High efficiency ultra-thin sputtered CdTe solar cells

Large scale manufacturing of CdTe PV modules at the GW/yr level may be constrained due to the limited availability of the relatively rare (Te) element and the volume of potentially hazardous (Cd) material being used in the typically 3-8 mu m thick CdTe absorber layer. However, we find that it is possible to reduce the CdTe layer thickness without much compromise in efficiency. The CdS/CdTe solar cells were fabricated using magnetron sputtering with ultra-thin CdTe layers in the range of 0.5-1.28 mu m. The ultra-thin films and cells were characterized using X-ray diffraction (XRD), optical transmission, scanning electron microscopy (SEM), current-voltage and quantum efficiency measurements. These results were compared with those of standard 2.3 mu m thick CdTe sputtered cells. Different post-deposition processing parameters were required for cells with ultra-thin and standard CdTe thicknesses to achieve high efficiency. Ultra-thin CdTe cells showed crystallographic texture and CdTe1-xSx alloy formation after CdCl2 treatment very similar to standard CdTe cells. Optimization of the post-deposition CdCl2 treatment and back-contact processing yielded cells of 11.2% efficiency with 0.7 mu m CdTe compared to 13.0% obtained with standard 2.3 mu m CdTe cells. (c) 2006 Elsevier B.V. All rights reserved.