Improvement of Open-Circuit Voltage in Organic Photovoltaic Cells with Chemically Modified Indium-Tin Oxide

Khayankhyarvaa Sarangerel, Byambasuren Delgertsetseg, Namsrai Javkhlantugs, Masaru Sakomura, Chimed Ganzorig

Center for Nanoscience and Nanotechnology, Department of Chemical Technology, School of Chemistry and Chemical Engineering, National University of Mongolia, Ulaanbaatar, Mongolia.
Center for Nanoscience and Nanotechnology, Department of Chemical Technology, School of Chemistry and Chemical Engineering, National University of Mongolia, Ulaanbaatar, Mongolia;Faculty of Engineering, New Mongol Institute of Technology, Ulaanbaatar, Mongolia.
Department of Chemistry, Chemical Engineering and Life Science, Yokohama National University, Yokohama, Japan.
Department of Electronics and Computer, School of Power Engineering, Mongolian University of Science and Technology, Ulaanbaatar, Mongolia.

DOI: 10.4236/wjnse.2013.34016                

Abstract

The possibility of the increase in open-circuit voltage of organic photovoltaic cells based primarily indium-tin oxide (ITO)/rubrene/fullerene/Al structure by changing the work function of ITO anodes and Al cathodes was described in this work. To change built-in potential preferably in order to increase the open-circuit voltage, the work function of ITO should be increased and work function of Al should be decreased. The correlation between the change in work functions of electrodes and performance of the organic photovoltaic cells before and after surface modifications was examined in detail. The enhancement of open-circuit voltage depends on a function of work function change of both ITO and Al electrode. We could show that the built-in potential in the cells played an important role in open-circuit voltage.

