High efficiency CIGS and CIS cells with CVD ZnO buffer layers

This paper describes investigations of CIS and CIGS solar cells with ZnO buffer layers. These studies are a result of a team effort between investigators at Washington State University (WSU), the Institute Of Energy Conversion (IEC) and the National Renewable Energy Laboratory (NREL). Cells with ZnO buffer layers were fabricated with both Siemens CIS and NREL CIGS substrates. An active area efficiency of 13.95% was achieved for a ZnO/CIGS cell. ZnO buffer layers are grown by reacting a zinc adduct with tetrahydrofuran using a two-step approach: growth of approximately 100 Å of ZnO at 250°C; and then growth of 500 to 700 Å of ZnO at 100°C. The high temperature step is necessary to achieve good cell performance. It appears that exposure of CIGS to hydrogen at 250°C may remove contaminants and/or passivate recombination centers on the surface and subsurface regions