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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 2
BKCSDE 32(2)
February 20, 2011 

 
Title
Synthesis and Characterization of Quinoxaline-Based Thiophene Copolymers as Photoactive Layers in Organic Photovoltaic Cells
Author
Yoon Suk Choi, Woo hyung Lee, Jae Ryoung Kim, Sang Kyu Lee, Won Suk Shin, Sang Jin Moon, Jong Wook Park, In Nam Kang*
Keywords
Organic solar cell, Quinoxaline, Oligothiophene, Thin film transistor, Conjugated polymers
Abstract
A series of new quinoxaline-based thiophene copolymers (PQx2T, PQx4T, and PQx6T) was synthesized via Yamamoto and Stille coupling reactions. The Mws of PQx2T, PQx4T, and PQx6T were found to be 20,000, 12,000, and 29,000, with polydispersity indices of 2.0, 1.2, and 1.1, respectively. The UV-visible absorption spectra of the polymers showed two distinct absorption peaks in the ranges 350 - 460 nm and 560 - 600 nm, which arose from the π-π* transition of oligothiophene units and intramolecular charge transfer (ICT) between a quinoxaline acceptor and thiophene donor. The HOMO levels of the polymer ranged from ‒5.37 to ‒5.17 eV and the LUMO levels ranged from ‒3.67 to ‒3.45 eV. The electrochemical bandgaps of PQx2T, PQx4T, and PQx6T were 1.70, 1.71, and 1.72 eV, respectively, thus yielding low bandgap behavior. PQx2T, PQx4T, and PQx6T had open circuit voltages of 0.58, 0.42, and 0.47 V, and short circuit current densities of 2.9, 5.29 and 9.05 mA/cm2, respectively, when PC71BM was used as an acceptor. For the solar cells with PQx2T-PQx6T:PC71BM (1:3) blends, an increase in performance was observed in going from PQx2T to PQx6T. The power conversion efficiencies of PQx2T, PQx4T, and PQx6T devices were found to be 0.69%, 0.73%, and 1.80% under AM 1.5 G (100 mW/cm2) illumination.
Page
417 - 423
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