Keywords

Open-Circuit Voltage; Chemical Modification; Indium-Tin Oxide

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	C. Lee, P. Linneman, P. Peumans, A. Yakimow and S. R. Forrest, “Small Molecular Weight Organic Thin-Film Photodetectors and Solar Cells,” Journal of Applied Physics, Vol. 93, No. 7, 2003, pp. 3693-3723. http://dx.doi.org/10.1063/1.1534621
[2]	S. R. Forrest, “The Path to Ubiquitous and Low-Cost Organic Electronic Applications on Plastic,” Nature, Vol. 428, No. 6994, 2004, pp. 911-918. http://dx.doi.org/10.1038/nature02498
[3]	T. Kietzke, “Recent Advances in Organic Solar Cells,” Advances in OptoElectronics, Vol. 2007, No. 40285, 2007, pp. 1-15. http://dx.doi.org/10.1155/2007/40285
[4]	J. Xue, “Perspectives on Organic Photovoltaics,” Polymer Reviews, Vol. 50, No. 4, 2010, pp. 411-419. http://dx.doi.org/10.1080/15583724.2010.515766
[5]	F. C. Krebs, “Polymeric Solar Cells: Materials, Design, Manufacture,” DEStech Publications, Inc., Lancaster, 2010.
[6]	C. W. Tang, “Two-Layer Organic Photovoltaic Cell,” Applied Physics Letters, Vol. 48, No. 2, 1986, pp. 183-185. http://dx.doi.org/10.1063/1.96937
[7]	Z. R. Dai, Z. W. Pan and Z. L. Wang, “Novel Nanostructures of Functional Oxides Synthesized by Thermal Evaporation,” Advanced Functional Materials, Vol. 13, No. 1, 2003, pp. 9-24. http://dx.doi.org/10.1002/adfm.200390013
[8]	J. Xue, S. Uchida, B. P. Rand and S. R. Forrest, “4.2% Efficient Organic Photovoltaic Cells With Low Series Resistances,” Applied Physics Letters, Vol. 84, No. 16, 2004, pp. 3013-3016. http://dx.doi.org/10.1063/1.1713036
[9]	J. Xue, S. Uchida, B. P. Rand and S. R. Forrest, “Asymmetric Tandem Organic Photovoltaic Cells with Hybrid Planar-Mixed Molecular Heterojunctions,” Applied Physics Letters, Vol. 85, No. 23, 2004, pp. 5757-5759. http://dx.doi.org/10.1063/1.1829776
[10]	C. F. Lin, M. Zhang, S. W. Liu, T. L. Chiu and J. H. Lee, “High Photoelectric Conversion Efficiency of Metal Phthalocyanine/Fullerene Heterojunction Photovoltaic Device,” International Journal of Molecular Sciences, Vol. 12, No. 1, 2011, pp. 476-505. http://dx.doi.org/10.3390/ijms12010476
[11]	G. Dennler, M. C. Scharber and C. J. Brabec, “Polymer-Fullerene Bulk-Heterojunction Solar Cells,” Advanced Materials, Vol. 21, No. 13, 2009, 1323-1338. http://dx.doi.org/10.1002/adma.200801283
[12]	H. Y. Chen, et al., “Polymer Solar Cells with Enhanced Open-Circuit Voltage and Efficiency,” Nature Photonics, Vol. 3, No. 11, 2009, pp. 649-653. http://dx.doi.org/10.1038/nphoton.2009.192
[13]	G. E. Morse and T. P. Bender, “Boron Subphthalocyanines as Organic Electronic Materials,” ACS Applied Materials & Interfaces, Vol. 4, No. 10, 2012, pp. 5055-5068. http://dx.doi.org/10.1021/am3015197
[14]	G. Li, R. Zhu and Y. Yang, “Polymer Solar Cells,” Nature Photonics, Vol. 6, No. 3, 2012, pp. 153-161. http://dx.doi.org/10.1038/nphoton.2012.11
[15]	J. Yang, L. Qian, R. Zhou, Y. Zheng, A. Tang and P. H. Holloway, “Hybrid Polymer: Colloidal Nanoparticle Photovoltaic Cells Incorporating a Solution-Processed, Multi-Functioned ZnO Nanoscrystal Layer,” Journal of Applied Physics, Vol. 111, No. 4, 2012, pp. 044323-044330. http://dx.doi.org/10.1063/1.3689154
[16]	P. Peumans and S. R. Forrest “Very-High-Efficiency Double-Heterostructure Copper Phthalocyanine/C60 Photovoltaic Cells,” Applied Physics Letters, Vol. 79, No. 1, 2001, pp. 126-128. http://dx.doi.org/10.1063/1.1384001
[17]	M. A. Green, K. Emery, Y. Hishikawa and W. Warta, “Solar Cell Efficiency Tables (Version 37),” Progress in Photovoltaics, Vol. 19, No. 1, 2011, pp. 84-92. http://dx.doi.org/10.1002/pip.1088
[18]	T. Taima, J. Sakai, T. Yamanari and K. Saito, “Realization of Large Open-Circuit Photovoltage in Organic Thin-Film Solar Cells by Controlling Measurement Environment,” Japanese Journal of Applied Physics, Vol. 45, No. 37, 2006, pp. L995-L997. http://dx.doi.org/10.1143/JJAP.45.L995
[19]	K. L. Mutolo, E. I. Mayo, B. P. Rand, S. R. Forrest and M. E. Thompson, “Enhanced Open-Circuit Voltage in Sub- phthlocyanine/C60 Organic Photovoltaic Cells,” Journal of the American Chemical Society, Vol. 128, No. 25, 2006, pp. 8108-8109. http://dx.doi.org/10.1021/ja061655o
[20]	M. Fujihira and C. Ganzorig, “Conjugated Polymer and Molecular Interfaces,” In: A. Kahn, J. J. Pireaux, W. R. Salaneck and K. Seki, Eds., Marcel Dekker, New York, 2002, pp. 817-858.
