Hybrid solar cells (HSCs) with water soluble polythiophene sodium poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate] (PTEBS) thin films produced using electrospray deposition (ESD) were fabricated, tested, and modeled and compared to devices produced using conventional spin coating. A single device structure of FTO/TiO2/PTEBS/Au was used to study the effects of ESD of the PTEBS layer on device performance. ESD was found to increase the short circuit current density ( ) by a factor of 2 while decreasing the open circuit voltage ( ) by half compared to spin coated PTEBS films. Comparable efficiencies of 0.009% were achieved from both device construction types. Current-voltage curves were modeled using the characteristic solar cell equation and showed a similar increase in generated photocurrent with an increase by two orders of magnitude in the saturation current in devices from ESD films. Increases in are attributed to an increase in the interfacial contact area between the TiO2 and PTEBS layers, while decreases in are attributed to incomplete film formation from ESD. 1. Introduction Hybrid solar cells (HSCs) consist of an inorganic semiconducting electron acceptor and an organic polymer electron donor sandwiched between a transparent conducting oxide anode and a metal cathode. Polymer-based solar cells have attracted considerable attention due to low production cost, solution processing, and an array of different materials suitable for device fabrication [1–3]. HSCs take advantage of the high electron mobilities ( ？cm2？V？1？s？1) [4, 5] in inorganic semiconductors to compensate for the poor hole mobilities in organic polymers (polythiophene polymers ≈ 0.00001–0.1？cm2？V？1？s？1) [6–9] which severely limit the electron diffusion length (~10？nm) [10, 11]. The interface between the inorganic semiconductor and the organic polymer in HSCs must be within one diffusion length of exciton generation to effectively separate excitons into holes and electrons. This presents a challenge to bilayer devices due to a limited interfacial contact area between the electron donor and acceptor layers. HSC devices have been designed with nanostructures (nanorods, nanoribbons, and interpenetrating layers) to increase the interfacial surface area [12–14]. An electrospray is a fine aerosol produced when electrical forces overcome surface tension forces in a liquid resulting in nebulization. While electrospray aerosols can be formed in a number of ways, the most common method is to apply a high electrical potential to a liquid inside of a metallic capillary tube. The liquid at the tip of
References
[1]
H. Hoppe and N. S. Sariciftci, “Morphology of polymer/fullerene bulk heterojunction solar cells,” Journal of Materials Chemistry, vol. 16, no. 1, pp. 45–61, 2006.
[2]
D. Gebeyehu, C. J. Brabec, N. S. Sariciftci et al., “Hybrid solar cells based on dye-sensitized nanoporous TiO2 electrodes and conjugated polymers as hole transport materials,” Synthetic Metals, vol. 125, no. 3, pp. 279–287, 2002.
[3]
W. U. Huynh, J. J. Dittmer, and A. P. Alivisatos, “Hybrid nanorod-polymer solar cells,” Science, vol. 295, no. 5564, pp. 2425–2427, 2002.
[4]
E. Hendry, F. Wang, J. Shan, T. F. Heinz, and M. Bonn, “Electron transport in TiO2 probed by THz time-domain spectroscopy,” Physical Review B, vol. 69, no. 8, Article ID 081101, 2004.
[5]
R. K？nenkamp, “Carrier transport in nanoporous TiO2 films,” Physical Review B, vol. 61, pp. 57–64, 2000.
[6]
K. M. Coakley, B. S. Srinivasan, J. M. Ziebarth, C. Goh, Y. Liu, and M. D. McGehee, “Enhanced hole mobility in regioregular polythiophene infiltrated in straight nanopores,” Advanced Functional Materials, vol. 15, no. 12, pp. 1927–1932, 2005.
[7]
A. J. Mozer and N. S. Sariciftci, “Negative electric field dependence of charge carrier drift mobility in conjugated, semiconducting polymers,” Chemical Physics Letters, vol. 389, no. 4–6, pp. 438–442, 2004.
[8]
A. J. Mozer, N. S. Sariciftci, A. Pivrikas et al., “Charge carrier mobility in regioregular poly(3-hexylthiophene) probed by transient conductivity techniques: a comparative study,” Physical Review B, vol. 71, no. 3, Article ID 035214, 2005.
[9]
H. Sirringhaus, N. Tessler, and R. H. Friend, “Integrated optoelectronic devices based on conjugated polymers,” Science, vol. 280, no. 5370, pp. 1741–1744, 1998.
[10]
X. Yang, J. Loos, S. C. Veenstra et al., “Nanoscale morphology of high-performance polymer solar cells,” Nano Letters, vol. 5, no. 4, pp. 579–583, 2005.
[11]
J.-M. Nunzi, “Organic photovoltaic materials and devices,” Comptes Rendus Physique, vol. 3, no. 4, pp. 523–542, 2002.
