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.
