15% Efficiency Tandem Organic Solar Cell Based on a Novel Highly Efficient Wide-Bandgap Nonfullerene Acceptor with Low Energy Loss

A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low-bandgap materials with broad absorption in long-wavelength region for back subcells has attracted considerable attention. However, wide-bandgap materials for front cells that have both high short-circuit current density (J(SC)) and open-circuit voltage (V-OC) are scarce. In this work, a new fluorine-substituted wide-bandgap small molecule nonfullerene acceptor TfIF-4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB-T-2F is selected as the donor, the device offers an extremely high V-OC of 0.98 V, a high J(SC) of 17.6 mA cm(-2), and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB-T-2F:TfIF-4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB-T-2F:TfIF-4FIC and PTB7-Th:PCDTBT:IEICO-4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells.