As a promising technology for renewable energy, organic solar cells (OSCs) have attracted particular interest from both industrial and academic communities. One of the main challenges to promote practical applications of OSCs is their less competitive power conversion efficiency than that of the counterpart photovoltaic technologies such as inorganic silicon, CIGS, or perovskite solar cells.
The photovoltaic performance of bulk-heterojunction OSCs is determined by open-circuit voltage, short-circuit current density and fill factor. The optimal performances require state-of-the-art pair of the electron-donor and electron-acceptor in the light-harvesting layer, which should have complementary absorption profiles, excellent miscibility, and appropriate frontier molecular orbital energy levels. Specifically, for the electron-donor materials, the deep highest occupied molecular orbital (HOMO) energy level is much appreciated as it is favorable for open-circuit voltage; however, it may negatively affect charge transfer when pairing with acceptors with shallow HOMO levels.
Very recently, Professor Yong Cao’s group in South China University of Technology demonstrated an unprecedented power conversion efficiency of over 16% for single-junction OSCs. This remarkable photovoltaic performance is achieved based on a home-made wide-bandgap polymer P2F-EHp, which has an appropriate HOMO energy level and can form complementary absorption profile and optimal morphology of the bulk-heterojunction photoactive layer with a recently emerging non-fullerene acceptor. In particular, this electron-donating polymer, which contains an imide-functionalized benzotriazole (TzBI) unit, is versatile in matching with various categories of electron-acceptors, and thus presents great promise for constructing high-performance OSCs.