Modulation of optoelectronic properties in Cl and Br doped GUASnI3 based perovskite solar cells: A Density Functional Theory analysis

Partial substitution of I by Cl or Br improves the performance of hybrid lead halide perovskite materials. Here, a systematic density functional theory (DFT)-based investigation has been carried out in some mixed halide perovskites having the general formula GUASnX3-yX ' y, where GUA = guanidinium cation, X = iodine (I), X ' = chlorine (Cl) or bromine (Br), and y = 0, 1, 1.5, and 2. Results obtained have been compared with the pure iodine -based compound to understand the impact of doping ratio on physical, optoelectronic, and photovoltaic properties of the hybrid halide perovskite materials. From the analysis, it has been observed that all the designed compounds form thermodynamically stable three-dimensional perovskite structures. In addition, the designed compounds possess band gap (Eg) values within the range of 0.91-2.33 eV. However, Eg decreases with an increase in iodine content. Complex dielectric function and absorption coefficient analysis led to the conclusion that all the investigated compounds exhibit absorption maxima in the visible range of the electromagnetic spectrum. Moreover, photovoltaic performance analysis reveals that GUASnI3 exhibits the highest theoretical power conversion efficiency (PCE) of 27.78% among the studied compounds. The study also shows that the pure iodine -based compound is superior to the corresponding mixed halide compounds in terms of their optoelectronic and photovoltaic properties. Hence, it is expected that the study will provide researchers a basis to further investigate mixed halide perovskite based materials in the future.