TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Cell: In the solar cell, the bandgap of consecutive quantum well layers decreases on moving away from a surface of the solar cell upon which, in use, sunlight will be incident. The constituent element may be at least two group II to group VI elements. The constituent elements are selected from aluminum, gallium, indium and nitrogen. The content of at least one group II to VI element in consecutive quantum well layers increases on moving further away from an extent of the solar cell upon which, in use, sunlight is incident. The thickness of consecutive quantum well layers decreases on moving further away from an extent of the solar cell upon which, in use, sunlight is incident. Composition of individual quantum well layers is substantially constant throughout their extent. Composition of individual quantum well layers varies in a continuous fashion on proceeding through the quantum well layer from a region contacting one adjacent barrier layer to a region contacting the next adjacent barrier layer. The solar cell is the relative content of at least two group III elements selected from indium, aluminum and gallium which varies. The material forming the quantum well layers is a group III nitride, arsenide or phosphide. The material forming the quantum well layers is selected from indium gallium nitride, aluminum indium gallium nitride, indium aluminum nitride, aluminum gallium nitride, indium gallium arsenide, indium gallium arsenide nitride, aluminum indium gallium arsenide nitride indium gallium phosphide, indium gallium arsenide phosphide, indium arsenide phosphide, indium aluminum arsenide and indium aluminum gallium arsenide. The quantum well layers comprise indium gallium nitride and the indium and gallium contents vary between consecutive quantum well layers. Quantum well layer having the highest bandgap and being located at the end of the solar cell closest to the surface adapted to receive sunlight will be the quantum well layer with the lowest indium content. Each quantum well layer is less than 15 nm, preferably less than 10 nm, more preferably less than 7 nm thick. Each quantum well layer is between 1 to 5 nm thick, more preferably about 3 nm thick. The barrier layers are formed from the same or different materials to the quantum well layers. The barrier layers comprise material selected from gallium nitride, aluminum nitride, indium gallium nitride, indium aluminum nitride and aluminum indium gallium nitride. The barrier layers are gallium nitride layers. Barrier layers are selected such that the bandgaps of the barrier layers are higher than the bandgap of the sandwiched quantum well layer. The solar cell further comprises one or more blocking layers. The cell is a p-i-n structure and is grown to have at least one blocking layer present before the p-layer and after the n-layer. One or more blocking layers are aluminum gallium nitride layers. The junction layer closest to the sunlit surface has a higher bandgap than the subsequent quantum well or barrier layers. The first and second junction layers independently comprise gallium nitride, indium gallium nitride or indium aluminum gallium nitride. Preferred Method: In forming solar cell, the quantum well layers are indium gallium nitride layers and the indium and gallium content vary in consecutive layers. The method comprises increasing the content of at least one group II to VI element in consecutive quantum well layers on moving further away from an extent of the solar cell upon which, in use, sunlight is incident; maintaining the content of at least one group II to VI element substantially constant within individual quantum well layers; forming a junction layer on a substrate and subsequently forming the first barrier layer or quantum well layer upon the junction layer; forming a further junction layer on top of the final quantum well layer to be formed; forming the multiple quantum well structure such that the content of at least one group II to VI element in consecutive quantum well layers decreases on moving further away from an extent of the solar cell upon which, in use, sunlight is incident; and separating the multiple quantum well structure from an underlying substrate and reversing the structure such that the content of at least one group II to VI element in consecutive quantum well layers increases on moving further away from an extent of the solar cell upon which, in use, sunlight is incident. The substrate is transparent. The method also comprises growing the quantum well layers having the lowest indium content before those having higher indium contents; and growing one or more aluminum gallium nitride (AlGaN) or aluminum nitride (AlN) thin layers to reduce strain in the solar cell.