Investigation of capacitance transients in CuInS2 due to ionic migration

Transport of mobile ions in n-TiO₂/n-CuInS₂/p-CuInS₂ thin-film devices is studied with the transient ion-drift (TID) method. In contrast to the normal TID method, a mobile ion profile is created in the CuInS₂ layer, which can be described by the Gouy-Chapman theory. Activation energies for diffusion of 0.5 and 1.0 eV are found. We postulate that these activation energies are related to the associated defect, ( In_Cu)^x, which introduces a deep electronic state inside the bandgap of CuInS₂. This defect can accept or release an electron and drift out of the depletion region. This will lower the concentration of recombination centers in the depletion region, which explains the self-healing property of CuInS₂.     

Radical-induced degradation mechanism of perfluorinated polymer electrolyte membrane

The degradation mechanism induced by radicals was investigated for Nafion^®-117 by solution analysis. Nafion^® was exposed independently to three kinds of radicals, OH, H and O₂⁻ which were produced separately by γ-irradiation. Based on the eluted elements, the scission site in the membrane was analyzed. The results showed that the scission site was classified into two and these locations were closely relating to oxidative and reductive reactions. The decreasing rate of proton conductivity was more significant under the influence of reductive radicals. The progression of the unzipping reaction of main chain was suggested to be initiated by the production of tertiary carbon radical by reductive radicals such as H and O₂⁻ with the aid of OH. The structural degradation such as collapse of cluster and the cluster decomposition as well as the performance degradation was found to be initiated by such reductive radicals.     

Synthesis and characterization of co-electroplated Cu2ZnSnS4 thin films as potential photovoltaic material

Cu₂ZnSnS₄ thin films have been successfully prepared by a novel synthesis process that involves a single step deposition of Cu₂ZnSnS₄ followed by a post-annealing treatment at 550 °C for 60 min in the atmosphere of N₂+H₂S (5%). The microstructure, morphology, composition and optical property of the film have been investigated in detail. It is found that the Na₂S₂O₃5H₂O concentration in the solution has a significant effect on the Cu₂ZnSnS₄ thin films. X-ray diffraction data indicates that the annealed Cu₂ZnSnS₄ thin films have a kesterite structure with preferred orientation along the (1 1 2) plane. Uniform and compact topographies are observed in some annealed films. From the energy dispersive X-ray spectroscopy analysis, it can be seen that Cu-poor and Zn-rich Cu₂ZnSnS₄ thin films have been obtained. The direct band gap energy of the film is about 1.5 eV.