Semi-transparent organic solar cells claim efficiency record

March 24, 2014 // By Paul Buckley
Heliatek GmbH is claiming a new record in the efficiency of transparent solar cells.  The latest development allows transparency levels up to 40% with an efficiency of more than 7%.

The company already holds the world record of 12% cell efficiency for opaque (non-transparent) organic solar cells.  

The latest generation of organic solar cells with a 40% light transparency have reached an efficiency record of 7.2%. The measurement follows standard testing conditions using a white background.  Heliatek has succeeded in generating an optimal energy conversion for transparent HeliaFilm. Currently, its opaque cells achieve 12% efficiency.  The 7.2% cells mirror the same efficiency, since the partial transparency allows the usage of 60% of the light for the energy harvesting.  Depending on the application, the balance between light let through and electricity generated can be adjusted.  The production of transparent HeliaFilm is possible with the introduction of transparent conductive layers at the front- and back-side of the solar cells.

The lab development underpins Heliatek's strategy to supply its transparent HeliaFilm to glass manufacturers for both building integration (BIPV) and car roofs.  

"The transparency of our products is at the core of our market approach.  Our HeliaFilm is customized to meet our partners specific needs," added Thibaud Le Séguillon, Heliatek CEO.  "We are a component supplier and this component is a film which can combine transparency and energy generation.  This unique combination widens our market potential."

Both BIPV and car roofs 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 HeliaFilm 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 HeliaFilm enable electricity to be discretely generated on the outside envelope of a building.

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