Side-Chain Engineering for Fine-Tuning of Energy Levels and Nanoscale Morphology in Polymer Solar Cells

A series of four polymers containing benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and 5,6‐difluoro‐4,7‐diiodobenzo[c][1,2,5]thiadiazole (2FBT), PBDT2FBT, PBDT2FBT‐O, PBDT2FBT‐T, and PBDT2FBT‐T‐O, are synthesized with their four different side chains, alkyl‐, alkoxy‐, alkylthienyl‐, and alkoxythienyl. Experi...

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Bibliographic Details
Published in:Advanced energy materials 2014-07, Vol.4 (10), p.np-n/a
Main Authors: Lee, Jaewon, Kim, Min, Kang, Boseok, Jo, Sae Byeok, Kim, Heung Gyu, Shin, Jisoo, Cho, Kilwon
Format: Article
Language:English
Subjects:
Additives
alkoxythienyl side chains
Chains (polymeric)
conjugated polymers
Crystal structure
Energy conversion efficiency
Energy levels
morphology
Nanostructure
organic solar cells
Photovoltaic cells
Polymers
R&D
Research & development
side-chain engineering
Solar cells
Tuning
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Summary:A series of four polymers containing benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and 5,6‐difluoro‐4,7‐diiodobenzo[c][1,2,5]thiadiazole (2FBT), PBDT2FBT, PBDT2FBT‐O, PBDT2FBT‐T, and PBDT2FBT‐T‐O, are synthesized with their four different side chains, alkyl‐, alkoxy‐, alkylthienyl‐, and alkoxythienyl. Experimental results and theoretical calculations show that the molecular tuning of the side chains simultaneously influences the solubilities, energy levels, light absorption, surface tension, and intermolecular packing of the resulting polymers by altering their molecular coplanarity and electron affinity. The polymer solar cell (PSC) based on a blend of PBDT2FBT‐T/[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) exhibits the best photovoltaic performance of the four PBDT2FBT derivatives, with a high open‐circuit voltage of 0.98 V and a power conversion efficiency of 6.37%, without any processing additives, post‐treatments, or optical spacers. Furthermore, PBDT2FBT‐T‐O, which has a novel side chain alkoxythienyl, showed promising properties with the most red‐shifted absorption and strong intermolecular packing property in solid state. This study provides insight into molecular design and fabrication strategies via structural tuning of the side chains of conjugated polymers for achieving highly efficient PSCs. A systematic investigation of side‐chain effects on photovoltaic performance of polymer solar cells is presented for four polymers containing alkyl‐, alkoxy‐, alkyltheinyl‐, and alkoxythienyl side chains. The fine‐tuning of the side‐chain architecture enhances the optoelectronic and morphological properties of bulk‐heterojunction solar cells, resulting in an increased power conversion efficiency of up to 6.4% without any processing additives or post‐treatments.
ISSN:1614-6832
1614-6840
DOI:10.1002/aenm.201400087