Weak Fermi level pinning and low barrier interfacial contact: 2D lead-free perovskites on multilayer GaN

Abstract

Metal halide perovskites (MHPs) have shown great potential in photovoltaic and electronic fields due to their high charge carrier mobility, adjustable band gap and extremely high absorption coefficient. The formation of a type-II band alignment heterojunction between a perovskite and an electron transport layer is a commonly used method to enhance electron transport. However, traditional heterojunctions have strong Fermi level pinning (FLP) and high contact potential barriers that limit electron transfer efficiency. In this work, we report a novel semiconductor–semiconductor junction (SSJ) based on MHPs to simultaneously address the limitations of potential barriers and FLP on electron transport. By integrating Ba²⁺ passivated 2D lead-free perovskites with GaN nanosheets to construct the Ba–CsSrI₃/GaN SSJ, we eliminate high potential barriers and overcome interfacial gap states to achieve effective carrier migration. It is found that the negative electron affinity (NEA) formed at the Ba/GaN (0001) interface eliminates the adverse effects of interface dipole moments, allowing electrons to spontaneously cross the interface through GaN layers. The Schottky–Mott rule proves that the FLP is controlled within a very small range. In addition, as the number of GaN layers increases, the NEA at the interface remains unchanged and the type-II band alignment changes to a zero band gap while still maintaining the ability to extract electrons, forming a low barrier contact with a high conductivity of 7.79 × 10³ S cm⁻¹. These findings demonstrate the significant potential of GaN as the electron transport layer of the Ba–CsSrI₃ perovskite in applications such as photovoltaic devices, photodetectors, and integrated circuits.