Metallic/chalcogen dual phase effects on dielectric relaxations, resonance and spectroscopic impedance in amorphous chalcopyrite Cu_xIn_yGa₁₀Se_70−xTe_20−y thin films

Copper Indium Gallium Diselenide (CIGS) is a well-known chalcopyrite photovoltaic material for its highest efficiency and flexibility. It is necessary to maintain this technology economic and affordable for better commercial use without affecting performance. We fabricate the structurally complex, the pentanary Cu_xIn_yGa₁₀Se_70−xTe_20−y (CIGST) composition in bulk and thin film form through economic melt-quench and thermal evaporation technique respectively to enhance the light trapping centers by obviating unnecessary reflection through structural complexities. We are first to report the frequency dependent optical parameters and dielectric response of compounds having composition varied from metallic rich phase to chalcogen rich phase at around 10% of constant Gallium to understand their interaction in an electromagnetic field through UV–Vis spectroscopy and LCR meter experiment. Enhanced absorbance edge with multiple band gap has translated the divergence of complex dielectric function from the standard Drude model at optical (higher) frequencies. Multiple relaxations occur along with the dipolar relaxation at electrical (lower) frequencies depicts the varied Debye behavior. Photo-response has been measured through impedance spectroscopy which shows a loss in the order of 3 KΩ under illumination depicts the significant charge carrier generation, led to the excellent photovoltaic properties of CIGST cells.