Solvothermal synthesis and thermoelectric properties of indium telluride nanostring-cluster hierarchical structures

A simple solvothermal approach has been developed to successfully synthesize n-type α-In2Te3 thermoelectric nanomaterials. The nanostring-cluster hierarchical structures were prepared using In(NO3)3 and Na2TeO3 as the reactants in a mixed solvent of ethylenediamine and ethylene glycol at 200°C for 24 h. A diffusion-limited reaction mechanism was proposed to explain the formation of the hierarchical structures. The Seebeck coefficient of the bulk pellet pressed by the obtained samples exhibits 43% enhancement over that of the corresponding thin film at room temperature. The electrical conductivity of the bulk pellet is one to four orders of magnitude higher than that of the corresponding thin film or p-type bulk sample. The synthetic route can be applied to obtain other low-dimensional semiconducting telluride nanostructures

Impurity analysis of CdCl₂ used for thermal activation of CdTe-based solar cells

We present an impurity analysis of cadmium chloride (CdCl2) using inductively coupled plasma mass spectrometry. Six batches of CdCl2 with different nominal purity ranging from 99.999% to 95% were analysed. Each batch turned out to be different in terms of the nature and concentration of impurities. However, all batches generally contained four impurity elements present with concentrations that were characteristic for that element, these being Na (~25 ppm (parts per million)), In (< 1 ppm), Pb (~0.5 ppm) and Te (< 3 ppm), regardless of the nominal purity or the supplier. In all the batches investigated, the major part of the impurities detected (between 83% and 91%) was found to comprise potentially electrically active dopants in CdTe. These impurities are therefore of importance to CdTe/CdS thin film solar cells, where the thermal activation is based on the use of CdCl2

Fabrication and assessment of optimized InGaAs single-junction TPV cells

Using a modeling approach, InP lattice-matched InGaAs-based TPV cell structures were optimized as a function of the doping concentration and thickness of the active region. The devices were subsequently grown, fabricated and assessed. The modeling study shows that low doping concentrations for the active layers lead to an improved overall device performance as indicated by an increase of all the device parameters. The effect of the thickness of the active layers was investigated and indicates that relatively thin structures can be achieved within the optimal device parameters calculated. The variation of the device parameters as a function of the illumination conditions such as the black-body source temperature and incident intensity was also modeled and will be discussed. The device structures were grown on InP substrates using MOVPE and different doping concentrations and thicknesses were used. The devices were processed into mesa diodes and the device parameters extracted from the IN characteristics were compared and discussed in light of the modeling predictions

Does CdTe deposition affect the impurity profile in sputtered CdS window layers?

We report a multi-element study of impurities in CdS window layers by dynamic and quantitative SIMS. Two CdS/TCO/glass samples, grown separately using nominally the same conditions, were considered. In2O3:F grown on soda lime glass was used as TCO followed by a sputtered CdS layer. One of the samples was subsequently used as a substrate for growth of CdTe by CSS. SIMS was carried out on both samples, and O, Na, Si, Cl, Sb, In, Zn, Sri, Ph, Cu, Te, S and Cd were depth profiled. It was shown that before CdTe growth most of the impurity elements showed flat levels in the CdS ranging from 2-3x10(20) cm for Zn and O to 2-3x10(17) cm(-3) for Na, Cl, Sb and Te. Si was found to segregate at the CdS/TCO interface with a maximum level of 10(18) cm(-3). However, following CdTe growth, the impurities in the CdS layer showed higher concentrations and different profile shape compared to those before CdTe growth. Some of the impurities also showed a diffusion-like profile following the CdTe growth as compared to before. Possible explanations of these changes are discussed in terms of the purity of the starting materials and the growth environments, as well as the diffusion from the TCO and glass

Efficiency improvement in thin-film solar cell devices with oxygen-containing absorber layer

The CdTe∕CdSCdTe∕CdSsolar cell devices were grown using a dry process consisting of sputtering for the transparent conducting oxide and CdS window layers, and close-space sublimation for CdTe absorber layer. These devices were back contacted using Mo∕Sb2Te3Mo∕Sb2Te3 sputtered layers following the CdCl2CdCl2 activation process carried out in air. It was shown that when oxygen is intentionally introduced in the CdTe layer during its growth, this leads to a significant improvement in all the device parameters yielding an efficiency of 14% compared to 11.5% for devices fabricated in the same conditions but without intentional oxygen incorporation in CdTe. The data obtained were not altered following a light soaking. The devices were investigated by quantitative secondary ion mass spectrometry, which allowed insight into the distribution and amount of oxygen and chlorine within the entire device structure. Both impurities showed an increased concentration throughout the CdTe absorber layer