Study of Copper Indium Gallium Selenide (CIGS) Solar Absorber Thin Film with Grading Bandgap

Abstract

High cost and low efficiency are key challenges facing the Photo voltaic solar industry, copper indium gallium selenide (CIGS) has emerged as a promising material for thin-film solar cells due to its high absorption coefficient, tunable bandgap, and efficient charge generation. However, further efficiency improvements are sought to make CIGS technology fully competitive in the renewable energy market which can be addressed by improvising the material properties and developing cost-effective large-scale fabrication routes. The optimization of bandgap in CIGS absorber layer can be achieved by introducing external dopant or changing the ratio of constituent elements. In this research work, variation in the energy band gap of the CIGS active layer is investigated by changing the indium to gallium ratio to enhance and improve the absorption spectral range using density functional theory in CASTEP numerical coding software. The electronic and optical properties are studied using CASTEP with different Ga concentration using GGA-PBE functional as exchange and correlation with kinetic cutoff energy of 880 eV and norm-conversing pseudopotential. Among all the under-investigation materials, CISe2 has shown the highest bandgap of 1.377eV. As the Ga is introduced in CISe2 structure, the band gap reduces until it reaches to 1.286eV for CI0.5G0.4Se2 and again increases for CI0.4G0.6Se2 to 1.333eV until it reaches 1.252eV for CGSe2 because of increase in the p states of gallium across the Fermi level and similar behavior of absorption co-efficient is observed. The maximum absorption is observed within ultra-violet region of solar spectrum.