Electrical Analysis of Mobile Ion Reaction According to the Applied Voltage for Lead Halide Perovskite Solar Devices

Lead halide perovskite has significantly improved efficiency and stability over the past decade. This has been achieved by various passivation and surface treatment, such as understanding the trap density and interface of the perovskite thin film. For trap density analysis, dark current-voltage curve is typically used by various fitting formulas of space charge limited current (SCLC). In addition, it is possible to extract charge carrier, depletion region, built in potential (V_bi), and trap density inside the device measured by capacitance-voltage (C-V) curve. However, perovskite still has limitations in exactly device analysis due to its unusual electrical behavior. Especially, mobile halogen elements cause perturbation with peripheral carriers by continuous electric fields. Since the general electrical measurement methods applied to the device by continuous voltage, it is difficult to exclude the effect of mobile halogen ions. Here, we have investigated the dark current-voltage and capacitance-voltage characteristics using pulsed voltage for more accurate analysis of perovskite solar device. The use of pulsed voltage could be measured by limiting the movement of halogen elements and changing the inside of the perovskite film from an abnormal state to a normal state. In the case of methyl-ammonium lead tri-iodide (MAPbI₃), migration of halogen ions was suppressed, and reproducible V_bi was observed even after multiple measurements. The calculated trap density from the low temperature C-V curve was obtained as 5x10¹⁶ cm^-3, which is equivalent to the value extracted from the SCLC curve measured by pulse voltage.