The behavior of a CuInSe2 (CIS) solar mini-module during a light/dark cycle and continuous light irradiation tests was investigated. Under both test conditions, the conversion efficiency was improved during the early stages, then subsequently deteriorated. The major factors causing this phenomenon are changes in the fill-factor and open-circuit voltage. The details of some parameters relevant to these factors are considered herein. (C) 2002 Elsevier Science B.V. All rights reserved.