Analysis of Cu(In,Ga)Se2 grading evolution during low deposition temperature co-evaporation process by GD-OES and XPS measurements. Impact on solar cell performances and modelling

One of the key parameters to achieve high efficiency Cu(In,Ga)Se2 (CIGS) solar cells is the proper control of Ga grading. From previous results, by using bulk material characterization, a first assessment of the CIGS growth on polyimide foils at low temperature was performed. Moreover, a maximum efficiency of 17.8% has been achieved with steep Ga grading. Here, a first step to the establishment of a growth model of CIGS grown at low temperature is proposed by coupling surface and volume characterization. Then, simulation of the photovoltaic performances of the cell is used to complete experimental observations and to explain the beneficial effect of steep Ga grading.