SnO₂–TiO₂ Hybrid Electron\nTransport Layer for Efficient and Flexible Perovskite Solar Cells

Abstract

Inorganic\nelectron transport layers (ETLs), such as titanium dioxide\n(TiO₂) and tin dioxide (SnO₂), are important\nin n–i–p structured perovskite solar cells (PSCs). In\nparticular, the ETLs for flexible PSCs (f-PSCs) using a polymer substrate\nrequire strong adhesion with a transparent conducting oxide (TCO)\nand formation of a uniform thin film at a temperature below 150 °C.\nHence, SnO₂ colloidal nanoparticles are primarily used\nto meet these demands. Nevertheless, there exist further opportunities\nfor improvement in terms of efficiency, uniform coating, and adhesion\non TCO. In this study, we prepared a SnO₂–TiO₂ hybrid electrode by adding a certain amount of TiO₂ nanosol, which functions as an inorganic binder, to a SnO₂ colloidal solution. In comparison with the SnO₂ colloid\nalone, f-PSC fabricated with a SnO₂–TiO₂ hybrid electrode demonstrated not only better mechanical reliability\nagainst bending due to strong adhesion to the substrate but also greatly\nimproved efficiency because of improved energy alignment. Eventually,\nthe SnO₂–TiO₂ hybrid electrode resulted\nin an efficiency of 21.02% and even an efficiency of over 16% in a\nmini-module (7 × 7 cm²) due to the uniform coating\nover a large area. This study provides a new strategy for the ETL\nof high-efficiency f-PSCs.