Design of Mixed‐Cation Tri‐Layered Pb‐Free Halide Perovskites for Optoelectronic Applications

Abstract

the recorded photovoltaic (PV) efficiency is over 23% in the laboratory. [1,[4][5][6] Such merits for high-performance optoelectronics are governed by their unique electronic structure features, which can mainly be attributed to the ns 2 lone-pair electrons of Pb 2+ and Sn 2+ cations. [7,8] The presence of ns 2 cations in these perovskites gives rise to pronounced curvature in both valence and conduction band edges through considerable antibonding hybridization with the halide anions. This facilitates the formation of the shallow defect states to induce carriers, balanced and low electron and hole effective masses for efficient charge transport and carrier extraction. [8,9] Additionally, the enhanced Born effective charges (relative to nominal ionic charges) and large static dielectric constant contribute to screening charged defects and impurities, thereby suppressing carrier scattering and trapping. [7,10] Despite the progress achieved in halide perovskites for optoelectronic applications, the poor long-term material and device stability under normal operation condition impedes their commercialization, [4,11,12] though protecting active perovskite layers, [4,6,9] mixing organic and inorganic A site ions, [13,14] and exploiting low-dimensional counterparts have shown enhanced stability. [14][15][16] More importantly, at this stage it is not clear whether the toxic issue of Pb 2+ ions would hinder the practical device application of halide perovskites.In this regard, eco-friendly Bi 3+ -and Sb 3+ -based perovskites with the similar ns 2 electron configuration as Pb 2+ have attracted significant research interest. [17][18][19] Within the threedimensional (3D) perovskite framework formed by cornersharing octahedral motifs, lead-free double halide perovskites have been proposed by hetero-substituting Pb 2+ with the cation pair of monovalent metal (e.g., Na + , Ag + ) and trivalent metal (e.g., Sb 3+ , Bi 3+ , and In 3+ ) by exploiting the cation transmutation principle in conventional tetrahedral semiconductors. [20][21][22][23] It is worth noting that the predicted inorganic double perovskites, such as Cs 2 AgBiCl 6 , Cs 2 AgBiBr 6 , Cs 2 AgInCl 6 , have been experimentally proved more stable against decomposition under humidity and light emission. [21,22,24] However, these quaternary double perovskites exhibit weak light emission/absorption because of the indirect bandgap feature or the parity-forbidden band-edge transition. [21,24,25] While for the purely Sb 3+ -and Bi 3+ -based perovskites, they show enhanced air-stability but To eliminate the toxic Pb 2+ cation in hybrid halide perovskites, M′ 3+ cations of Bi/Sb-based layered halide perovskites are being increasingly investigated for optoelectronic applications. However, such M′ 3+ trivalent cations constrain the face-sharing bioctahedral or the bi-layered perovskites required to meet the charge neutrality condition. This usually gives rise to oversized indirect bandgaps and inferior carrier transport. Recent experiment suggested a mixed-cation tri-layered ha...

High‐throughput computational materials screening and discovery of optoelectronic semiconductors

“…They successfully identified six orthorhombic lead‐free hybrid organic–inorganic perovskites with ideal bandgap (0.9–1.6 eV) and room temperature thermal stability from 5,158 unexplored hybrid organic–inorganic perovskites. Liu et al 188 identified a set of mixed‐cation tri‐layered Pb‐free halide perovskites (A 4 MM′ 2 X 12 ) with the HT material screening framework. First, they selected four ground state scaffold structure as the structure prototypes.…”

Exotic Structural and Optoelectronic Properties of Layered Halide Double Perovskite Polymorphs

“…As shown in Figure a–c and Figure S4, Supporting Information, ground‐state Rb 4 SnSb 2 Br 12 may be stable in the region of −1.3 eV ≦ Δμ Sn ≦ −0.6 eV, which is consistent with a previous study (≈−1.4 eV to −0.5 eV). [ 35 ] Therefore, growing high quality Rb 4 SnSb 2 Br 12 thin film is expected to be challenging, similar to other quaternary compounds. [ 36–38 ] It is worth noting that density functional theory (DFT) calculations might underestimate the stability of some perovskite compounds.…”

High‐throughput computational design of halide perovskites and beyond for optoelectronics

“…They also found that thickness adjustment of the inserted layers can tune the compounds’ bandgaps and effective masses. Later in 2019, Liu et al studied A 4 MM' 2 X 12 compounds by computational screening of different element combinations, namely A = (K + and Cs + ), M = (Zn 2+ and Sn 2+ ), M' = (Bi 3+ and Sb 3+ ), and X = (Cl − , Br − , and I − ) 114 . The authors first determined the ground‐state scaffold structure of the compounds by comparing different crystal structures and M/M' configurations.…”

“…Later in 2019, Liu et al studied A 4 MM' 2 X 12 compounds by computational screening of different element combinations, namely A = (K + and Cs + ), M = (Zn 2+ and Sn 2+ ), M' = (Bi 3+ and Sb 3+ ), and X = (Cl − , Br − , and I − ). 114 The authors first determined the ground-state scaffold structure of the compounds by comparing different crystal structures and M/M' configurations. Second, they checked decomposition pathways and phase diagrams to screen the thermodynamic stability.…”