Cd1−XZnXTe thin films and junctions

Cadmium zinc telluride has a tunable band gap in the 1.45–2.26 eV range and is therefore a suitable candidate for the top cell in tandem solar cell applications. The aim of this work is to investigate the potential of polycrystalline thin films of Cd1−XZnXTe for solar cell applications. Two deposition technologies, cosputtering and co-close-spaced sublimation (co-CSS) were used for the deposition of Cd1−XZnXTe. Both processes were calibrated to yield a band gap of 1.65–1.75 eV, the optimum range for tandem solar cells. Single-phase Cd1−XZnXTe films have been obtained with both technologies. Films deposited by cosublimation exhibited larger grain size and overall better microstructure than films deposited by sputtering. Cd1−XZnXTe-based junctions of the superstrate configuration have been fabricated. Various wide band gap materials, such as CdS, SnO2, ZnO, and ZnSe were utilized as window layers. Solar cell performance for as-deposited junctions was found to be limited due to poor collection. Improvements in collection and overall solar cell characteristics can be attained by subjecting the devices to a postdeposition heat treatment. Although junctions based on CdS yielded the highest VOC's, the most improved collection and highest JSC's were demonstrated with CZT/SnO2 junctions.