Mixed Valence Cs₄SbBiCl₁₂ Perovskite Derivative As Photovoltaic Absorber:A First Principle Investigation

In the age of high-profile solar cells,the lead-based perovskite solar cells have demonstrated unprecedented progress in efficiency and its architecture evolved in just several years,due to its numerous unique advantages.However,its application in photovoltaic devices is often limited by the inherent toxicity of lead and the poor structural stability of lead-based perovskites.This fact opened up a new research field on lead-free metal halide perovskites,which is currently remarkably vivid.In theory and experiment,both of the trivalent and pentavalent antimony/bismuth-based halides lead-free low-dimensional perovskites have been proposed as photovoltaic absorber materials.However,the band gaps of trivalent and pentavalent metal-based compounds are wider and the holes of pentavalent metal-based perovskite derivatives are heavier.Herein,we present density functional theory?DFT?investigation of the electronic properties of Sb⁵⁺and Bi³⁺-based zero-dimensional mixed valence perovskite derivative Cs₄SbBiCl₁₂ and its bandgap engineering,as well as the light absorption curves of the semiconductors.We find that the narrow indirect band gap of Cs₄SbBiCl₁₂perovskite derivative?1.03 eV?is much smaller than the monovalent two-dimensional?-Cs₃Sb₂Cl₉?3.18 eV?and zero-dimensional CsSbCl₆?3.04 e V?chlorides.As a result,the steeper valence band edges consist of the strong antibonding interactions between the Bi s lone pair states and Cl pstates;the conduction band edges are derived from antibonding interactions between Sb s orbital and Cl p orbital.The band gap of Cs₄SbBiCl₁₂ is regulated from indirect to direct band gap in two methods.Firstly,the bandgap can be tuned from indirect to direct by trivalent cations In³⁺and Tl³⁺substitution for Bi³⁺,forming the structurally similar Cs₄SbInCl₁₂ and Cs₄Sb TlCl₁₂stable substitutions.The corresponding direct band gaps were 1.93 eV and 1.63 eV,respectively.Additionally,the order-disordered transition of B-sites double cations Sb and Bi is realized and indirect-direct band adjustment can also be achieved in some stable disordered structures.In the visible light range,the semiconductor materials including the ordered and partial disordered Cs₄SbBiCl₁₂ as well as two Cs₄SbInCl₁₂and Cs₄SbTlCl₁₂ substitutions show the satisfactory optical absorptions over 10⁴ cm^-1.The results legitimately prove that the Cs₄SbBiCl₁₂ perovskite derivative have potential applications in solar cell photovoltaic devices as absorber materials due to their suitable tunable bandgaps and outstanding light absorptions,which also provides a new way to design low dimensional but narrow gaps perovskite or perovskite derivatives with high oxidation metals.