Sputtered zinc selenide buffer layers for Cu(InGa)Se2 substrate and superstrate solar cells

RF magnetron sputtered ZnSe was used as a Cd-free buffer layer in Cu(InGa)Se₂ solar cells. Devices in substrate configuration showed relatively low short circuit current compared to those with a CdS buffer layer. Cu(InGa)Se₂ with various Ga contents were tested and J_sc improvement was observed with an increase in Ga/III ratio. Temperature dependent JV measurements showed that ZnSe/Cu(InGa)Se₂ formed a spike conduction band offset at the interface, acting as an electron blocking barrier. The barrier height could be reduced by incorporating more Ga into Cu(InGa)Se₂. Superstrate Cu(InGa)Se₂ cells showed efficiencies less than 4%. SEM and XPS depth profiling revealed that ZnSe inter-diffused into Cu(InGa)Se₂ at high temperature absorber growth.