Correlation between polymer structure and polymer:fullerene blend morphology and its implications for high performance polymer solar cells

Title
Correlation between polymer structure and polymer:fullerene blend morphology and its implications for high performance polymer solar cells
Authors
손선경김연수손해정고민재김홍곤이도권김진영최동훈김경곤김봉수
Keywords
Polymer solar cells; Low band gap polymers; Power conversion efficiency; Crystalline structure; Film morphology
Issue Date
2014-02
Publisher
The Journal of Physical Chemistry C
Citation
VOL 118, NO 5, 2237-2244
Abstract
We synthesized four polymers (pT3DPP-HD, pT3DPP-OD, pT2TTDPP-HD, and pT2TTDPP-OD) and characterized their photovoltaic properties as a function of the backbone planarity, alkyl side chain length, and film morphology. The polymers were donor–acceptor type low-band-gap (1.2–1.3 eV) polymers employing terthiophene (T3) or thiophene–thieno[3,2-b]thiophene–thiophene (T2TT) as the donor and 2,5-bis(2-hexyldecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione (DPP-HD) or 2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione (DPP-OD) as the acceptor. The T2TT moiety in the polymer backbone is more planar than the T3; the OD moiety as the alkyl side chain ensured a higher solubility than the HD moiety. Polymer solar cells (PSCs) were fabricated, and their properties were characterized. The photoactive layer consisted of one of the four polymers and one of the fullerene derivatives (PC70BM or PC60BM). For a given fullerene derivative, the PCEs prepared with each of the four polymers were ordered according to pT3DPP-OD, pT2TTDPP-HD, pT3DPP-HD, and pT2TTDPP-OD. Studies on the morphologies of the polymer:fullerene layers revealed that the pT3DPP-OD:PC70BM blend exhibited an optimal degree of phase separation between the polymer and the fullerene, while retaining a high degree of interconnectivity, thereby yielding the highest PCE measured in this series. By contrast, the pT2TTDPP-OD:fullerene yielded the lowest PCE because of too high crystalline fibrous polymer domains. In conclusion, we demonstrate that minute variations in the polymer chemical structure strongly affects both (i) the nanoscale miscibility between the polymers and fullerenes and (ii) the interconnectivity of the polymer chains, and these properties are tightly correlated with the solar cell performance.
URI
http://pubs.kist.re.kr/handle/201004/48377
ISSN
19327447
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KIST Publication > Article
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