Research on solar cells focusses on finding devices that have the simultaneous promise of high efficiency, long lifetime and low cost. Therefore observers have been excited about the recent development of two new solar cells with efficiencies of 12–13&percent; that might be many times cheaper than silicon cells—if they fulfil their potential to be made by thin‐film techniques. The potential of these two devices for solar‐energy conversion was recognized by Sigurd Wagner and Joseph Shay of Bell Laboratories as they were investigating new materials and components for optical communications systems. One of these cells consists of a thin film of cadmium sulfide deposited on a single‐crystal substrate of indium phosphide.1The other has a cadmium‐sulfide layer on a single‐crystal substrate of copper indium diselenide.2