Alternative back contact materials for thin film Cu(In,Ga)Se2 solar cells

We fabricate Cu(In,Ga)Se-2 thin film solar cells with a variety of different back contact metals (W, Mo, Cr, Ta, Nb, V, Ti, Mn) on glass substrates. A compositional analysis of absorber layers on the metallized substrates identifies W, Mo, Ta and Nb as being inert during the Cu(In,Ga)Se-2 deposition. We investigate solar cells with decreasing absorber thickness, focussing on the increasing influence of the back contact as an optical reflector. The best device efficiencies obtained are 14.2% on W, 13.8% on Mo, 13.3% on Ta, 10% on Nb, 5.9% on Cr and 3.4% on V For Ta and Nb, a Ga-grading at the back side improves the passivation of the absorber/back contact interface. (C) 2003 Elsevier Science B.V. All rights reserved.