Effect of Side Chain of Oligothiophene Derivatives on Bulk Heterojunction Structure in Organic Photovoltaic Devices

Kenichi Sasaki, Yosei Shibata, Ming Lu, Yuji Yoshida, Reiko Azumi, Yasukiyo Ueda

Graduate School of Engineering, Kobe University, Hyogo, Japan.
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Kanagawa, Japan.
National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki, Japan.

DOI: 10.4236/ampc.2013.32026                

Abstract

The effect of the molecular structure on photovoltaic performance was investigated by comparing two types of active layers. One is an active layer formed by sexithiophene (6T) and C₆₀ molecules which don’t have side chains. Another one is an active layer formed by a,ω-bis(2-hexyldecyl)sexithiophene (BHD6T) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) molecules which have side chains. The 6T:C₆₀ active layer exhibited an excessive crystallization of 6T, which led to the low photovoltaic performance. In the BHD6T:PCBM active layer, the crystallization of BHD6T was suppressed. The crystallization of BHD6T was also easily controlled by thermal annealing, which led to improved photovoltaic performance.

Keywords

Organic Photovoltaic Cells; Sexthiophene; Bulk Heterojunction; Morphology

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	W. Wang, H. Wu, C. Yang, C. Luo, Y. Zhang, J. Chen and Y. Cao, “High-Efficiency Polymer Photovoltaic Devices from Regioregular-Poly(3-hexylthiophene-2,5-diyl) and [6,6]-Phenyl-C61-butyric Acid Methyl Ester Processed with Oleic Acid Surfactant,” Applied Physics Letters, Vol. 90, No. 18, 2007, Article ID: 183512. doi:10.1063/1.2735937
[2]	F. Padinger, R. S. Ritberger and N. S. Sariciftci, “Effects of Postproduction Treatment on Plastic Solar Cells,” Advanced Functional Materials, Vol. 13, No. 1, 2003, pp. 85-88. doi:10.1002/adfm.200390011
[3]	B. Sun, H. J. Snaith, A. S. Dhoot, S. Westenhoff and N. C. Greenham, “Vertically Segregated Hybrid Blends for Photovoltaic Devices with Improved Efficiency,” Journal of Applied Physics, Vol. 97, No. 1, 2005, Article ID: 014914. doi:10.1063/1.1804613
[4]	E. Wang, L. Wang, L. Lan, C. Luo, W. Zhuang, J. Peng and Y. Cao, “High-Performance Polymer Heterojunction solar Cells of a Polysilafluorene Derivative,” Applied Physics Letters, Vol. 92, No. 3, 2008, Article ID: 033307. doi:10.1063/1.2836266
[5]	Z. Li and C. R. McNeill, “Transient Photocurrent Measurements of PCDTBT:PC70BM and PCPDTBT:PC70BM Solar Cells: Evidence for Charge Trapping in Efficient Polymer/Fullerene Blends,” Journal of Applied Physics, Vol. 109, No. 7, 2011, Article ID: 074513. doi:10.1063/1.3573394
[6]	F. Wudl, “The Chemical Properties of Buckminsterfullerene (C60) and the Birth and Infancy of Fulleroids,” Accounts of Chemical Research, Vol. 25, No. 3, 1992, pp. 157-161. doi:10.1021/ar00015a009
[7]	Y. Zhang and P. W. M. Blom, “Enhancement of the Hole Injection into Regioregular Poly(3-hexylthiophene) by Molecular Doping,” Applied Physics Letters, Vol. 97, No. 8, 2010, Article ID: 083303.
[8]	S. Ebadian, B. Gholamkhass, S. Shambayati, S. Holdcroft and P. Servati, “Effects of Annealing and Degradation on Regioregular Polythiophene-Based Bulk Heterojunction Organic Photovoltaic Devices,” Solar Energy Materials & Solar Cell, Vol. 94, No. 12, 2010, pp. 2258-2264. doi:10.1016/j.solmat.2010.07.021
