Perovskite halides have attracted substantial attention as materials for solar cell applications because of their fascinating optoelectronic and photovoltaic properties.We report the results of the first-principles calculations of the strain effects on electronic and optical properties and carrier mobility of vacancy-ordered Cs 2 SnI 6 double perovskite. The calculated band gap energy of unstrained Cs 2 SnI 6 is about 1.257 eV when using the Tran-Blaha modified Becke Johnson (mBJ) exchange potential, which is in good agreement with experimental measurements. Under the applied strains, the energy band gap value increases up to 1.316 eV for À4% compressive strain and decreases to 1.211 eV for 4% tensile strain. This effect is mainly due to the fact that the conduction band minimum shifts under compressive and tensile strains. Based on carrier mobility calculations, we notice that under tensile strain the hole and electron carrier mobility diminish, whereas the carrier mobility increases by 16.3% for electrons and by 9.1% for holes under À4% compressive strain. Moreover, data of the calculated optical constants indicate that applied strains can affect the optical properties of Cs 2 SnI 6 perovskite. | INTRODUCTIONOver the last few years, there has been a growing interest in developing and designing metal halide perovskite solar cell materials because of their impressive optoelectronic and photovoltaic properties. Among them, lead-based halide perovskites, with a general formula ABX 3 , have recently reached an efficiency of about 25.2% [1]. This high efficiency is attributed to the tunable energy band gaps, high optical absorption coefficients, low exciton binding energy, big carrier diffusion lengths, and long carrier lifetimes of the lead-bearing ABX 3 perovskites [2-6]. However, the instability of these materials [7-9] and toxicity of lead (Pb) is undesirable properties. With the aim of overcoming these undesirable properties, scientists have made a lot of attempts to find alternatives for substitution of lead, in particular using replacement of this toxic chemical element by more eco-friendly tin and germanium. Nevertheless, the maximum process cycle efficiency (PCE) of approximately 13% was reported in reference 10 for Sn-based perovskites that is lower than those of Pb-based perovskites, even if they possess suitable band gaps and high absorption coefficients [11][12][13][14].Recently, halides with a general formula A 2 BX 6 have attracted much attention as new alternative candidates for substituting lead-bearing ABX 3 perovskites [15][16][17][18][19][20][21][22][23][24][25]. In these perovskite derivatives, the B atoms are positioned at the centers of the [BX 6 ] À2 octahedra and the half of the B-sites are unoccupied; therefore, the [BX 6 ] À2 octahedra are isolated in these compounds [26]. Among these perovskite derivatives, the Cs 2 SnI 6 compound attracts a special attention due to its high stability at normal conditions and the Sn +4 oxidation state, instead of the Sn +2 state detected in the case of the...

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Owing to the fascinating optoelectronic and photovoltaic properties, perovskite halide materials have attracted much attention for solar cells applications. Using the first-principles approaches, we present here results of calculations of the strain effects on electronic and optical properties as well as carriers mobility of CsSnI double perovskite. The calculated band gap energy of unstrained CsSnI is about 1.257 eV when using Tran-Blaha modified Becke Johnson (mBJ) exchange potential that is in fair agreement with experimental measurements. Under the applied strains, this band gap value increases up to 1.316 eV for -4% compressive strain and decreases till 1.211 eV for 4% tensile strain. This effect is mainly due to the fact that the conduction band minimum shifts under compressive and tensile strains. From carrier mobility calculations, we notice that under tensile strain both hole and electron carrier mobilitiy diminishes, whereas the carrier mobility increases by 25.7 % for electron and by 15 % for holes under -4% compressive strain. Moreover, the optical analysis reveals that applied strain can affect the optical properties of CsSnI perovskite.