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We report seminal advances in fabrication and understanding of group V (As) doped thin-film polycrystalline CdTe-based solar cells. The devices are fabricated using a novel approach, by sublimating layers of CdSeTe and CdSeTe:As. This new method allowed us to achieve minority carrier lifetime of over 1 µs, carrier concentration of more than 5×l015cc−1 and external radiative efficiency of over 2 % in a device configuration. We find an increase in open-circuit voltage when comparing As-doped, Cu-doped and undoped devices. The choice of CdSeTe instead of a CdTe-only absorber has been explained using first-principle density functional theory model. A SCAPS device model is used to analyze the potential causes for lower open-circuit voltage.

In-situ doping of CdTe/CdSeTe films with arsenic is performed using pre-doped source material prepared by high pressure Bridgman (HPB) melt growth. Arsenic level in the source material is varied from 1018-1020 cm−3. Correspondingly, dopant incorporation in the films prepared using vapor transport deposition (VTD) varied from 3×1017 cm−3-1×1018cm−3. In this range, dopant activation is found to inversely correlate with the dopant incorporation, suggesting compensation. The results from this study indicate film properties can be adjusted by source material.

Efficient, safe and cost-effective synthesis of CdTe from elements is rather challenging in silica sealed ampoules due to the high vapor pressure of Cd. In this article, we report on the integrated synthesis and crystal growth of high-purity CdTe using the high pressure Bridgman (HPB) technique that is scalable to large volumes. The process lends itself for cost competitive industrial production of polycrystalline feedstock material for photovoltaics, sensors and electro-optic applications. Cadmium telluride (CdTe) crystals exceeding 1 kg in size were synthesized from elemental Cd and Te sources with purity comparable to state-of-the-art gamma ray detector crystals. In addition, synthesis of highly-doped CdTe feedstock for thin film photovoltaics applications demonstrating effective incorporation of group V (As, Sb) dopants was achieved at growth speeds of ~500 mm/hr. The technique may be applicable to produce other II-VI compounds with volatile components.