The trap properties of ZnO/CdS/CuInSe2 and ZnO/CdS/CuGa0.3In0.7Se2 PV cells were investigated. It is believed that an argon (Ar) annealing prior to the junction formation could reduce the density of deep traps close to the mid-gap of single-crystal CuInSe2. While no minority carrier traps were observed in ZnO/CdS/CuInSe2 PV cells, results on ZnO/CdS/CuGa0.3In0.7Se2 PV cells suggested the co-existence of both the majority and minority carrier traps. Furthermore, there is evidence showing deep traps close to the mid-gap of Ar annealed single-crystal CuGa0.3In0.7Se2.