A Compact Electron Transport Layer Using a Heated Tin‐Oxide Colloidal Solution for Efficient Perovskite Solar Cells

Tin dioxide is a frequently reported electron transporting material for perovskite solar cells (PSCs) that yields high‐performance devices and can be solution processed from aqueous colloidal solutions. While being very simple to process, electron transport layers deposited in this manner often lead to nonuniform film morphology, significantly affecting the morphology of the subsequent perovskite layer, lowering the overall device performance. Herein, it is shown that heating the SnO 2 colloidal solution (70 °C) results in compact SnO 2 films with increased surface coverage and fewer gaps in the SnO 2 film. Such films possess threefold higher lateral electrical conductivity than those obtained from room‐temperature solutions. The narrow gaps in the SnO 2 film also reduce the chances of direct contact between the indium tin oxide electrode and the perovskite layer, yielding better contact with less voltage loss. The improved SnO 2 surface coverage induces larger perovskite grains (≈565 nm) than those prepared from the room‐temperature solution (≈273 nm). Finally, using these compact SnO 2 layers, efficient and stable PSCs that retain ≈85% of the initial power conversion efficiency of 20.67% after 100 h of maximum power point tracking are demonstrated.