One aspect of the present invention includes method of making a photovoltaic device. The method includes disposing an absorber layer on a window layer, wherein the absorber layer includes a first region and a second region. The method includes disposing the first region adjacent to the window layer in a first environment including oxygen at a first partial pressure; and disposing the second region on the first region in a second environment including oxygen at a second partial pressure, wherein the first partial pressure is greater than the second partial pressure. One aspect of the present invention includes a photovoltaic device.