A team of researchers from NIA Member Imperial College London, have collaborated with six other worldwide institutions to help create a new set of rules to help design more efficient organic solar cells, namely those made using non-fullerene acceptor (NFA) materials.

Organic solar cells have been gaining a lot more interest over traditional silicon solar cells in recent years and this is evident by the number of scientists undertaking research in the field.  Even though their current energy conversion efficiency is not as high as inorganic solar cells, there is a lot of promise because they can be used to create flexible solar cells.  The organic constituents can also be formulated into an ink, which can then be used to print solar cells.  Hence their appeal.

NFA-based solar cells have been found to be significantly more efficient than other types of organic solar cells, and the researchers set out to find out why. The researchers used ultrafast laser techniques to discover that the electrons and holes at the semiconducting junction combine with no current being generated. They also return to their initial excited state with the same amount of energy as the photon which caused the recombination mechanism to occur. This mechanism was found to minimize energy loss and promote the energy conversion efficiency.

Using this information on how these types of solar cell work, the researchers have now developed a new set of rules, which include providing a low energy offset between donor and acceptor states and a high photoluminescence yield of the low-gap material, to help create more efficient solar cells in the future.

Sources: Imperial College London, Nature Materials