Photovoltaic devices and method of making

A photovoltaic device, comprising:

• a layer stack;
• and
• an absorber layer disposed on the layer stack, the absorber layer having a front interface proximate to the layer stack and a back interface opposite the front interface, wherein:
• the absorber layer comprises a CdTe1-xSex alloy, where x is less than 0.4 throughout the absorber layer;
• an atomic concentration of selenium varies across a thickness of the absorber layer;
• the atomic concentration of selenium in the absorber layer is greater proximate to the front interface relative to the back interface of the absorber layer;
• the atomic concentration of selenium varies non-linearly 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;
• the first region has a thickness between 100 nanometers to 3000 nanometers;
• the second region has a thickness between 100 nanometers to 3000 nanometers;
• an average atomic concentration of selenium in the first region is greater than an average atomic concentration of selenium in the second region;
• and
• a ratio of an average atomic concentration of selenium in the first region to an average atomic concentration of selenium in the second region is greater than 2.