Review of progress in inorganic electron transport layers for perovskite solar cell applications

Perovskite solar cells (PSCs) have emerged as a revolutionary photovoltaic technology, achieving remarkable power conversion efficiencies (PCEs) above 26.61%, while offering low-cost and scalable fabrication. Among the critical components of PSCs, the electron transport layer (ETL) plays a vital role in charge extraction, transport, and recombination suppression. This review provides a comprehensive analysis of recent advancements in inorganic ETLs, particularly focusing on widely studied materials such as TiO₂, SnO₂, and ZnO. While TiO₂ has historically been the benchmark ETL, challenges such as high-temperature processing and photocatalytic instability have led researchers to explore alternative materials. SnO₂ has gained prominence due to its superior electron mobility, low temperature processability, and excellent optical transparency, making it a strong candidate for high-performance PSCs. ZnO, with its high conductivity and facile synthesis, also shows promise, but faces stability concerns. The review further highlights the significance of surface modifications, doping strategies, and interface engineering to optimize charge transport dynamics and enhance device longevity. Additionally, we discuss emerging alternatives and future perspectives on scalable, cost-effective, and stable ETLs that could drive PSCs toward commercialization. By bridging fundamental material properties with device performance, this work provides insights into the next generation of high-efficiency and durable PSCs.