the 
 development of inexpensive and efficient photovoltaic devices 
 is still a topic of high scientific importance .
the vast majority 
 of today s commercially available photovoltaic elements are 
 based on inorganic semiconductors .
the impressive advancements in 
 the field of organic semiconductors within the last two decades have 
 introduced the realistic potential for a much cheaper way to produce 
 electrical energy from light .
organic 
 semiconductors combine the general properties of semiconductors with 
 the easy processability of organic molecules , while manufacturing 
 of solar cells based on inorganic semiconductors still requires high 
 vacuum - based coating processes .
thin - film photovoltaic 
 devices based on organic semiconductors can be easily printed on lightweight , 
 rugged , and flexible substrates .
another clear advantage of organic semiconductors is the possibility 
 to chemically modify the material properties .
additionally , the electronic 
 structure of organic semiconductors can be relatively easy modified 
 by changing the molecular structure via chemical synthesis .
in contrast to all these advantages , the initial synthesis of new 
 organic semiconductors is a time - consuming and expensive process .
a large number of physical and chemical properties of organic semiconductors 
 can be investigated by electrochemical and photoelectrochemical measurements .
the degree of electrochemical doping 
 may be monitored via electrochemical impedance spectroscopy ( eis ) .
cyclic voltammetry offers an 
 appropriate way to determine the position of homo and lumo levels 
 of organic semiconductors .
various other in situ 
 spectroscopic methods have been developed to study optical and electronic 
 changes induced by electrochemical processes .
however , for all of them , individual samples need 
 to be prepared which is a rather time and material - consuming process . 

in addition , concurrent 
 or subsequent processes such as photodegradation or photodoping can 
 be investigated using photoelectrochemistry .
even when only partially studying the electrochemical and 
 photoelectrochemical 
 properties , different samples and overall relatively big amounts of 
 material are required .
therefore , finding a way of drastically decreasing 
 the amount of material required for investigation is highly relevant . 

one attempt is based on a strong miniaturization of the area addressed 
 by the electrochemical cell , which automatically leads to a drastic 
 reduction of the amount of material to be consumed .
this approach 
 can be realized by , for example , photoelectrochemical scanning droplet 
 cell microscopy ( pe - sdcm ) , as it is capable of performing all common 
 photoelectrochemical and electrochemical techniques on a single substrate .
the central idea behind pe - sdcm is that only 
 a small electrolyte droplet released from the tip of a capillary with 
 a small inner diameter comes into contact with the sample surface 
 that is acting as the working electrode ( we ) . in this paper , 
 a modified version of a pe - sdcm adapted for use 
 with nonaqueous electrolyte solutions
the photoelectrochemical properties of a thin 
 film of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene ] 
 ( mdmo - ppv ) , which is a model ppv - based donor organic semiconductor , 
 was studied in detail .
recently , the 
 doping effect on the optical properties of mdmo - ppv was reported .
although its applicability in photovoltaic devices 
 was already shown , no detailed photoelectrochemical characterization 
 of this material was done up to now . using the pe - sdcm ,
all common 
 electrochemical and photoelectrochemical experiments were performed 
 on spot sizes of less than 0.04 mm .
the user can easily 
 switch between electrochemical and photoelectrochemical experiments 
 without having to change the cell or the substrate .
using pe - sdcm , 
 more than 100 electrochemical experiments on individual spots could 
 be performed on a single 15  15 mm substrate consuming 
 less than 2 ml of electrolyte .
performing such a large number 
 of experiments on a single substrate drastically reduces the amount 
 of consumed material , reduces the time for sample preparation , and 
 eliminates possible variations between different samples .
also , different 
 light sources like lasers , leds , or halogen lamps can be used to meet 
 various experimental requirements .
to demonstrate the measurement capabilities of pe - sdcm for electrochemical 
 and photoelectrochemical characterization of organic semiconductors 
 under nonaqueous conditions , a thin film of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene ] 
 ( mdmo - ppv ; covion gmbh , frankfurt , germany ) was used .
the structure 
 of the polymer is presented in figure 1 . at 
 first , the organic semiconductor was dissolved in pyridine ( 99+% , 
 alfa aesar ) with a concentration of 10 g l. the 
 thin film used for electrochemical characterization was prepared by 
 spin - casting the dissolved polymer molecules onto a precleaned 15 
  15 mm ito / glass slide ( 15  sq , kintec co. ) the glass / ito substrate was cleaned by consecutive 
 sonication in isopropanol , acetone and deionized water .
the film thickness 
 was measured using a dektak xt stylus profilometer ( bruker corp .
all electrochemical 
 and photoelectrochemical measurements shown in this publication were 
 carried out using a special photoelectrochemical scanning droplet 
 cell microscope adapted for the use of nonaqueous , organic - based electrolytes . 

