Evaluation of the optical properties of the lead-free mixed-halide iron perovskite CH3NH3FeI2Br for application in solar cells: A computational study

Abstract

Performance of the proposed lead-free mixed halide iron perovskite CH3NH3FeI2Br as the light absorber layer of the perovskite solar cells is evaluated based on the analysis of the calculated optical properties. Crystal structure of this mixed halide iron perovskite is optimized at spin-polarized DFT GGA-PBE/FP-LAPW+lo level of theory. Structural analysis shows that the optimized unit cell parameters of this CH3NH3FeI2Br perovskite are all smaller than their corresponding values for the pure iodide iron perovskite CH3NH3FeI3. Thermodynamic analysis based on the total SCF energies calculated for the CH3NH3FeI2Br, CH3NH3FeI3, I2 and Br2 lattices shows also that the mixed halide iron perovskite CH3NH3FeI2Br is more stable than the pure iodide iron perovskite CH3NH3FeI3 by 1477.5 kJmol−1. Band structure, density of states and band gaps are calculated with the GGA-PBE(mBJ)/FP-LAPW+lo method. Analysis of the results show that the mixed halide iron perovskite CH3NH3FeI2Br is a direct band gap semiconductor having band gaps of 3.041 and 0.689 eV for its spin-up and spin-down states, respectively. The absorption spectrum calculated for the mixed halide iron perovskite MAFeI2Br and its corresponding Brewster angles calculated for the TiO2/perovskite and perovskite/spiro interfaces, the proposed mixed halide iron perovskite MAFeI2Br can be regarded as a promised candidate for application as light-harvesting layer of perovskite solar cells due to its good optical performance in the 500–630 nm range of wavelengths of the sunlight spectrum. Stability of the proposed CH3NH3FeI2Br perovskite is also validated based on the analysis of the calculated octahedral and Goldschmidt tolerance factors (0.465 and 1.009, respectively).