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Cobalt replacements make solar cells more sustainable By Paul Buckley The journal Chemical Communications has published the results of the Cu-Co cells. Dye-sensitized solar cells (DSCs) transform light to electricity. The cells consist of a Semiconductor on which a dye is anchored. The coloured complex absorbs light and through an electron transfer process produces electrical current. Electrolytes act as electron transport agents inside the DSCs. Usually, iodine and iodide serve as an electrolyte. Chemists at the University of Basel have now been able to successfully replace the iodine-based electron transport system in copperbased DSCs by a cobalt compound. Tests showed no loss in performance. The replacement of iodine increases the sustainability of solar cells. “Iodine is a rare element, only present at a level of 450 parts per billion in the Earth, whereas cobalt is 50 times more abundant,” explained the Project Officer Dr. Biljana Bozic- Weber. The replacement also removes one of the long-term degradation processes in which copper compounds react with the electrolyte to form copper iodide and thus improves the long-term stability of DSCs. The research group supporting the Basel chemistry professors Ed Constable and Catherine Housecroft is currently working on optimizing the performance of DSCs based on copper complexes. The group had previously shown in 2012 that the rare element ruthenium in solar cells could be replaced by copper derivatives. This is the first report of DSCs, which combine copper-based dyes and cobalt electrolytes and represents a critical step towards the development of stable iodide-free copper solar cells. However, many aspects relating to the efficiency need to be addressed before commercialization can begin in anything other than niche markets. “In changing any one component of these solar cells, it is necessary to optimize all other parts as a consequence,” said Ed Constable. This is part of a new approach termed ‘Molecular Systems Engineering’ in which all molecular and material components of a system can be integrated and optimized to approach new levels of sophistication in nanoscale machinery. In the publication, the engineering of the electrolyte, the dye and the Semiconductor are all described. The systems chemistry approach is particularly appropriate for the engineering of inorganic-biological hybrids and is the basis of ongoing collaborations with the ETH Department of Biosystems Engineering in Basel (D-BSSE) and EMPA. A joint proposal by the University of Basel and D-BSSE for a new National Centre of Competence in Research in this area is currently in the final stages of appraisal. Portable tablet relies on the old analog TV RF frequencies By Nick Flaherty researchers at the Japanese nationalInstitute of Information and Communications Technology (NICT) developed a frequency converter for the tablet that enables IE802.11-based radio communication in TV bands (470-710 MHz). The Android tablet uses wireless LAN system for radio communication in TV bands with an inquiry in the white-space database developed by NICT. The original 2.4GHz band of a WLAN system is also available and it is possible that the tablet terminal automatically selects the radio communication band according to data traffic. Due to the explosive growth of mobile portable devices such as smartphones and tablet terminals, communication traffic has been increasing and a frequency resource shortage problem has been aggravating. To solve this problem, the use of TV white spaces is studied and the establishment of radio rules designed for TV white-space operation has been started in the US, the UK and Japan. NICT has contributed to standardization on various radio communication systems using TV white spaces, and has developed stationary prototypes based on the standards. Although future TV white-space utilization by portable devices will contribute to the further effective use of frequency resources, it is difficult to miniaturize components and circuits for portable devices due to its lower operational frequency than existing WiFi or cellular bands and its relatively wide frequency range of 470-710 MHz. In addition, technology to avoid interference with TV broadcasts is necessary to be implemented in portable devices. On the other hand, propagation characteristic evaluation supposing practical operation is required for the feasibility study on TV white-space utilization. The tablet is based on an off-the-shelf terminal and a frequency converter newly developed by NICT is implemented for using TV white spaces. This tablet terminal can operate in the frequency considered not to interfere with TV broadcasts according to calculation results provided by the white-space database developed by NICT, and can automatically select the optimal frequency according to data traffic, through control by the network manager. www.electronics-eetimes.com Electronic Engineering Times Europe September 2013 17


EETE SEPT 2013
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