Carrier Transfer Behaviors at Perovskite/Contact Layer Heterojunctions in Perovskite Solar Cells

Hybrid halide perovskite based on CH3NH3PbI3 and related materials has emerged as the most exciting development in the next generation photovoltaic technologies. There is still requirement for an effective method to establish a relationship between the charge transfer behaviors and photovoltaic properties. This study presents Kelvin probe force microscopy and conductive atomic force microscopy measurements of versatile perovskite films that participate in the formation of different heterojunctions, exploring local current, contact potential difference (CPD), and charge activities at the nanoscale. By comparing the values of CPD and current of these perovskite films in dark and under illumination, the charge transfer behaviors are locally illustrated, suggesting that the perovskite roles in these heterojunctions are strictly dependent on the contact layers. Furthermore, the average difference (Delta V) of the CPD values obtained in dark and under illumination for each heterojunction can be set to analyze the efficacy of the perovskite/contact layer interfaces. The Delta V polarity is related to the type of charge carrier (hole or electron), while the Delta V magnitude is related to the number of charge carrier. These results emphasize the importance of understanding of these heterojunction systems that could guide the design and optimization of the photovoltaic configuration.