Regulating the Packing of Non-Fullerene Acceptors via Multiple Noncovalent Interactions for Enhancing the Performance of Organic Solar Cells

Abstract

Three noncovalently fused-ring electron acceptors (FOC6-IC, FOC6-FIC, and FOC2C6-2FIC) are synthesized. Single crystals of FOC6-IC and FOC2C6-2FIC are prepared, and structure analyses reveal that the molecular backbone can be planarized via the formation of the intramolecular noncovalent interactions. These acceptor molecules can be packed closely in the solid state via π–π stacking and static interactions between the central phenylene unit and the terminal group with a distance of 3.3–3.4 Å. Besides, multiple intermolecular noncovalent interactions can be observed in the single crystal structure of the fluorinated acceptor FOC2C6-2FIC, which help increase the crystallinity of acceptors and the charge mobility of the blends. Photovoltaic devices based on FOC2C6-2FIC give a power conversion efficiency of 12.36%, higher than 12.08% for FOC6-FIC and 10.80% for FOC6-IC.

Structure dependent photostability of ITIC and ITIC-4F

“…This hypothesis seems aligned with fluorine substituent being capable of forming electrostatically driven and stabilizing F-p noncovalent interactions with aromatic molecular species, in donor:acceptor blends. 37,38 Alternatively, the slight different energy levels could also be playing a role. In particular, the LUMO of ITIC-4F is À4.07 eV, 39 compared to À3.92 eV for ITIC.…”

“…Other mechanisms involving the presence of photosensitized production of singlet oxygen may also contribute to degradation of organic photovoltaic materials, as recently reported by Turkovic et al 45 On the other side, fluorine substitution in the end-group of the ITIC molecule increases the non-covalent interactions with the consequent introduction of a favored cell packing. 46 Moreover, fluorination lowers the HOMO/LUMO levels, increases the electron affinity 47 and enhances the molecular electron-pulling effect, with the result of a more efficient delocalization of the electron cloud over the electron-withdrawing site, and a reduced oxidative effect. Similar results on fullerene-and non-fullerene based blends have inversely correlated the higher polymer photobleaching of the photo active layers, with smaller electron affinity.…”

Electron‐Deficient and Quinoid Central Unit Engineering for Unfused Ring‐Based A1–D–A2–D–A1‐Type Acceptor Enables High Performance Nonfullerene Polymer Solar Cells with High Voc and PCE Simultaneously

“…Moreover, the F–H distance of 2.10 Å and the N–S distance of 2.86 Å are within their van der Waals radii (≈2.46 and ≈3.26 Å), respectively, indicating the existence of their intramolecular interaction. [ 83,84 ] Thus, a cis structure with the F–H and N–S noncovalent interaction is preferred conformation. As shown in Figure 2c,d, the lowest unoccupied molecular orbital (LUMO) energy level is distributed on the ending group, whereas the HOMO energy level is mainly localized on the unfused core segment (D–A 2 –D).…”

“…Moreover, BT2FIDT‐4Cl exhibits a slightly upshifted HOMO level than BO2FIDT‐4Cl , which is consistent with the trend of the related polymer with such two central units. [ 83 ] Therefore, through the substituents change on the central electron‐withdrawing unit, absorption, and energy levels could be facile tuned for unfused ring A 1 –D–A 2 –D–A 1 ‐type SMAs, which provide enough room in designing various highly efficient SMAs.…”

“…The reason of relative large π–π stacking distance of our NF‐SMAs is possible due to the relative weaker F–H interaction and axisymmetric molecular structure of our unfused ring NF‐SMAs in comparison with that of other reported unfused ring NF‐SMAs. [ 58,63,83 ] Based on the crystal coherence length of the in‐plane (100) lamellar peak, the significantly larger value (4.7 nm) was obtained for BT2FIDT‐4Cl compared to that of BO2FIDT‐4Cl (2.6 nm). Furthermore, the smaller π–π stacking distance of BT2FIDT‐4Cl neat film might be attributed to the intermolecular S–S interaction of difluorobenzothiadiazole central unit.…”