Theoretical Prediction of Mixed-Valence Layered Halide Perovskites Cs₄M(IV)M(II)₂X₁₂ (M = Ge, Sn; X = Cl, Br)

Abstract

Charge-ordered compounds (i.e., Cu+/Cu2+, Au+/Au3+, In+/In3+, Tl+/Tl3+, Sb3+/Sb5+, and Bi3+/Bi5+) have been widely explored because of their unique physical properties. Here, a new class of ⟨111⟩-oriented mixed-valence layered halide perovskites Cs4M­(IV)­M­(II)2X12 (M = Ge, Sn; X = Cl, Br) with C2/m, R-3m, and I41/amd space groups was predicted by first-principles calculations. Based on the decomposition enthalpy, the phonon spectrum, and the mechanical stability criteria, we found that Cs4GeGe2Cl12 (C2/m and R-3m), Cs4GeGe2Br12 (R-3m), and Cs4GeGe2Br6Cl6 (R-3m) exhibit thermodynamic, dynamical, and mechanical stability. The electronic structure calculations show that the predicted band gap of stable Cs4Ge­(IV)­Ge­(II)2X12 varies from 1.16 to 2.25 eV. And an isolated intermediate conduction band contributed by the Ge­(IV) 4s states below the Ge­(II)/Ge­(IV) 4p states is observed in these compounds, which is similar to previously reported Cs4CuSb2Cl12 but different from Cs4CdM­(III)2Cl12 (M = Sb, Bi). In addition, the calculated static dielectric constant and optical absorption coefficient of Cs4GeGe2Br12 are close to those of typical double perovskites (e.g., Cs2AgBiBr6). We believe that our work enriches the family of mixed-valence halide perovskites and provides a new platform for potential optoelectronic semiconductor design.

Investigation of Defects in Cs2SnI6‐Based Double Perovskite Solar Cells Via SCAPS‐1D

“…[4,5] Although there are various lead substitutes (Sn, Ge, etc.) available, [6] these substitutions obstruct band alignment as the B-cation and halide play a vital role in band edge creation in the ABX 3 structure which impacts optoelectronic characteristics. Many researchers have been working to develop lead-free [7,8] and environmentally acceptable perovskites for green-energy photovoltaics.…”

Morphology and structure of lead‐free CuSb‐based double perovskites for photocatalytic CO2 reduction

“…have been extensively investigated. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Han and colleagues reported the colloidal synthesis of air-stable Cu(I) − Sb-based DP Cs 2 CuSbCl 6 nanocrystals (NCs) with a bandgap of 1.66 eV, which showed that these NCs would have great potential to be used as a light-absorbing material. [34] The stable Cs 4 CuSb 2 Cl 12 layered DP powders and NCs with a direct small bandgap and superior optoelectronic properties were reported.…”

Thermal Transport and Thermoelectric Properties of Rb2PdX6 (X=Cl, Br) from First‐principles Study

“…Perovskite materials are widely used in the field of optoelectronics, and many perovskites have excellent performance in the field of thermoelectricity. [5][6][7][8][9][10][11][12][13] Compared with simple perovskite, double perovskite has the advantages of nontoxicity and structural stability, and it is an excellent potential TE because of its rich elemental variety and low cost. Among them, halide based double perovskites are suggested new type of TE materials due to good electrical transport and low phonon transport properties.…”

“…Perovskite materials are widely used in the field of optoelectronics, and many perovskites have excellent performance in the field of thermoelectricity [5–13] . Compared with simple perovskite, double perovskite has the advantages of non‐toxicity and structural stability, and it is an excellent potential TE because of its rich elemental variety and low cost.…”