Enhanced Efficiency of Air-Stable CsPbBr₃ Perovskite Solar Cells by Defect Dual Passivation and Grain Size Enlargement with a Multifunctional Additive

The perovskite solar cells (PSCs) based on cesium lead bromide (CsPbBr3) with outstanding environmental stability and low preparation cost are regarded as one of the most promising photovoltaic devices for commercial applications. However, the performance of CsPbBr3 PSCs can be badly deteriorated by the intense charge recombination arising from the ionic defects at the grain boundaries of perovskite film. To cope with this issue, we adopt an amino acid of l-lysine with two amino and one carboxyl groups as a chemical additive to incorporate into perovskite film to simultaneously anchor the uncoordinated Pb2+ (Cs+) and halogen ion defects. Further, the grain size of CsPbBr3 perovskite is boosted from 688 to over 1000 nm after l-lysine incorporation as a result of the decreased nucleation rate and the sufficient growth of perovskite, which effectively reduce the grain boundaries for load defects. As expected, the optimized device achieves a best power conversion efficiency of 9.69% attributed to the remarkably reduced charge recombination and enhanced charge extraction arising from the efficient defects dual-passivation and enlarged grain size of perovskite film as well as the improved energy level alignment at the device interface after the introduction of l-lysine, which is elevated by 61.23% in comparison to 6.01% efficiency of the pristine one. Moreover, the unencapsulated device with l-lysine incorporation exhibits remarkable long-term stability in air with 80% RH at 25 °C and 0% RH at 80 °C as well as under continuous illumination conditions. This work provides an effective multifunctional additive for imperfection passivation and grain size enlargement of perovskite to build PSCs with high efficiency and stability.