Influence of A site cation on nonlinear band gap dependence of 2D Ruddlesden–Popper A₂Pb_1−xSn_xI₄ perovskites

Abstract

Ruddlesden-Popper phase (RPP) perovskites of the form A1n−1A22BnX3n+1 show great promise in stable photovoltaic (PV) devices or as light emitting diodes (LEDs). In particular, n= 1, mono-layer RPPs of the...

Theoretical investigation of octahedral tilting and bandgap non‐linearity in monolayer Ruddlesden‐Popper A 2 Pb 1‐x Ge x I 4 perovskites

“…The structural analysis was performed using an atomic simulations environment (ASE) 76 . The band structure and density of states (DOS) were post‐processed using Matplotlib, SciPy, NumPy, and Seaborn 23 . Following the frozen core approximation, the active valence orbitals of contributing atoms were considered as: Pb 14 (5d 10 6s 2 6p 2 ), Ge 14 (3d 10 4s 2 4p 2 ), I 7 (5s 2 5p 5 ), C 4 (2s 2 2p 2 ), H 1 (1s 1 ), and N 5 (2s 2 2p 3 ).…”

“…For x = 0.50, depending on the nearest neighbouring or diagonally located Ge‐atoms in the simulation cell, the permutations were classified as “columns‐(C50%)” and “battenberg‐(B50%),” respectively. A non‐linear fitting to theoretical bandgap data was performed using the parabolic function in line with previous work, 23,52 describing the bandgap non‐linearity, given by Equation (). The bowing parameter ( b ) measures the nonlinear dependence of the bandgap. …”

“…To combat these challenges of toxicity and instability simultaneously, 22 it is required to design alternative lead‐free and hydrophobic perovskites and investigate their electronic properties to simulate/fabricate in solar cells. Following lead‐free directives, toxic Pb 2+ (6s 2 ) can be replaced with similarly configured ns 2 ‐elements belonging to Group‐IV 23 . In this concern, Tin (Sn 2+ ‐5s 2 ) and Germanium (Ge 2+ ‐4s 2 ) are reasonable choices, without compromising much on the higher photoconversion efficiency of Pb‐based PSCs, and thus lead toxicity can be alleviated 24 .…”

“…Following lead-free directives, toxic Pb 2+ (6s 2 ) can be replaced with similarly configured ns 2 -elements belonging to Group-IV. 23 In this concern, Tin (Sn 2+ -5s 2 ) and Germanium (Ge 2+ -4s 2 ) are reasonable choices, without compromising much on the higher photoconversion efficiency of Pb-based PSCs, and thus lead toxicity can be alleviated. 24 To date, several theoretical and experimental investigations have reported successful Pb-replacement with Sn as CsPb 1Àx Sn x I 2 Br which is proved as an ideal perovskite with a favourable bandgap 25 but there are still some knowledge gaps left to achieve reasonable and promising accuracy.…”

“…Fu et al 50 relaxed the Goldschmidt tolerance factor requirement for 2D-perovskites allowing various large organic cations to occupy the cuboctahedral cavity of the perovskite cage in 2D-perovskites. Ruddlesden-Popper (RP) phase 23,46,48,51,52 as an important class of 2Dperovskites has monoamine R-NH 3 cations as PEA + . 53 These bulky hydrophobic organic spacer cations fill the voids between inorganic sheets of metal-halide octahedral cages (BX 6 ) 4À , thus could be a promising solution to address the stability issue.…”