Pandech Narasak, Kongnok Thanundon, Palakawong Nirawith, Limpijumnong Sukit, Lambrecht Walter R L, Jungthawan Sirichok
School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok 10400, Thailand.
ACS Omega. 2020 Oct 1;5(40):25723-25732. doi: 10.1021/acsomega.0c03016. eCollection 2020 Oct 13.
In hybrid perovskite materials like CHNHPbI, methylammonium (MA) lead iodide (MAPI), the orientation of the MA cations and their ordering can significantly affect the structure of the inorganic framework. Although the states near the band edges are known to be primarily derived from the Pb and halogen orbitals rather than from the organic ion, the latter may have an indirect effect through their impact on the structural relaxation. In this work, we investigate both the structural relaxation effects of the inorganic framework in response to the MA orientation and their impact on the electronic structure near the band edges. Calculations are performed for MA(Pb,Sn) with ( = I, Br, and Cl) materials for both Pb- and Sn-based compounds. The work focuses on the high-temperature α-phase, which is nominally cubic if averaged over all possible MA orientations and in which no alternating rotations of the octahedral occur, so that the unit cell is the smallest possible. The effects of van der Waals (vdW) corrections to density functional theory on the structural relaxation are investigated. Our results reveal that the vdW interactions between the MA cation and the inorganic framework can strongly affect the optimized orientation and position of the molecule and the resulting distortion of the inorganic framework. Consequently, it also affects the electronic properties of the materials and specifically can change the band structure from direct to indirect band gaps. The robustness of this result is studied by comparing hybrid functional calculations and quasiparticle self-consistent GW calculations as well as spin-orbit coupling.
在诸如CH₃NH₃PbI₃（甲脒铅碘，简称MAPI）这样的混合钙钛矿材料中，甲脒阳离子（MA）的取向及其有序排列会显著影响无机骨架的结构。尽管已知带边附近的态主要源自铅和卤素轨道而非有机离子，但后者可能通过对结构弛豫的影响产生间接作用。在这项工作中，我们研究了无机骨架响应MA取向的结构弛豫效应及其对带边附近电子结构的影响。对MA(Pb,Sn)X₃（X = I、Br和Cl）材料的铅基和锡基化合物都进行了计算。这项工作聚焦于高温α相，若对所有可能的MA取向进行平均，该相名义上为立方结构，且八面体不存在交替旋转，因此晶胞是可能的最小晶胞。研究了密度泛函理论中的范德华（vdW）校正对结构弛豫的影响。我们的结果表明，MA阳离子与无机骨架之间的vdW相互作用会强烈影响分子的优化取向和位置以及无机骨架由此产生的畸变。因此，它也会影响材料的电子性质，具体而言会使能带结构从直接带隙变为间接带隙。通过比较杂化泛函计算、准粒子自洽GW计算以及自旋轨道耦合来研究这一结果的稳健性。