the main body of the cell was made from an acrylic block ( 22 mm  
 22 mm  12 mm ) into which three connected channels ( 3.3 mm in 
 diameter ) were drilled ( see figure 2 ) .
each 
 channel was sealed using polypropylene ( pp ) screws with an o - ring 
 underneath the head of each screw .
a -ag / agcl system adapted 
 for use in organic - based solvents was used as a micro quasi reference 
 electrode ( -qre ) .
the potential sensitive part of the -qre 
 was prepared by electrodeposition of agcl on the first 10 mm of a 
 longer 100 m in diameter ag wire in 1 m hcl .
the partially coated wire was inserted into a small glass 
 capillary for increased mechanical stability , leaving the potential 
 sensing part exposed outside it . to avoid contact between the uncoated 
 part of the ag wire and electrolyte ,
the glass capillary was sealed 
 on both ends using two component epoxy resin ( uhu gmbh , germany ) . 

this leads to increased mechanical stability of the -qre and 
 avoids possible cross contaminations .
the potential of this electrode 
 was 0.211 v versus standard hydrogen electrode ( she ) .
the counter 
 electrode ( ce ) used for the pe - sdcm was made from a flattened 100 
 m in diameter au wire ( 99.999% , wielandt dentaltechnik , germany ) . 

flattening of the au wire increases the surface area of the ce and 
 results in a high ce / we surface ratio .
scheme of the photoelectrochemical 
 scanning droplet cell microscope 
 ( pe - sdcm ) .
the lower part of the pe - sdcm , 
 from which the droplet is released , 
 was made from a borosilicate glass capillary with an outer diameter 
 of 2.5 mm .
it was tailored using a commercial capillary puller ( pc-10 , 
 narishige , tokyo , japan ) .
the size of the tip was adjusted to the 
 final desired size using an in - house developed capillary polisher 
 equipped with 2400 and 4000 grade sic sandpaper ( struers a / s , ballerup , 
 denmark ) . after polishing ,
the glass tube was thoroughly cleaned with 
 acetone and isopropanol , followed by deionized water , and blown dry 
 using nitrogen .
a silicone seal was formed at the rim of the capillary 
 by dipping it into liquid silicone ( rtv , momentive , albany , u.s.a . ) 
 and dried under constant nitrogen flow for several hours .
this gasket 
 allows operation of the pe - sdcm in contact mode , where the tip of 
 the cell is pressed against the surface of the sample .
this approach 
 leads to a very high reproducibility of the area addressed by the 
 pe - sdcm due to confinement of the electrolyte droplet within the inner 
 volume defined by the silicone sealing .
additionally , such a sealing 
 strongly reduces contamination of the electrolyte ( e.g. , water ) by 
 eliminating direct exposure of the electrolyte to the atmosphere during 
 measurements .  
next , this capillary was mounted in a screw allowing 
 an easy way 
 of fixing it to the acrylic block . in order to locally illuminate 
 the area addressed by the pe - sdcm
the length of the fiber , re and ce were chosen in 
 such a way that all three , when installed inside the tip capillary , 
 are in close proximity to the surface ( see figure 2b ) .
this ensures homogeneous illumination of the wetted area 
 and minimizes potential drop between re and sample surface ( we ) . inside 
 a third screw a 800 m in diameter stainless steel capillary 

was installed using a two - component epoxy glue ( uhu gmbh , germany ) . 

