Potential Applications of Halide Double Perovskite Cs2AgInX6 (X = Cl, Br) in Flexible Optoelectronics: Unusual Effects of Uniaxial Strains

The discovery of halide double perovskite Cs2AgInX6 (X = Cl, Br) has provided an efficient way to search promising solar cell absorbers. Here, theoretical calculations on strained Cs2AgInX6 (X = Cl, Br) not only comprehensively and firstly help understand their physical properties but also provide a guideline to extend their potential applications. Although Cs2AgInX6 possesses a similar structure, the variations of physical properties of strained Cs2AgInX6 are different. Only compressive Cs2AgInBr6 undergoes a direct-to-indirect transition, which enables it to be a good radiation detection material. Moreover, the mobility of Cs2AgInCl6 is reduced by strains, while that of Cs2AgInBr6 is enhanced (reduced) by compression (tension). That is because the contribution degrees of Ag-d z2, d x2- y2 and In-d z2, d x2- y2 on the band edges of Cs2AgInX6 (X = Cl, Br) are inconsistent. In addition, the absorption coefficients of Cs2AgInX6 (X = Cl, Br) are deteriorated negligibly by strain, making it a potential material for further applications of photovoltaics and flexible optoelectronics.