Non-Uniform Chemical Corrosion of Metal Electrode of p-i-n Type of Perovskite Solar Cells Caused by the Diffusion of CH3NH3I

Although perovskite solar cells have shown high power conversion efficiency, performance stability is still insufficient. Herein, the decay kinetics of the p-i-n type of perovskite cells under light illumination is monitored. It is found that the degradation of the performance is mainly caused by the decrease in short-circuit current (J(SC)), which is directly related to the loss of active area. Secondary ion mass spectrometry (SIMS) analysis confirms that both CH3NH3+ and I- migrate toward the metal electrode during aging through the thin PC61BM layer. Atomic force microscope (AFM) and scanning electron microscope (SEM) analyses reveal that some part of the PC61BM layer is too thin to cover the rough surface of the perovskite film fully. Therefore, chemical corrosion of the metal electrode by CH3NH3I leads to the loss of active area and the consequent short circuit current is proposed to be the performance decay mechanism of perovskite solar cells, which is further supported by the stability improvement of the cells by inserting a thin bathocuproine (BCP) buffer layer between the metal electrode and PC61BM, where the CH3NH3I migration is blocked by the BCP layer.