancy of molecular orbital distributions resulting from the particular

The spatial distribution of the HOMO orbital of P-CPDTBT3 is dominantly localized over the main conjugated backbone. While, that of SM-CPDTDPP is mainly located on the central part of the conjugated framework. The LUMOof P-CPDTBT3 is dispersed over the central CPDT unit indicating a high steric hindrance rising from the strong electron withdrawing group effect of dicyanomethylene group [50]. In the case of SM-CPDTDPP, the LUMO is centered over the DPP substituted group and the thiophene π-spacer units. These distributions may increase the π → π\* electronic transitions and reinforce the ICT ability. Besides, these materials dispose narrow band gap energies (1.62 eV) for P-CPDTBT3 and 1.42 eV for SM-CPDTDPP) that lead to improve the electron transition and light harvesting. The 2D molecular electrostatic maps of studied materials have been simulated to better understand the intra-molecular interactions (See **Figure 5**). As revealed from **Figure 5**, the central part is the most conjecturable zone into the conjugated framework of the studied molecules that is in good agreement with the

Ionization potential (IP) and Electron Affinity (EA) were calculated from the neutral, cation and anion optimized structures. IP and EA describe the barrier injection energies of electron and hole, respectively. The application of the considered materials in OCSs requires relevant IP and EA in order to promote the electron injection and hole transport. Thus, it is revealed from the FMOs analysis the significant effect of building blocks on the electronic properties that are related

**70**

**Figure 5.**

*2D molecular electrostatic maps of studied materials.*

FMOs analysis.

to the charge delocalization.

The optical absorption spectrum in the solar spectral zone also its intensity are the main factors that influence the value of short-circuit current density (JSC) of OSCs [51]. Fundamentally, the JSC is a function of the external quantum efficiency (EQE) with the photon number *S*(λ ) coveringall the frequencies providedfrom the solar spectrum, as above [52]:

$$J\_{\rm SC} = q \left[ EQE.S(\lambda)d\lambda \right] \tag{1}$$

Where, EQE presents the product of light harvesting efficiency (ηλ), exciton diffusion efficiency (ηED), charge separation efficiency (ηCS), and charge collection efficiency (ηCC). As revealed from the following expression, the donor material absorption capability remains a crucial parameter for increasing the organic solar cell efficiency. The light harvesting efficiency (ηλ) is related to the oscillator strength (f) of the maximum optical absorption wavelength as expressed above [53]:

$$
\boldsymbol{\eta}\_{\boldsymbol{\lambda}} = \mathbf{1} - \mathbf{1} \mathbf{0}^{-\boldsymbol{\beta}} \tag{2}
$$

In order to explore the photo-physical properties of the considered compounds, the optical absorption spectra were simulated using TD-DFT approach as costeffective method [54, 55].

**Figure 6.** *Optical absorption spectra of P-CPDTBT3 and SM-CPDTDPP simulated at TD-DFT//B3LYP/6-311 g(d,p) level of theory.*

**Table 2.**

*Calculated electronic transition energy Eex (eV), maximum absorption wavelengths,* λ*max (nm), oscillator strength (f) and major configuration at TD-DT//B3LYP/6-311 g(d,p) level.*

TD-DFT simulations were performed at the optimized ground state (S0) geometries in gaseous phase (See **Figure 6**) and the related optical parameters are listed in **Table 2**.

As we can see from **Figure 6**, these materials exhibit, as expected, abroad absorption bands in the wavelength range from 550 nm to 900 nm which covers a relevant part of the solar spectrum, where the maximum optical absorption within the solar spectrum is at about 700 nm [56]. The broad absorption in the visible and near infrared region, displayed by the considered materials, leads to reinforce BHJ-OCSs performances. The maximum absorption peaks were found at 693 nm and 737 nm for P-CPDTBT3 and SM-CPDTDPP, respectively.

In fact, these maximum wavelengths are generated mainly from HOMOs to LUMOs electronic transitions of ground to first excited state (S0 → S1) of electrons associated with high oscillator strength (f) values. Where, the pronounced absorption peaks are generated by π → π\* electronic transitions from the electron donating CPDT moieties to theelectron acceptor BT or DPP moieties [57]. The simulated absorption spectrum of P-CPDTBT3 is in convenient agreement with the experimental results reported in ref. [58], that confirms the accuracy of TD-DFT approach in reproducing the experimental data.

SM-CPDTDPP absorption spectrum was found red shifted by 44 nm compared to that of P-CPDTBT3. The slight red shift detected can be explained by the present of the thiophene π-spacer that may enhance the electron delocalization within the main conjugated framework.

The large absorption band ranging from 900 nm to 1500 nm is attributed to the ICT generated from the sulfur rich electron to the electron withdrawing dicyanomethylene group within the CPDT units [59]. A promising organic donor material should exhibit a large light harvesting efficiency (ηλ) in order to reach high photocurrent signal [60, 61]. From **Table 2**, we reveal that these materials exhibit high ηλ values close to one leading to an important light harvesting.

