N‑Octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione-Based Low Band Gap Polymers for Efficient Solar Cells

We report the synthesis, characterization, and solar cell properties of new donor–acceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD) as the acceptor. The newly deve...

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Bibliographic Details
Published in:Macromolecules 2013-05, Vol.46 (10), p.3861-3869
Main Authors: Kim, Seul-Ong, Kim, Youn-Su, Yun, Hui-Jun, Kang, Il, Yoon, Youngwoon, Shin, Nara, Son, Hae Jung, Kim, Honggon, Ko, Min Jae, Kim, BongSoo, Kim, Kyungkon, Kim, Yun-Hi, Kwon, Soon-Ki
Format: Article
Language:English
Subjects:
Applied sciences
Energy
Exact sciences and technology
Natural energy
Organic polymers
Photovoltaic conversion
Physicochemistry of polymers
Polymers with particular properties
Preparation, kinetics, thermodynamics, mechanism and catalysts
Solar cells. Photoelectrochemical cells
Solar energy
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Summary:We report the synthesis, characterization, and solar cell properties of new donor–acceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD) as the acceptor. The newly developed DTPD moiety was carefully designed to lower a band gap via strong interaction between donor–acceptor moieties and keep polymer energy levels deep. Remarkably, the DTPD acceptor moiety effectively widens the light absorption range of the polymers up to ∼900 nm while positioning their HOMO and LUMO levels in the optimal range, i.e., −5.3 and −4.0 eV, respectively, for high power conversion efficiencies (PCEs) as we intended. Solar cell devices were fabricated according to the structure ITO/PEDOT:PSS/photoactive (polymer:PC70BM)/TiO2/Al. The POBDTPD devices exhibited a PCE of 4.7% with a V oc of 0.70 V, a J sc of 10.6 mA/cm2, and a FF of 0.64. The PEBDTPD devices yielded a higher PCE of 5.3% with a V oc of 0.72 V, a J sc of 13.5 mA/cm2, and a FF of 0.54. AFM, TEM, and PL quenching measurements revealed that the high J scs are a result of the appropriate morphology and efficient charge separation. In comparing the performances of the two polymer devices, the higher J sc for the PEBDTPD device was attributed to its better nanoscale phase separation, smoother surface, and higher carrier mobility in the polymer:PC70BM blend films. The higher FF for the POBDTPD device was ascribed to a good balance between the hole and electron mobilities. Overall, we demonstrate that the DTPD unit is a promising electron-accepting moiety to develop high performance low band gap polymers.
ISSN:0024-9297
1520-5835
DOI:10.1021/ma400257q