New solar cells that could increase the efficiency of solar panels by over 25 percent have been developed by scientists at Cambridge University’s Department of Physics.
Solar panels work by capturing particles of light from the sun, called photons, and then converting to units of energy, called electrons. Thus far, solar panels have only been able to capture a part of the sun’s light, leaving the remainder to escape as heat. The Cambridge scientific team, which is led by Professor Neil Greenham and Professor Sir Richard Friend, has helped to change that by developing a hybrid cell which absorbs red light. It harnesses the extra energy of blue light which then boosts the electrical current. By adding pentacene, which is an organic semiconductor, means that solar cells can generate two electrons for every photon in the blue light spectrum. This enables solar cells to capture 44 percent of the sun’s energy instead of the 34% previously obtainable. It is the pentacene which captures the blue light but it has to be combined with other material. “If our cells just relied on pentacene, they would only absorb blue light,” Professor Greenham says. “The trick is to combine the pentacene with a second material in the same cell that also absorbs the red light. That way we can use the red light and the blue light efficiently within the same cell.”
Greenham chose pentacene because it works very quickly using a process called ‘singlet fission’. The resulting level of energy absorption is still low but there are all the signs that it could improve quickly. “Everyone is working to improve cells to take them closer to the physical limit.” Greenham says “Our new strategy raises the limit that we can chase. If we can use our strategy to improve cells that are already working efficiently then that should make a real impact. Our strategy works within a single cell, and the materials— organic molecules and inorganic semiconductor nanocrystals—are compatible with printing processes, so they have the potential to be both cheap and efficient.”
Bruno Ehrler is the lead author on the new paper and a scientist at Cambridge University’s Cavendish Laboratory. “Organic and hybrid solar cells have an advantage over current silicon-based technology” he said, “because they can be produced in large quantities at low cost by roll-to-roll printing. However, much of the cost of a solar power plant is in the land, labour, and installation hardware. As a result, even if organic solar panels are less expensive, we need to improve their efficiency to make them competitive.” Dr. Akshay Rao, co-author on the paper said: “This is just the first step towards a new generation of solar cells and we are very excited to be a part of this effort.”
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