Method for forming copper indium gallium chalcogenide layer with shaped gallium profile
View Patent ↗Precursor layers and methods of forming Group IBIIIAVIA solar cell absorbers with bandgap grading using such precursor layers are described. The Group IBIIIAVIA absorber includes a top surface with a Ga/(Ga+In) molar ratio in the range of 0.1-0.3. The Group IBIIIAVIA solar cell absorber is formed by reacting the layers of a multilayer material structure which includes a metallic film including Cu, In and Ga formed on a base, a layer of Se formed on the metallic film, and a second metallic layer substantially including Ga formed on the layer of Se.
1. A process of forming a Cu(In,Ga)Se 2 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)Se 2 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)Se 2 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.
2. The process of claim 1 , wherein a Ga/(In+Ga) molar ratio in the first sub-layer of the precursor structure is in the range of 0.2-0.5 and a Cu/(In+Ga) molar ratio of the precursor structure is in the range of 0.7-1.0.
3. The process of claim 2 , wherein the first time period is about 0.5-5 minutes and the second time period is about 0.5-10 minutes.
4. The process of claim 2 , wherein a thickness of the layer of Ga in the second sub-layer is in the range of 10-50 nm.