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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 2
BKCSDE 33(2)
February 20, 2012 

Novel 4,7-Dithien-2-yl-2,1,3-benzothiadiazole-based Conjugated Copolymers with Cyano Group in Vinylene Unit for Photovoltaic Applications
Jinwoo Kim, Mihee Heo, Youngeup Jin, Jaehong Kim, Joo Young Shim, Suhee Song, Il Kim, Jin Young Kim, Hongsuk Suh*
Carbazole, Benzothiadiazole, Alternating copolymer
Two novel conjugated copolymers utilizing 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT) coupled with cyano (-CN) substituted vinylene, as the electron deficient moeity, have been synthesized and evaluated in bulk heterojunction solar cell. The electron deficient moeity was coupled with carbazole and fluorene unit by Knoevenagel condition to provide poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)- 2-thienyl)ethenyl)-alt-9-(1-octylnonyl)-9H-carbazol-2-yl-2-butenenitrile) (PCVCNDTBT) and poly(bis-2,7- ((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9,9-dihexyl-9H-fluoren- 2-yl) (PFVCNDTBT). The optical band gaps of PCVCNDTBT (1.74 eV) and PFVCNDTBT (1.80 eV) are lower than those of PCDTBT (1.88 eV) and PFVDTBT (2.13 eV), which is advantageous to provide better coverage of the solar spectrum in the longer wavelength region. The high Voc value of the PSC of PCVCNDTBT (~0.91 V) is attributed to its lower HOMO energy level (–5.6 eV) as compared to PCDTBT (–5.5 eV). Bulk heterojunction solar cells based on the blends of the polymers with [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) gave power conversion efficiencies of 0.76% for PCVCNDTBT under AM 1.5, 100 mW/cm2.
629 - 635
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