Dip coated SnO2 film as electron transport layer for low temperature processed planar perovskite solar cells

Abstract

Perovskite solar cells (PSCs) made their mark in the photovoltaic research community due to their accelerating efficiencies, bandgap tunability, ease of fabrication, choice of substrates, etc. The electron transport layer (ETL) plays a decisive role in determining the performance and scalability of PSCs. SnO2 is a potential candidate for ETL in PSCs due to its high transmittance, low sintering temperatures, and suitable deep conduction and valence band positions that allows efficient electron extraction at the interfaces. In this work, we developed a simple, solution-processable low-temperature deposition of SnO2 on fluorine-doped tin oxide (FTO) glass substrates employing dip-coating technique for the first time. The number of dipping cycles are optimized to attain uniform coverage of the SnO2 layer on FTO. Formamidinium lead tri-iodide (FAPbI3) perovskite is deposited onto the dip-coated SnO2 electrode by vapor assisted solution process. XRD reveals the successful SnO2 phase formation by a low-temperature dip-coating method and FAPbI3 perovskite film formation by vapor assisted solution process with an unremarkable presence of the photo inactive δ phase. The surface morphology of the FAPbI3 films is smooth with an average grain size of 220 nm. A preliminary study on the planar device's photovoltaic performance using CuSCN as hole transport material (HTM) and Au as back contact exhibited a power conversion efficiency of 3.2% using four deposition cycles of SnO2 by dip-coating as the electron transport layer. This study demonstrates the utilization of dip-coating as a cost-effective method to deposit ETL that paves the way for PSCs' scale-up.