Periodic Acid Modification of Chemical‐Bath Deposited SnO(2) Electron Transport Layers for Perovskite Solar Cells and Mini Modules

Chemical bath deposition (CBD) has been demonstrated as a remarkable technology to fabricate high‐quality SnO(2) electron transport layer (ETL) for large‐area perovskite solar cells (PSCs). However, surface defects always exist on the SnO(2) film coated by the CBD process, impairing the devices’ performance. Here, a facile periodic acid post‐treatment (PAPT) method is developed to modify the SnO(2) layer. Periodic acid can react with hydroxyl groups on the surface of SnO(2) films and oxidize Tin(II) oxide to Tin(IV) oxide. With the help of periodic acid, a better energy level alignment between the SnO(2) and perovskite layers is achieved. In addition, the PAPT method inhibits interfacial nonradiative recombination and facilitates charge transportation. Such a multifunctional strategy enables to fabricate PSC with a champion power conversion efficiency (PCE) of 22.25%, which remains 93.32% of its initial efficiency after 3000 h without any encapsulation. Furthermore, 3 × 3 cm(2) perovskite mini‐modules are presented, achieving a champion efficiency of 18.10%. All these results suggest that the PAPT method is promising for promoting the commercial application of large‐area PSCs.