[9]	F. Zhang, K. G. Jespersen, C. Björström, M. Svensson, M. R. Andersson, V. Sundström, K. Magnusson, E. Moons, A. Yartsev and O. Inganäs, “Influence of Solvent Mixing on the Morphology and Performance of Solar Cells Based on Polyfluorene Copolymer/Fullerene Blends,” Advanced Functional Materials, Vol. 16, No. 5, 2006, pp. 667-674. doi:10.1002/adfm.200500339
[10]	J. W. Jeong, J. W. Huh, J. I. Lee, H. Y. Chu, I. K. Han and B.-K. Ju, “Effects of Thermal Annealing on the Efficiency of Bulk-Heterojunction Organic Photovoltaic Devices,” Current Applied Physics, Vol. 10, No. 3, 2010, S520-S524. doi:10.1016/j.cap.2010.02.023
[11]	C.-J. Ko, Y.-K. Lin and F.-C. Chen, “Microwave Annealing of Polymer Photovoltaic Devices,” Advanced Materials, Vol. 19, No. 21, 2007, pp. 3520-3523. doi:10.1002/adma.200700741
[12]	J. Peet, C. Soci, R. C. Coffin, T. Q. Nguyen, A. Mikhailovsky, D. Moses and G. C. Bazana, “Method for Increasing the Photoconductive Response in Conjugated Polymer/Fullerene Composites,” Applied Physics Letters, Vol. 89, No. 25, 2006, Article ID: 252105. doi:10.1063/1.2408661
[13]	H. Hoppe and N. S. Sariciftci, “Morphology of Polymer/Fullerene Bulk Heterojunction Solar Cells,” Journal of Materials Chemistry, Vol. 16, No. 1, 2006, pp. 45-61. doi:10.1039/b510618b
[14]	S. Bertho, W. D. Oosterbaan, V. Vrindts, J. D’Haen, T. J. Cleij, L. Lutsen, J. Manca and D. Vanderzande, “Controlling the Morphology of Nanofiber-P3HT:PCBM Blends for Organic Bulk Heterojunction Solar Cells,” Organic Electronics, Vol. 10, No. 7, 2009, pp. 1248-1251.
[15]	S. Nagamatsu, M. Misaki, M. Chikamatsu, T. Kimura, Y. Yoshida, R. Azumi, N. Tanigaki and K. Yase, “Article Crystal Structure of Friction-Transferred Poly(2,5-dioctyloxy-1,4-phenylenevinylene),” The Journal of Physical Chemistry B, Vol. 111, No. 17, 2007, pp. 4349-4354. doi:10.1021/jp067555m
[16]	N. Ohashi, T. Miyadera, T. Taima and Y. Yoshida, “MgxC60 Fabricated by Using Mg:C60 Co-Evaporation Method for Carrier Doping,” Molecular Crystals and Liquid Crystals, Vol. 538, No. 1, 2011, pp. 193-198. doi:10.1080/15421406.2011.563723
[17]	W. Ma, C. Yang, X. Gong, K. Lee and A. J. Heeger, “Thermally Stable, Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology” Advanced Functional Materials, Vol. 15, No. 10, 2005, pp. 1617-1622. doi:10.1002/adfm.200500211
[18]	E. Verploegen, R. Mondal, C. J. Bettinger, S. Sok, M. F. Toney and Z. Bao, “Effects of Thermal Annealing Upon the Morphology of Polymer-Fullerene Blends,” Advanced Functional Materials, Vol. 20, No. 20, 2010, pp. 35193529. doi:10.1002/adfm.201000975
[19]	S. Lilliu, T. Agostinelli, E. Pires, M. Hampton, J. Nelson and J. E. Macdonald, “Dynamics of Crystallization and Disorder during Annealing of P3HT/PCBM Bulk Heterojunctions,” Macromolecules, Vol. 44, No. 8, 2011, pp. 2725-2734. doi:10.1021/ma102817z
[20]	B. W. Boudouris, V. Ho, L. H. Jimison, M. F. Toney, A. Salleo and R. A. Segalman, “Real-Time Observation of Poly(3-alkylthiophene) Crystallization and Correlation with Transient Optoelectronic Properties” Macromolecules, Vol. 44, No. 17, 2011, pp. 6653-6658. doi:10.1021/ma201316a
[21]	G. Yu, J. Gao, J. C. Hummelen, F. Wudl and A. J. Heeger, “Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions,” Science, Vol. 270, No. 5243, 1995, pp. 1789-1791. doi:10.1126/science.270.5243.1789
