Surface Engineering of Tin Oxide Nanoparticles by pH Modulation Facilitates Homogeneous Film Formation for Efficient Perovskite Solar Modules

Uniform film deposition over an entire substrate is indispensable to achieve efficient perovskite solar modules (PSMs) by minimizing the gap with high‐performance perovskite solar cells (PSCs). Only a few microscopic pinholes on the film in PSMs directly give rise to debase the performance and stimulate the degradation of the devices. Herein, a strategy of the homogeneous and defect‐reduced electron‐transport layer for high‐performance PSMs is reported. pH modulation of tin oxide (SnO2) nanoparticles colloidal dispersion by a small amount of nitric acid (HNO3) addition leads to the removal of hydroxy groups on the SnO2 surface acting as electronic defects as well as superb regularity of the thin films by forming a network of the SnO2 nanoparticles. The surface engineering of SnO2 nanoparticles brings out the high performance of 23.7% efficiency for a unit cell, 20.3% efficiency for a 24.5 cm2 minimodule, and 19.0% efficiency for a 214.7 cm2 submodule, respectively, where all efficiencies are averaged from results obtained by the reverse/forward scan. In outdoor tests with the submodules, a target PSM generates 16.5% higher cumulative electricity for a month as compared to a control PSM. Furthermore, under damp heat environments, the target PSM maintains 80% efficiency compared to an initial efficiency of 1080 h. The development of perovskite solar modules is of essence to commercialization of perovskite photovoltaics regarded as one of the next‐generation sustainable energy conversion technologies. Electron‐transport layer acts as the key factor determining performance and reliability. This work demonstrates surface engineering by pH modulation in SnO2 colloidal dispersion leads to homogeneous and defect‐reduced electron‐transport layer, resulting in high‐performance, and reliability against damp heat and outdoor conditions.