this capillary was used as electrolyte inlet and was connected via 
 a teflon tube to a high - precision syringe pump ( world precision instruments , 
 u.s.a . ) .
the pump served as an electrolyte reservoir and was additionally 
 used to precisely control the size of the electrolyte droplet formed 
 at the tip of the capillary . to determine the area wetted by the pe - sdcm , 
 a sputter deposited ti thin film was anodized in an aqueous 0.1 m 
 na2so4 solution .
the area of the colored oxide spot was determined using an automated 
 optical pattern recognition software ( nis elements d , nikon , japan ) .
all photoelectrochemical 
 experiments presented in this work were performed using a 532 nm , 
 diode pumped solid state laser module with built - in auto power control . 

this specific wavelength was chosen to match the absorption maximum 
 of mdmo - ppv , which was determined by spectroscopic ellipsometry ( se ) . 

various different light sources , for example , high - power leds , uv / vis 
 continuum emitters , monochromators with optical fiber output , and 
 different kinds of lasers have already been successfully used with 
 pe - sdcm .
the 532 nm laser was coupled 
 externally into the fiber using an in - house developed fiber port . 
 to avoid any disturbance of the measurements by ambient light sources , 

the intensity of the light source was adjusted by using a gray - shade 
 filter ( thorlabs , u.s.a . ) positioned midway between laser source and 
 fiber port .
blockage of the laser beam was done by means of a manually 
 operated shutter . to determine the optical power density on the area 
 addressed by the pe - sdcm
, a fully assembled pe - sdcm was positioned 
 on the detector window of an optical power meter ( coherent lasermate 
 q ) .
the pe - sdcm was positioned on the sample surface in a fully automated 
 fashion using a gantry robot build from three linear stages . for maximum 
 reproducibility of the wetted area
the applied force was continuously 
 monitored using a small force sensor ( me - messsysteme , germany ) and , 
 if necessary , readjusted by feedback to the z - axis .
the complete setup was controlled by an in - house developed 
 labview program . as electrolyte , a 0.1 m solution of tetrabutylammonium 
 hexafluorophosphate ( tbapf6 , 99% , fluka analytical , 
 u.s.a ) dissolved in propylene carbonate ( pc , 99.7% , sigma - aldrich ) 
 was used .
the electrolyte was prepared and stored in a glovebox to 
 avoid possible contaminations caused by , for example , oxygen or water . 

all experiments were carried out in a three - electrode configuration 
 using a potentiostat with a built - in frequency response analyzer for 
 electrochemical impedance spectroscopy ( eis ) measurements ( compactstat , 
 ivium technologies , the netherlands ) .
in order 
 to characterize the electrochemical properties of the mdmo - ppv , cyclic 
 voltammetry was performed . using this technique ,
detailed information 
 about the oxidation / reduction processes as well as their kinetics 
 can be obtained .
first , cyclic voltammetry with different scan rates 
 was done . to avoid any interaction , for each measurement
, the pe - sdcm 
 was moved to a different location , and measurements with scan rates 
 of 1 , 3 , 10 , 30 , and 100 mv s were performed on 
 sequentially addressed spots .
all these cycles are presented together 
 in figure 3 to allow a direct comparison .
as 
 can be seen , the observed maximum of the current density increases 
 when increasing the scan rate , which can be easily explained by increased 
 mass transport at higher scan rates . due to the strong overlapping 
 of the experimental data , the curves corresponding to the first three 
 potential scan rates ( up to 10 mv s ) are displayed 
 separately in the inlet of figure 3 .
interesting 
 observations can be done , if looking at the shape of the current  voltage 
 curves as a function of the scan rate . for scan rates up
to 10 mv 
 s two oxidation peaks are found ( see inlet figure 3 ) .
for the first experiment with a scan rate of 
 1 mv s , the oxidation peaks are found at 0.8 and 
 1.3 v. when increasing the speed of change of polarization up to 10 
 mv s , the oxidation peaks are shifted to higher 
 potentials . the lower potential oxidation peak shifts to 0.83 v , while 
 the higher potential oxidation peak shifts to 1.44 v. the scan rate 
 dependent peak position suggests a kinetic hindrance of the electrochemical 
 oxidation process . as a result ,
higher potentials are needed for the 
 same oxidation process to occur . moreover , in all three experiments , 
 no clear reduction peak could be observed , but instead , a very broad 
 negative current distribution is noticeable . when comparing current 
voltage 
 characteristics measured with different polarization speeds , the different 
 behavior of the reduction part of the voltammograms could be explained 
 by a dissolution process of the previously oxidized mdmo - ppv , which 
 becomes more significant at lower polarization speeds where a second 
 oxidation peak was detected . for higher scan rates ( 30 and 100 mv 
 s ) ,
only one clear oxidation peak is found with 
 a maximum at 0.86 and 0.9 v , respectively .
as compared to the previously 
 discussed case of low polarization speeds , the second oxidation peak 
 is absent probably due to kinetic hindrance of the oxidation process . 
 additionally , for the high scan rate cases , a broad reduction peak 
 centered at 0.8 v is observed .
in order to get a better 
 understanding of the polymer oxidation 
 and reduction processes , a series of cyclic voltammograms was measured 
 with a scan rate of 10 mv s on a single spot . 
 in this experiment ,
the maximum potential was incrementally increased 
 in steps of 0.05 v up to the final potential of 1.5 v. the results 
 are plotted in figure 4 . during experiments , 

