CuInSe2 cell with CdO window layer

Using monocrystalline p-type substrates of CuInSe₂ obtained from single crystal ingots of Bridgman-grown material, photovoltaic cells were fabricated with the layer structures CuInSe₂/CdO and CuInSe₂/CdS/CdO, where the CdO window layer, for both kinds of device, was deposited by DC reactive sputtering. The second kind of cell, where the lattice-matching CdS interlayer was deposited by a chemical bath method, showed a conversion efficiency of about 6.8% and a dark forward ideality factor of 1.7. By comparison, the device without the interlayer, where the lattice mismatch between the CuInSe₂ and the CdO was about 23%, showed a surprising efficiency of 6.3%, despite a larger dark ideality factor of 2.7. This result, indicating that the defect centers at the CuInSe₂-CdO interface arising from the large lattice mismatch play a smaller role than expected, suggests that the seat of photovoltaic action may lie away from the substrate-window layer interface