Better Back Contacts for Solar Cells on Flexible Substrates

Improved low-resistance, semitransparent back contacts, and a method of fabricating them, have been developed for solar photovoltaic cells that are made from thin films of I-III-VI2 semiconductor materials on flexible, high-temperature-resistant polyimide substrates or superstrates. [The term 'I-III-VI2' is an abbreviated indication that the semiconductor materials are compounds of elements in periods IB, IIIA, and VIA of the periodic table in the stoichiometric ratio of 1:1:2. More specifically, these are compounds of general empirical formula Cu(In, Ga, or Al)(Se or S)2.] The innovative aspect of the present development lies in the extension, to polyimide substrates or superstrates, of a similar prior development of improved low-resistance, semitransparent back contacts for I-III-VI2 solar cells on glass substrates or superstrates. A cell incorporating this innovation can be used either as a standalone photovoltaic device or as part of a monolithic stack containing another photovoltaic device that utilizes light of longer wavelengths.