Overall, the molecules under investigation have shown interesting absorption properties by covering the amount of the visible and the near infrared regions which leads to potential photo-physical properties and JSC improvement.

#### **3.4 Charge transfer properties**

Efficient BHJ-OSCs dispose high charge carrier's mobility. The free chargers generated from the exciton dissociation/separation will be diffused/transported within the compound. Thus, efficient donor material should exhibit high hole transport ability to improve the photo-generation of charge carriers, and then the JSC.

The charge hopping process is selected to arrange the hole mobility into the compound at room temperature. This process is commonly described as the

**73**

*Designing Well-Organized Donor-Bridge-Acceptor Conjugated Systems Based…*

λ

λ

self-exchange and charge transport between two adjacent molecules. The hole transport rate (khole) is approximated based on Marcus theory, as above [62]:

**P-CPDTBT3** 0.255 0.205 1.66 14 10+ × **SM-CPDTDPP** 0.224 0.315 4.99 14 10+ ×

2 2 2

λ

Where, h is Planck's constant, *kB* is Boltzmann's constant and *T* is the

From Eq. (3), hole transfer integral (thole) and reorganization energy for hole

abilities. The hole transfer integral is influenced by the intra-molecular staking of

Where, EHOMO and EHOMO-1 define the energies of HOMO and HOMO-1 at neutral state, respectively. This expression defines the electron coupling strength of

determined fromenergy system's variation between neutral and charge states. The

explained by the electronegative discrepancy within the over conjugated framework. As well, thole value found for P-CPDTBT3 is lower than that found for SM-CPDTDPP, which shows the higher energy levels overlap within the polymer than the small molecule. Mostly, the investigated materials possess interesting hole mobility capability that will improve the electrical properties of BHJ-OSC devices.

Transition density matrix (TDM) analysis provides an insight into the interactions of donor and acceptor fragments at the first excited state (S1), the electron excitation process and the electron–hole coherence. TDM is a helpful tool to estimate the exciton escape possibility from the Coulomb attraction [64, 65]. The efficient separation of created exciton improves the charge transfer ability within

TDM plots simulated upon S0 → S1 excitation configuration are shown in **Figure 7**. It is observed from the **Figure 7** that the electron–hole coherences are primarily concentrated upon the diagonal box (D-D, A-A) and the off-diagonal (D-A) for photo-excitation. The wide distribution in the diagonal box (D-D, A-A)

validates the high π → π\* transitions within donor and acceptor regions.

two adjacent segments of the molecule. The hole reorganization energy (

λ

*hole*

*of the considered molecules. All these parameters are given in eV.*

conjugated molecules, as expressed bellow [63]:

**3.5 Transition density matrix (TDM) analysis**

temperature (298 K).

**Compound**

**Table 3.**

λ

charge transport properties (

transport (

in **Table 3**. The λ

the BHJ-OSC.

*t k*

π

1

 π− =

*hole B B*

*hole* ) arecrucial parameters to precisely evaluate the charge transport

( HOMO HOMO 1 ) 1 E E

*hole* value of SM-CPDTDPP is lower than that of P-CPDTBT3 that could be

*kT kT*

 λ

hole *), hole integral transfer (thole) and hole transport rate (khole)*

hole **thole khole**

2 *hole t* = − − (4)

*hole* , thole and khole) of the studied materials are listed

(3)

λ*hole* ) is

exp h 4 *hole hole*

*DOI: http://dx.doi.org/10.5772/intechopen.94874*

*Reorganization energies for hole transport (*

*Designing Well-Organized Donor-Bridge-Acceptor Conjugated Systems Based… DOI: http://dx.doi.org/10.5772/intechopen.94874*

**Table 3.**

*Solar Cells - Theory, Materials and Recent Advances*

in **Table 2**.

**Table 2.**

TD-DFT simulations were performed at the optimized ground state (S0) geometries in gaseous phase (See **Figure 6**) and the related optical parameters are listed

**P-CPDTBT3** 1.7887 693 1.0184 H → L + 3 (50%) 0.9041 1.2065 1027 0.5411 H → L (82%) **SM-CPDTDPP** 1.6803 737 1.1021 H → L + 2 (60%) 0.9209 1.1318 1095 0.3962 H → L (88%)

ηλ

As we can see from **Figure 6**, these materials exhibit, as expected, abroad absorption bands in the wavelength range from 550 nm to 900 nm which covers a relevant part of the solar spectrum, where the maximum optical absorption within the solar spectrum is at about 700 nm [56]. The broad absorption in the visible and near infrared region, displayed by the considered materials, leads to reinforce BHJ-OCSs performances. The maximum absorption peaks were found at 693 nm and

*Calculated electronic transition energy Eex (eV), maximum absorption wavelengths,* λ*max (nm), oscillator*

**Compound Eex** λ**max f Major configuration**

In fact, these maximum wavelengths are generated mainly from HOMOs to LUMOs electronic transitions of ground to first excited state (S0 → S1) of electrons associated with high oscillator strength (f) values. Where, the pronounced absorption peaks are generated by π → π\* electronic transitions from the electron donating CPDT moieties to theelectron acceptor BT or DPP moieties [57]. The simulated absorption spectrum of P-CPDTBT3 is in convenient agreement with the experimental results reported in ref. [58], that confirms the accuracy of TD-DFT approach

