A photovoltaic device , comprising: a layer stack , wherein the layer stack is transparent; and an absorber layer disposed on the layer stack and configured to receive solar radiation through the layer stack, wherein: the absorber layer comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer , the absorber layer comprises a first region and a second region , the first region disposed proximate to the layer stack 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 and the absorber layer having a percentage of coverage of an underlying layer of the layer stack of less than 20%, wherein the underlying layer is an interlayer or a buffer layer . a layer stack , wherein the layer stack is transparent; and an absorber layer disposed on the layer stack and configured to receive solar radiation through the layer stack, wherein: the absorber layer comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer , the absorber layer comprises a first region and a second region , the first region disposed proximate to the layer stack 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 comprises selenium, an atomic concentration of selenium varies across a thickness of the absorber layer , the absorber layer comprises a first region and a second region , the first region disposed proximate to the layer stack 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 and the absorber layer having a percentage of coverage of an underlying layer of the layer stack of less than 20%, wherein the underlying layer is an interlayer or a buffer layer . <EOS>