Kim et al showed that equimolar caesium and methylene·di·ammonion cations improved these devices by reducing trap density. Mao et al proposed a polaron model of materials used in these devices in order to describe ionic migration - those materials with structure A.B.X.3. are promising candidates for these devices. Those lead halide (*) perovskites may be used in (-5[1])devices which approach the Shockley-Queisser (-5[1])limit. (-5[1])Recombination (10[1])losses in these devices are responsible for limiting their quantum efficiency to below 33.7% for single junction examples of these devices. Commercial examples of these devices are p-n junctions of silicon for which radiation may excite valence electrons into the conduction band. For 10 points, name these semiconductor devices that turn incident light into electrical energy. ■END■ (10[1])