all curves with the maximum potential up to 0.8 v , showed only background 
 current .
this is observable in the inlet of figure 4 , where only the first five experiments ( with final potential 
 up to 0.95 v ) are presented . in the scan with a final potential of 
 0.85 v , a sharp and well - defined peak with maximum at 0.84 v ,
was 
 found . in the next scan , with a final potential of 0.9 v the intensity 
 of this peak reduces and a broadening can be observed .
additionally , 
 a second anodic peak can now be observed at 0.68 v. the presence of 
 this new peak is related to an initial oxidation of the mdmo - ppv . 

this peak was not measured before , probably due to the formation of 
 an interfacial barrier on the polymer surface causing the previously 
 discussed peak at 0.84 v. the next scan with a final potential of 
 0.95 v has only the initial oxidation peak centered at 0.68 v with 
 a slightly higher current density than in the previous scan . for final 
 potentials above 0.95
v , the peak characterizing the first oxidation 
 step shifts toward higher potentials . the current density value at 
 the peak maximum increases gradually up to 0.03 ma cm in the case of the scan with the highest final potential . for the 
 last three measured scans ( 1.41.5 v ) the position of the first 
 oxidation peak
is shifted for about 50 mv up to 0.8 v for each additional 
 experiment . for cyclic voltammograms with the final potential above 
 1 v , a strong increase in the current can be observed at the end of 
 the anodic sweep .
all performed cyclic voltammograms that show a clear 
 faradaic current have a rather undefined broad reduction peak . when 
 increasing the maximum potentials of the scans , the maximum current 
 density of the reductive current is shifted toward more positive potentials .
all scans with reverse potentials up to 1.5 v and scans with reverse 
 potentials up to 0.95 v ( inset ) . besides cyclic 
 voltammetry , a series of potentiostatic experiments were performed . 
 in this
study the constant potential applied was increased stepwise . 
 within the entire measurement series ,
the addressed area of the mdmo - ppv 
 layer was kept at the corresponding potential , while the resulting 
 current was measured for 70 s. the obtained results are displayed 
 as a 3d graph in figure 5 . in order to obtain 
 a more detailed description of the electrochemical processes caused 
 by small changes in the applied potential , sufficiently small potential 
 steps were used .
a potential increase of 50 mv for each step was previously 
 found to be suitable for investigating electrochemical doping of polymers 
 and was used also for this study .
time - dependent 
 potentiostatic measurements on mdmo - ppv at different 
 applied potentials . for applied potentials 
 below 0.75 v , only a background current 
 density in the order of 10 ma cm could be measured .
the recorded current stays constant within the 
 70 s time frame of each measurement . in the potential range between 
 0.750.85 v
the increase in 
 the current density is related to the oxidation of mdmo - ppv and to 
 the potential corresponding to the interfacial barrier previously 
 discussed in the cyclic voltammetry studies . during the first 5 s 
 of each potentiostatic measurement , a significant decrease in the 
 current density
can be observed , caused by the occurring electrochemical 
 processes . at a later stage ,
when increasing the applied potential 
 even further ( above 0.85 v ) , the final current density measured after 
 70 s increases from one curve to the next .
this effect can be explained 
 by an increased conductivity of the oxidized organic semiconductor 
 due to doping . as previously found , a significant decrease in current 
 density within the first 5 s is observed .
the magnitude of the onset 
 current decrease ( during the first 5 s ) depends on the applied potential 
 and gets significantly lower for the highest potentials .
a numerical 
 integration of the potentiostatic curves presented 
 in figure 5 was performed in order to quantify 
 the total charge taking part in the electrochemical processes at the 
 semiconductor / electrolyte interface .
this total charge is plotted 
 as a function of the applied potential and the results are plotted 
 in figure 6 to allow for a further discussion 
 of the electrochemical processes .
up to 0.75 v , a constant charge 
 density of about 3 c cm is observed .
this 
 charge density is directly related to the background electrochemical 
 current of the system .
similar to the previously discussed current 
 transient experiments , at 0.85 v , a small oxidation is evidenced by 
 a charge density increase .
when increasing the potential further up 
 to about 1.1 v , the charge density slowly increases up to about 0.6 
 mc cm . for potentials between 1.1 and 1.4 v , an 
 almost exponential growth of the charge density is observed .
this 
 charge density increase is mainly related to the second oxidation 
 step of the mdmo - ppv , as observable in the fast decaying ( within the 
 first 5 s ) current density curves plotted in figure 5 .
as the applied potential increases from 1.4 to 1.5 v , the 
 charge density increase can be also related to degradation processes . 

