Capacitance measurements on ZnO/CdS/Cu(In1-xGa)Se2 solar cells

Capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements have been carried out on heterojunction ZnO/CdS/Cu(In_1-xGa_x)Se₂ solar cells with different Ga content. These cells were fabricated on polished monocrystalline samples prepared by the Bridgman method. The C-V measurements indicated a significant effect of interface or surface states, especially for the non-annealed samples. Different hole deep levels and different shapes of DLTS spectrum were found in Cu(In_1-xGa_x)Se₂ crystals with different Ga content. It is believed that Ga content has a great impact in the formation of deep levels in Cu(In_1-xGa_x)Se₂ crystals. The DLTS results combined with the conversion efficiencies of the solar cells indicate the interfacial states could dominate the cell performance rather than the deep levels in the semiconductor.