Ab-initio study of halogen inter-substituted perovskite cesium lead halides for photovoltaic applications

We report the ab-initio study of structural, electronic and optical properties of perovskite cesium lead halides within density functional theory. The lattice constants computed from energy-volume plots are employed to compute band structure within improved Becke-Johnson potential modified by Tran and Blaha for exchange and LDA as for correlation effects. The computed band gap values for pristine CsPbCl3, CsPbBr3 and CsPbI3 are in good agreement with the experimental reports. The obtained band structure has been employed for obtaining optical properties of the studied halides CsPbX3 (X = Cl, Br, I) within RPA. The effect of halide inter-substitution in CsPbX3-xYx (X, Y = Cl, Br, I) system has also been studied. We find that CsPbCl2I and CsPbBr2I have high absorption peaks in real and imaginary parts of dielectric function indicating high absorption and capacity to store electrostatic energy. The Born stability conditions indicate that CsPbCl2I is stable whereas CsPbBr2I is not. Our study also finds the possibility of auxetic character in inter-substituted halide perovskites as reflected from negative Poisson's ratio. Therefore, CsPbCl2I seems best suited for optoelectronic devices and photovoltaic applications.