Cadmium Tin Oxide and Zinc Magnesium Oxide Prepared by Hollow Cathode Sputtering for CdTe Photovoltaics

This work reports the fabrication and characterization of superstrate-type Zn1-xMgxO/CdTe heterojunction solar cells on both CdxSnyO and commercial SnO2:F transparent conducting oxides (TCOs) in which the ZMO and CTO layers are produced for the first time by hollow cathode sputtering. The sputtering is conducted in a reactive mode using metal or alloyed metal targets fitted to a custom-made linear cathode. It is notable that the CdS buffer layer conventionally employed in CdTe solar cells is entirely replaced by the ZMO window layer. The use of ZMO is found to eliminate the blue loss associated with CdS optical absorption and further results in a higher open-circuit voltage. Key parameters were found to be the conduction band offset at the ZMO/CdTe interface and the ZMO thickness. It was discovered that the ZMO exhibits intense photoluminescence even at room temperature. Most of the solar cells were fabricated in the FTO/ZMO/CdTe configuration although CTO/ZMO/CdTe solar cells were also demonstrated. The CTO was produced with an electron mobility of 46 cm² V^-1s^-1 without any post-deposition annealing or treatment.