An organic solar cell with a high level of transparency and high power conversion efficiency may soon be able to capture energy needs as light flows through a window.
These windows can become productive solar cells that help decrease reliance on fossil fuels and advance toward a greener and cleaner environment.
Today’s commercial solar panels consist of wafer-based crystalline silicon solar cells which are efficient in converting solar radiation into electrical power (approximately 15 percent conversion efficiency), but with several important obstacles standing in the way of maximum exploitation. One obstacle is they must be precisely oriented to receive direct sunlight and even then have limits in their ability to absorb diffused light. In addition, they are heavy, opaque, and take up a great deal of space.
Organic solar cell technology has been around for 30 years, however, it is just now starting to attract substantial interest due to its low production cost, according to researchers at the Institute of Photonic Sciences (ICFO). While organic cells have not yet reached the efficiency values of silicon based cells, these Organic Photovoltaic (OPV) cells are lighter in weight, more flexible (they are capable of adapting to curved surfaces), and even more sensitive to low light levels as well as indirect sun light, making them an appealing photovoltaic technologies for everyday applications. One property that makes them even more interesting is their potential as a semi-transparent device.
OPVs, like any other photovoltaic technology, achieve maximum light to electricity conversion efficiency with opaque devices. To turn these cells into transparent ones, the back metal electrode must thin down to just a few nanometers, drastically reducing the device’s capacity to collect sunlight.
ICFO researchers have been able to implement a semi-transparent cell incorporating a photonic crystal and reach a cell performance almost as good as its opaque counterpart. By adding such extra photonic crystal to the cell, ICFO’s scientists were able to increase the amount of infrared and ultraviolet light absorbed by the cell, reaching a 5.6 percent efficiency while preserving a transparency almost indistinguishable from normal glass. The results in efficiency and transparency make these cells an extremely competitive product for Building-Integrated Photovoltaic (BIPV) technologies. To reach the adequate architectural look, it is possible to alter the color of the cells by changing the layer configuration of the photonic crystal.
“Applications for this type of technology in BIPV are just a few steps away, but the technology has not reached its saturation point yet,” said Jordi Martorell, UPC Professor at ICFO in Barcelona, Spain, and leader of the study. “ICFO’s discovery opens the path for innovation to other industrial applications of transparent photovoltaics. In the midterm we expect to reach the extremely high transparencies and efficiencies needed to power up devices such as displays, tablets, and smart phones.”
A just approved European project entitled SOLPROCELL1 will allow a consortium of top European researchers and industries led by ICFO to boost the study of the capabilities of these cells, improving their stability and lifetimes as well as obtaining the material needed to substantially raise their efficiency.