Influential effects of π-spacers, alkyl side chains, and various processing conditions on the photovoltaic properties of alkylselenyl substituted benzodithiophene based polymers

π-spacers and alkyl side chains play a key role in the optical, electrochemical, and photovoltaic properties of π-conjugated polymers. To investigate the collective effects of π-spacers, alkyl side chains, and various processing conditions on the photovoltaic properties, an array of four new low ban...

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Published in:Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2015-01, Vol.3 (4), p.796-808
Main Authors: Kranthiraja, Kakaraparthi, Gunasekar, Kumarasamy, Cho, Woosum, Park, Young Geun, Lee, Jin Yong, Shin, Yurim, Kang, In-Nam, Song, Myungkwan, Chae, Keun Hwa, Kim, BongSoo, Jin, Sung-Ho
Format: Article
Language:English
Subjects:
Chains (polymeric)
Devices
Methyl alcohol
Optical properties
Photovoltaic cells
Polymers
Solar cells
Thiophenes
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Summary:π-spacers and alkyl side chains play a key role in the optical, electrochemical, and photovoltaic properties of π-conjugated polymers. To investigate the collective effects of π-spacers, alkyl side chains, and various processing conditions on the photovoltaic properties, an array of four new low bandgap (LBG) π-conjugated polymers ( P1–P4 ) was designed and synthesized for their application as donor materials in bulk heterojunction polymer solar cells (BHJ PSCs). These π-conjugated polymers contain a benzodithiophene (BDT) donor unit substituted with 2-ethylhexylselenyl or 2-hexyldecylselenyl as π-conjugated side chains and a dialkoxybenzothiadiazole (dialkoxyBT) electron deficient unit connected with thiophene or selenophene as π-spacers. Among the four polymers, the absorption spectra of P3 with the thiophene π-spacer showed a well enhanced vibronic shoulder peak between 620 and 650 nm, indicating that P3 possesses a strong interchain aggregation tendency and attains a planar backbone structure due to the non-covalent interactions arising between the sulfur atom in thiophene and the oxygen atom in dialkoxyBT. Under suitable device processing conditions optimized pristine PSCs of P3 showed a maximum power conversion efficiency (PCE) of 4.09%. After employing 1,8-diiodooctane as an additive, one of the PSC devices based on P2 displayed a PCE of 5.34%. The active layers of P1–P4 showed a positive response towards methanol treatment, especially the P3 -based devices delivered an improved PCE of 5.63%, which was further assessed by electrical impedance spectroscopy. These findings in the current article provide a good specimen for efficiently fine tuning the optical and photovoltaic properties of π-conjugated polymers via varying the size of alkyl chains, π-spacer groups and device processing conditions for the imminent growth of LBG π-conjugated polymers.
ISSN:2050-7526
2050-7534
DOI:10.1039/C4TC02092H