CHARACTERIZATION OF VARIABLE-BAND-GAP THIN-FILM CU(IN,GA)SE-2 - A SIMPLE-MODEL FOR THE INTERDIFFUSION OF IN AND GA IN ALLOY STRUCTURES

Thin-film photovoltaic devices based upon the Cu(In,Ga)Se-2 material s ystem continue to advance with total-area cell efficiencies approachin g 16%. Fabrication processes have been developed that may easily be tr ansferred to industrial scale systems. Device designs incorporating va riable-band-gap absorbers have been successful in realizing the full p otential of the alloy material system. The final In and Ga distributio n and phase nature of the variable-band-gap absorber is highly depende nt on the fabrication process. A growth model describes the interdiffu sion of CuInSe2 and CuGaSe2 for three fabrication scenarios. The incor poration of the In and Ga has been accomplished in such a manner that a range of device parameters results. Higher open-circuit voltage devi ces offer the opportunity for lower interconnect losses at the module level. The highest efficiency device fabricated to date exhibits the f ollowing characteristics: area = 0.43 cm(2), V-oc = 650 mV, J(sc)(tota l-area)= 32.2 mA/cm(2), FF = 76.1%, and eta = 15.9%. our work at The N ational Renewable Energy Laboratory is presently focusing on realizing these improvements, scaling to 100 cm(2) submodule sizes, and transfe rring the processes to a non-physical vapor deposition equipment syste ms.