Multicyclic molecule could boost silicon solar cell efficiency

A potential way to boost the efficiency limit on solar cells is to slather them with materials that can convert unusable, high-energy photons into lower-energy charge carriers that the cell can use to generate electricity. When a photon hits a solar cell, it generates charge packets called excitons, which consist of a paired electron and a positively charged hole. Organic molecules such as tetracene can split excitons into multiple lower-energy excitons. This fission has been shown to work in prototype solar cells, but it’s far from practical, in part because the second-generation excitons recombine in nanoseconds, says Luis Campos, a chemist at Columbia University. His lab has been experimenting with organic molecules engineered to keep excitons from recombining. The researchers found that a tetracene flanked by two pentacenes (PTP, shown) works better. Thanks to pentacene’s lower-energy state, after each exciton splits, the two second-generation excitons are pulled away from the central tetracene to the pentacene units, like two balls rolling down opposite sides of a hill. PTP can keep split excitons apart for about 20 µs (Nat. Chem. 2019, DOI: 10.1038/s41557-019-0297-7). Campos’s group is tweaking the molecule for use in a silicon solar cell.