Negligible hysteresis planar perovskite solar cells using Ga-doped SnO2 nanocrystal as electron transport layers

Planar perovskite solar cells (PSCs) have been demonstrated as a promising architecture for efficient, large-scale, flexible and tandem solar cell. To date, unfortunately, most planar PSCs suffer from current-voltage hysteresis, which derives from interface mismatch, surface defects, ion migration, and ferroelectric property et al. Here, we demonstrate a facile strategy to significantly reduce the hysteresis and improve the performance of planar PSCs by doping gallium (Ga) into tin oxide (SnO2) nanocrystal electron-transport layer using low-temperature solution-processed method. It is revealed that the Ga-doped SnO2 ETL owning better band alignment with the perovskite absorption layer, which is helpful for electron extraction. It is found that gallium doping severely decreases the trap state density in SnO2, leading to a lower recombination rate and negligible hysteresis. With the optimized doping concentration of Ga ions, the champion device achieves a highest PCE of 18.18% and the hysteresis index is reduced from 23.9% to 1.7%.