Halide perovskites: third generation photovoltaic materials empowered by metavalent bonding

TL;DR

This paper explains how metavalent bonding in halide perovskites leads to their excellent photovoltaic properties, offering a blueprint for designing advanced third-generation PV materials.

Contribution

It introduces the concept of metavalent bonding in halide perovskites and links it to their superior opto-electronic properties for photovoltaic applications.

Findings

Metavalent bonding differs from ionic, metallic, covalent bonds.

Halide perovskites exhibit small effective masses and strong optical absorption.

A bond map provides a blueprint for designing new PV materials.

Abstract

Third-generation photovoltaic (PV) materials combine many advantageous properties, including a high optical absorption together with a large charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABX3, where X is I, Br or Cl) appear to be the most promising third-generation PV materials at present. Their opto-electronic properties are governed by the B-X bond. A quantum-chemical bond analysis reveals that this bond differs significantly from ionic, metallic or covalent bonds. Instead, it is better regarded as metavalent, since it shares approximately one p-electron between adjacent atoms. The resulting sigma-bond is half-filled, which causes pronounced optical absorption. Electron transfer and lattice distortions open a moderate band gap, resulting in charge carriers with small effective masses. Hence metavalent bonding explains the favorable PV properties of halide perovskites. This is summarized in a map for different bond types, which provides a blueprint to design third-generation PV materials.