SM-CPDTDPP absorption spectrum was found red shifted by 44 nm compared to that of P-CPDTBT3. The slight red shift detected can be explained by the present of the thiophene π-spacer that may enhance the electron delocalization within the

The large absorption band ranging from 900 nm to 1500 nm is attributed to the ICT generated from the sulfur rich electron to the electron withdrawing dicyanomethylene group within the CPDT units [59]. A promising organic donor material should exhibit a large light harvesting efficiency (ηλ) in order to reach high photocurrent signal [60, 61]. From **Table 2**, we reveal that these materials exhibit high ηλ

Overall, the molecules under investigation have shown interesting absorption properties by covering the amount of the visible and the near infrared regions which leads to potential photo-physical properties and JSC improvement.

Efficient BHJ-OSCs dispose high charge carrier's mobility. The free chargers generated from the exciton dissociation/separation will be diffused/transported within the compound. Thus, efficient donor material should exhibit high hole transport ability to improve the photo-generation of charge carriers, and then

The charge hopping process is selected to arrange the hole mobility into the compound at room temperature. This process is commonly described as the

737 nm for P-CPDTBT3 and SM-CPDTDPP, respectively.

*strength (f) and major configuration at TD-DT//B3LYP/6-311 g(d,p) level.*

values close to one leading to an important light harvesting.

in reproducing the experimental data.

main conjugated framework.

**3.4 Charge transfer properties**

**72**

the JSC.

 All these parameters are given in eV.*

self-exchange and charge transport between two adjacent molecules. The hole transport rate (khole) is approximated based on Marcus theory, as above [62]:

$$\mathcal{k}\_{\text{hole}} = \frac{2\pi t\_{\text{hole}}^2}{\text{h}} \left(\frac{\pi}{\mathcal{A}\_{\text{hole}} k\_B T}\right)^{\frac{1}{2}} \exp\left(\frac{-\mathcal{A}\_{\text{hole}}}{4k\_B T}\right) \tag{3}$$

Where, h is Planck's constant, *kB* is Boltzmann's constant and *T* is the temperature (298 K).

From Eq. (3), hole transfer integral (thole) and reorganization energy for hole transport ( λ*hole* ) arecrucial parameters to precisely evaluate the charge transport abilities. The hole transfer integral is influenced by the intra-molecular staking of conjugated molecules, as expressed bellow [63]:

$$\mathbf{t}\_{\text{hole}} = \frac{\mathbf{1}}{\mathbf{2}} (\mathbf{E}\_{\text{HOMO}} - \mathbf{E}\_{\text{HOMO}-1}) \tag{4}$$

Where, EHOMO and EHOMO-1 define the energies of HOMO and HOMO-1 at neutral state, respectively. This expression defines the electron coupling strength of two adjacent segments of the molecule. The hole reorganization energy ( λ*hole* ) is determined fromenergy system's variation between neutral and charge states. The charge transport properties ( λ*hole* , thole and khole) of the studied materials are listed in **Table 3**.

The λ*hole* value of SM-CPDTDPP is lower than that of P-CPDTBT3 that could be explained by the electronegative discrepancy within the over conjugated framework. As well, thole value found for P-CPDTBT3 is lower than that found for SM-CPDTDPP, which shows the higher energy levels overlap within the polymer than the small molecule. Mostly, the investigated materials possess interesting hole mobility capability that will improve the electrical properties of BHJ-OSC devices.

#### **3.5 Transition density matrix (TDM) analysis**

Transition density matrix (TDM) analysis provides an insight into the interactions of donor and acceptor fragments at the first excited state (S1), the electron excitation process and the electron–hole coherence. TDM is a helpful tool to estimate the exciton escape possibility from the Coulomb attraction [64, 65]. The efficient separation of created exciton improves the charge transfer ability within the BHJ-OSC.

TDM plots simulated upon S0 → S1 excitation configuration are shown in **Figure 7**. It is observed from the **Figure 7** that the electron–hole coherences are primarily concentrated upon the diagonal box (D-D, A-A) and the off-diagonal (D-A) for photo-excitation. The wide distribution in the diagonal box (D-D, A-A) validates the high π → π\* transitions within donor and acceptor regions.

**Figure 7.** *TDM plots at the first excited state (S1) of the investigated materials.*

The weaker coupling of electron and holes makes easier the dissociation of exciton. The contour plots of TDM show also the exciton dissociation in the studied molecules may be easy regarding the weak electron–hole correlation that involves the charge transfer from main CPDT units to the dicyanomethylene bridge group [66]. The coefficients correlation of D-A within P-CPDTBT3 are slightly higher than those of SM-CPDTNDPP. Hence, the exciton dissociation is expected to be comparatively easier in the case of SM-CPDTNDPP than that in the case of P-CPDTBT3. The TDM analysis demonstrates the efficiency of charge separation within these molecules which leads to a considerable improvement of the Jsc.