Electrochemical and atomic force microscopy investigations of the effect of CdS on the local electrical properties of CH3NH3PbI3:CdS perovskite solar cells

Abstract

The effects of the incorporated CdS on the local optoelectronic properties of CH₃NH₃PbI₃:CdS bulk heterojunction (BHJ) perovskite solar cells (PSCs) are studied using Kelvin probe force microscopy (KPFM), conductive atomic force microscopy (c-AFM) and electrochemical impedance spectroscopy (EIS). The KPFM and c-AFM results clearly show that as the amount of incorporated CdS increases, the incorporated CdS creates more uniform and compact perovskite films. Moreover, the incorporated CdS nanoparticles lead to a higher surface potential and a more uniform and higher photocurrent distribution on the CH₃NH₃PbI₃:CdS active layer, which indicates that the CdS nanoparticles can lead to more effective photo-generated electron transfer from the CH₃NH₃PbI₃ to the CdS and proves experimentally that the CdS nanoparticles can form a continuous photo-generated electron transport channel. The EIS results show that the CdS can effectively decrease the contact resistances at the active layer/electron transport layer and the active layer/hole transport layer interfaces and it helps in the charge collection of the cells, which further confirms that the CdS nanoparticles can play the role of transporting electrons. Our study provides a nanoscale understanding of the improved device performance of CH₃NH₃PbI₃:CdS PSCs.