CdTe thin film solar cells have demonstrated efficiencies over 20%, but CdTe has a somewhat higher band gap than optimal for single-junction terrestrial solar-cell power generation. A reduction in the band gap could therefore result in an overall improvement in performance. To reduce the band gap, selenium was alloyed with CdTe using a novel co-sublimation extension of the close-space-sublimation process. Co-sublimated layers of CdSeTe with various selenium concentrations were characterized for optical absorption and atomic concentrations, as well as to track changes in their morphology and crystallinity. The lower band-gap CdSeTe films were then incorporated into the front of CdTe cells. This two-layer band-gap structure demonstrated higher current collection and increased quantum efficiency at longer wavelengths.
Photovoltaic technologies have shown efficiencies of over 40%, however, manufacturing costs have prevented a more significant energy market penetration. To bridge the gap between the high efficiency technology and low cost manufacturing, a research and development tool and process was built and tested. This fully automated single vacuum photovoltaic manufacturing tool utilizes multiple inline close space sublimation (CSS) sources with automated substrate control. This maintains the proven scalability of the CSS technology and CSS source design but with the added versatility of independent substrate motion. This combination of a scalable deposition technology with increased cell fabrication flexibility has allowed for high efficiency cells to be manufactured and studied. The single vacuum system is capable of fabricating a 3.1 × 3.6 in. substrate every 45 min with a cell efficiency of 12% with a standard deviation of 0.6% as measured over 36 months. The substrate is generally scribed into 25 small area devices allowing for over 250 small area devices to be fabricated each day. The system can operate uninterrupted for maintenance for over 21 days.
Photovoltaic cells utilizing the CdS/CdTe structure have improved substantially in the past few years. Despite the recent advances, the efficiency of CdS/CdTe cells is still significantly below their Shockley–Queisser limit. CdTe based ternary alloy thin films, such as Cd1−xMgxTe (CMT), could be used to improve efficiency of CdS/CdTe photovoltaic cells. Higher band gap Cd1−xMgxTe films can be the absorber in top cells of a tandem structure or an electron reflector layer in CdS/CdTe cells. A novel cosublimation method to deposit CMT thin films has been developed. This method can deposit CMT films of band gaps ranging from 1.5 to 2.3 eV. The cosublimation method is fast, repeatable, and scalable for large areas, making it suitable for implementing into large-scale manufacturing. Characterization of as-deposited CMT films, with x varying from 0 to 0.35, reveals a linear relationship between Mg content measured by energy dispersive x-ray spectroscopy and the optical band gap. Glancing angle x-ray diffraction (GAXRD) measurements of Cd1−xMgxTe films show a zinc-blende structure similar to CdTe. Furthermore, increasing Mg content decreases the lattice parameter and the grain size. GAXRD shows the films are under mild tension after deposition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.