High Efficiency Quasi‐2D/3D Pb–Ba Perovskite Solar Cells via Phenethylammonium Chloride Addition

The existence of toxic Pb in perovskite solar cells may hinder the pace of commercialization. Based on the previous work, Ba 2+ is most suitable for partially replacing Pb 2+ among alkaline‐earth metal cations. However, a high substitution ratio may lead to poor film coverage. A detailed study of the effects on film formation with phenethylammonium chloride (PEACl) additive for large n (n > 40) quasi‐2D/3D mixed‐cation Pb–Ba perovskite (i.e. PEA x MA 0.4− x FA 0.6 Pb 0.9 Ba 0.1 I y Cl 3− y ) is presented. The perovskite layer with defects passivation exhibits efficient charge‐carrier transport, suppression of trap‐assisted recombination, and improved electron extraction capability. The mapping distribution of surface potentials is quantified by photo‐assisted Kelvin probe force microscopy to verify the carrier generation. Consequently, the power conversion efficiency (PCE) of the PEA x MA 0.4− x FA 0.6 Pb 0.9 Ba 0.1 I y Cl 3− y perovskite solar cell is enhanced significantly from an averaged PCE of 15.0% of the pristine active layer to 18.1% and the champion PCE can achieve 19.1%. The corresponding device shows outstanding long‐term stability in air, retaining 90% of its initial PCE for more than 700 h. Herein, a promising strategy to passivate defects and improve the perovskite film quality for superior optoelectronic properties is provided.