Effects of Different Ring‐Expanded Strategies for Nonfullerene Acceptors in Organic Photovoltaics under Donor and Acceptor Excitation

Abstract

The ring‐expanded strategy in nonfullerene acceptors (NFAs) with the acceptor–donor–acceptor backbone has been reported to be an effective method to improve the fill factor (FF), open circuit voltage (VOC), and short circuit current (JSC) simultaneously in organic photovoltaics. However, design control is still missing in the ring‐expanded strategy, and is urgently needed to further develop the origins and rules. To give insight into this strategy, a detailed theoretical study of the ring‐expanded mechanism is performed on the systems comprising different 9,9′‐bifluorenylidene‐based cores and 1,1‐dicyanomethylene‐3‐indanone group. Some main parameters involved in photoelectric conversion mechanism under the donor excitation (DE) and/or acceptor excitation (AE) are assessed by changing the position and size of ring‐expanded modes. The results show that the external ring‐expanded modes can not only maintain the original advantage as much as possible, variations in sizes and positions also offer them an opportunity to regulate the aforementioned parameters systematically, leading to better improvement regardless of AE or DE. Thus, the steady improvement in performance mentioned previously is the key to overcoming the negative correlation among FF, VOC, and JSC. This insight and discovery of the ring‐expanded strategy provides new design approaches for the next generation of NFAs.

Monomer morphology selection rules for an accurate design of bulk heterojunction: An updated theoretical account

“…It is well known that, compared with fullerenes, the better tunability of NFAs is accompanied by more flexible structure, which could lead to large deformation. This has been fully demonstrated in our previous work [62][63][64]. The dominant dihedral angles (∠α1, ∠α2, ∠β, and ∠γ) were calculated at the B3LYP/6-31G(d) level using the potential energy surface scanning method [8,52] (Figures 5, S4 and S5).…”

Nonradiative Energy Loss Generated by Two Hidden Trade-Offs in Non-Fullerene Organic Solar Cells with the Positive Correlation between JSC and VOC

“…k nr increases gradually following PM6/IT-4F → PM6/IOM-4F → PM6/IM-4F along the 3 CT → 3 LE D pathway, which is attributed to the increased Δ E CT–LE and V el . Generally, the parameters located on the exponential term have a higher impact than the quadratic term in the Marcus hopping model. , But here, the quadratic term (in fact could be V el ) decides k nr of the 3 CT → 3 LE D pathway according to the same identification method in the previous chapter. In the 3 CT → LE D pathway, PM6/IT-4F → PM6/IOM-4F, k nr is improved by 4 orders of magnitude from 10 10 to 10 14 s –1 .…”

Synthesis, properties, and application of phenanthrenone: an undeveloped building block and a photocatalyst

“…After extensive attempts under different coupling conditions, the carbonyl coupling reaction of 3a with Woollins’ reagent was finally accomplished, giving the dimer 5 in 33% isolated yield, which can be used as an electron acceptor and represents the planar fragmentation of C60. 14 Furthermore, 3a can be reduced to give 6 in 50% yield, while its Knoevenagel condensation with malononitrile could yield the cyanated derivative 7 in 87% yield.…”