الطباعة الرقمية من ثاني أكسيد التيتانيوم للخلايا الشمسية صبغ الحساس
Summary
This paper investigates the suitability of inkjet printing for the manufacturing of dye-sensitized solar cells. A binder-free TiO2 nanoparticle ink was formulated and printed onto a FTO glass substrate. The printed layer was fabricated into a cell with an active area of 0.25 cm2 and an efficiency of 3.5%.
Abstract
Silicon solar cell manufacturing is an expensive and high energy consuming process. In contrast, dye sensitized solar cell production is less environmentally damaging with lower processing temperatures presenting a viable and low cost alternative to conventional production. This paper further enhances these environmental credentials by evaluating the digital printing and therefore additive production route for these cells. This is achieved here by investigating the formation and performance of a metal oxide photoelectrode using nanoparticle sized titanium dioxide. An ink-jettable material was formulated, characterized and printed with a piezoelectric inkjet head to produce a 2.6 µm thick layer. The resultant printed layer was fabricated into a functioning cell with an active area of 0.25 cm2 and a power conversion efficiency of 3.5%. The binder-free formulation resulted in a reduced processing temperature of 250 °C, compatible with flexible polyamide substrates which are stable up to temperatures of 350 ˚C. The authors are continuing to develop this process route by investigating inkjet printing of other layers within dye sensitized solar cells.
Introduction
Conventional silicon solar cells are made from highly pure materials that require expensive and high-energy consuming specialist equipment. These conventional silicon cells incorporate a p-n junction that requires highly pure materials at the interface to generate electron-hole pairs. Dye-sensitized solar cells (DSSCs) have a fundamentally different working principle, where charge generation takes place at the materials interface. This means that processing under vacuum, ultrahigh temperatures or the use of clean room facilities are not required1. Therefore they are seen as a potentially low cost alternative; however up-scaling from small laboratory test cells into large prototypes for industrial manufacturing involves overcoming several issues including the rapid patterning of substrates.
Electronics manufacturing generally requires a degree of patterning, which is either achieved by masking or selective removal of the material after deposition. These steps can be removed through the use of “additive” digital printing techniques such as inkjet printing or spray coating. Digital printing is a promising method for direct deposition of functional materials for electronic devices. The technique can be described as printing from a digital-based pattern directly to a variety of substrates2. They are non-contact methods, which will not damage or contaminate the substrate surface and deposit material only where it is required, resulting in little or no wastage3. These techniques have been highlighted as being ideally suited to being scaled up to high-volume production3. Since digital printing methods use liquid forms of materials dispersed in a solvent, it is critical to understand the deposition of ink to determine the applications of the technique.
DSSCs have three main components: a porous layer of wide bandgap metal oxide material, a dye that covers the particles, and a “charge transporter” that infiltrates the pores within the porous layer of semiconductor. These are sandwiched in between a transparent conductive electrode and a counter electrode4. The counter electrode is coated with a catalytic material for electron transfer, which in most cases is platinum. Under illumination, the dye molecules will absorb energy in the form of photons. The dye molecules then become excited and charge separation occurs at the interface of the titanium dioxide and the dye. Electrons are ejected into the adjacent metal oxide particles and ‘holes’ are left behind on the dye molecule. The injected electrons travel through the metal oxide particles and reach the transparent conductive electrode. When a load is connected, the electrons move to the counter electrode through the external circuit and are finally reunited with their counter charges through the redox couple present in the electrolyte1. The nano-structured metal oxide layer within DSSCs plays a critical role in the overall performance of the cell, with material choice, processing methods and nature of the structure all having influencing factors5-10. One of the most important requirements for the photoanode is that it needs to have an extremely large surface area. This is achieved through the deposition of nanoparticle materials, commonly TiO21,11. This has been fabricated by countless different processes, however wet coating techniques such as screen-printing and doctor-blading, are still the most popular approach9,12,13.
Inkjet technology is a potential manufacturing route for dye-sensitized solar cells. It uses the movement of a piezoelectric crystal to expel a fixed quantity of liquid through a nozzle onto the desired substrate. This deposition method allows material to be jetted very accurately but also at high frequency with a potentially high print speed or deposition rate. Inkjet technology is sensitive to the viscosity of the ink used and this was previously a barrier to the development of functional inks. Recent work in the development of solvents suitable for ink formulation has helped to alleviate this problem, and printing of electronic components using 2D layered materials such as graphene has been demonstrated14. The viscosity of nanoparticle suspensions such as these has been found to depend on the nanoparticle size and concentration15. High concentrations of nanoparticles result in higher viscosities, therefore particle loadings are usually around 10 wt% to avoid nozzle blockages16, however higher concentrations have been achieved17.
