Near-Infrared Electron Acceptors with Unfused Architecture for Efficient Organic Solar Cells

Abstract

The absorption of nonfullerene acceptors (NFAs) at near-infrared (NIR) regions is crucial for obtaining high current densities in organic solar cells (OSCs). Herein, two narrow-band gap NFAs with unfused backbones possessing broad (600–900 nm) and strong absorption are developed by the conjugation of a benzothiadiazole core to halogenated end groups through a cyclopentadithiophene bridge. Compared with the fluorinated counterpart BCDT-4F, the chlorinated NFA BCDT-4Cl shows stronger J-aggregation and closer molecular packing, leading to an optimized blend morphology when paired with the polymer donor, PBDB-T. Thus, an obvious improvement in external quantum efficiency response was obtained for BCDT-4Cl-based OSCs, presenting a higher efficiency of 12.10% than those (9.65%) based on BCDT-4F. This work provides a design strategy for NIR acceptors in the combination of electron-deficient core and halogenated terminal in unfused backbones, which results in not only fine-tuning the optoelectronic properties but also simplifying the synthetic complexities of molecules.

Regulating the Aggregation of Unfused Non‐Fullerene Acceptors via Molecular Engineering towards Efficient Polymer Solar Cells

“…[16][17][18][19] As an alternative candidate to alleviate above issues, unfused non-fullerene acceptors (UF-NFAs) have attracted broad interest recently. [19][20][21] However, the current PCEs of UF-NFAs-based PSCs [22][23][24][25][26][27][28][29] still lag behind those based on F-NFAs. Therefore, the development of efficient UF-NFAs is of great urgency.…”

Modulating Energy Level on an A‐D‐A′‐D‐A‐Type Unfused Acceptor by a Benzothiadiazole Core Enables Organic Solar Cells with Simple Procedure and High Performance

“…In recent reports, Chen et al and Huang et al's research communities first began to utilize benzothiadiazole (BT) as electrondeficient core to build up A-D-A 0 -D-A-type UFAs through the noncovalent interactions between central core and π-linkers which have excellent effects on their electronic and aggregation properties. [36,37] Wang and co-workers adopted difluorobenzothiadiazole as the central core to establish such special backbone through F•••S noncovalent interaction. [38] Moreover, due to the up-distributed highest occupied molecular orbital (HOMO) level, most of these UFAs are combined with donor polymer PBDB-T or PM7, which still has a quite complex synthesis route as well.…”

Intrinsically Chemo- and Thermostable Electron Acceptors for Efficient Organic Solar Cells

“…Finally, we employed Stille coupling to obtain Q1-XF between IT and IDT with excellent yields of ~ 90%. The characterization of the chemical structure included 1 H, 13 C and 19 F nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) Mass Spectroscopy ( Figure S1). Single crystals of IT-1F reveal the planar structure with F-substituent at meta-position (Scheme 1c).…”

“…With the development of non-fullerene acceptors (NFAs), organic solar cells (OSCs) have rapidly reached over 17 % power conversion efficiency (PCE) in recent years. [1][2][3][4][5] Though promising for the tunable optoelectronic properties of acceptor-donor-acceptor (A-D-A) NFAs, [6][7][8][9][10][11][12][13] it is worth noting that their synthetic strategy exclusively employs the condensation of aldehyde and active methylene through Knoevenagel condensation reaction (KCR), [14][15][16][17][18][19] leaving a vulnerable exocyclic vinyl group between the donor core and terminal acceptor group in A-D-A NFAs. [20][21][22][23][24] These structural factors potentially undermine the intrinsic chemo-and photostability of NFAs, [25][26] wherein oxygen and water can attack the vulnerable exocyclic vinyl groups between D and A units, hence accelerating the degradation of photoexcited acceptors.…”