Abstract
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.
Highlights
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells
power conversion efficiencies (PCEs) exceeding 15% have been achieved in single-junction OPV cells[21,22], further improvement is still needed to compete with other photovoltaic technologies, such as silicon solar cells and perovskite solar cells
We have demonstrated that chlorination has great potential for constructing OPV materials with superior performances compared to fluorination[40]
Summary
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. We report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and displays a higher voltage than its fluorinated counterpart in the devices This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Designing low bandgap materials to have a good match with the solar spectrum is a general method for improving the short-circuit current density (JSC) and thereby the PCEs of OPV cells[23,24,25,26,27,28]. One of the biggest problems of chlorinated acceptors is that they usually exhibit downshifted lowest unoccupied molecular orbit (LUMO) levels, leading to reduced open-circuit voltages (VOCs) in the resulting OPV cells. The overall PCE is even decreased compared with that of the IT-4F-based device
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