[12]
A. J. Breeze, Z. Schlesinger, S. A. Carter, and P. J. Brock, “Charge transport in TiO2/MEH-PPV polymer photovoltaics,” Physical Review B, vol. 64, no. 12, Article ID 125205, 2001.
[13]
A. M. Peiró, P. Ravirajan, K. Govender et al., “Hybrid polymer/metal oxide solar cells based on ZnO columnar structures,” Journal of Materials Chemistry, vol. 16, no. 21, pp. 2088–2096, 2006.
[14]
D. Cheyns, K. Vasseur, C. Rolin, J. Genoe, J. Poortmans, and P. Heremans, “Nanoimprinted semiconducting polymer films with 50？nm features and their application to organic heterojunction solar cells,” Nanotechnology, vol. 19, no. 42, Article ID 424016, 2008.
[15]
A. Jaworek and A. T. Sobczyk, “Electrospraying route to nanotechnology: an overview,” Journal of Electrostatics, vol. 66, no. 3-4, pp. 197–219, 2008.
[16]
A. Jaworek, Electrospray Technology for Thin-Film Deposition, Nova Science Publishers, New York, NY, USA, 2010.
[17]
J.-S. Kim, W.-S. Chung, K. Kim et al., “Performance optimization of polymer solar cells using electrostatically sprayed photoactive layers,” Advanced Functional Materials, vol. 20, no. 20, pp. 3538–3546, 2010.
[18]
T. Fukuda, K. Takagi, T. Asano et al., “Bulk heterojunction organic photovoltaic cell fabricated by the electrospray deposition method using mixed organic solvent,” Physica Status Solidi, vol. 5, no. 7, pp. 229–231, 2011.
[19]
S.-E. Park, J.-Y. Hwang, K. Kim, B. Jung, W. Kim, and J. Hwang, “Spray deposition of electrohydrodynamically atomized polymer mixture for active layer fabrication in organic photovoltaics,” Solar Energy Materials and Solar Cells, vol. 95, no. 1, pp. 352–356, 2011.
[20]
T. Fukuda, K. Takagi, and Y. Liao, “Insertion of fullerence layer for bulk heterojunction organic photovoltaic cell fabricated by electrospray deposition method,” Physica Status Solidi (RRL), vol. 7, pp. 1055–1058, 2013.
[21]
N. Ju, Y. Yamagata, and T. Higuchi, “Thin-film fabrication method for organic light-emitting diodes using electrospray deposition,” Advanced Materials, vol. 21, no. 43, pp. 4343–4347, 2009.
[22]
V. Vohra, U. Giovanella, R. Tubino, H. Murata, and C. Botta, “Electroluminescence from conjugated polymer electrospun nanofibers in solution processable organic light-emitting diodes,” ACS Nano, vol. 5, no. 7, pp. 5572–5578, 2011.
[23]
W. Hwang, G. Xin, M. Cho, S. M. Cho, and H. Chae, “Electrospray deposition of polymer thin films for organic light-emitting diodes,” Nanoscale Research Letters, vol. 7, article 52, pp. 1–13, 2012.
[24]
T.-W. Zeng, H.-H. Lo, C.-H. Chang, Y.-Y. Lin, C.-W. Chen, and W.-F. Su, “Hybrid poly (3-hexylthiophene)/titanium dioxide nanorods material for solar cell applications,” Solar Energy Materials and Solar Cells, vol. 93, no. 6-7, pp. 952–957, 2009.
[25]
P. Ravirajan, S. A. Haque, J. R. Durrant, D. D. C. Bradley, and J. Nelson, “The effect of polymer optoelectronic properties on the performance of multilayer hybrid polymer/TiO2 solar cells,” Advanced Functional Materials, vol. 15, no. 4, pp. 609–618, 2005.
[26]
D. Gebeyehu, C. J. Brabec, N. S. Sariciftci et al., “Hybrid solar cells based on dye-sensitized nanoporous TiO2 electrodes and conjugated polymers as hole transport materials,” Synthetic Metals, vol. 125, no. 3, pp. 279–287, 2002.
[27]
Q. Qiao, J. Beck, R. Lumpkin, J. Pretko, and J. T. Mcleskey Jr., “A comparison of fluorine tin oxide and indium tin oxide as the transparent electrode for P3OT/TiO2 solar cells,” Solar Energy Materials and Solar Cells, vol. 90, no. 7-8, pp. 1034–1040, 2006.
[28]
U.S. Department of Labor, Solvents—Safety and Health Topics-OSHA, 2007.
[29]
R. S？ndergaard, M. Helgesen, M. J？rgensen, and F. C. Krebs, “Fabrication of polymer solar cells using aqueous processing for all layers including the metal back electrode,” Advanced Energy Materials, vol. 1, no. 1, pp. 68–71, 2011.
[30]
N. S. Lewis and D. G. Nocera, “Powering the planet: chemical challenges in solar energy utilization,” Proceedings of the National Academy of Sciences of the United States of America, vol. 103, no. 43, pp. 15729–15735, 2006.
