First-principles study of the effect of strain on the structural and optoelectronic properties of flexible photovoltaic material Cs2AgInBr6

Abstract

The lead-free double-perovskite halide materials are promising materials for photovoltaics. Recently, Cs2AgInBr6 (CAIB) has been synthesized with the estimated direct nature of a band gap value of 1.57 eV. To cover the wide solar spectrum for photo-conversion, the applied strain is one of the promising approaches to achieve it through band gap tuning. The density functional theory (DFT) is used to investigate the effect of compressive strain on the structural, electronic, and optical properties of CAIB. The elastic constants follow the Born-Huang stability criterion and show the mechanical stability of the composition even under compressive strain. The Poisson's ratio in the range of 0.23 to 0.26 and B/G >1.75 indicate the ductile and soft nature of the material. The band gap increases monotonically without changing the direct nature of the band gap by increasing the compressive strain.  However, the larger value of strain reproduces more dispersive conduction band minima and valence band maxima, resulting in lower effective masses and consequently larger carrier mobilities. The variations in the optical properties of CAIB are explored under compressive strain. The structural, electronic, and good photoresponse of the material in the visible and ultraviolet regions indicate the suitability of the material for flexible photovoltaics.