Angular-Shaped 4,10-Dialkylanthradiselenophene and Its Donor-Acceptor Conjugated Polymers: Synthesis, Physical, Transistor, and Photovoltaic Properties

Yu Ying Lai, Huan Hsuan Chang, Yun Yu Lai, Wei Wei Liang, Che En Tsai, Yen-Ju Cheng*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

An angular-shaped and isomerically pure 4,10-di(2-octyl)dodecylanthradiselenophene (aADS) was successfully developed. The expedient synthesis to form the framework of aADS with two lateral side chains regioselectively at its 4,10-positions is via a base-induced propargyl-allenyl isomerization/6π-electrocyclization/aromatization protocol. This pentacyclic distannylated aADS unit was then copolymerized with dithienyldiketopyrrolopyrrole (DPP) and dithienyl-5,6-difluoro-2,1,3-benzothiadiazole (DTFBT) acceptors with different alkyl side chains to afford four donor-acceptor copolymers: PaADSDPP, PaADSDTFBT-C4, PaADSDTFBT-C8, and PaADSDTFBT-C8C12. UV-vis spectroscopy and cyclic voltammetry revealed that PaADSDPP has the narrowest energy band gap, and PaADSDTFBT-C8C12 has larger band gap than PaADSDTFBT-C4 and PaADSDTFBT-C8. Two layer ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) calculations were implemented to investigate the disparity in optical, electrochemical, and device properties between these polymers. Both experimental and theoretical data suggest that the aliphatic side chains play a significant role in determining the physical, transistor, and photovoltaic properties of the polymers. PaADSDTFBT-C4 and PaADSDTFBT-C8 exhibited organic-field-effect-transistor hole mobilities of 2.7 × 10-2 and 1.0 × 10-2 cm2 V-1 s-1, greatly outperforming that of PaADSDTFBT-C8C12 with a mobility of 5.4 × 10-6 cm2 V-1 s-1. Polymer solar cells were fabricated on the basis of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al configuration. The efficiency decreased as the increase of bulkiness of the aliphatic side chains installed on DTFBT units (4.4% for PaADSDTFBT-C4, 3.5% for PaADSDTFBT-C8, 0.3% for PaADSDTFBT-C8C12). Atomic force microscopy images reveal that the degree of aggregation for the polymer:fullerene blends is influenced significantly by the bulkiness of aliphatic side chain installed on DTFBT. Noticeable aggregation was found for the PaADSDTFBT-C8C12:PC71BM blend. These results are in good agreement with the computational results elucidating that the intermolecular interactions between the polymers and PC71BM are sterically hindered by the bulky 2-octyldodecyl groups. This work not only presents a promising selenophene-based aADS building block but also provides insights into the side-chain engineering for donor-acceptor conjugated copolymers.

Original languageEnglish
Pages (from-to)6994-7006
Number of pages13
JournalMacromolecules
Volume48
Issue number19
DOIs
StatePublished - 5 Oct 2015

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