[31]
Q. Qiao, L. Su, J. Beck, and J. T. McLeskey Jr., “Characteristics of water-soluble polythiophene: TiO2 composite and its application in photovoltaics,” Journal of Applied Physics, vol. 98, no. 9, Article ID 094906, 2005.
[32]
Q. Qiao, Y. Xie, and J. T. McLeskey Jr., “Organic/inorganic polymer solar cells using a buffer layer from all-water-solution processing,” Journal of Physical Chemistry C, vol. 112, no. 26, pp. 9912–9916, 2008.
[33]
Q. Qiao and J. T. McLeskey Jr., “Water-soluble polythiophenenanocrystalline TiO2 solar cells,” Applied Physics Letters, vol. 86, no. 15, Article ID 153501, 2005.
[34]
A. J. Miller, R. A. Hatton, and S. R. P. Silva, “Water-soluble multiwall-carbon-nanotube-polythiophene composite for bilayer photovoltaics,” Applied Physics Letters, vol. 89, no. 12, Article ID 123115, 2006.
[35]
J. Yang, A. Garcia, and T.-Q. Nguyen, “Organic solar cells from water-soluble poly(thiophene)/fullerene heterojunction,” Applied Physics Letters, vol. 90, no. 10, Article ID 103514, 2007.
[36]
QCR Solutions, Materials for Organic Solar Cells—PHT105A, 2010.
[37]
A. Andersson, N. Johansson, P. Br？ms, N. Yu, D. Lupo, and W. R. Salaneck, “Fluorine tin oxide as an alternate to indium tin oxide in polymer LEDs,” Advanced Materials, vol. 10, no. 11, pp. 859–863, 1998.
[38]
P. A. Anderson, “Work function of gold,” Physical Review, vol. 115, no. 3, pp. 553–554, 1959.
[39]
S. Aazou and E. M. Assaid, “Modelling real photovoltaic solar cell using Maple,” in Proceedings of the 21th International Conference on Microelectronics (ICM '09), pp. 394–397, December 2009.
[40]
A. Jain and A. Kapoor, “Exact analytical solutions of the parameters of real solar cells using Lambert W-function,” Solar Energy Materials and Solar Cells, vol. 81, no. 2, pp. 269–277, 2004.
[41]
L. Schmidt-Mende and M. Gr？tzel, “TiO2 pore-filling and its effect on the efficiency of solid-state dye-sensitized solar cells,” Thin Solid Films, vol. 500, no. 1-2, pp. 296–301, 2006.
[42]
H. Han, U. Bach, Y.-B. Cheng, and R. A. Caruso, “Increased nanopore filling: effect on monolithic all-solid-state dye-sensitized solar cells,” Applied Physics Letters, vol. 90, no. 21, Article ID 213510, 2007.
[43]
P. Ravirajan, S. A. Haque, J. R. Durrant, D. D. C. Bradley, and J. Nelson, “The effect of polymer optoelectronic properties on the performance of multilayer hybrid polymer/TiO2 solar cells,” Advanced Functional Materials, vol. 15, no. 4, pp. 609–618, 2005.
[44]
A. F. Nogueira, C. Longo, and M.-A. De Paoli, “Polymers in dye sensitized solar cells: overview and perspectives,” Coordination Chemistry Reviews, vol. 248, no. 13-14, pp. 1455–1468, 2004.
[45]
Y. Shen, K. Li, N. Majumdar, J. C. Campbell, and M. C. Gupta, “Bulk and contact resistance in P3HT:PCBM heterojunction solar cells,” Solar Energy Materials and Solar Cells, vol. 95, no. 8, pp. 2314–2317, 2011.
[46]
P. Schilinsky, C. Waldauf, J. Hauch, and C. J. Brabec, “Simulation of light intensity dependent current characteristics of polymer solar cells,” Journal of Applied Physics, vol. 95, no. 5, pp. 2816–2819, 2004.
[47]
G. del Pozo, B. Romero, and B. Arredondo, “Evolution with annealing of solar cell parameters modeling the S-shape of the current-voltage characteristic,” Solar Energy Materials and Solar Cells, vol. 104, pp. 81–86, 2012.
[48]
S. Tanaka, “Performance simulation for dye-sensitized solar cells: toward high efficiency and solid state,” Japanese Journal of Applied Physics, vol. 40, no. 1, pp. 97–107, 2001.
[49]
J. Song, Z. Xu, F. Zhang et al., “The effect of annealing treatment on the performance of bulk heterojunction solar cells with donor and acceptor different weight ratios,” Science in China G, vol. 52, no. 10, pp. 1606–1610, 2009.
[50]
Y. Zhang, Z. Li, S. Wakim et al., “Bulk heterojunction solar cells based on a new low-band-gap polymer: morphology and performance,” Organic Electronics, vol. 12, no. 7, pp. 1211–1215, 2011.
