Electrochemical Reduction in Alkaline Electrolyte Removes CuS Phase to Form CuInS 2 -Based Solar Cells
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ized as Nondestructive Method of Buried Corrosion Detection The use of second harmonic generation (SHG) signal as a means of corrosion detection for bodies coated with paint has been demonstrated by a group from the Departments of Physics and of Electrical 4
Engineering at City College of New York. While scientists desire the ability to detect the onset of corrosion underneath layers of paint, current nondestructive methods are limited. As reported in the August 15 issue of Optics Letters, such a task is made possible by the use of a focused laser in the near infrared region to map out a 2D/3D corrosion profile. The output of a modelocked Ti:sapphire laser, with an 810 nm wavelength, 120 fs pulse duration, and 76 MHz pulse repetition rate, was used to scan the volume of a coated-uncorroded, an uncoated-corroded, and a coated-corroded sample. The incident optical beam is focused with a 20X lens (Numerical Aperture 0.4) providing a focal spot of ≈ 10 µm extent. The SHG signal is a backreflected signal, redirected back through the same lens, through a beam splitter, and into a photomultiplier tube and depends critically on the position of the focal volume with respect to the various layers sampled. The corroded samples consisted of blocks of iron exposed to open air. The uncorroded sample was hand polished. A 30-µm thick layer of paint was painted onto one corroded and the uncorroded sample. Of the painted, rusted, and metallic iron samples, the surface paint layer generated the largest SHG signals and the metallic iron generated the least. By using signal contrast and a computerized motor translation stage to control the lateral and longitudinal position of the focused laser spot, a 2D/3D map of the system profile could be generated. However, the paint transmission characteristic was only 0.09% within the spectral range of 400–800 nm. The scientists suggest adapting different light sources for different types of coating in order to maximize transmission to the underlayers. This work provides a new means of early corrosion detection for aircraft, structures, and other industrial equipment. JUNE LAU
Electrochemical Reduction in Alkaline Electrolyte Removes CuS Phase to Form CuInS2-Based Solar Cells
A team of researchers in the Solar Energetics division of the Hahn-MeitnerInstitute (HMI) in Berlin, Germany, has reported a method for the removal of unwanted CuS from the surface of CuInS2-based photovoltaic cells. Instead of the traditional cyanide washing, a straightforward electrochemical reduction in an alkaline electrolyte and subsequent dissolution are employed, leading to complete removal of the covellite (CuS) phase and a photoactive CuInS2 material.
Thin film solar cells based on CuInS2 are promising materials for large-scale applications, as they show high performance at low production costs. CuInS2 has a high absorption coefficient and a bandgap energy around the maximum of the solar spectrum. “However, there are several problems that hinder the further development”, said H.J. Lewerenz, professor at the HMI. “
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