additionally , the mentioned strong charge density increase is confirming 
 the previously discussed electrochemical processes , which results 
 in a conductivity increase of the mdmo - ppv due to the electrochemical 
 oxidation .
overall , in the charge density dependence on the applied 
 potential presented in figure 6 , no abnormal 
 behavior of the system could be identified .
this indicates long - term 
 reliability of the pe - sdcm since the coulometric data is only confirming 
 the electrochemical processes previously evidenced in the potentiostatic 
 investigations from figure 5 .
total charge density 
 measured on mdmo - ppv as a function of applied 
 potential in the potentiostatic study . in an attempt to study the electrical properties of the mdmo - ppv / electrolyte 
 system , electrochemical impedance spectroscopy was performed using 
 the pe - sdcm . usually , conjugated polymers in their undoped form have 
 insulating properties . upon doping ,
generally , at low doping levels they are considered 
 as semiconductors . with increasing the doping level , their electrical 
 resistance further decreases and they can show metal - like behavior . 
 during the eis study shown here , the frequency dependent changes of 
 the impedance are monitored as a function of the applied dc bias ( offset ) . 
 before each eis experiment ,
a potentiostatic pretreatment was performed 
 for 70  s in order to equilibrate the electrochemical processes . 

the used equilibration time of 70 s was chosen in agreement to the 
 previous potentiostatic experiments , which showed a current density 
 stabilization after this time interval ( see figure 5 ) .
all impedance spectra were recorded at a single addressed 
 spot using sequentially increasing biases up to 1.4 v. after each 
 spectrum , the bias was increased by 0.2 v and the frequency dependence 
 of the impedance was determined again . in figure 7 , the corresponding bode plots are shown in part ( a ) together 
 with the associated phase shifts in part ( b ) . as can be noticed , for 
 biases below 0.6 v ,
there is no change in the shape and value of the 
 impedance . in this bias range
, the high frequency impedance suggests 
 an electrolyte resistance of approximately 10 . 
 similarly , the impedance value observable at the lowest frequency 
 indicates a working electrode resistance in the order of 10 . starting with the applied bias of 0.6 v , a deviation of 
 both the impedance and phase shift at low frequencies appears .
this 
 decrease is related to the oxidation of mdmo - ppv , resulting in an 
 expected insulator - to - metal transition .
this decrease is continuing up to a bias of 1 v , where the working 
 electrode impedance decreases by almost 2 orders of magnitude . in 
 the same time
, the phase shift changes substantially , finally reaching 
 a value under 25 , observable at the middle of the investigated 
 frequency range . at even higher applied potentials , an unexpected 
 increase in the impedance can be observed .
this effect can be related 
 to dissolution of the oxidized mdmo - ppv layer , resulting in a change 
 in the working electrode geometry .
when 
 a semiconductor is illuminated with light having an energy larger 
 than the semiconductor bandgap , the energy of the photons can be absorbed 
 and excited electrons and holes are generated in the conduction and 
 valence band , respectively . when these photoexcited electrons or holes 
 are in the space charge region they migrate toward the electrode surface 
 where they participate in charge transfer reactions giving a photocurrent . to demonstrate the functionality of pe - sdcm 
