Semiconducting conjugated polymers consisting of alkoxy or alkyl selenophene-substituted
benzodithiophene and thiophene units for organic photovoltaic devices
Sang-Suk Hana, Ji-Hoon Kima, Jong Baek Parka, In-Nam Kangb, Do-Hoon Hwanga,*
a Department
of Chemistry and Chemistry Institute for Functional Materials, Pusan National University,
Busan 609-735, Republic of Korea
b Department of Chemistry, The Catholic University of Korea, Gyeonggi-do, Republic of Korea
dohoonhwang@pudsan.ac.kr
Abstract
Full donor-type conjugated polymers containing benzodithiophene and thiophene derivative units were
synthesized as electron donors for organic photovoltaic devices. The alkoxy-substituted benzo[1,2b:4,5-b’]dithiophene (BDT) monomer, 2,6-bis(trimethyltin)-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:4,5b’]dithiophene, was polymerized with 2,5-dibromothiophene through a Pd(0)-catalyzed Stille coupling
reaction. To enhance the inter-chain interactions between polymers chains,an alkyl selenophene
substituted BDT derivative was newly synthesized, and copolymerized with the same counter monomer
parts. The two newly synthesized polymers were characterized for use in organic photovoltaic devices
as electron donors. Measured optical band gap energies of the polymers were 2.10 and 1.96 eV,
depending on polymer structure. Field-effect transistors were fabricated using the polymers to measure
their hole mobilities, which ranged from 10−3 to 10−5 cm2 V−1 s−1 depending on the polymer structure.
Bulk heterojunction organic photovoltaic cells were fabricated using conjugated polymers as electron
donors and a [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as an electron acceptor. One
fabricated device showed a power conversion efficiency of 2.73%, an open-circuit voltage of 0.72 V, a
short-circuit current of 7.73 mA cm−2, and a fill factor of 0.46, under air mass (AM) 1.5 global (1.5 G)
illumination conditions(100 mW cm−2).
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