The key advantages of inkjet technology include it being non-contact, additive patterning and maskless18. The latter two attributes are due to the ability to position many nozzles together on one or more printheads, with each nozzle separately addressable by the control software. This allows highly complex, multi-layered patterns to be created very rapidly as the printheads move across the substrate. No masking between materials or layers is required as the position of each ink drop is accurately controlled, in some systems to an accuracy of ~1.5 µm19. One of the key benefits is that inkjet technology is mature, with significant development carried out in the latter half of the twentieth century. The result is that the inkjet is a very scalable technology, with roll-to-roll systems capable of printing accurately onto flexible substrates at rates of many meters per second. Traditionally this was used for high volume production, e.g., newspapers. However, developments in technology have allowed the inkjet to be used in roll-to-roll production of electronic circuits using nanoparticulate silver inks20. The inkjet is therefore an attractive process for the potential production of dye-sensitized solar cells by digital printing.
Protocol
Representative Results
Discussion
A particular challenge when formulating inks is the natural tendency for nanoparticles to cluster together. These are known as either aggregates or agglomerates, depending on the nature and strength of the bonds between the particles. The energy of simply stirring particles into water or binder is not great enough to overcome the particle attractive forces preventing the breakup of agglomerates. Ball milling, high shear mixing or ultrasonication are commonly used to break up agglomerated nanoparticles. Various anionic, nonionic, and cationic surfactants and polymers can also be used to provide long-term stabilization. By minimizing the number of these agglomerates, a good quality suspension can be achieved. The fluids should be filtered through the correct size filter just before loading into the cartridge to remove large particle aggregates which can clog the nozzles.
The particle size within the TiO2 layer also has been shown to influence the overall efficiency of DSSCs. The photocatalytic activity of titanium dioxide increases as particle sizes decrease due to an increase in the specific surface area40. A study comparing the efficiency of DSSCs incorporating TiO2 nanoparticles with 5 different sizes ranging from 400 nm to 14 nm and found that those with smaller particle sizes resulted in better electrical conversion efficiencies33.
Inkjet printing is a non-contact deposition technique capable of multi-pass printing. This presents the unique opportunity to rapidly fabricate multilayer devices in one operation on a wide range of substrates with minimal material waste. It also potentially provides a way to integrate other components (such as batteries) into the system through the printing of functional materials41. Although the representative results shown for the inkjet printed devices do not perform as well as the doctor-bladed devices, it demonstrates the potential for the deposition technique. With further ink optimization, it could perform on a comparable level to currently used methods and may provide further scope for cost-effective, environmentally friendly integration of photovoltaic cells onto a wide range of substrates. We hope to improve the efficiency of the inkjet printed devices by increasing the thickness of the printed layer closer to that of the doctor-bladed TiO2 and will continue to look at the printing of other materials and layers within DSSCs.
Disclosures
The authors have nothing to disclose.
Acknowledgements
يجري هذا البحث بامتنان بدعم من الهندسة والعلوم الفيزيائية مجلس البحوث (EPSRC) الممول من خلال منحة تدريب الدكتوراه. وقد تم تمويل الوصول المفتوح رسوم معالجة المادة (ناقلات الجنود المدرعة) من خلال مجالس البحوث في المملكة المتحدة (RCUK). يتم توفير كافة البيانات بالكامل في قسم نتائج ورقة. وقد سبق أن نشرت نتائج ممثلة من قبل المؤلفين 42.
ونود أن نشكر الدكتور Senthilarasu سوندارام من جامعة إكستر لمساعدته في تشخيص الأداء الكهربائي للخلايا.
Materials
| Titanium dioxide | Sigma Aldrich | 718467 | |
| Deionized water | Supplied from a filter in the laboratory | ||
| Hydrochloric acid, 2M(2N) | Fisher Scientific | J/4250/17 | |
| Dimethylformamide (DMF) | Fisher Scientific | D/3840/08 | |
| Ethanol | VWR Chemicals | 20721.33 | |
| Dispersing additive | Air Products | ||
| Defoaming agent | Air Products | ||
| Ethylene glycol | Fluka | 107-21-1 | |
| Polyvinylidene fluoride (PVDF) syringe filter | VWR International | ||
| Cleaning detergent | Fisher Scientific | 10335650 | |
| Fluorine doped tin oxide (FTO) glass, 8 Ω/sq | Pilkington | ||
| Ruthenizer dye | Solaronix | 21613 | |
| Pre-cut 60 µm thick thermoplastic sealing film | Solaronix | 74301 | |
| 50 mM iodide/tri-iodide electrolyte in acetonitrile | Solaronix | 31111 | |
| Platinum coated FTO glass | Solaronix | 74201 | |
| Vac'n'Fill Syringe | Solaronix | 65209 | |
| Polyimide tape (6.35 mm) | Onecall Farnell | 1676087 |
References
- Docampo, P., et al. Lessons Learned: From Dye-Sensitized Solar Cells to All-Solid-State Hybrid Devices. Adv. Mater. 26, 4013-4030 (2014).
