Position Influence of Sputtered ZnMgO/ZnMgO:Al Layers in Flexible and Cd-Free Cu(In,Ga)(S,Se) Solar Cells.

Flexible, Cd-free, and all-dry process Cu(In,Ga)(S,Se) (CIGSSe) solar cells on stainless steel (SUS) substrates are fabricated, and their structure consists of SUS/glass (SiO)/Mo/CIGSSe absorber/sputtered ZnMgO/sputtered ZnMgO:Al transparent conductive oxide (TCO). The effect of the sample position during the sputtering of ZnMgO buffer and ZnMgO:Al TCO layers of the solar cells is examined to avoid intense plasma exposure. The sample position plays a vital role in improving the cell performance. Namely, the sample position close to the material targets of the sputtering system causes severe exposure of the sample to the intense plasma, giving rise to low and nonuniform local external quantum efficiency (EQE) with very weak electroluminescence (EL) imaging, thereby reducing photovoltaic performance. On the other hand, the deviation of the sample position from material targets helps to avoid the intense plasma, thus resulting in high and uniform local EQE with bright EL imaging as well as reducing carrier recombination rates (or carrier lifetimes) throughout the solar cells. Ultimately, the conversion efficiency of flexible, Cd-free, and all-dry process CIGSSe solar cells is enhanced to 16.5% under the optimized sample position deviation from material targets to avoid intense plasma exposure.