Surface phase diagram of CsSnI$_3$ from first-principles calculations

TL;DR

This study uses first-principles calculations to map the surface phase diagram of CsSnI$_3$, revealing how surface stability and electronic states vary with chemical conditions, informing better optoelectronic device design.

Contribution

It provides the first detailed surface phase diagrams of CsSnI$_3$ surfaces under various conditions, identifying stable surfaces and their electronic properties.

Findings

I-rich conditions stabilize Cs vacancy surfaces with surface states.

I-poor conditions favor stable, surface-state-free (100) surfaces.

I-poor (Sn-rich) conditions are more suitable for device performance.

Abstract

CsSnI$_3$ is widely studied as an environmentally friendly Pb-free perovskite material for optoelectronic device applications. To further improve material and device performance, it is important to understand the surface structures of CsSnI$_3$. We generate surface structures with various stoichiometries, perform density functional theory calculations to create phase diagrams of the CsSnI$_3$ (001), (110), and (100) surfaces, and determine the most stable surfaces under a wide range of Cs, Sn, and I chemical potentials. Under I-rich conditions, surfaces with Cs vacancies are stable, which lead to partially occupied surface states above the valence band maximum. Under I-poor conditions, we find the stoichiometric (100) surface to be stable under a wide region of the phase diagram, which does not have any surface states and can contribute to long charge carrier lifetimes. Consequently, the I-poor (Sn-rich) conditions will be more beneficial to improve the device performance.