Influences of Quinoid Structures on Stability and Photovoltaic Performance of Nonfullerene Acceptors

Abstract

Although benzoazole-fused rings with strong quinoid character have successfully been used to construct high-performance small-molecule nonfullerene acceptors (NFAs), studies into how these units influence the stabilities of NFAs and their corresponding device performances are few to date. To address it, four new NFAs, SSTI, SNTI, NTI and NTTI, which adopt BBT, TBZ, and BTAZ as the cores, respectively, are designed and investigated. It is found that SSTI and SNTI based on BBT and TBZ cores with stronger quinoid resonance effects show features of more red-shifted absorptions and deeper energy levels, but worse thermal and light stabilities than NTI and NTTI with a BTAZ core, especially in solutions and/or films blended with polymer donors. Through matrix-assisted laser desorption ionization time of flight mass spectrometry analysis of the degradation products, it is disclosed that the C═C double bond cleavage would be accelerated by stronger quinoid effects. Therefore, NTI and NTTI with relatively weaker quinoid characteristics show improved photovoltaic properties. Especially, NTTI based devices yield a good efficiency of 8.61% as the side chains on sp3-hybrid C atoms can prevent the formation of large aggregates. These findings can provide invaluable knowledge for the molecular design of NFAs with both high-efficiency and high-stability

Quinoidal conjugated polymers with open-shell character

“…11 Their electronic, optical, and magnetic properties also show promising potential to be applied in organic electronics and spintronics. [12][13][14][15][16] Quinoidal molecules with open-shell diradical character are also good candidates for singlet fission processes, which play an important role in the latest development of organic photovoltaic applications. 17,18 Related literature reports on small molecules and oligomers have already been summarized in several reviews and accounts.…”

Non-fused ring acceptors for organic solar cells

“…With the exception of the A-D-D'-D-A-type structure, in light of numerous easily-available electronwithdrawing units, significant attention has been drawn to research into A-D-A'-D-A-type NFRAs featuring electron-withdrawing units as the central core, such as BT [50,58,67] , benzotriazole (BTz) [68][69][70] , benzo-[1,2-c:4,5c']dithiophene-4,8-dione (BDD) [71,72] , benzobis(thiazole) (BBTz) [73] , quinoxaline (Q) [74] , thieno[3,4-c]pyrrole-4,6-dione (TPD) [71,75] , isoindigo (IID) [76] and so on [Figure 4]. Among them, BT and BTz have been widely adopted as A' units to construct NFRAs for their unique merits: (1) quinoidal structures are beneficial for broadening the absorption range; (2) the 5,6-positions of BT and BTz can be readily functionalized; and (3) the N•••S noncovalent interaction can be formed between the BT/BTz core and adjacent thiophene rings.…”

“…Other modifications on BDD-based NFRAs, including replacement of the D units (BDIC2F), have also been reported, where similar photovoltaic performance was reported [71,72] . A few other electron-deficient building blocks were also used as the central A' units to construct NRFAs [Figure 4], which played a unique role in adjusting the absorption, energy level, molecule conformation and active layer morphology [69,71,[73][74][75][76][77] . The relevant performance data are listed in Table 2.…”

Research Advances on Benzotriazole-based Organic Photovoltaic Materials

“…基于 PBDB-T/Y14(w/w, 1∶1, 1.0 vol% CN, 100 nm)反向器件的 V oc 为 0.80 V, J sc 为 26.2 mA/cm 2 , FF 为 71.5%, PCE 为 14.92%, 且所制备 的透过率为 23.69%的半透明器件的 PCE 仍可达到 12.67%; 同样, 他们又以双氯化的 INCN 作为末端"A" 单元, 在 Y9 分子结构的基础上合成了 Y15(图 21h) [141] , 基于 PM6/Y15(w/w, 1∶1.8, 0.3 vol% DIO)器件的 V oc 为 0.87 V, J sc 为 23.8 mA/cm 2 , FF 为 68.5%, PCE 为 14.13%. 通过在 Y16 末端引入氟原子, 邹应萍等 [ 142 ] 合成了 Y18(图 21i), 基于 PM6/Y18(w/w, 1∶1.5, 0.5 vol% CN) 器件的 V oc 为 0.84 V, J sc 为 25.7 mA/cm 2 , FF 为 76.5%, PCE 为 16.52%, 且 E loss 均仅为 0.53 eV, 添加 7.4 wt% 2020 年, 陈红征等 [146] 设计合成了基于 BTA 单元的 非稠环受体材料 SNTI、NTI 和 NTTI(图 21l), 探讨了具 有醌式效应的吸电子性苯并唑类稠环结构对受体材料 的稳定性以及光伏性能的影响. 研究表明受体分子的吸 收、 能级和光热稳定性都与其醌式效应的强度密切相关.…”