We performed accelerated tests on various sealed CIGS solar cells in a complex light/damp heat environment, and investigated the behavior of P-max and other properties over time. The half-life time of P-max in well-sealed cells was found to be 40-80 times greater than that in non-sealed cells, and the degradation of P-max was dependent on changes in V-oc and FF. The cause of these changes was examined based on the behavior of photo IV characteristics under conditions of feeble light, dark IV, and CV. (C) 2003 Elsevier Ltd. All rights reserved.