 for photoelectrochemical measurements on organic semiconductors , photoinduced 
 phenomena were studied on the mdmo - ppv film .
the area addressed by 
 the pe - sdcm was illuminated by the built - in optical fiber with a radiation 
 of 532 nm wavelength ( green ) provided by an external laser .
the wavelength 
 of the radiation was chosen to match the maximum absorption of the 
 polymer , as reported in a previous study .
photocurrents caused by photogenerated electrons ( cathodic currents ) 
 or holes ( anodic current ) are negligible when they are the majority 
 charge carriers . under these conditions ,
however , their photocurrent becomes 
 significant when the reacting electrons or holes are minority charge 
 carriers . in this case their concentration is greatly increased by 
 photoexcitation as compared with the concentration of the minority 
 charge carriers in the absence of radiation ( in the dark ) .
therefore , 
 photocurrents can only be observed with reactions in which the participating 
 carriers are minority charge carriers .
this means transfer of holes 
 at n - type electrodes and electrons at p - type electrodes leading to 
 anodic and cathodic photocurrents , respectively . in figure 8 ,
photocurrent 
 transients measured on mdmo - ppv under chopped light at different applied 
 potentials are displayed .
after approximately 10 s in the dark , the 
 polymer was irradiated for another 10 s , defining one exposure cycle . 
 in total , four exposure cycles were performed for applied potentials 
 of 0.0 , 0.2 , and 0.4 v. for all potentials , the material is acting 
 as a photocathode under illumination , which is a clear proof of the 
 p - type nature of this polymer . also , the measured photocurrents are 
 overall decreasing with time due to the photodegradation of the material . 
 within each illumination cycle , the measured photocurrent is highest 
 at the beginning and is decreasing toward the end of each irradiation 
 period
. the strongest decay in photocurrent within each cycle is found 
 for the first exposure cycle and is continuously getting smaller for 
 the following cycles .
the dark current after each illumination cycle 
 returns to its initial background value . when increasing the applied 
 potential toward more positive values , the measured photocurrent becomes 
 smaller for all experiments .
this can be explained by the system being 
 brought closer to flat - band conditions , thereby decreasing the electric 
 field inside the space - charge region .
photocurrent transients measured under intensity 
 modulated green 
 laser light . to study the long - term 
 stability of the polymer under irradiation
, 
 photocurrent transients were measured for 600 s during illumination 
 with the green laser light at different potentials .
the same potentials 
 of 0.0 , 0.2 , and 0.4 v used in the previous irradiation / dark sequence 
 analysis were also applied here to enable a direct comparison .
the 
 measured current transients are shown in figure 9 , and the 600 s exposure time interval is indicated in the figure . 

the initial dark current densities are shown in the figure before 
 opening the optical shutter in order to indicate the current density 
 background ( dark ) level . immediately after opening
, the shutter allowing 
 laser irradiation of the mdmo - ppv / electrolyte interface , the maximum 
 in photocurrent is observed for all applied potentials . within the 
 next 200 s ,
after 600 s of illumination , 
 no clear distinction can be done anymore between photo- and dark current . 

