Solvent-Assisted Crystallization of an α-Fe<sub>2</sub>O<sub>3</sub> Electron Transport Layer for Efficient and Stable Perovskite Solar Cells Featuring Negligible Hysteresis
Akbar Ali Qureshi, Sofia Javed, Muhammad Aftab Akram, Lukas Schmidt‐Mende, Azhar Fakharuddin
Abstract
High Resolution Image Download MS PowerPoint Slide 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-Fe 2 O 3 ) 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-Fe 2 O 3 -based PSCs is far lower than that of state-of-the-art PSCs owing to the poor quality of the α-Fe 2 O 3 ETL. In this work, solvent-assisted crystallization of α-Fe 2 O 3 ETLs was carried out to examine the impact of solvents on the optoelectronic properties of α-Fe 2 O 3 thin films. Among the various solvents used in this study (deionized water, ethanol, iso-propanol, and iso-butanol), optimized ethanol-based α-Fe 2 O 3 ETLs 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 SnO 2 ETL. Through a series of experiments spanning structural, morphological, and optoelectronic properties of the various α-Fe 2 O 3 thin 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-Fe 2 O 3 ETL, 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.