Ion Diffusion and Charge Transport Across 2D/2D and 2D/3D Perovskite Heterostructures

Heterostructures of two-dimensional (2D) materials have been shown to display unique charge transport properties across the junction region beneficial for many device architectures. 2D metal halide perovskites provide a versatile platform of tunable structures and band energies from which 2D heterostructures have been utilized for light-emitting diodes and 2D/3D halide perovskite heterostructures have been extensively utilized in solar cell devices. We have carefully controlled the identity of the individual single-crystal 2D perovskite phases to assemble well-defined vertical 2D/2D or 2D/3D perovskite heterostructures, a more robust method than traditional thin film fabrication. While anion diffusion in halide perovskites has been extensively studied, our results reveal that A-site and B-site cation diffusion also needs to be carefully considered. A-site diffusion, shown through 2D/3D heterostructures, appears to often occur regardless of LA spacer or A-site cation identity. In contrast, B-site cation diffusion across heterostructures appears to be much slower. Control of the heterojunctions is imperative to understanding charge transfer across the heterostructures. With stability boundaries established, we study how charge transfer occurs across a variety of perovskite heterostructure combinations, exploring potential type I and type II band gap alignments. Such fundamental understanding could help to guide the rational design of high-performance perovskite optoelectronic devices.