A Pyrrole‐Fused Asymmetrical Electron Acceptor for Polymer Solar Cells with Approaching 16% Efficiency

Abstract

Selecting suitable aromatic rings to develop asymmetric small‐molecule acceptors (SMAs) is of great significance. Herein, two asymmetric SMAs, namely, BTN‐4F and BTSe‐4F, are successfully synthesized by incorporating pyrrole and selenophene unit into the cores, respectively. Compared with the selenophene‐fused counterpart BTSe‐4F, BTN‐4F displays slightly upshifted energy levels and red‐shifted absorption spectrum (about 40 nm in film) due to the strong electron‐donating ability of N atoms in pyrrole. When matching with PM6, the BTN‐4F‐based device gives a higher power conversion efficiency (PCE) (15.82%) due to the simultaneously enhanced open circuit voltage (VOC), short‐circuit current density (JSC), and fill factor (FF), compared with those of the BTSe‐4F‐based device. The higher VOC coincides with the shallower lowest unoccupied molecular orbital (LUMO) energy level of BTN‐4F; the enhanced JSC mainly results from the broadened and enhanced absorption; the increased FF can be ascribed to the weaker bimolecular recombination, more balance charge transport, and more favorable morphology. It should be mentioned that the BTN‐4F‐based device yields a lower energy loss than that of the BTSe‐4F‐based device. Overall, the work demonstrates that pyrrole‐fused SMAs shows great potential in realizing low Eloss while yielding high JSC and PCE, which paves a new way to develop high‐performance SMAs.

Recent Progress of Y6‐Derived Asymmetric Fused Ring Electron Acceptors

“…As a result, the PM6:BTN-4F OSCs obtained a PCE of 15.82%, with a V OC of 0.82 V, a J SC of 25.05 mA cm -2 , and a FF of 77.3%, higher than that (13.79%) of the PM6:BTSe-4F device. [88] Lately, Yang et al reported two asymmetric FREAs with A-DA 1 D'-A structure, namely C-shaped BDTP-4F and S-shaped BTDTP-4F. [89] The maximum extinction coefficient (ε max ) of BTDTP-4F was 2.61 × 10 5 m −1 cm −1 at 761 nm, higher than that of BDTP-4F (2.40 × 10 5 m −1 cm −1 at 750 nm) in chloroform solution.…”

Heteroheptacene-based acceptors with thieno[3,2-b]pyrrole yield high-performance polymer solar cells

“…Commonly used outermost aromatic rings in A–D–A-type SMAs include thiophene, selenophene, thieno[3,2- b ]thiophene, thieno[3,2- b ]selenophene [ 27–30 ], dithieno[3 , 2- b : 2 ′ , 3 ′ - d ]thiophene [ 31–33 ] and dithieno[3 , 2- b : 2 ′ , 3 ′ -d]pyrrole (DTP) [ 34–36 ]. In comparison with thiophene and selenophene, pyrrole is the most electron-rich five-membered single aromatic ring, which can enhance the ICT effect, reduce optical band gaps ( E g opt ) and increase the energy level of the LUMO of SMAs [ 37–39 ]. Additionally, fine-tuning the side chains on pyrrole can improve the molecular packing, the solubility and the mobility of SMAs.…”

Isomerization of Asymmetric Ladder‐Type Heteroheptacene‐Based Small‐Molecule Acceptors Improving Molecular Packing: Efficient Nonfullerene Organic Solar Cells with Excellent Fill Factors

“…[9][10][11][12][13][14][15] In recent years, a number of nonfullerene small-molecule acceptors (SMAs) have been exploited to remedy the drawbacks of fullerene acceptors. [16][17][18][19][20] Among the different types of SMAs, the most popular SMAs consist of acceptor-donor-acceptor (A-D-A) architecture, which produces most of the devices with top-of-the-line efficiencies and low energy losses. [21][22][23][24][25][26][27][28][29][30] The evolution of SMAs in the past five years mainly aims to improve the physical and chemical properties of the molecules, including the absorption spectra, energy levels, and molecular packing behaviors.…”