Intermediate band solar cells based on highly mismatched II-VI oxide semiconductors

Highly mismatched alloys are a class of materials whose fundamental properties are dramatically modified through the substitution of a relatively small fraction of host atoms with an element of very much different electronegativity. In ZnTe, the incorporation of a small amount of isoelectronic O leads to the formation of a narrow, O-derived intermediate band (IB, E-) located well below the conduction band (CB, E+) edge of the ZnTe through an anticrossing interaction between localized states of O and the CB of the ZnTe matrix. Therefore, ZnTe_1-xO_x (ZnTeO) alloy is one of the potential candidates for an absorber material in a bulk intermediate band solar cell (IBSC). We have previously demonstrated the generation of photocurrent induced by two-step photon absorption (TSPA) in ZnTeO IBSCs using n-ZnO window layer. Here, we review our recent progress on the development of ZnTeO based IBSCs using n-ZnS window layer and Cldoped ZnTeO. With n-ZnS window having a small conduction band offset with ZnTe, the open circuit voltage of ZnTeO IBSC was improved. Cl-doping was performed to introduce electrons into the IB of ZnTeO that is required to be halffilled with electrons for the efficient operation of an IBSC. Low temperature photoluminescence spectra indicated that the doped Cl atoms act as donors in ZnTeO. The improved photovoltaic properties were demonstrated in the IBSC using Cl-doped ZnTeO.