Browsing by Author "Teng, Chin-Min"

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Molecular-weight-dependent nanoscale morphology in silole-containing cyclopentadithiophene polymer and fullerene derivative blends
(2011-11-01)
Huang, Jen-Hsien
;
Chen, Fang-Chung
;
Chen, Cheng-Lun
;
Huang, Annie Tzuyu
;
Hsiao, Yu-Sheng
We have investigated the effect of polymer molecular weight (MW) on the morphology and efficiency of bulk heterojunction (BHJ) solar cells comprised of poly[(4,4'-bis(2-ethyl-hexyl)dithieno[3,2-b: 2',3'-d] silole)-2,6-diyl-alt-(5,5'-thienyl-4,4'-dihexyl-2,2'-bithiazole)2,6- diyl] (Si-PCPDTTBT) and [6,6]-phenyl C(61) butyric acid methyl ester (PCBM). Striking morphological changes are observed in BHJ films upon the change of the polymer MW. Atomic force microscopy and transmission electron microscopy studies suggest that high MW polymer generated high degree of phase separation, leading to formation of an inter-penetrating network for carrier transport. The X-ray diffraction investigation indicated that increased pi-pi stacking in Si-PCPDTTBT with increasing polymer MWs results in an increase in hole mobility of Si-PCPDTTBT and electron mobility of PCBM as well as the red shift absorption spectrum in BHJ films. The solar cells based on PCBM with high-MW Si-PCPDTTBT deliver power conversion efficiencies of 3.33%. (C) 2011 Elsevier B.V. All rights reserved.
Nanoscale Correlation between Exciton Dissociation and Carrier Transport in Silole-Containing Cyclopentadithiophene-Based Bulk Heterojunction Films
(2011-02-10)
Huang, Jen-Hsien
;
Teng, Chin-Min
;
Hsiao, Yu-Sheng
;
Yen, Feng-Wen
;
Chen, Peilin
Understanding the effects of conjugated polymer structures on exciton lifetimes and morphologies within bulk heterojunction (BHJ) films is a necessary step toward the development of better organic solar cells. Studying the impact of a polymer's structure on the optical, morphological, and performance characteristics of a device can lead to advances in the design of new polymers. In this study, we synthesized carbon- and silicon-bridged cyclopentadithiophene- (CPDT-) based polymers and determined their photophysical properties and morphologies by measuring the exciton lifetime distributions in their BHJ films The silicon-bridged CPDT-based polymer/[6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) BHJ exhibited a higher degree of luminescence quenching, suggesting that thermodynamically favorable mixing on the molecular scale and nanoscale phase separation occurred simultaneously in the blend film. We attribute this favorable morphology to the presence of strong pi-pi stacking in the silicon-bridged CPDT-based polymers. Under AM 1.5 G illumination (100 mA cm(-2)), a device incorporating the silicon-bridged CPDT-based polymer and PCBM (1:2, w/w) gave an overall power conversion efficiency of 3.5% with a short-circuit current of 9.0 mA cm(-2), an open-circuit voltage of 0.72 V, and a fill factor of 53.6%.