Photovoltaic devices and method of making

A photovoltaic device, comprising:

• a transparent layer stack;
• a p+ type semiconducting layer;
• and
• an absorber layer in direct contact with the transparent layer stack at a front interface of the absorber layer, wherein:
• the absorber layer consists of a thickness of the absorber layer between the front interface of the absorber layer and a back interface of the absorber layer,
• the front interface of the absorber layer is closer to the transparent layer stack than the back interface of the absorber layer,
• the absorber layer comprises cadmium, selenium, and tellurium,
• an atomic concentration of selenium varies across the thickness of the absorber layer,
• the atomic concentration of selenium is greater at the front interface of the absorber layer relative to the back interface of the absorber layer,
• the absorber layer is a p-type layer,
• the absorber layer consists of a first region and a second region,
• the first region extends from the front interface of the absorber layer to the second region,
• the second region extends from the first region to the back interface of the absorber layer,
• 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 10,
• the absorber layer is between the transparent layer stack and the p+ type semiconducting layer,
• the p+ type semiconducting layer comprises at least one of:
• zinc telluride, magnesium telluride, manganese telluride, beryllium telluride, mercury telluride, arsenic telluride, antimony telluride, or copper telluride, and
• the photovoltaic device has no window layer.