Influence of Different Length Alkyl Ammonium Chains on the Optoelectronic Properties of Two-Dimensional A′₂CsPb₂Br₇ Perovskites

Two-dimensional (2D) layered organic–inorganic halide perovskites have received increasing research attention because their multiple chemical components impart them with tunable photophysical characteristics. In this study, the influence of organic alkyl ammonium chains on the electronic structures and optical properties of hybrid 2D Ruddlesden–Popper (RP) phase layered halide perovskites A′ 2 Cs m –1 Pb m Br 3 m +1 ( m = 2) were investigated using first-principles calculations, wherein A′ (A′ = C 4 H 9 NH 3 (including n-butylamine (CH 3 (CH 2 ) 3 NH 3, BA), isobutylamine ((CH 3 ) 2 CHCH 2 NH 3, iBA)), C 6 H 13 NH 3, C 8 H 17 NH 3, C 10 H 21 NH 3, and C 12 H 25 NH 3 ) denotes the long alkyl ammonium chain, and m represents the number of inorganic perovskite layers between the long organic chains. The tunable anisotropic structures, electronic structures, transition dipole moments (TDM), and optical properties of these layered halide perovskites were computed, and the obtained results indicated that the in-plane structural distortion caused by the variation in the length of the organic chain led to changes in the band gap. The reduced in-plane structural distortion in these perovskites favors the stronger degeneracy between the top PbBr 2 layer and the bottom PbBr 2 layer, and is responsible for the reduced band gap. Moreover, these 2D layered halide perovskites with a large degree of structural distortion in the [PbBr 6 ] 4– octahedra exhibited a small TDM value.