Band alignment of ZnS/ZnTe interface suitable for intermediate band solar cells

Efficient photogenerated carrier extraction is crucial for the realization of high-performance ZnTeO-based intermediate band solar cells (IBSCs). In this work, we experimentally determined the band offset at the interface between an n-ZnS electron transport layer and an undoped ZnTe barrier layer, grown under the same conditions as those employed in previously reported ZnTeO-based IBSC devices, using X-ray photoelectron spectroscopy (XPS). The conduction band offset (CBO) was found to be +0.33 eV, exhibiting a type-I alignment. This result deviates from the undesirable cliff-like CBO predicted by the simple Anderson's rule, highlighting the importance of the direct experimental characterization of heterojunctions. The measured offset lies within the range reported to be favorable for suppressing interfacial recombination without impeding electron transport, and thus provides a quantitative interfacial-energetics basis for the improved open-circuit voltage previously reported for ZnTeO-based IBSCs employing ZnS electron transport layers.