Photovoltaic characterization of Copper–Indium–Gallium Sulfide (CIGS2) solar cells for lower absorber thicknesses

Abstract

Chalcopyrites are important contenders among thin-film solar cells due to their direct band gap and higher absorption coefficient. Copper–Indium–Gallium Sulfide (CIGS2) is a chalcopyrite material with a near-optimum band gap of ~ 1.5 eV. Record efficiency of 11.99% has been achieved on a 2.7 μm CIGS2 film prepared by sulfurization at the Florida Solar Energy Center (FSEC) PV Materials Lab. In this work, photovoltaic performance analysis has been carried out for a 1.5 μm absorber prepared under similar conditions as that of a 2.7 μm thick absorber sample. It was observed that there is an increase in diode factor and reverse saturation current density when the absorber thickness was decreased. The diode factor increased from 1.69 to 2.18 and reverse saturation current density increased from 1.04 × 10 − 10 mA/cm 2 to 1.78 × 10 − 8 mA/cm 2. This can be attributed to a decrease in the grain size when the absorber thickness is decreased. It was also observed that there is an improvement in the shunt resistance. Improvement in shunt resistance can be attributed to optimized value of i:ZnO for lower absorber thickness and less shunting paths due to a smoother absorber.