The effect of positive ion bombardment on unencapsulated CdS/Cu2S thin film solar cells has been studied using monoenergetic positive ions (of1H,4He,16O,32S,35Cl,40Ar,63Cu,84Kr,112Cd or132Xe) with energies in the range 10–50 keV. The current-voltage characteristics of the cells have been analysed in terms of a five parameter model. The cell degradations produced by radiation damage have been shown to be dependent on the range of the incident particle. A reduction of the short circuit current was shown to result from damage to the cuprous sulphide layer of the cell whereas damage to the junction region was found to give rise to a reduction in the open circuit voltage. Annealing effects on radiation-degraded unencapsulated solar cells have been studied and the fractional recoveries of the cell parameters have been compared.