Single-Crystal CdTe Solar Cells with Voc Greater than 900 mV

We fabricated single-crystal CdTe photovoltaic devices in a heterojunction structure with an In-doped CdS window layer and ZnO/Al-doped ZnO front contact. By replacing the polycrystalline absorber layer of a CdTe solar cell with a single crystal, we were able to achieve open-circuit voltage (V_oc) as high as 929 mV. Simulations and measurements indicate that increased minority-carrier lifetime and carrier concentration can explain this high V _oc. Cu and Na both introduce transient effects in single-crystal CdTe similar to those observed in polycrystalline CdTe, suggesting that Group I dopants pose stability problems that are linked fundamentally to their defect chemistry in CdTe, regardless of the presence of grain boundaries.