Method for forming copper indium gallium chalcogenide layer with shaped gallium profile

A process of forming a Cu(In,Ga)Se2 film on a base, the process comprising:

• depositing a precursor structure on the base, the precursor structure comprising a first sub-layer formed on the base and a second sub-layer formed on the first sub-layer;
• and
• reacting the first sub-layer and the second sub-layer with each other by increasing the temperature of the precursor structure to a first temperature range for a first time period and then to a second temperature that is higher than the first temperature range for a second time period to form the Cu(In,Ga)Se2 film on the base, wherein;
• the first sub-layer is substantially metallic and comprises Cu, In and Ga,
• the second sub-layer comprises a layer of Se formed directly on and in contact with the first sub-layer and a layer of Ga formed directly on in contact with the layer of Se;
• and,
• wherein the first temperature range is 220-450° C. and the second temperature is at least 500° C., and wherein the step of reacting forms the Cu(In,Ga)Se2 film to include a surface region, a bulk region and a transition region between the surface region and the bulk region, wherein a transition region Ga/(Ga+In) molar ratio in the transition region is lower than a surface region Ga/(Ga+In) ratio in the surface region and a bulk region Ga/(Ga+In) molar ratio in the bulk region.