Completely non-fused electron acceptor with 3D-interpenetrated crystalline structure enables efficient and stable organic solar cell

Abstract

Non-fullerene acceptors (NFAs) based on non-fused conjugated structures have more potential to realize low-cost organic photovoltaic (OPV) cells. However, their power conversion efficiencies (PCEs) are much lower than those of the fused-ring NFAs. Herein, a new bithiophene-based non-fused core (TT-Pi) featuring good planarity as well as large steric hindrance was designed, based on which a completely non-fused NFA, A4T-16, was developed. The single-crystal result of A4T-16 reveals that a three-dimensional interpenetrating network can be formed due to the compact π–π stacking between the adjacent end-capping groups. A high PCE of 15.2% is achieved based on PBDB-TF:A4T-16, which is the highest value for the cells based on the non-fused NFAs. Notably, the device retains ~84% of its initial PCE after 1300 h under the simulated AM 1.5 G illumination (100 mW cm−2). Overall, this work provides insight into molecule design of the non-fused NFAs from the aspect of molecular geometry control.

Recent progress in organic solar cells based on non-fullerene acceptors: materials to devices

“…Recently, Hou et al reported a totally unfused SMA named A4T-16, which contains bithiophene-based non-fused core (TT-Pi) with good planarity as well as large steric hindrance. 67 This molecule exhibited a three-dimensional interpenetrating network due to the compact π–π stacking between the adjacent end-capping groups. OSCs based on PBDB-TF:A4T-16 exhibited a high PCE of 15.2% with a FF of 79.8%.…”

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.…”

“…After device optimization, a moderate photovoltaic performance of BTCIC-4Cl was achieved, with a PCE of 10.50%, a V OC of 0.75 V and a J SC of 21.00 mA cm -2 . Based on the abovementioned results, Wang et al [58] then systematically investigated the effects of H (BT-IC4F), F (BT2F-IC4F) and alkoxy chains (BTOR-IC4F) at the 5,6-positions of the BT core on the molecular configuration and device performance. The ladder-like molecular structures locked by the N•••S, F•••S and O•••S noncovalent interactions were formed for these acceptors, as suggested by DFT calculations.…”

“…were explored to lock the conformation of NFRAs. With these interactions, the rotation of single bonds could be effectively restricted and thus rigid and coplanar structures can also be formed in NFRAs [55][56][57][58] . As a result, ordered molecular packing in the solid state and efficient electron transport can be realized in NFRAs.…”

Phenalene—A New Ring-Locked Vinyl Bridge for Nonfullerene Acceptors With Enhanced Chemical and Photochemical Stabilities

“…However, such design always involves high synthetic complexity, thereby limiting their further practical applications. In this context, many researchers have paid attention to explore new A-D-A-type NFAs with semi-fused (Li et al, 2018;Huang et al, 2019;Liu X. et al, 2020;Luo et al, 2021) and even fully unfused electronrich cores (Bi et al, 2021;Ma et al, 2021;Wen et al, 2021;Zhou et al, 2021).…”