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

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