Steric engineering of metal-halide perovskites with tunable optical band gaps

TL;DR

This paper demonstrates that the optical band gap of metal-halide perovskites can be tuned by controlling the metal-halide-metal bond angle through steric effects, enabling targeted design of materials for solar cell applications.

Contribution

It introduces a simple structural descriptor, the largest metal-halide-metal bond angle, for predicting and tuning the band gap of perovskites, facilitating rational design.

Findings

Bond angle correlates with optical band gap.

Steric control of cations tunes bond angles.

Predicted and synthesized novel low-gap perovskites.

Abstract

Owing to their high energy-conversion efficiency and inexpensive fabrication routes, solar cells based on metal-organic halide perovskites have rapidly gained prominence as a disruptive technology. An attractive feature of perovskite absorbers is the possibility of tailoring their properties by changing the elemental composition through the chemical precursors. In this context, rational in silico design represents a powerful tool for mapping the vast materials landscape and accelerating discovery. Here we show that the optical band gap of metal-halide perovskites, a key design parameter for solar cells, strongly correlates with a simple structural feature, the largest metal-halide-metal bond angle. Using this descriptor we suggest continuous tunability of the optical gap from the mid-infrared to the visible. Precise band gap engineering is achieved by controlling the bond angles through the steric size of the molecular cation. Based on these design principles we predict novel low-gap perovskites for optimum photovoltaic efficiency, and we demonstrate the concept of band gap modulation by synthesising and characterising novel mixed-cation perovskites.