High-quality ZnO:Al films have been prepared by using RF-magnetron-sputtering method with resistivity ranging from 10(-1) to 10(-4) Omega cm and transmittance above 90% in visible region. We have fabricated small area (1 cm(2)) double junction (a-Si/a-Si) solar cells using ZnO/Al and ZnO/Ag as back contact. The conversion efficiency of double junction a-Si solar cell increases from 9.9% to 10.9% by using ZnO/Al back contact and to 11.4% by using ZnO/Ag as back contact. Effect of variation of thickness of i-layer on performance of the cell has also been studied. (C) 2002 Elsevier Science B.V. All rights reserved.