CuGaSe2-based superstrate solar cells

We grow polycrystalline CuGaSe2 thin films by simultaneous evaporation of the elements in high vacuum for use as absorber layers in superstrate solar cells. The films are grown on a stack of intrinsic and Al:doped ZnO deposited by sputtering on soda lime glass. We systematically vary the CuGaSe2 growth temperature T-s between 530 degreesC and 630 degreesC and investigate the resulting changes of the electrical properties of the devices. The CuGaSe2. films are measured by X-ray diffraction. The full width at half maximum of the CuGaSe2, [112] reflex displays a value of 0.19 degrees for T-s = 630 degreesC compared to 0.490 for T-s = 530 degreesC. Both the X-ray diffraction and the electrical analysis favor the higher growth temperature. We achieve open circuit voltages above 800 mV which is comparable to the best CuGaSe2, substrate devices. The efficiency of 3.5% is limited by the low fill factor. Light soaking under AM1.5 illumination increases the fill factor from 27 to 46% with only a small impact on short circuit current and open circuit voltage. (C) 2001 Elsevier Science B.V. All rights reserved.