Reducing the Trade-Off between Charge Generation and Nonradiative Voltage Loss via Asymmetric Strategy Enables Binary Organic Solar Cells over 19.5%

Halogenation and asymmetry strategy on the 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) terminal groups are effective approaches for constructing efficient nonfullerene acceptors (NFAs). In this study, we introduced iodine-based I-INCN and the chlorine-based Cl-INCN into one molecule named BOCl-I, in which I-INCN is beneficial for suppressing nonradiative recombination and Cl-INCN makes for charge generation. An impressive power conversion efficiency (PCE) of 19.60% was achieved in the PM6:BOCl-I-based device, which is one of the champion PCEs among the reported binary organic solar cells to date. Detailed analyses revealed that the PM6:BOCl-I based device strikes a balance between efficient charge generation and suppressed nonradiative recombination, leading to a low nonradiative voltage loss of 0.228 eV and higher short circuit current density of 28.7 mA·cm –2 . This work demonstrates a feasible way to reduce the trade-off between charge generation and nonradiative recombination via the synergetic effect of halogenation and asymmetric strategy.