The correlation of the cell performance of wide-gap Cu(ln(1-x)Ga(x))Se-2 (CIGS) solar cells with the thickness of highly resistive i-ZnO layers, which are commonly introduced between the buffer layer and the transparent conductive oxide (TCO) layer in CIGS solar cell devices, was studied. It was found that cell parameters, in particular, the fill factor (F.F.) varied with the thickness of the i-ZnO layers and the variation of the F.F. was directly related to cell efficiency. A 16%-efficiency was achieved without use of an anti-reflection coating from wide-gap (Eg similar to 1.3 eV) CIGS solar cells by adjusting the deposition conditions of the i-ZnO layers. (c) 2004 Elsevier B.V. All rights reserved.