First-principles investigation of intrinsic point defects in perovskite CsSnBr3

Lead-free perovskites $\mathrm{CsSn}{\mathrm{Br}}_{3}$ were predicted to be promising for photovoltaic applications, yet the measured performance is rather disappointing. To understand the mechanism behind the large discrepancy and to further improve the functionality, we study the stability, transition energy levels, and diffusion of different intrinsic defects in pure $\ensuremath{\alpha}\ensuremath{-}\mathrm{CsSn}{\mathrm{Br}}_{3}$ using density-functional theory calculations. Our results reveal the unique characteristics of the intrinsic defects and their effects on the optoelectronic properties of perovskite $\mathrm{CsSn}{\mathrm{Br}}_{3}$. Among the low formation energy defects, the vacancy defects ${V}_{\mathrm{Sn}}$ and ${V}_{\mathrm{Cs}}$ can form shallow energy levels to provide $p$-type conductivity, while the antisite defects ${\mathrm{Br}}_{\mathrm{Sn}}$ and $\mathrm{Br}{}_{\mathrm{Cs}}$ can act as detrimental recombination centers to deteriorate the performance of devices. Moreover, the mobile defects ${V}_{\mathrm{Sn}}^{2\ensuremath{-}}$ and ${V}_{\mathrm{Cs}}^{\ensuremath{-}}\phantom{\rule{0.28em}{0ex}}$ also degrade device performance by the field-screening effect. The effect of the chemical potential modulation of $\mathrm{Sn}{\mathrm{F}}_{2}$ addition into $\mathrm{CsSn}{\mathrm{Br}}_{3}$ is also discussed. These results provide in-depth insights into defect behaviors in the Sn-based perovskites and shed light on related optoelectronic applications.