Design of All-Fused-Ring Electron Acceptors with High Thermal, Chemical, and Photochemical Stability for Organic Photovoltaics

Abstract

High-performance donor-acceptor electron acceptors containing 2-(3-oxo-2,3-dihydro-1H-inden-1ylidene)malononitrile (INCN)-type terminals are labile toward photooxidation and basic conditions, and new molecular designs toward electron acceptors that can achieve both high power conversion efficiencies and high stability are urgently needed. By replacing the central benzene ring in the classical ladder-type n-type semiconductor, 2,2′-(indeno[1,2b]fluorene-6,12-diylidene)dimalononitrile, with the electron-rich 4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene, we report herein the design of 2,2′- (7,7,15,15-tetrahexyl-7,15-, a new type of all-fused-ring electron acceptor (AFRA). A threestep reaction including a key Pd-catalyzed double C-H activation/intramolecular cyclization is established for the efficient synthesis of such type of electron acceptors. ITYM is confirmed by singlecrystal X-ray analysis, which shows a planar nonacyclic structure with strong π-π stacking. Compared with the classical carbon-bridged INCN-type acceptors, ITYM exhibits extraordinary stability with very promising performance. The AFRA concept opens a new avenue toward high-efficiency and -stability organic photovoltaics (OPVs).

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

“…Compared with the classical carbon-bridged INCN-type acceptors, ITYM exhibits superior thermal, and chemical stability with very promising performance compared to the classical carbon-bridged NFAs. 267…”

Stable dinitrile end-capped closed-shell non-quinodimethane as a donor, an acceptor and an additive for organic solar cells

“…46 Furthermore, most emerging NFAs containing 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC)-type terminals are synthesized by the Knoevenagel condensation reaction, which would make them prone to decompose under persistent light irritation. 47–53 It has been demonstrated that the photodegradation products of typical NFAs such as ITIC with IC end groups contain fused-ring isomers via a 6-e electrocyclic reaction between the dicyanomethylene unit and the thiophene ring. 50 A promising and efficient method is employing robust carbon–carbon bonds instead of the vulnerable exocyclic double bonds to link the donor unit and the acceptor unit of NFAs, which can not only lead to intrinsically stable acceptors but also successfully adjust the optoelectronic properties of NFAs.…”

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

“…As one of the third-generation photovoltaic techniques, organic solar cells (OSCs) have demonstrated outstanding potentials in the fields of flexible devices, semi-transparent devices, indoor photovoltaics, and so on (Liu et al, 2021c;Dauzon et al, 2021;Kini et al, 2021;Xie et al, 2021). Excitingly, the record power conversion efficiency (PCE) of OSCs has been continuously rising in recent years, and a value exceeding 19% has been achieved already Wang et al, 2021), attributed to the innovative design and exploitation of photovoltaic materials and device architecture (Li et al, 2019;Cui and Li, 2021;Liu W. et al, 2021;Gao et al, 2021;Ren et al, 2021;Yin et al, 2021;Zheng et al, 2021). In particular, A-D-A-type nonfullerene acceptors (NFAs) play the most critical role in achieving high-performance OSCs since the emergence of the representative NFA molecule, namely ITIC, reported by Zhan et al, in 2015(Lin et al, 2015, where "D" and "A" represent the electron-donating and electron-accepting units, respectively.…”