Nano adopts the ancient skill of mending

PSD Staff Written



Renewable-energy efficiencies, certainly in the photovoltaic sector, have a long and steady history as the PV cell has been continuously improved for space use, picking out better- to best-suited raw materials. That classic in technical graphics must be that of NREL showing Best Research Cell Efficiencies, and that tracked advances in multijunction concentrators, Crystalline Si, TFT (thin-film technologies), and emerging organic cells from 1975 to 2000. Currently one of Europe's more intriguing projects underway has the UK's NPL (National Physical Laboratory) working in it on a European project to find a way to overcome the damage caused by nano defects on flexible electronics. It's a €7.25m project, with the University of Huddersfield leading the field and involves measurements of surface topography and defect geometry, using optical super-resolution techniques. NPL of course has its own design instruments, such as the Areal (for 3-D surface parameters), MAFM (metrological atomic-force microscope), and NanoSurf IV, providing high accuracy and direct traceability to the metre. In addition to these, it has an extensive range of commercial instruments, including a stylus instrument and non-contact instruments—scanning white light interferometer, variable focus and confocal microscopy—also available. Flexible electronics for solar modules (and digital display) are highly vulnerable to defects that range from fine dust particle to pin holes. The project's aim is to develop imaging, detection, and correction technologies for use in high speed manufacturing of these products. There are two pilot lines in the current mend project. One is being developed for the manufacturing lines of polymer-coated-paper packaging at Finland's Stora Enso, to extend the shelf life of carton drinks, and use less material. The other is for the manufacturing lines of the Swiss flexible solar-cell start up, FLISOM. Nanomend will be used to detect and correct defects within various layers of the solar module to increase its efficiency, lifespan, and economic viability for consumers. FLISOM has already worked with the scientific sector gaining help from the Swiss EMPA team, who made significant progress in low-temperature growth of CIGS layers, yielding more flexible CIGS cells with record values rising from 14.1% in 2005 to the high score of 18.7% for any type of flexible solar cell grown on polymer or metal foil. It was achieved by reduction in recombination losses, improving the structural properties of the CIGS layer and the proprietary low-temperature deposition process for growing the layers, as well as in situ doping with Na (sodium) during the final stage. With these results, polymer films have for the first time proven to be superior to metal foils as the carrier substrate for highest efficiency. "Results clearly show the advantages of the low-temperature CIGS deposition process for achieving highest efficiency flexible solar cells on polymer as well as metal foils", says PV and TFT expert Professor Ayodhya Tiwari. After mending, one suspects, the future for smart materials at least will have to be that layer deeper, as self-heal or auto-mend become obligatory. Power Systems Design