Correlation of Dimer-Linker-Induced Conformational\nLock with Nonradiative Energy Loss in Organic Solar Cells

The\nefficiencies of dimer-based devices still lag those of their\nsmall molecule-based counterparts. This is primarily due to the considerable\ndihedrals in the dimer skeleton, which compromises the molecular packing,\nthus influencing the charge generation and nonradiative voltage loss\n(Δ<i>V</i><sub>oc</sub>,<sub>nr</sub>). Herein, we\ndeveloped two dimeric acceptors with varied π-linkers to investigate\nthe influence of linker-induced conformational lock on Δ<i>V</i><sub>oc</sub>,<sub>nr</sub>. We find that the helically\nlapped <i>O</i>-shaped dimer delivers better intermolecular\npacking than the planar <i>S</i>-shaped one that incorporates\na bulkier π-linker. However, its planar skeleton is instead\nmore favorable for forming a compact and ordered stacking with the\nhost acceptor in ternary blend. This possibly promotes exciton dissociation,\nthus reducing the nonradiative decay of excited states. Moreover,\nits longer exciton lifetime could offer additional charge-transfer\nchannels. These contributions effectively minimize Δ<i>V</i><sub>oc</sub>,<sub>nr</sub> to 0.195 eV, while delivering\na high efficiency approaching 20% in the derived ternary device.