Study on the quasi Fermi level splitting of Cu(In, Ga)Se2 absorber layers with Cu-rich and Cu-poor composition

With in this study several Cu(In, Ga)Se2 absorber layers with varying gallium content and different copper over indium + gallium ratios are investigated by photoluminescence. The quasi Fermi level splitting of absorber layers grown under copper excess is 120 meV lower compared to absorbers with a [Cu]/([In]+[Ga]) ratio below one. Possible explanations for this are the gallium gradient within the absorber layer or a gallium related defect. Comparing the quasi Fermi level splitting of an absorber to the open circuit voltage of the corresponding solar cell, the difference for copper poor cells is much lower (60 meV) than for copper rich cells (140 meV).