Strong Electron Localization in Tin Halide Perovskites.

Hassan Ouhbi,Francesco Ambrosio,Filippo De Angelis,Julia Wiktor

doi:10.1021/acs.jpclett.1c01326

Abstract

Tin halide perovskites (THPs) have been established as a lower-toxicity alternative to lead halide perovskites. In spite of the increasing interest, the behavior of photoexcited charges has not been well understood in this class of materials. We here investigate the behavior of excess electrons in a series of tin halide perovskites by employing advanced electronic-structure calculations. We first focus on CsSnBr3 and show that electron localization is favorable in this compound and that bipolaronic states are the most stable form of self-trapped electrons. We then extend the analysis to CsSnI3, CsSnCl3, MASnBr3, FASnBr3, and DMASnBr3 and show that electron bipolarons are stable in all these compounds, thus indicating that strong electron localization is recurrent in THPs.

Highlights

Tin halide perovskites (THPs) have been established as a lower-toxicity alternative to lead halide perovskites
The highest efficiencies to date have been obtained with compounds containing lead, a toxic element.[2−5] Tin halide perovskites (THPs) exhibit a lower toxicity[6] and are considered as one of the most promising replacement of LHPs because of their high absorption coefficients, long lifetimes of photogenerated charges, and low impact of defects.[7−10] The main issue hindering the successful use of THPs is related to their stability, which is hampered by charge-trapping processes
Intrinsic to tin chemistry, might be circumvented by either deploying surface passivation strategies[10] or by alloying tin with lead[13] in lead-alleviated perovskites. These strategies address mainly hole-trapping processes while not accounting for electron localization, which may play a major role in THPs, as their band edges are generally closer to the vacuum level with respect to LHPs.[10]

Summary

Introduction

Tin halide perovskites (THPs) have been established as a lower-toxicity alternative to lead halide perovskites. We first consider single- and double-electron polarons in “polymorphous”[14] cubic structures of CsSnBr3 and extend the analysis to other THPs. We show that double polarons (bipolarons), associated with the formation of Sn−Sn bonds and leading to strong electron-trapping, are stable in all the studied THPs, indicating a common behavior for this class of materials.

Results

Conclusion