Dynamics of Internal Electric Field Screening in Hybrid Perovskite Solar Cells Probed Using Electroabsorption

Abstract

Electric fields arising from the distribution of charge in metal-halide perovskite solar cells are critical for understanding the many weird and wonderful optoelectronic properties displayed by these devices. Mobile ionic defects are thought to accumulate at interfaces to screen electric fields within the bulk of the perovskite semiconductor on application of external bias, but tools are needed to directly probe the dynamics of this process. Here, we show that electroabsorption measurements allow the electric field within the active layer to be tracked as a function of frequency or time. The magnitude of the electroabsorption signal, corresponding to the strength of the electric field in the perovskite layer, falls off for externally applied low-frequency voltages or at long times following voltage steps. Our observations are consistent with drift-diffusion simulations, impedance spectroscopy, and transient photocurrent measurements. They indicate charge redistribution on timescales ranging from 10 ms to 100 s, depending on the device interlayer material, perovskite composition, dominant charged defect, and illumination conditions. The method can be used on typical solar-cell structures and has the potential to become a routine characterization tool for optimizing hybrid perovskite devices.