therefore , it may be concluded that this polymer suffers from severe 
 photodegradation when being in contact with tbapf6 electrolyte . 
 as already previously observed in figure 8 , 

this can be explained by a decrease in the space 
 charge region allowing a less efficient exciton separation at the 
 electrochemical interface .
in addition to photocurrent 
 measurements , the photopotential of 
 mdmo - ppv in tbapf6 electrolyte was measured for 300 s , 
 and the results are shown in figure 10 , as 
 obtained from the open circuit potentials measured versus the reference 
 electrode . when a space charge region is present at the semiconducting 
 polymer interface , the photoexcited electrons and holes are separated 
 and each one is moving in opposite direction under the influence of 
 the electric field inside the space charge region .
this field - assisted 
 migration of the photoexcited charge carriers induces an opposite 
 potential in the electrode which decreases the potential difference 
 across the space charge region .
this reduction further leads to shifting 
 of the fermi level by a certain energy which can be detected by measuring 
 the photopotential .
the electrode potential 
 in the dark continuously decreases from 0.13 v down to 0.05 v. this 
 time variation can be related to the porous nature of the electrode 
 most likely being penetrated more and more by the electrolyte molecules 
 with time .
the photopotential measured under green light irradiation 
 stays constant at about 0.46 v for about 50 s and then gradually decreases 
 to 0.22 v within the remaining 250 s of measurement time .
however , 
 this decrease is stronger than the decrease of the potential in the 
 absence of irradiation
a modified version of a 
 photoelectrochemical scanning droplet cell 
 microscope adapted for use with nonaqueous electrolytes is presented . 

the possibility for localized measurements on single addressed small 
 areas ( 0.04 mm ) on a polymer surface is exploited .
the 
 small dimension of the cell allows considerably lower consumption 
 of both electrolyte and studied material , as compared to using conventional 
 electrochemical cells .
this advantage is evidenced by a detailed electrochemical 
 and photoelectrochemical characterization of a model organic semiconductor 
 ( mdmo - ppv ) .
two oxidation peaks were found during the cyclic voltammetry 
 studies , which were confirmed by potentiostatic investigations .
the 
 characteristics of the oxidation processes were studied using scan 
 rate dependent experiments as well as variable maximum potential applied 
 during the potential scan .
electrochemical impedance spectroscopy was 
 successfully performed at the micrometer scale revealing the changes 
 in the film resistance as a function of the applied potential .
the 
 photovoltaic response of the mdmo - ppv was studied using the described 
 pe - sdcm under irradiation with 532 nm wavelength .
high signal - to - noise 
 ratios ( > 1000 ) were obtained during the photocurrent measurements 
 on the addressed spot in a reproducible manner .
the photopotential of the 
 electrode was also successfully characterized in order to test the 
 applicability of pe - sdcm for photovoltaic studies .
 a model 
 organic semiconductor ( mdmo - ppv ) was used for testing a 
 modified version of a photoelectrochemical scanning droplet cell microscope 
 ( pe - sdcm ) adapted for use with nonaqueous electrolytes and containing 
 an optical fiber for localized illumination . 
 the most attractive features 
 of the pe - sdcm are represented by the possibility of addressing small 
 areas on the investigated substrate and the need of small amounts 
 of electrolyte . 
 a very small amount ( ng ) of the material under study 
 is sufficient for a complete electrochemical and photoelectrochemical 
 characterization due to the scanning capability of the cell . 
 the electrochemical 
 behavior of the polymer was studied in detail using potentiostatic 
 and potentiodynamic investigations as well as electrochemical impedance 
 spectroscopy . 
 additionally , the photoelectrochemical properties were 
 investigated under illumination conditions , and the photocurrents 
 found were at least 3 orders of magnitude higher than the dark ( background ) 
 current , revealing the usefulness of this compact microcell for photovoltaic 
 characterizations . 
Introduction
Experimental
Section
Results
and Discussion
Conclusions