Chemical Bath Deposition of SnO2 Films on PEN/ITO Substrates for Efficient Flexible Perovskite Solar Cells

Abstract Flexible perovskite solar cells (f-PSCs) have achieved significant success. However, high-quality tin dioxide (SnO 2 ) electron transport layers (ETLs) fabricated via chemical bath deposition (CBD) have not been achieved on flexible PEN/ITO substrates. This limitation is primarily due to the corrosion of the poor-quality ITO layer by the strongly acidic CBD solution. Here, we analyzed the reasons for the poor corrosion resistance of ITO films on PEN substrate from multiple perspectives, such as element composition, microstructure, and crystallinity. Then, we proposed a modified CBD method for SnO 2 films suitable for flexible PEN/ITO substrates. We employed SnCl 2 ·2H 2 O as the tin source and regulated the pH of the CBD solution by NH 3 ·H 2 O, which effectively avoided the corrosion of the ITO layer by the CBD solution and achieved high-quality SnO 2 films on the ITO layers. Compared to the commercial SnO 2 dispersion, the SnO 2 films prepared by this method have smaller grains and higher transmittance. As a result, we achieved an unprecedented power conversion efficiency (PCE) of 20.71% for f-PSCs fabricated on PEN/ITO substrates with SnO 2 ETLs by CBD method. This breakthrough facilitates the development of high-performance f-PSCs by a low-cost and large-scale chemical bath deposition of high-quality ETLs on flexible substrates.