Absorber layer for a thin film photovoltaic device with a double-graded band gap

A method of forming a thin-film solar cell absorber layer, the absorber layer having a first surface that is light receiving, the method comprising:

• forming a first layer on a substrate, wherein the first layer comprises copper, indium, gallium, and selenium and includes a gallium-rich region;
• exposing the first layer to trimethyl gallium (TMGa) and a selenium-containing gas to form a second layer above the first layer, wherein the second layer comprises gallium (Ga) and selenium (Se);
• and
• heating the second layer to convert the second layer to a gallium rich region at the light receiving surface of the absorber layer.

A method of forming a thin-film solar cell absorber layer, the absorber layer having a first surface that is light receiving, the method comprising:

• forming a first layer on a substrate, wherein the first layer comprises copper, indium, gallium, and selenium and includes a gallium-rich region;
• forming a second layer above the first layer via thermal pyrolysis of trimethyl gallium (TMGa);
• exposing the second layer to heat and a selenium-containing gas to convert the second layer to a third layer that comprises gallium (Ga) and selenium (Se);
• and
• heating the third layer to convert the third layer to a gallium rich region at the light receiving surface of the absorber layer.