Grain Boundary Defect Passivation in Quadruple Cation Wide-Bandgap Perovskite Solar Cells

Development of high-performance wide-bandgap perovskites is a key component to enable tandem solar cells with either a silicon or low-bandgap perovskites. However, the presence of defects in the Br-rich wide-bandgap perovskites, especially in the grain boundaries (GBs) has been particularly challenging and limits its performance. Herein, to accomplish the passivation of these defects, a combination of cation management with rubidium (Rb) introduction into the triple cation combination of cesium/formamidinium/methylammonium (CsFAMA) is exercised. Passivation is further enhanced by secondary growth (SG) using guanidinium iodide. In-depth assessments of GB defect passivation are performed using Kelvin probe force microscopy (KPFM) and nanoscale charge-carrier dynamics mappings provide insightful details on the presence of GBs defects and their suppression by the cation management and SG techniques. Reduction of unreacted PbX2 to realize a highly crystalline perovskite surface is achieved after incorporating Rb and SG treatment. As a result, a champion cell for 1.78 eV (FA(0.79)MA(0.16)Cs(0.05))(0.95)Rb0.05Pb(I0.6Br0.4)(3) wide-bandgap perovskite with an efficiency of 17.71% along with enhancement in all photovoltaic parameters is achieved. This study introduces a new way to analyze GB defects and reveals the consequence of defect passivation on charge-carrier dynamics for realizing efficient perovskites.

Automated summary

The study presents a method for passivating defects in wide-bandgap perovskites using cation management and secondary growth techniques. Reduction of unreacted PbX2 achieves a highly crystalline perovskite surface, leading to an enhanced efficiency of wide-bandgap perovskite solar cells.