[22]	F. Padinger, R. S. Rittberger and N. S. Saricifici, “Effects of Postproduction Treatment on Plastic Solar Cells,” Advanced Functional Materials, Vol. 13, No. 1, 2003, pp. 85-88. doi:10.1002/adfm.200390011
[23]	A. Mishra and P. Bäuerle, “Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology,” Angewandte Chemie International Edition, Vol. 51, No. 9, 2012, pp. 2020-2067. doi:10.1002/anie.201102326
[24]	F. Gamier, A. Yassar, R. Hajlaoui, G. U. Horowitz, F. G. Deloffre, B. Serve, S. Ries and P. Alnot, “Molecular Engineering of Organic Semiconductors: Design of SelfAssembly Properties in Conjugated Thiophene Oligomers,” Journal of the American Chemical Society, Vol. 115, No. 19, 1993, pp. 8716-8721.
[25]	F. Garnier, R. Hajlaoui, A. El Kassmi, G. Horowitz, L. Laigre, W. Porzio, M. Armanini and F. Provasoli, “Dihexylquaterthiophene: A Two-Dimensional Liquid Crystal-Like Organic Semiconductor with High Transport Properties,” Chemistry of Materials, Vol. 10, No. 11, 1998, pp. 3334-3339. doi:10.1021/cm970704g
[26]	A. Facchetti, J. Letizia, M. H. Yoon, M. Mushrush, H. E. Katz and T. J. Marks, “Synthesis and Characterization of Diperfluorooctyl-Substituted Phenylene-Thiophene Oligomers as n-Type Semiconductors. Molecular StructureFilm Microstructure-Mobility Relationships, Organic FieldEffect Transistors, and Transistor Nonvolatile Memory Elements,” Chemistry of Materials, Vol. 16, No. 23, 2004, pp. 4715-4727.
[27]	N. Kiriy, A. Kiriy, V. Bocharova, M. Stamm, S. Richter, M. Plötner, W. J. Fischer, F. C. Krebs, I. Senkovska and H. J. Adler, “Conformation, Molecular Packing, and Field Effect Mobility of Regioregular β,β‘-Dihexylsexithiophene,” Chemistry of Materials, Vol. 16, No. 23, 2004, pp. 4757-4764. doi:10.1021/cm049686a
[28]	J. A. Letizia, A. Facchetti, C. L. Stern, M. A. Ratner and T. J. Marks, “High Electron Mobility in Solution-Cast and Vapor-Deposited Phenacyl—Quaterthiophene-Based Field-Effect Transistors: Toward N-Type Polythiophenes,” Journal of the American Chemical Society, Vol. 127, No. 39, 2005, pp. 13476-13477. doi:10.1021/ja054276o
[29]	J. Locklin, D. Li, S. C. B. Mannsfeld, E. J. Borkent, H. Meng, R. Advincula and Z. Bao, “Organic Thin Film Transistors Based on Cyclohexyl-Substituted Organic Semiconductors,” Chemistry of Materials, Vol. 17, No. 13, 2005, pp. 3366-3374. doi:10.1021/cm047851g
[30]	J. Sakai, T. Taima and K. Saito, “Efficient Oligothiophene: Fullerene Bulk Heterojunction Organic Photovoltaic Cells,” Organic Electronics, Vol. 9, No. 5, 2008, pp. 582-590. doi:10.1016/j.orgel.2008.03.008
[31]	M. Lu, S. Nagamatsu, Y. Yoshida, M. Chikamatsu, R. Azumi and K. Yase, “Solution-Processable Oligothiophene Derivatives with Branched Alkyl Chains and Their Thin-Film Transistor Characteristics,” Chemistry Letters, Vol. 39, No. 1, 2010, pp. 60-61. doi:10.1246/cl.2010.60
[32]	R. Mens, S. Chambon, S. Bertho, G. Reggers, B. Ruttens, J. D’Haen, J. Manca, R. Carleer, D. Vanderzande and P. Adriaensens, “Description of the Nanostructured Morphology of [6,6]-Phenyl-C61-butyric Acid Methyl Ester (PCBM) by XRD, DSC and Solid-State NMR,” Magnetic Resonance in Chemistry, Vol. 49, No. 5, 2011, pp. 242247. doi:10.1002/mrc.2741