Electronic properties of MAPb<i>x</i>Sn1−<i>x</i>I3 hybrid perovskite alloys: k.p modeling for tetragonal crystal symmetry with C4<i>v</i> point group

Abstract

MAPb x Sn 1 − x I 3 alloys are highly promising for photovoltaic, optoelectronic, and spintronics applications. Using k.p calculations, we derived the fundamental band parameters of these tetragonal hybrid halide perovskites as a function of Pb content (x). Our study focuses on the experimentally confirmed C4v point group structures: P4mm for Sn-rich alloys and I4cm for Pb-rich alloys. Our theoretical model successfully reproduces the non-monotonic behavior of the bandgap and provides detailed insights into the electron, hole, and reduced exciton masses (me, mh, and μ). We find that hole masses are slightly larger than electron masses, with both increasing linearly as x rises. At the structural transition (x=0.5) between P4mm and I4cm, we observe a discontinuity in hole masses and a steeper linear increase in Pb-rich structures. The calculated exciton masses show excellent agreement with experimental data across a wide range of alloy compositions. Additionally, we predict the Landé g-factors for charge carriers (ge, gh) and excitons (gX). For Pb-rich alloys, ge increases with decreasing bandgap energy, while for Sn-rich alloys, ge decreases. Exciton g-factors gX are predominantly governed by the large positive ge values, as the smaller negative gh values provide minimal compensation. Consequently, gX is not constant but varies with the bandgap, ranging from 2.4 and 4.8 for Pb-rich alloys and from 4.8 and 3.7 for Sn-rich alloys. These results highlight the tunable electronic and spin properties of MAPbxSn1−xI3 alloys, positioning them as versatile candidates for next-generation device applications.