A new record in the efficiency of transparent solar cells has been set by a development that allows transparency levels up to 40% with an efficiency of over 7%, by Heliatek GmbH. The company already holds the world record of 12% cell efficiency for opaque (non-transparent) organic solar cells. This lab development underscores the company's strategy to supply its transparent HeliaFilm™ to glass manufacturers for both building integration (BIPV) and car roofs. The production of HeliaFilm™ is based on small molecules (oligomers). Oligomers are deposited at low temperatures in a roll-to-roll vacuum process. Their selective absorption of the solar spectrum targets different colors and transparency to convert sunlight into electricity. The production of the transparent film is possible with the introduction of transparent conductive layers at the front- and back-side of the solar cells. The transparency of the products is at the core of the film customized to meet partners' specific needs. This is a film which can combine transparency and energy generation. Both these application areas use tinted glass to reduce glare which can be done by applying a film, so changing the film to one that generates electricity as well is a drop-in for manufacturers. Using the film in glass car roofs will not only generate energy, but will also allow the car manufacturers to claim Eco-innovation credits towards CO2 emission goals. Architectural glass panels and windows incorporating the film enable electricity to be discretely generated on the outside envelope of a building. 40% light transparency with an efficiency record of 7.2% - this measurement follows standard testing conditions using a white background. Heliatek thus succeeded in generating an optimal energy conversion for transparent HeliaFilm™. 7.2% cells mirror the same efficiency, since the partial transparency allows the usage of only 60% of the light for the energy harvesting. Depending on the application, the balance between light let through and electricity generated can be adjusted. Importantly for these applications, the technology continues to be effective at generating electricity at low light levels, any orientation and at high temperatures, which are conditions where conventional solar lose efficiency.
Inventing a new solar technology that can compete commercially with today’s solar cells is difficult, given existing deployment methods. But a transparent photovoltaic (PV) cell would change the rules of the game. MIT researchers are making transparent solar cells that could turn everyday products such as windows and electronic devices into power generators - without altering how they look or function today. Their new solar cells absorb only infrared and ultraviolet light. Visible light passes through the cells unimpeded, so they are invisible to the eyes. Using simple room-temperature methods, the researchers have deposited coatings of their solar cells on various materials and have used them to run electronic displays using ambient light. They estimate that using coated windows in a skyscraper could provide more than a quarter of the building’s energy needs without changing its look. They are now beginning to integrate their solar cells into consumer products, including mobile device displays.