Isomers of Dithienocyclopentapyrene‐Based Non‐Fullerene Electron Acceptors: Configuration Effect on Photoelectronic Properties

Abstract

One pair of isomers, centrosymmetric anti‐Py‐1 and axisymmetric syn‐Py‐2, was designed and synthesized with an acceptor–donor–acceptor (A–D–A) structure by choosing dithienocyclopentapyrene with four 4‐hexylphenyl side chains as the D unit, and 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile as the A unit. In‐depth structure–property relationship studies revealed that the isomers have similar UV/Vis absorption, fluorescence emission, and energy levels but significant differences in molecular shape, polarity, and charge mobility. Solution‐processed bulk‐heterojunction (BHJ) small‐molecule organic solar cells with Py‐1 as the electron‐acceptor material and PTB7‐Th as the electron‐donor material exhibit a power conversion efficiency (PCE) of 6.07 %, or 60 % higher than that of Py‐2 (3.7 %), which could be mainly attributed to the higher and more balanced hole/electron mobilities and better phase separation of the Py‐1‐based active layer.

Isomerization Strategy of Nonfullerene Small‐Molecule Acceptors for Organic Solar Cells

“…For instance, Huang and co‐workers utilized dithienocyclopentapyrene with 4‐hexylphenyl side chains as the central donor unit and IC2F moieties as the acceptor unit to synthesize a pair of syn/anti isomers, Py‐1 and Py‐2, which exhibited nearly identical energy levels, UV–vis absorption, and fluorescence emission. [ 112 ] According to the DFT calculations, the syn/anti isomerization changes the electrostatic potential and the molecular dipole moment, which in turn significantly influences its surface energy. Compared with the PTB7‐Th:Py‐2 blend, the PTB7‐Th:Py‐1 blend film showed better phase separation, and exhibited higher and more balanced hole/electron mobilities.…”

Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: On Constitutional Isomerization and Photovoltaic Performance

“…developed configurational anti-and syn-isomers of dithienocyclopentapyrene-based NFAs, whereas the anti-isomer exhibited higher and more balanced hole/electron mobilities and thus better photovoltaic performance than the syn-isomer (6.07% vs 3.07%). 54 All these results could inspire furthermore exploration of such isomeric effects on their photoelectronic properties.…”

“…Meanwhile when recalling the common isomeric phenomena in organic electronics, it is well-known that isomerization has a significant effect on the thermal-, optical-, and electrochemical-properties, charge carrier mobility, and eventually device performance. − Very recently, the constitutional isomeric effects of NFAs just have been investigated, − among which Zhan et al revealed that a NFA FNIC2 based on a thieno­[3,2- b ]­thiophene-fused benzo­[1,2- b :4,5- b′ ]­dithiophene core showed a red-shifted absorption, higher crystallinity, optimized morphology, and higher PCE of 13.0% than its isomer analogue FNIC1 (10.3%) . Huang et al developed configurational anti- and syn-isomers of dithienocyclopentapyrene-based NFAs, whereas the anti-isomer exhibited higher and more balanced hole/electron mobilities and thus better photovoltaic performance than the syn-isomer (6.07% vs 3.07%) . All these results could inspire furthermore exploration of such isomeric effects on their photoelectronic properties.…”

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors─Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties

“…The molecules 8-46 (Py-1) and 8-47 (Py-2) bear a dithienocyclopentapyrene core and INCN-2F acceptor groups, whereby 8-46 is the centrosymmetric and 8-47 the axisymmetric isomer . While the optical band gap ( 8-46 , 1.95 eV; 8-47 , 1.97 eV) and the energy levels show no significant difference, the centrosymmetric isomer shows a significantly higher electron mobility in the blend with PTB7-Th, which also results in an increased PCE of 5.75% (compared to 3.47% for a PTB7-Th/ 8-47 -based solar cell) …”