Journal
ORGANIC ELECTRONICS
Volume 13, Issue 12, Pages 3234-3243Publisher
ELSEVIER
DOI: 10.1016/j.orgel.2012.10.001
Keywords
Conjugated polymers; Polymer solar cells; Nanostructures; Open circuit voltage
Funding
- National Natural Science Foundation of China [91027031, 21004015]
- Ministry of Science and Technology of China [2009CB930400, 2010DFB63530, 2011CB932300]
- Chinese Academy of Sciences
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Two donor-acceptor (D-A) type conjugated polymers using dodecyl-and ethylhexyl-thiophene substituted benzo[1,2-b: 4,5-b'] dithiophene (BDT-DDT and BDT-EHT, respectively) as donors and n-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor were synthesized and characterized. The thiophene substituted BDT unit was recognized as a two-dimensional (2D) pi-extended segment with high carrier mobility and TPD unit was a relatively strong electron-drawing acceptor, which could lead to deep-lying highest occupied molecular orbital (HOMO) levels of the polymers. The optical properties, electrochemical behavior, and charge carrier properties of the polymers were compared in parallel. The results indicated that ethylhexyl-substitution could optimize the polymer structures and properties. The bulk-heterojunction polymer solar cells (PSCs) based on the two polymers were fabricated and characterized. The devices based on ethylhexyl-substituted polymer showed better performance than that of dodecyl-substituted one. Further analysis proved that the improvement was mainly ascribed to the formation of well-defined nanostructures by using branched ethylhexyl side chains, which facilitated charge separation and transport in the bicontinous active layer. This study suggests that obtaining appropriate film morphology and phase separation by altering alkyl side chains is extraordinary important for high performance PSCs based on D-A type polymers. (C) 2012 Elsevier B.V. All rights reserved.
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