An 800 nm CdSeTe layer was added to the CdTe absorber used in high-efficiency CdTe cells to increase the current and produce an increase in efficiency. The CdSeTe layer employed had a band-gap near 1.41 eV, compared with 1.5 eV for CdTe. This lower band-gap enabled a current density increase from approximately 26 to over 28 mA/cm2. The open-circuit voltage obtained in the high-efficiency CdTe-only device was maintained and the fill-factor remained close to 80%. Improving the short-circuit current density and maintaining the open-circuit voltage lead to device efficiency over 19%. External quantum efficiency implied that about half the current was generated in the CdSeTe layer and half in the CdTe. Cross-sectional STEM and EDS showed good grain structure throughout. Diffusion of Se into the CdTe layer was observed. This is the highest efficiency polycrystalline CdTe photovoltaic device demonstrated by a university or national laboratory.

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.

The aim of this investigation is to apply advanced microstructural characterization techniques to study the effect of cadmium chloride treatment on the physical properties of cadmium telluride (CdTe) solar cells deposited via close-spaced sublimation and relate these to cell performance. A range of techniques have been used to observe the microstructural changes as well as the chemical changes before and after the cadmium chloride treatment. Electrical measurements that link the device performance with the microstructural properties of the cells have also been undertaken. Transmission electron microscopy (TEM) has revealed high densities of stacking faults in the as-grown CdTe samples. Further, it has been observed that these stacking faults are removed during the cadmium chloride treatment. These observations show that the presence of chlorine plays an important role in the removal of these defects and the subsequent production of high efficiency thin-film CdTe solar cells. Elemental analysis in the TEM indicates chlorine-rich regions appearing at the CdTe/CdS interface as well as at grain boundaries after the treatment.