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The optical and electrical properties of n-type chlorine-doped Sb2Se3 single crystals, with free carrier concentrations above 1016 cm−3 at room temperature, have been studied. The experiments reveal a strongly polarized temperature-dependent long-wavelength infrared absorption attributable to conduction band electrons within the material. For wavelengths between 1.6 and 6 μm, the room temperature absorption varies as λ 2.5 ± 0.3 , suggesting that longitudinal optical mode scattering is the dominant electron scattering mechanism. The results are most consistent with the hypothesis that electron transport in Sb2Se3 is band-like and not intrinsically limited by small-polaron self-trapping. [ABSTRACT FROM AUTHOR]

The cost of CdTe photovoltaic modules has now dropped below one US dollar per watt and the cost of power generation is rapidly approaching grid parity (2). A key stage [...], Cadmium telluride, CdTe, is now firmly established as the basis for the market-leading thin-film solar-cell technology. With laboratory efficiencies approaching 20 per cent (1), the research and development targets for CdTe are to reduce the cost of power generation further to less than half a US dollar per watt (ref. 2) and to minimize the environmental impact. A central part of the manufacturing process involves doping the polycrystalline thin-film CdTe with Cd[Cl.sub.2]. This acts to form the photovoltaic junction at the CdTe/CdS interface (3,4) and to passivate the grain boundaries (5), making it essential in achieving high device efficiencies. However, although such doping has been almost ubiquitous since the development of this processing route over 25 years ago (6), Cd[Cl.sub.2] has two severe disadvantages; it is both expensive (about 30 cents per gram) and a water-soluble source of toxic cadmium ions, presenting a risk to both operators and the environment during manufacture. Here we demonstrate that solar cells prepared using Mg[Cl.sub.2], which is non-toxic and costs less than a cent per gram, have efficiencies (around 13%) identical to those of a Cd[Cl.sub.2]-processed control group. They have similar hole densities in the active layer (9 x [10.sup.14] [cm.sup.-3]) and comparable impurity profiles for Cl and O, these elements being important p-type dopants for CdTe thin films. Contrary to expectation, Cd[Cl.sub.2]-processed and Mg[Cl.sub.2]-processed solar cells contain similar concentrations of Mg; this is because of Mg out-diffusion from the soda-lime glass substrates and is not disadvantageous to device performance. However, treatment with other low-cost chlorides such as NaCl, KCl and Mn[Cl.sub.2] leads to the introduction of electrically active impurities that do compromise device performance. Our results demonstrate that Cd[Cl.sub.2] may simply be replaced directly with Mg[Cl.sub.2] in the existing fabrication process, thus both minimizing the environmental risk and reducing the cost of CdTe solar-cell production.

Deep-level transient spectroscopy research shows the deep levels in polycrystalline n-CdS/p-CdTe photovoltaic structures are distributed in an independent fashion after being treated with post-growth treatments such as heat, post-deposition and heat and CdCl2. Spectra samples have a hole trap localized at Ev+0.48 eV. Heat treated samples have metastable hold and electron traps.