Thin-Film CIGS Photovoltaic Technology; Annual Technical Report, Phase I; 16 April 1998 - 15 April 1999

This report describes work performed by Energy Photovoltaics, Inc. (EPV) under Phase I of this subcontract. EPV's new FORNAX process for CIGS formation is capable of producing devices with high V{sub oc} (>600 mV) and no dark aging effects. Parameters of the best device so far are V{sub oc} = 611 mV, J{sub sc} = 27.5 mA/cm{sup 2}, FF = 74.5%, and efficiency = 12.5%. A 34-cm{sup 2} 16-cell minimodule was produced using FORNAX CIGS with V{sub oc} = 9.58 V, I{sub sc} = 52.0 mA, FF = 69.8%, and efficiency = 10.2%. A new version of EPV's linear evaporation source was developed with improved rate and uniformity for Cu deposition over a width of 45 cm. Using the new linear source, the FORNAX process was implemented on 0.43-m{sub 2} substrates in EPV's CIGS pilot line, with V{sub oc} = 537 mV and FF = 70.3% being achieved on a device. The EPV Subteam of the National CIS R&D Team has produced Cd-free ZnO/CIGS devices on NREL CIGS using the ROMEAO process (reaction of metal and atomic oxygen) for ZnO deposition. After soaking, the best device exhibited a V{sub oc} of 565 mV and an efficiency of 12.3%. Novel bias drive methods were devised for field soaking/anti-soaking experiments as a function of time and temperature. Scaling laws and an activation energy of 0.51 eV were found. Thermally stimulated capacitance reveals the existence of three distinct contributions to ZnO/CIGS device capacitance, two appearing to be gap-state effects and one related to net doping concentration. The coating time of the sputtered pilot-line ZnO:Al has been reduced by a factor of 3 while maintaining film quality. The deposition rate is 48 A s{sup -1}. Plans are under way to increase the substrate size from 0.43 m{sup 2} to 0.79 m{sup 2}