Flexo-photovoltaic effect and above-bandgap photovoltage in halide perovskites

TL;DR

This paper investigates the flexo-photovoltaic effect in halide perovskites, demonstrating that strain gradients can generate large photovoltages exceeding the bandgap, offering a new pathway for photovoltaic enhancement beyond traditional junction limits.

Contribution

It is the first to measure and compare the flexo-photovoltaic effect in halide perovskites, revealing its potential to surpass conventional photovoltaic limits through strain engineering.

Findings

Flexo-photovoltaic effect in halide perovskites is significantly larger than in oxides.

Photovoltages exceeding the bandgap can be achieved with sufficient strain gradients.

The effect adds to native bulk photovoltage, which is hysteretic and switchable.

Abstract

Halide perovskites have outstanding photovoltaic properties which have been optimized through interfacial engineering. However, as these materials approach the limits imposed by the physics of semiconductor junctions, it is urgent to explore alternatives, such as the bulk photovoltaic effect, whose physical origin is different and not bound by the same limits. In this context, we focus on the flexo-photovoltaic effect, a type of bulk photovoltaic effect that was recently observed in oxides under strain gradients. We have measured the flexo-photovoltaic effect of MAPbBr3 and MAPbI3 crystals under bending and found it to be orders of magnitude larger than for SrTiO3, the benchmark flexo-photovoltaic oxide. For sufficiently large strain gradients, photovoltages bigger than the bandgap can be produced. Bulk photovoltaic effects are additive and, for MAPbI3, the flexo-photovoltage exists on top of a native bulk photovoltage that is hysteretic, consistent with the electrically switchable macroscopic polarization of this material. The results suggest that harnessing the flexo-photovoltaic effect through strain gradient engineering can provide a functional leap forward for halide perovskites.