A photovoltaic device (100, 200), comprising: a layer stack (110, 210), wherein the layer stack is transparent; and an absorber layer (120, 220) disposed on the layer stack (110, 210) and configured to receive solar radiation through the layer stack, wherein: the absorber layer (120, 220) comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer (120, 220), the absorber layer (120, 220) comprises a first region and a second region, the first region disposed proximate to the layer stack (110, 210) relative to the second region, an average atomic concentration of selenium in the first region is greater than an average atomic concentration of selenium in the second region, a ratio of the average atomic concentration of selenium in the first region to the average atomic concentration of selenium in the second region is greater than 10, and at least a portion of the selenium is present in the absorber layer (120. 220) in the form of a ternary compound of cadmium, selenium, and tellurium, and wherein the photovoltaic device is completely free of a cadmium sulfide layer, or the photovoltaic device comprises a cadmium sulfide layer interposed between the layer stack (110, 210) and the absorber layer (120, 220) having a percentage of coverage of an underlying layer of the layer stack (110, 210) of less than 20%, wherein the underlying layer is an interlayer or a buffer layer. a layer stack (110, 210), wherein the layer stack is transparent; and an absorber layer (120, 220) disposed on the layer stack (110, 210) and configured to receive solar radiation through the layer stack, wherein: the absorber layer (120, 220) comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer (120, 220), the absorber layer (120, 220) comprises a first region and a second region, the first region disposed proximate to the layer stack (110, 210) relative to the second region, an average atomic concentration of selenium in the first region is greater than an average atomic concentration of selenium in the second region, a ratio of the average atomic concentration of selenium in the first region to the average atomic concentration of selenium in the second region is greater than 10, and at least a portion of the selenium is present in the absorber layer (120. 220) in the form of a ternary compound of cadmium, selenium, and tellurium, the absorber layer (120, 220) comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer (120, 220), the absorber layer (120, 220) comprises a first region and a second region, the first region disposed proximate to the layer stack (110, 210) relative to the second region, an average atomic concentration of selenium in the first region is greater than an average atomic concentration of selenium in the second region, a ratio of the average atomic concentration of selenium in the first region to the average atomic concentration of selenium in the second region is greater than 10, and at least a portion of the selenium is present in the absorber layer (120. 220) in the form of a ternary compound of cadmium, selenium, and tellurium, and wherein the photovoltaic device is completely free of a cadmium sulfide layer, or the photovoltaic device comprises a cadmium sulfide layer interposed between the layer stack (110, 210) and the absorber layer (120, 220) having a percentage of coverage of an underlying layer of the layer stack (110, 210) of less than 20%, wherein the underlying layer is an interlayer or a buffer layer.