Effect of substrate temperature and depostion profile on evaporated Cu(InGa)Se2 films and devices

This paper addresses the effect of substrate temperature (T-SS) and deposition profile for Cu(InGa)Se-2 films deposited by multisource elemental evaporation on film structure and solar cell performance. Different temporal Cu flux profiles are utilized to give either a graded deposition incorporating a Cu-rich growth step, with [Cu] > [In] + [Ga], before achieving the final film composition with [Cu] < [In] + [Ga], or a uniform deposition with [Cu] < [In] + [Ga] throughout. The Cu(InGa)Se-2 morphology, including quantitative analysis of the grain size distributions, and the performance of completed solar cells are compared at T-SS = 400 and 550 degrees C. The higher T-SS gives larger grains and better device performance with the best devices obtained in this work having efficiencies of 16.4% for 550 degrees C and 14.1% for 400 degrees C. At 550 degrees C, Cu-rich film growth gives bigger grains than a uniform flux process, but there is no difference in the device performance. With T-SS = 400 degrees C, there is no significant difference in the grain size with the different flux profiles, but the Cu-rich growth is needed for improved devices. (C) 2000 Elsevier Science S.A. All rights reserved.