Facile fabrication of highly efficient ETL-free perovskite solar cells with 20% efficiency by defect passivation and interface engineering.

Tetramethylammonium hydroxide (TMAH) is employed to modify the surface and electrical properties of fluorine-doped tin oxide (FTO) electrodes in perovskite solar cells. Synchronously, owing to the flow of unbound TMA+ ions into the perovskite, the trap density of the perovskite overlayer is largely reduced. Conductivity of the grain boundaries in the perovskite layer is also greatly increased. A high efficiency of 20.1% along with a reduced J-V hysteresis in our champion perovskite solar cells without electron transport layers is achieved.