High-efficiency Cd/sub 2/SnO/sub 4//Zn/sub 2/SnO/sub 4//Zn/sub x/Cd/sub 1-x/S/CdS/CdTe polycrystalline thin-film solar cells

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Abstract
CdTe-based thin-film solar cells have been limited to the conventional SnO/sub 2//CdS/CdTe device structure. In this paper, we report a modified device structure consisting of Cd/sub 2/SnO/sub 4//Zn/sub 2/SnO/sub 4//Zn/sub x/Cd/sub 1-x/S/CdS/CdTe layers, that yields improved performance and reproducibility. Cadmium stannate (Cd/sub 2/SnO/sub 4/, or CTO) transparent conductive oxide (TCO) films have several significant advantages over conventional SnO/sub 2/ films. CTO-based CdTe cells have approximately 1 mA/cm/sup 2/ higher J/sub sc/ than SnO/sub 2/-based CdTe cells. Integrating zinc stannate (Zn/sub 2/SnO/sub 4/, or ZTO) into the device as a buffer layer helps maintain high V/sub oc/ and fill factor when reducing CdS thickness to improve J/sub sc/. XPS and SIMS results show substantial interdiffusion between the CdS and ZTO layers. This feature can be used to optimize device performance and reproducibility. We have fabricated a Cd/sub 2/SnO/sub 4//Zn/sub 2/SnO/sub 4//Zn/sub x/Cd/sub 1-x/S/CdS/CdTe cell with an NREL-confirmed total-area efficiency of 15.8%.

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