98/00453 A close-form solution for the maximum-power operating point of a solar cell array

Abstract

Sub-micron thick Cu(In,Ga)Se2 (CIGS) thin films were deposited on Mo-coated soda-lime glass substrates under various conditions by single-stage co-evaporation. Generally, the short circuit current (Jsc) decreased with the decreasing thickness of the absorber layer. However, in this study, Jsc was nearly unchanged with decreasing thickness, while the open circuit voltage (Voc) and fill factor (FF) decreased by 31.9 and 31.1%, respectively. We believe that the remarkable change of Voc and FF can be attributed to the difference in the total amount of injected thermal energy. Using scanning electron microscopy, we confirmed that the surface morphology becomes smooth and the grain size increased after the annealing process. In the X-ray diffraction patterns, the CIGS thin film also showed an improved crystal quality. We observed that the electric properties were improved by the in-situ annealing of CIGS thin films. The reverse saturation current density of the annealed CIGS solar cell was 100 times smaller than that of reference solar cell. Thus, sub-micron CIGS thin films annealed under a constant Se rate showed a 64.7% improvement in efficiency.