Synergistic Effects of Chlorination and Branched Alkyl Side Chain on the Photovoltaic Properties of Simple Non‐Fullerene Acceptors with Quinoxaline as the Core

Abstract

To date, the fused-ring electron acceptors show the best photovoltaic performances, and the development of simple non-fullerene acceptors via intramolecular noncovalent interactions can reduce synthetic costs. In this work, four simple non-fullerene acceptors with an A-D-A'-D-A configuration (QCIC1, QCIC2, QCIC3, and QCIC4) were synthesized. They contained the same conjugated backbone (A': quinoxaline; D: cyclopentadithiophene; A: dicyano-indanone) but different halogen atoms and alkyl side chains. Due to the chlorination on the end-groups and the most and/or longest branched alkyl side chains on the backbone, the blended film composed of QCIC3 and donor poly{[2,6'-4,8-di(5-ethylhexylthienyl)benzo [1,2-b : 4,5-b']dithiophene]-alt- [5,5-(1',3'-di-2-thienyl-5',7'-bis(2ethylhexyl)benzo [1',2'-c : 4',5'-c']dithiophene-4,8-dione)]} (PBDB-T) exhibited the strongest π-π stacking and the most suitable phase-separation domains among the four blended films. Therefore, the QCIC3-based organic solar cells yielded the highest power conversion efficiency of 10.55 %. This work provides a pathway to optimize the molecular arrangements and enhance the photovoltaic property of simple electron acceptors through subtle chemical modifications.

Exploiting Novel Unfused‐Ring Acceptor for Efficient Organic Solar Cells with Record Open‐Circuit Voltage and Fill Factor

“…[25] Chen and co-workers and Yang and coworkers used alkoxy-substituted quinoxaline (QX) as the central-core unit to develop new acceptors QClC3 and QOC6-4Cl, achieving a PCE of 10.55 and 12.32 %, respectively, but the low V oc and FF still limited the efficiency improvement. [26,27] These results demonstrate that selecting electron-deficient units as the central core is a very effective strategy to construct highly efficient UFAs. However, the low V oc and FF of the currently reported AÀ DÀ A'À DÀ A-type UFAs is the major barrier for performance improvement.…”

“…When blended with J52, the PCE of the OSCs was improved to 14.82 % [25] . Chen and co‐workers and Yang and co‐workers used alkoxy‐substituted quinoxaline (QX) as the central‐core unit to develop new acceptors QClC3 and QOC6‐4Cl, achieving a PCE of 10.55 and 12.32 %, respectively, but the low V oc and FF still limited the efficiency improvement [26,27] . These results demonstrate that selecting electron‐deficient units as the central core is a very effective strategy to construct highly efficient UFAs.…”

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.…”

A New End Group on Nonfullerene Acceptors Endows Efficient Organic Solar Cells with Low Energy Losses

“…[1][2][3][4][5][6][7][8][9] And their device performances have also achieved rapid progresses, which mainly benefit from the innovations in the molecular design of active layer materials, especially nonfullerene acceptors (NFAs), effectively regulating the optoelectronic properties and molecular packing. [10][11][12][13][14][15][16][17] Nowadays, most of high-efficiency NFAs are fused-ring electron acceptors (FREAs), which adopt an A-D-A framework, including one centrally electron-donating fused-ring (D) and two electron-withdrawing end groups (A). As the first-generation FREAs, the ITICseries molecules had greatly promoted the development of OSCs, elevating the power conversion efficiencies (PCEs) to ≈15%.…”