a photovoltaic device utilizing compound semiconductor materials that are stable when operated at high temperatures . hostile environments , and in particular , thermally stressful enviornments such as those generated by use of light concentrating systems , require encapsulation of the device . sealing of the photo - active junction , the conductive grid , the exposed semiconductor surfaces , and the pads contacting the grid away from the junction area provide such thermal stability . a heterojunction structure can be used along with barrier materials providing a conductive grid in contact with the photo - active surface thereby reducing interdiffusion of that surface with the conductive grid .