Inorganic–organic metal halide perovskite solar
cells (PSCs)
show power conversion efficiency values approaching those of state-of-the-art
silicon solar cells. In a quest to find suitable charge transport
materials in PSCs, hematite (α-Fe2O3)
has emerged as a potential electron transport layer (ETL) in n–i–p
planar PSCs due to its low cost, UV light stability, and nontoxicity.
Yet, the performance of α-Fe2O3-based
PSCs is far lower than that of state-of-the-art PSCs owing to the
poor quality of the α-Fe2O3ETL. In this
work, solvent-assisted crystallization of α-Fe2O3ETLs was carried out to examine the impact of solvents on
the optoelectronic properties of α-Fe2O3thin films. Among the various solvents used in this study (deionized
water, ethanol, iso-propanol, and iso-butanol), optimized ethanol-based
α-Fe2O3ETLs lead to champion device performance
with a power conversion efficiency of 13% with a reduced hysteresis
index of 0.04 in an n–i–p-configured PSC. The PSC also
exhibited superior long-term inert and ambient stabilities compared
to a reference device made using a SnO2ETL. Through a
series of experiments spanning structural, morphological, and optoelectronic
properties of the various α-Fe2O3thin
films and their devices, we provide insights into the reasons for
the improved photovoltaic performance. It is noted that the formation
of a pinhole-free compact morphology of ETLs facilitates crack-free
surface coverage of the perovskite film atop an α-Fe2O3ETL, reduces interfacial recombination, and enhances
charge transfer efficiency. This work opens up the route toward novel
ETLs for the development of efficient and photo-stable PSCs.