Efficient Modeling Workflow for Accurate Electronic Structures of Hybrid Perovskites

Abstract

Hybrid organic−inorganic halide perovskites are the most promising photovoltaic absorber materials to substitute or complement silicon in high-efficiency solar cells. These hybrid materials are often constrained by their low stability and critical elements like lead. Computational high-throughput screening studies, based on solid-state electronic-structure theory, are useful to identify promising substitute materials with targeted properties. In this work, we present an efficient computational approach based on density-functional theory, which is suitable to predict band gaps for arbitrary compounds reliably and in good quantitative agreement with experimental band gap data for known compounds. This approach is described and demonstrated for the building blocks of one of the most promising hybrid perovskites, namely, (HC(NH 2 ) 2 ) x Cs 1−x Pb(I y Br 1−y ) 3 , with x and y varied between zero and one.

The Electronic Structure of Cs2AgBiBr6 at Room Temperature

“…As demonstrated in our previous study, [ 34 ] the efficient evaluation of the electronic structure with density‐functional theroy (DFT) using PBE + 1/2 + SOC, for crystal structures relaxed with DFT using PBE + TS gives accurate results that agree very well with data from more demanding self‐consistent many‐body calculations. The inclusion of SOC is crucial for HPs containing heavy elements on the B, B’, and X sites in double‐perovskite structures.…”

“…[ 42 ] We will show in the following that dynamical structure effects at RT [ 43,44 ] can be excluded to lead to an increase of the bandgap for this material, in contrast to the case of CsPbX 3 compounds (with X = I and Br). [ 34,45 ] We conclude that the highest reported bandgap values correspond to CABB crystals with the lowest concentration of point defects. Hence, the intrinsic value of the indirect bandgap of the defect‐free crystal should be about 2.2 eV.…”

“…[ 49,50 ] For instance for CsPbI 3 , it has been shown that structural changes that occur at RT change the bandgap by as much as 0.7 eV. [ 34,45 ] The effect on the indirect bandgap that the various investigated CABB phases have is also shown in Table 1. The maximal difference in the electronic bandgap when comparing the three crystalline phases, 0.16 eV, is moderate and much smaller than, for example, for CsPbX 3 (with X = Br and I).…”

“…The maximal difference in the electronic bandgap when comparing the three crystalline phases, 0.16 eV, is moderate and much smaller than, for example, for CsPbX 3 (with X = Br and I). [ 34 ] This means that due to the shallow energy landscape, fluctuations of about 0.16 eV are to be expected for bandgap values measured at RT, with the structure locally changing to the phase of lower symmetry. However, the structural stability against more pronounced octahedral tilts suggests an absence of more severe bandgap changes induced by such dynamical distortions, as they have been observed for CsPbX 3 .…”

“…However, the structural stability against more pronounced octahedral tilts suggests an absence of more severe bandgap changes induced by such dynamical distortions, as they have been observed for CsPbX 3 . [ 34,45 ]…”