Determination of open-circuit voltage in Cu(In,Ga)Se2 solar cell by averaged Ga/(In + Ga) near its absorber surface

The Cu(In,Ga)Se-2 (CIGS) solar cells are fabricated, where CIGS absorbers with various Ga/III, Ga/(In + Ga), profiles are prepared by the so-called "multi-layer precursor method" using multi-layer co-evaporation of material sources. The dependence of cell parameters upon several averaged Ga/III ratios, calculated in different depth ranges of the Ga/III profiles from the absorber surfaces, is performed. It is revealed that open-circuit voltage (V-OC) is mainly dependent on the averaged Ga/III, calculated near the surface area of the CIGS absorber (or in space charge region; SCR). The SCR width of similar to 0.32 mu m can be predicted, corresponding to the calculated value. Finally, the averaged Ga/III near the absorber surface is proposed as an indicator of V-OC before solar cell fabrication, as long as carrier concentration is almost constant. (C) 2013 AIP Publishing LLC.