Ladder-type
fused aromatic systems are important core structures
of small molecule acceptors for organic solar cells (OSCs). In this
study, a new ladder-type donor building block, based on the benzo[1,2-b:4,5-b′]dithiophene (BDT) unit
where the 3,7 positions of the BDT thiophene rings and the 3′
position of the thiophene rings of the vertical BDT were fused to
construct a seven-ring core structure named f-DTBDT, was investigated.
In the f-DTBDT structure, the fusion of the BDT core and the thiophene
rings at the 4,8 positions of BDT constrains all of the aromatic rings
in a coplanar structure. The newly designed f-DTBDT was successfully
employed as a core donor building block and conjugated with three
electron-withdrawing acceptors (2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2HIC), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC), and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2ClIC)) as acceptor–donor–acceptor
(A–D–A)-type acceptor materials for OSCs. Characterization
results showed that the three synthesized A–D–A acceptors
of DTBDT-IC, DTBDT-4F, and DTBDT-4Cl have high absorption behavior
in the vis–NIR region as result of an intramolecular charge
transfer interaction engendered by f-DTBDT and the ending group. The
absorption regions of the acceptors were complementary with that of
polymer PM6. Also, the frontier orbital energy levels of the new acceptors
and wide-band-gap PM6 are well matched. Bulk heterojunction OSCs were
fabricated using PM6 and the acceptors, and the highest power conversion
efficiency (PCE) of 10.15% was obtained when using PM6:DTBDT-4F as
the active layer.
A low dark current density (Jd) is critical for enhancing the performance of organic photodiodes (OPDs), which is evaluated by device parameters such as the signal-to-noise ratio, specific detectivity (D*),...
A sidechain optimization strategy is widely utilized in organic semiconductor materials to optimize both solubility and solid-state properties. Here, we introduced octyl rather than phenylalkyl groups onto indacenodithienothiophene (IDTT) to construct three acceptor−donor−acceptor′−donor−acceptor (A−D−A′−D−A)-type acceptors, CNDTBT-C8IDTT-INCN, CNDTBT-C8IDTT-FINCN, and CNDTBT-C8IDTT-ClINCN. Benefiting from the reduced steric bulk of the octyl group, these acceptors show closer π−π stacking distances (∼3.58 Å), which is beneficial for charge transport. A fluorine-substituted acceptor CNDTBT-C8IDTT-FINCN displays excellent performance in solar cells due to efficient suppression of the charge recombination process and good charge transport ability in blend films. A PBDB-T:CNDTBT-C8IDTT-FINCN-based device achieved the highest power conversion efficiency (PCE) of 12.06%, with opencircuit voltage V OC = 0.83 V, J SC = 20.58 mA cm −2 , and FF = 70%.
Fused aromatic rings are widely employed in organic solar cell (OSC) materials due to their planarity and rigidity. Here, we designed and synthesized four two-dimensional non-fullerene acceptors, D6-4F, D6-4Cl, DTT-4F, and DTT-4Cl, based on two new fused planar ring structures of f-DTBDT-C6 and f-DTTBDT. Owing to the desirable phase separation formed in the blend films and the higher energy levels induced by the extra alkyl groups, PM6:D6-4F-based devices achieved a high V OC = 0.91 V with PCE = 11.10%, FF = 68.54%, and J SC = 17.75 mA/cm 2 . Because of the longer π-conjugation of the f-DTTBDT core with nine fused rings, DTT-4F and DTT-4Cl showed high molar extinction coefficients and broad absorption bands that enhanced the current density of OSCs. Finally, the PM6:DTT-4F-based devices achieved a J SC = 19.82 mA/cm 2 with PCE = 9.68%, V OC = 0.83 V, and FF = 58.85%.
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