Patent ID: 8318530

Claim:
A method of forming a solar cell, comprising: providing a substrate; forming an absorber layer over the substrate, wherein the absorber layer includes at least one of Cu(In,Ga)Se 2 and CdTe; depositing a single buffer layer on the absorber layer in a single process step during which a composition of deposited material is changed to obtain a graded composition profile, wherein the single buffer layer includes a lower section and a top section, such that during the single process step the lower section is formed prior to the top section, and wherein the composition of deposited material of the lower section is CdS and the composition of deposited material of the top section is CdZnS with a graded amount of Cd and Zn within the top section, wherein the step of depositing the single buffer layer includes providing the graded amount of Cd and Zn within the top section such that the amount of Cd is reduced toward a top surface of the top section and the amount of Zn is increased toward the top surface of the top section, and wherein a ratio of Cd/(Cd+Zn) in the single buffer layer follows a shape determined by the graded composition profile with CdS material predominantly formed in a first growth location during a first period of the single process step, CdZnS material with varying Cd and Zn content formed in a second growth location during a second period of the single process step that follows the first period, and ZnS material without Cd predominantly formed in a third growth location during a third period of the single process step that follows the second period; and depositing a transparent conductive layer over the single buffer layer.