Methylammonium-chloride post-treatment on perovskite surface and its correlation to photovoltaic performance in the aspect of electronic traps

Herein, MACl post-treatment is utilized for MAPbI₃ and (Cs_0.05FA_0.79MA_0.16)Pb(I_0.84Br_0.16)₃ (MA, methylammonium; FA, formamidinium). Photoluminescence of both perovskite films exhibits a peak shift to the higher emission energy as well as a slower decay of recombination by the MACl treatment, suggesting the passivation of defects in band tail states. Photovoltaic performance is further correlated with the change of deep electronic traps in the bandgap, which is characterized through capacitance analyses of solar cells. Degradation of MAPbI₃ cells by the MACl treatment is attributed to the additional deep-trap formation, and the improvement of photovoltaic parameters for triple-cation perovskites is correlated with the reduction of deep traps with trap-level shifts toward the band edge. The reactive characters of MAPbI₃ against post-treatment conditions seem to be responsible for the deep-trap formation as evidenced by the microstructural/morphological results, and consequently, the improved resistance to trap the formation of triple-cation perovskites provides viability for further performance enhancement by surface passivation.