Optimization and design of gallium gradient for CIGS thin film solar cells high efficiency

Abstract

The effect of gallium gradient $Ga/(Ga + In)$ in a sub-layer of a based CIGS solar cell on the current density of short-circuit ( $J_{SC}$ ), voltage of open-circuit $(V_{OC})$ , fill factor $(FF)$ and conversion efficiency (η) has been investigated using Atlas module from SILVACO technology computer-aided design (TCAD). For this purpose, four photovoltaic (PV) cells were considered. The $Ga$ gradient was fixed at 0.15 within the CIGS bulk while it was being varied gradually within a CIGS sub-layer (0.15-0.15, 0.15-0.3, 0.15-0.4 and 0.15-0.6) for different graded CIGS sub-layer thicknesses of (0.05, 0.1, 0.15 and 0.2 μm). It was found that the best efficiency is obtained for the PV cell with the steepest gallium gradient. The efficiency increased from 20.30 (device 1) to 33.09 % (device 4) at a thin CIGS graded layer thickness of 0.1μm. Furthermore, the considered graded CIGS thin layer thicknesses had a negligible effect on the efficiency.