[21]	C. Ganzorig and M. Fujihira, “Chemically Modified Oxide Electrodes,” In: A. J. Bard and M. Stratmann, Eds., Modified Electrodes, WILEY-VCH Verlag GmbH, Weinheim, 2007, pp. 261-334.
[22]	N. R. Armstrong, et al., “Interface Modification of ITO Thin Films: Organic Photovoltaic Cells,” Thin Solid Films, Vol. 445, No. 2, 2003, pp. 342-352. http://dx.doi.org/10.1016/j.tsf.2003.08.067
[23]	S. Khodabakhsh, B. M. Sanderson, J. Nelson and T. S. Jones, “Using Self-Assembling Dipole Molecules to Improve Charge Collection in Molecular Solar Cells,” Advanced Functional Materials, Vol. 16, No. 1, 2006, pp. 95-100. http://dx.doi.org/10.1002/adfm.200500207
[24]	C. Ganzorig and M. Fujihira, “A Lithium Carboxylate Ultrathin Film on an Aluminum Cathode for Enhanced Electron Injection in Organic Electroluminescent Devices,” Japanese Journal of Applied Physics, Vol. 38, No. 11B, 1999, pp. L1348-L1350. http://dx.doi.org/10.1143/JJAP.38.L1348
[25]	H. Ishii, K. Sugiyama, E. Ito and K. Seki, “Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces,” Advanced Materials, Vol. 11, No. 8, 1999, pp. 605-625. http://dx.doi.org/10.1002/(SICI)1521-4095(199906)11:8<605::AID-ADMA605>3.0.CO;2-Q
[26]	A. J. Maxwell, P. A. Bronwiler, D. Arvanitis, J. Hasselstrom, M. K. J. Johansson and N. Martensson, “Electronic and Geometric Structure of C60 on Al(111) and Al(110),” Physical Review B, Vol. 57, No. 12, 1998, pp. 7312-7326. http://dx.doi.org/10.1103/PhysRevB.57.7312
[27]	J. Y. Lee, “Efficient Hole Injection in Organic Light Emitting Diodes Using C60 as a Buffer Layer for Al Reflective Anodes,” Applied Physics Letters, Vol. 88, No. 7, 2006, pp. 073512-073514. http://dx.doi.org/10.1063/1.2174838
[28]	S. K. M. Jonsson, W. R. Salaneck and M. Fahlman, “Photoemission of Alq3 and C60 film on Al and LiF Substrates,” Journal of Applied Physics, Vol. 98, No.1, 2005, pp. 014901-014907. http://dx.doi.org/10.1063/1.1929884
[29]	R. Mitsumoto, et al., “Electronic Structures and Chemical Bonding of Fluorinated Fullerenes Studied by NEXAFS, UPS and Vacuum-Absorption Spectroscopies,” Journal of Physical Chemistry A, Vol. 102, No. 3, 1998, pp. 552- 560. http://dx.doi.org/10.1021/jp972863t
[30]	M. Hayashi, H. Ishii, Y. Ouchi and K. Seki, “Examination of Band Bending at Buckminsterfullerene (C60) Metal Interfaces by the Kelvin Probe Method,” Journal of Applied Physics, Vol. 92, No. 7, 2002, pp. 3784-3793. http://dx.doi.org/10.1063/1.1504495
[31]	Y. Tanaka, K. Kanai, Y. Ouchi and K. Seki, “Oxygen Effect in the Interfacial Electronic Structure of C60 Film Studied by Photoelectron Spectroscopy,” Chemical Physics Letters, Vol. 441, No. 1-3, 2007, pp. 63-70. http://dx.doi.org/10.1016/j.cplett.2007.04.080
[32]	T. Yokoyama, D. Yoshimura, E. Ito, H. Ishii, Y. Ouchi and K. Seki, “Energy Level Alignment at Alq3/LiF/Al Interfaces Studied by Electron Spectroscopies: Island Growth of LiF and Size-Dependence of the Electronic Structures,” Japanese Journal of Applied Physics, Vol. 42, No. 6A, 2003, pp. 3666-3675. http://dx.doi.org/10.1143/JJAP.42.3666
[33]	S. Toyoshima, K. Kuwabara, T. Sakurai, T. Taima, K. Saito, H. Kato and K. Akimoto, “Electronic Structure of Bathocuproine on Metal Studied by Ultraviolet Photoemission Spectroscopy,” Japanese Journal of Applied Physics, Vol. 46, No. 4B, 2007, pp. 2692-2695. http://dx.doi.org/10.1143/JJAP.46.2692
[34]	C. Ganzorig, K. J. Kwak, K. Yagi and M. Fujihira, “Fine Tuning Work Function of Indium Tin Oxide by Surface Molecular Design: Enhanced Hole Injection in Organic Electroluminescent Devices,” Applied Physics Letters, Vol. 79, No. 2, 2001, pp. 272-274. http://dx.doi.org/10.1063/1.1384896
[35]	K. Sarangerel, C. Ganzorig, M. Fujihira, M. Sakomura and K. Ueda, “Influence of the Work Function of Chemically Modified Indium-Tin-Oxide Electrodes on the Open-Circuit Voltage of Heterojunction Photovoltaic Cells,” Chemistry Letters, Vol. 37, No. 7, 2007, pp. 778-779. http://dx.doi.org/10.1246/cl.2008.778
[36]	C. Ganzorig, M. Sakomura, K. Ueda and M. Fujihira, “Current-Voltage Behavior in Hole-Only Single-Carrier Devices with Self-Assembling Dipole Molecules on In- dium Tin Oxide Anodes,” Applied Physics Letters, Vol. 89, No. 26, 2006, pp. 263501-253603. http://dx.doi.org/10.1063/1.2420792
