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March 2017 • The PCB Design Magazine 61 apart from the fact that the 4,000K colour was non-negotiable, their customer requested that a new on-spec reference sample be made avail- able for re-testing in just 24 hours. Electrolube India General Manager Padmanabha Shaktive- lu sought advice from our UK-based technical support team who subsequently suggested two different approaches that Rockforest might con- sider to solve the problem. The first was a recommendation that they use an LED that provided a colour temperature below the specified colour temperature, in this case, one operating in the 2,500K to the 3,000K range. By potting these with the UR5634 resin to the specified 5.5 mm depth, it could poten- tially bring the light back to the desired colour. The second option was that Rockforest assesses the amount and type of resin they were using for this project to see if a thinner layer of resin over the top of the LED array would reduce the colour shift effect. In the end, Padmanabha recommended that Rockforest switch to our UR5635 semi-rigid "hazy/cloudy" polyurethane resin, which pro- vided the required environmental protection as well as offering a useful light dispersing prop- erty. Indeed, the diffused light produced by this resin meant that an additional diffuser medium was no longer necessary, allowing the customer to save costs while achieving the required aes- thetic appearance and, through trials with vari- ous resin potting depths, the specified colour temperature, and achieved to a tight deadline! These are just a couple of examples of resins bringing very real benefits to practical electron- ic and electrical engineering applications, more notably here for LED applications, and how im- portant it is to work closely with your supplier so you can move fast when circumstances de- mand it. Look out for my next column in April when I hope to take a closer look at some top trending resin queries from our technical support team. PCBDESIGN Alistair Little is global business/ technical director for Electrolube's Resin Division. CASTING A SPOTLIGHT ON RESIN APPLICATIONS Semi-transparent organic solar cells (OSCs) have potential for pro- viding low-cost, large-area energy conversion devices for various ap- plications such as windows, roof covers and greenhouses. However, it is challenging to achieve semi- transparent OSCs with high power conversion efficiency (PCE) and high transparency at the same time. Usually, the active ma- terials of OSCs consist of a binary blend of a visibly absorbing donor polymer and a fullerene acceptor. The average visible transmittance (AVT) of the cell can be increased by decreasing the binary film thick- ness; however, this goes at the expense of the PCE because less sunlight is absorbed by a thinner layer. In a Science and Technology of Advanced Materi- als (STAM) study, a team led by Mohammed Makha from the Swiss Federal Institute for Materials Science and Technology bypassed this trad- eoff between transparency and effi- ciency of OSCs by using a ternary mixture. The team added to a visibly ab- sorbing binary polymer-fullerene blend a dye as a third minority com- ponent. The dye absorbs light exclu- sively in the near-infrared (NIR) wave- length region and therefore does not reduce the visible transparency of the OSC. Due to the additional current generated via NIR absorption, the polymer content could be reduced without compromising the cell perfor- mance. Semitransparent OSCs with a uniform AVT or 51% and a PCE of 3% were demonstrated. The team believes that their ternary blend per- forms so well because of a specific intermixed phase between the NIR dye and the fullerene; therefore, the system could successfully work with other polymers. Uncompromising on Organic Solar Cells

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