Role of the CdS buffer layer as an active optical element in Cu(In,Ga)Se2 thin-film solar cells

ZnO/CdS/Cu(In,Ga)Se-2 (CIGS) thin-film heterojunction solar cells with US buffer layers of thicknesses between 0 and 85 nm are characterized by current-voltage, quantum efficiency, and optical reflection measurements. We investigate the correlation between the short-circuit current density and the US layer thickness, focusing on the counteracting effects of light absorption and reduced optical reflection induced by the US layer. Both effects almost compensate each other for CdS layer thicknesses between 0 and 40 nm. Thus, an optimization of the short-circuit current density is not achieved by omitting the US layer, but rather by replacing the CdS buffer with an alternative buffer material with higher bandgap energy and optical constants similar to those of CdS. Copyright (C) 2002 John Wiley Sons, Ltd.