Photogenerated Current By Two-Step Photon Excitation in ZnTeO Intermediate Band Solar Cells with n-ZnO Window Layer

We present the results of systematic experimental studies on ZnTeO intermediate band solar cells (IBSCs) with a n-ZnO window layer. In order to understand photovoltaic (PV) activities of ZnTeO IBSCs, we first describe PV properties of ZnO/ZnTe solar cells without the intermediate band (IB). The improved efficiency of 1.38% is demonstrated by using a n⁺-ZnO/ i-ZnO/ i-ZnTe/ p-ZnTe structure. Then, the PV properties of ZnTeO IBSCs fabricated using n-ZnO window layer with and without a blocking barrier for IB are compared. The device with a blocked IB shows higher open-circuit voltage than that without the blocking barrier. High external quantum efficiency (EQE) is observed in the photon energy range in which electron transitions from the valence band to the IB take place in ZnTeO IBSC without the blocking layer, whereas the device with the blocked IB shows a small EQE at the same energy range, implying the electron accumulation in IB. Finally, the production of photogenerated current by two-step photon excitation via IB is demonstrated.