Tandem solar cells having a top or bottom metal chalcogenide cell

A tandem solar cell comprising:

• a substrate;
• a first solar cell contact structure disposed on the substrate;
• a first solar cell active light absorber material disposed on the first solar cell contact structure and having a first band gap E1;
• a second solar cell contact structure disposed on the first solar cell active light absorber material, wherein the second solar cell contact structure is transparent to the solar spectrum;
• an insulator layer disposed on the second solar cell contact structure, wherein the insulator layer is transparent to the solar spectrum;
• a third solar cell contact structure disposed on the transparent insulating layer, wherein the third solar cell contact structure is transparent to the solar spectrum;
• a second solar cell active light absorber material disposed on the third solar cell contact structure and having a second band gap E2;
• a fourth solar cell contact structure disposed on the second solar cell active light absorber material, wherein the fourth solar cell contact structure is transparent to the solar spectrum;
• wherein at least one of the first solar cell active light absorber material and the second solar cell active light absorber material is a metal chalcogenide;
• wherein E2>E1;
• wherein at least one of the first solar cell active light absorber material and the second solar cell active light absorber material is doped to provide a p-n junction;
• wherein doping of the metal chalcogenide is provided by inclusion of one or more adjacent metal-oxide layers in one or more adjacent solar cell contact structures, wherein the metal-oxide layers are configured to provide doping of the metal chalcogenide by charge transfer.