In recent years, organometal trihalide perovskite (OTP) has been being an emerging material for application in high-efficiency solar cells. OTP-based solar cells have a lot of advantages including low cost, solution-processible availability. Despite high efficiency, the existence of defects in the bulk OTP materials and at the interface between them and other charge-transport materials is a hindering factor that deteriorates the performance of OTP photovoltaic devices. The effort of understanding the origin of those defects and their effects on the performance of OTP devices is the main goal of our work.
In this work, we studied and investigated the effect of several trap states existing within CH3NH3PbI3-based planar solar cells (PSCs) with copper-doped nickel oxide (Cu:NiOx) as hole-extraction layers (HELs). Experimental current-voltage (J-V) characteristics and Electrochemical Impedance Spectroscopy (EIS) spectra were guidelines for us to detect the existence of defect in the bulk CH3NH3PbI3 (MAPbI3) active layer (AL) and at the interface between ALs and HELs. Based on those experimental evidences and real device structure, we built a model and utilized Solar Cell Capacitance Simulator (SCAPS) to simulate J-V curves and capacitance-conductance-frequency (C-G-f) spectra simultaneously. We were able to find some important parameters of the microscopic model, especially those belong to defects, including their energy level, energetic distribution, density and charge trapping probability. In addition, the microscopic models of the defect were able to efficiently describe the hysteresis phenomenon, that exhibits in variations of device performance with scan rate and direction. The systematic approach we reported in this work is general enough to be applied to other solar cell systems to identify and quantify defects hampering device operation. Detailed identification and quantification of defects are prerequisites for developing efficient passivation technique that can minimize detrimental defect effects to improve device performance further.
