Electronic band structure, phonons, and exciton binding energies of halide perovskites CsSnCl3, CsSnBr3, and CsSnI3
Electronic band structure, phonons, and exciton binding energies of halide perovskites CsSnCl3, CsSnBr3, and CsSnI3
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DOI：
10.1103/physrevb.88.165203
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发表时间：
2013-10-17
影响因子：
3.7
通讯作者：
Lambrecht, Walter R. L.
中科院分区：
文献类型：
--
作者：
Huang, Ling-yi;Lambrecht, Walter R. L.
使用准粒子自洽引力波电子结构计算研究了卤化物钙钛矿 CsSnX3，其中 X = Cl、Br、I。人们发现这些材料具有与大多数半导体不同的“倒置”能带结构，具有非简并 s 型价带最大值 (VBM) 和三重简并 p 型导带最小值 (CBM)。小孔有效质量导致高空穴迁移率，与 CsSnI3 的最新报告一致。从 Cl 到 Br 再到 I 的相对较小的带隙变化分别是由于 VBM 和 CBM 的原子内 Sn s 和 Sn p 特性造成的。后者还导致这些直接带隙半导体中光学跃迁的高振荡器强度，从而产生强发光和吸收。带隙随晶格常数的变化也是反常的。它随着晶格常数的增加而增加，这是由于与阴离子 p 相互作用的 Sn 减少而导致价带宽度减少的结果。它导致间隙的异常温度依赖性。研究了不同低对称性晶体相中带隙的变化。根据 Wannier-Mott 激子理论和计算的介电常数和有效质量估计，自由激子的激子结合能比先前文献中声称的要小两个数量级，即 0.1 meV 量级。先前分配给自由激子的光致发光峰改为分配给受主束缚激子。计算伽玛点处的声子以及相关的介电常数增强。
The halide perovskites CsSnX3, with X = Cl, Br, I, are investigated using quasiparticle self-consistent GW electronic structure calculations. These materials are found to have an "inverted" band structure from most semiconductors with a nondegenerate s-like valence band maximum (VBM) and triply degenerate p-like conduction band minimum (CBM). The small hole effective mass results in high hole mobility, in agreement with recent reports for CsSnI3. The relatively small band gap changes from Cl to Br to I result from the intra-atomic Sn s and Sn p characters of the VBM and CBM, respectively. The latter is also responsible for the high oscillator strength of the optical transition in these direct-gap semiconductors and hence a strong luminescence and absorption. The band gap change with lattice constant is also anomalous. It increases with increasing lattice constant, and this results from the decreasing valence band width due to the decreased Sn s with anion p interaction. It leads to an anomalous temperature dependence of the gap. The changes in band gap in different lower-symmetry crystallographic phases is studied. The exciton binding energy of the free exciton, estimated from the Wannier-Mott exciton theory and the calculated dielectric constants and effective masses, is found to be two orders of magnitude smaller than previously claimed in literature, or of the order of 0.1 meV. The photoluminescence peak previously assigned to the free exciton is instead ascribed to an acceptor bound exciton. The phonons at the Gamma point are calculated as well as the related enhancement of the dielectric constants.