Impact of B-Site Cation Substitution on Ionic and Electronic Charge Transport in Metal Halide Perovskites

Investigation of the mixed electronic and ionic charge transport in metal halide perovskite semiconductors has been challenging due to undesirable ion migration effects that accompany electronic charge transport. This results in unusual nonlinear hysteretic characteristics and significant degradation of the device performance. Here, we develop an understanding of the ionic and electronic transport using a combination of charge transport, impedance spectroscopy, and lateral conductivity measurement to illustrate the difference in the vertical and lateral ionic and electrical conductivity in these classes of perovskite materials. Our measurements indicate that, although the vertical electronic charge transport remains unaffected by B-site compositional variation, the lateral conductivity increases by at least one order of magnitude upon substitution of Sn. Furthermore, the incorporation of Sn decreases both the vertical and lateral ionic conductivity. The observed decrease in the ionic conduction is attributed to the inherent Sn vacancy, which compensates for the ionic defects through the creation of neutral defect complexes. Our results provide clear guidance for developing strategies to control the ionic conductivity without significantly affecting the electronic conductivity, which can lead to stable hysteresis-free high-performance optoelectronic devices.