Relativistic origin of slow electron-hole recombination in hybrid halide perovskite solar cells

TL;DR

This paper explains the long-lived electron-hole pairs in hybrid halide perovskite solar cells by revealing a spin-split indirect bandgap caused by relativistic effects, which significantly reduces recombination rates and enhances solar cell efficiency.

Contribution

It demonstrates that the slow recombination in hybrid halide perovskites arises from a relativistic spin-split indirect gap, a novel insight into their electronic structure.

Findings

Recombination in MAPI is reduced by over 350 times compared to direct gap materials.

The indirect gap persists despite dynamic disorder in the material.

Carrier lifetime varies with light intensity and temperature, as predicted by QSGW calculations.

Abstract

The hybrid perovskite CH3NH3PbI3 (MAPI) exhibits long minority-carrier lifetimes and diffusion lengths. We show that slow recombination originates from a spin-split indirect-gap. Large internal electric fields act on spin-orbit-coupled band extrema, shifting band-edges to inequivalent wavevectors, making the fundamental gap indirect. From a description of photoluminescence within the quasiparticle self-consistent GW (QSGW) approximation for MAPI, CdTe and GaAs, we predict carrier lifetime as a function of light intensity and temperature. At operating conditions we find radiative recombination in MAPI is reduced by a factor of more than 350 compared to direct gap behavior. The indirect gap is retained with dynamic disorder.