Interfacial defect passivation in CH3NH3PbI3 perovskite solar cells using modifying of hole transport layer

In perovskite (PSK) solar cells, the selective contacts between interfaces of PSK and charge carrier have an important role in power conversion efficiency (PCE). The active defect sites in the device interfaces control the charge and ionic accumulation that can disturb the operation of devices. In this work, mesoporous PSK solar cells were fabricated and the interfacial defects between polymer HTL and PSK layers were neutralized by modifying HTL. 31% PCE enhancement was achieved by replacing poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) HTL instead of the P3HT HTL in the mesoporous perovskite device. The achieved PCE improvement strongly depends on the interface between PSK and HTM that was studied by optical and electrochemical impedance analyses. Introducing PCBM to P3HT HTL overcame the challenge of the interface defects caused by the non-uniformity of the PSK layer and the inappropriate presence of the pinholes. This architecture reduced the shunt-leakage paths and enhanced the incident photon harvesting, leading to the enhancement of PCE from 10 to 13.14%. These desired effects of P3HT: PCBM were confirmed by enhancement of the recombination resistance and reduction of the charge accumulation at the interfaces. Further, the defect passivation by interface modification reduced the hysteresis behavior of the PSK device.