Orientational migration of halide ion in lead halide perovskites

TL;DR

This study reveals the preferred directions of halide ion migration in lead bromide perovskite microplates by using built-in potentials, providing insights that could enhance perovskite solar cell performance.

Contribution

It introduces a novel experimental approach to observe ionic migration directions in lead halide perovskites using built-in potentials without external bias.

Findings

Halide ions migrate along specific crystal directions.

Reduction of Pb2+ to Pb0 occurs at un-irradiated centers.

Migration directions align with recent theoretical models.

Abstract

With the rapid evolution of lead halide perovskite solar cells, there are considerable evidences that the mobile ions strongly impact their properties. However, except the activation energy, the other properties of ionic migration are mostly explored with first principle calculations. Here we investigate the migration of halide ion (vacancy) in lead bromide perovskite single crystalline microplates. In contrast to conventional studies with external bias voltages, we introduce built-in potentials into the microplates via low-energy electron beams and study the corresponding ionic migrations. By aligning the potentials along particular crystal planes, the reduction of Pb2+ to Pb0 has been observed at the un-irradiated center of each cell, demonstrating that the migration of halide ion has preferred directions for the first time. Our observations are consistent with the recent theoretical models and shall open up a new route to improve the performances of perovskite solar cells.