[37]	S. W. Cho, et al., “Origin of Charge Transfer Complex Resulting in Ohmic Contact at the C60/Cu Interface,” Synthetic Metals, Vol. 157, No. 2-3, 2007, pp. 160-164. http://dx.doi.org/10.1016/j.synthmet.2007.01.006
[38]	C. J. Huang, D. Glozea, A. Turakn and Z. H. Lu, “Passivation Effect of Al/LiF Electrode on C60 Diodes,” Applied Physics Letters, Vol. 86, No. 3, 2005, pp. 033107-033109. http://dx.doi.org/10.1063/1.1854193
[39]	M. Vogel, S. Doka, Ch. Breyer, M. Ch. Lux-Steiner and K. Fostiropoulos, “On the Function of a Bathocuproine Buffer Layer in Organic Photovoltaic Cells,” Applied Physics Letters, Vol. 89, No. 16, 2006, pp. 163501- 163503. http://dx.doi.org/10.1063/1.2362624
[40]	J. Kido and T. Matsumoto, “Bright Organic Electroluminescent Devices Having a Metal-Doped Electron-Injecting Layer,” Applied Physics Letters, Vol. 73, No. 20, 1998, pp. 2866-2868. http://dx.doi.org/10.1063/1.122612
[41]	C. Ganzorig, K. Suga and M. Fujihira, “Alkali Metal Acetates as Effective Electron Injection Layers for Organic Electroluminescent Devices,” Materials Science and Engineering: B, Vol. 85, No. 2-3, 2001, pp. 140-143. http://dx.doi.org/10.1016/S0921-5107(01)00547-5
[42]	C. Ganzorig and M. Fujihira, “Evidence for Alkali Metal Formation at a Cathode Interface of Organic Electroluminescent Devices by Thermal Decomposition of Alkali Metal Carboxylates during Their Vapor Deposition,” Applied Physics Letters, Vol. 85, No. 20, 2004, pp. 4774- 4776. http://dx.doi.org/10.1063/1.1819984
[43]	N. Johansson, T. Osada, S. Stafstrom, W. R. Salaneck, V. Parente, D. A. dos Santos, X. Crispin and J. L. Bredas, “Electronic Structure of Tris(8-Hydroxyquinoline) Aluminum Thin Films in the Pristine and Reduced States,” Journal of Chemical Physics, Vol. 111, No. 5, 1999, pp. 2157-2163. http://dx.doi.org/10.1063/1.479486
[44]	C. Ganzorig and M. Fujihira, “A Possible Mechanism for Enhanced Electrofluorescence Emission through Triplet- Triplet Annihilation in Organic Electroluminescent Devi- ces,” Applied Physics Letters, Vol. 81, No. 17, 2002, pp. 3137-3139. http://dx.doi.org/10.1063/1.1515129
[45]	V. I. Srdanov, C. H. Lee and N. S. Sariciftci, “Spectral and Photocarrier Dynamics in Thin Films of Pristine and Alkali-Doped C60,” Thin Solid Films, Vol. 257, No. 2, 1995, pp. 233-243. http://dx.doi.org/10.1016/0040-6090(94)05707-9
[46]	B. A. Gregg and M. C. Hanna, “Comparing Organic to Inorganic Photovoltaic Cells: Theory, Experiment, and Simulation,” Journal of Applied Physics, Vol. 93, No. 6, 2003, pp. 3605-3614. http://dx.doi.org/10.1063/1.1544413
[47]	Y. Terao, H. Sasabe and C. Adachi, “Correlation of the Hole Mobility Exciton Diffusion Length, and Solar Cell Characteristics in Phthalocyanine/Fullerene Organic Solar Cells,” Applied Physics Letters, Vol. 90, No. 10, 2007, 103515-103517. http://dx.doi.org/10.1063/1.2711525
[48]	C. M. Ramsdale, et al., “The Origin of the Open-Circuit Voltage in Polyfluorene-Based Photovoltaic Devices,” Journal of Applied Physics, Vol. 92, No. 8, 2002, pp. 4266-4270. http://dx.doi.org/10.1063/1.1506385
[49]	G. G, Malliaras, J. R. Salem, P. J. Brock and J. C. Scott, “Photovoltaic Measurement of the Built-In Potential in Organic Light Emitting Diodes and Photodiodes,” Journal of Applied Physics, Vol. 84, No. 3, 1998, pp. 1583-1587. http://dx.doi.org/10.1063/1.368227
[50]	V. D. Mihailetchi, P. W. M. Blom, J. C. Hummelen and M. T. Rispens, “Cathode Dependence of The Open-Cir- cuit Voltage of Polymer: Fullerene Bulk Heterojunction Solar Cells,” Journal of Applied Physics, Vol. 94, No. 10, 2003, pp. 6849-6864. http://dx.doi.org/10.1063/1.1620683
[51]	P. W. M. Blom, V. D. Mihailetchi, L. J. A. Koster and D. E. Markov, “Device Physics of Polymer: Fullerene Bilk Heterojunction Solar Cell,” Advanced Materials, Vol. 19, No. 12, 2007, pp. 1551-1566. http://dx.doi.org/10.1002/adma.200601093
[52]	C. J. Brabec, et al., “Origin of the Open Circuit Voltage of Plastic Solar Cells,” Advanced Functional Materials, Vol. 11, No. 5, 2001, pp. 374-380. http://dx.doi.org/10.1002/1616-3028(200110)11:5<374::AID-ADFM374>3.0.CO;2-W
[53]	H. J. Snaith, N. C. Greenham and R. H. Friend, “The Origin of Collected Charge and Open-Circuit Voltage in Blended Polyfluorene Photovoltaic Devices,” Advanced Materials, Vol. 16, No. 18, 2004, pp. 1640-1645. http://dx.doi.org/10.1002/adma.200305766