Structural and electrical characterisation of CdS/CdTe devices with double layered CdS substrates

摘要

Thin film solar cells with a CdS layer grown by chemical bath deposition and a CdTe layer grown by close space sublimation (CSS) have been reported to give the highest efficiency CdS/CdTe solar cells [1]. Growth by CSS generally requires a high substrate temperature, and there is clearly potential for evaporative loss of the CdS layer during CdTe deposition. In addition, these elevated temperatures may cause interdiffusion between the CdS and CdTe layers, creating an intermediate layer of CdS{sub}xTe{sub}(1-x). Both of these processes affect the thicknesses of the CdS layer and the properties of completed devices. In our study we have examined the nature of the interface between these layers by investigating various heat treatments of the CdS before CdTe deposition. As deposited CdS layers were annealed under different conditions, with some including an additional, second CdS layer deposited on top of the original annealed CdS. Complete devices were made using CSS CdTe, and the structure of the CdS/CdTe heterojunctions was examined using X-ray diffraction and scanning electron microscopy. These were correlated with current voltage and quantum efficiency measurements.