Issue 28, 2012

The effect of side-chain length on regioregular poly[3-(4-n-alkyl)phenylthiophene]/PCBM and ICBA polymer solar cells

Abstract

The photovoltaic, charge transport, light absorption and morphology properties of a series of poly[3-(4-n-alkyl)phenylthiophene] (PAPT):acceptor (phenyl-C61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA)) blend films are reported as a function of alkyl side-chain length. Regioregular poly[3-(4-n-butyl)phenylthiophene] (PBPT), poly[3-(4-n-hexyl)phenylthiophene] (PHPT), poly[3-(4-n-octyl)phenylthiophene] (POPT), and poly[3-(4-n-decyl)phenylthiophene] (PDPT) were successfully synthesized by a modified Grignard metathesis (GRIM) polymerization method. The effects of the alkyl side-chain length on the optical, electrochemical and structural properties of the polymers were carefully investigated to establish a relationship between the molecular structure and device function. Bulk heterojunction solar cells made of PAPTs blended with either PCBM or ICBA showed a strong photovoltaic property dependence on the alkyl side-chain length. Among all PAPTs used in this study, the best performance was observed in PHPT-based devices. This is the first report of the use of PHPT in polymer solar cells. In addition, PAPT devices blended with ICBA generally showed higher open-circuit voltages (Voc) and power conversion efficiencies than PCBM-based devices. For example, a PHPT:ICBA photovoltaic device showed a Voc of 0.79 V and a power conversion efficiency of 3.7%, which is the highest performance reported thus far using PAPT polymers. While the optical properties of PAPT/electron acceptor films exhibit the strongest effect on the short-circuit current of the devices, a balance between the optical, electrical and morphological properties of blended films caused by the alkyl side-chain length determines the overall photovoltaic performance of these devices. Therefore, our work provides a fundamental understanding of the molecular structure–device function relationship, especially with respect to changes in the alkyl side-chain length in conjugated polymers.

Graphical abstract: The effect of side-chain length on regioregular poly[3-(4-n-alkyl)phenylthiophene]/PCBM and ICBA polymer solar cells

Supplementary files

Article information

Article type
Paper
Submitted
05 Mar 2012
Accepted
05 May 2012
First published
09 May 2012

J. Mater. Chem., 2012,22, 14236-14245

The effect of side-chain length on regioregular poly[3-(4-n-alkyl)phenylthiophene]/PCBM and ICBA polymer solar cells

C. Cho, H. J. Kim, H. Kang, T. J. Shin and B. J. Kim, J. Mater. Chem., 2012, 22, 14236 DOI: 10.1039/C2JM31371E

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