- Hudd, A., Magdassi, S. . The Chemistry of Inkjet Inks. , 3-18 (2009).
- Krebs, F. C. Fabrication and processing of polymer solar cells: A review of printing and coating. Sol. Energ. Mat. Sol. Cells. 93, 394-412 (2009).
- Reddy, P. J. . Solar Power Generation: Technology, New Concepts & Policy. , (2012).
- Gemeiner, P., Mikula, M. . Acta. Chem. Slov. 6, 29 (2013).
- Xue, Z., Jiang, C., Wang, L., Liu, W., Liu, B. Fabrication of Flexible Plastic Solid-State Dye-Sensitized Solar Cells Using Low Temperature Techniques. J. Phys. Chem. C. 118, 16352-16357 (2014).
- Oh, Y., Yoon, H. G., Lee, S. -. N., Kim, H. -. K., Kim, J. Inkjet-Printing of TiO2 Co-Solvent Ink: From Uniform Ink-Droplet to TiO2 Photoelectrode for Dye-Sensitized Solar Cells. J. Electrochem. Soc. 159, 34-38 (2011).
- Lin, L. -. Y., et al. Low-temperature flexible Ti/TiO2 photoanode for dye-sensitized solar cells with binder-free TiO2 paste. Prog. Photovolt. Res. Appl. 20, 181-190 (2012).
- Gong, J., Liang, J., Sumathy, K. Review on dye-sensitized solar cells (DSSCs): Fundamental concepts and novel materials. Renew. Sustainable Energy Rev. 16, 5848-5860 (2012).
- Bosch-Jimenez, P., Yu, Y., Lira-Cantu, M., Domingo, C., Ayllòn, J. A. Solution processable titanium dioxide precursor and nanoparticulated ink: Application in Dye Sensitized Solar Cells. J Colloid Interf Sci. 416, 112-118 (2014).
- Jose, R., Thavasi, V., Ramakrishna, S. Metal Oxides for Dye-Sensitized Solar Cells. J. Am. Ceram. Soc. 92, 289-301 (2009).
- Gemeiner, P., Mikula, M. Efficiency of dye sensitized solar cells with various compositions of TiO2 based screen printed photoactive electrodes. Acta. Chem. Slov. 6, 29-34 (2013).
- Lee, K. E., Charbonneau, C., Demopoulos, G. P. Thin single screen-printed bifunctional titania layer photoanodes for high performing DSSCs via a novel hybrid paste formulation and process. J. Mater. Res. 28, 480-487 (2013).
- Li, J., Lemme, M. C., östling, M. Inkjet Printing of 2D Layered Materials. ChemPhysChem. 15, 3427-3434 (2014).
- Rudyak, V. Y., Krasnolutskii, S. L. Dependence of the viscosity of nanofluids on nanoparticle size and material. Phys. Lett. A. 378, 1845-1849 (2014).
- Dispoto, G., Moroney, N., Hanson, E., Meyer, J. D., Allen, R. R. . Color Desktop Printer Technology Optical Science and Engineering. , 111-155 (2006).
- Hsien-Hsueh, L., Kan-Sen, C., Kuo-Cheng, H. Inkjet printing of nanosized silver colloids. Nanotechnology. 16, 2436 (2005).
- Singh, M., Haverinen, H. M., Dhagat, P., Jabbour, G. E. Inkjet Printing: Inkjet Printing-Process and Its Applications. Adv. Mater. 22, 673-685 (2010).
- Stüwe, D., Mager, D., Biro, D., Korvink, J. G. Inkjet Technology for Crystalline Silicon Photovoltaics. Adv. Mater. 27, 599-626 (2015).
- Perelaer, J., et al. Roll-to-Roll Compatible Sintering of Inkjet Printed Features by Photonic and Microwave Exposure: From Non-Conductive Ink to 40% Bulk Silver Conductivity in Less Than 15 Seconds. Adv. Mater. 24, 2620-2625 (2012).
- Hwang, M. -. s., Jeong, B. -. y., Moon, J., Chun, S. -. K., Kim, J. Inkjet-printing of indium tin oxide (ITO) films for transparent conducting electrodes. Mat. Sci. Eng. B. 176, 1128-1131 (2011).
- Hara, K., Arakawa, H. . Handbook of Photovoltaic Science and Engineering. , 663-700 (2003).
- Ryu, J., Wakida, T., Takagishi, T. Effect of Corona Discharge on the Surface of Wool and Its Application to Printing. Text. Res. J. 61, 595-601 (1991).
- Yang, L., Chen, J., Guo, Y., Zhang, Z. Surface modification of a biomedical polyethylene terephthalate (PET) by air plasma. Appl. Surf. Sci. 255, 4446-4451 (2009).
- Qian, B., Shen, Z. Fabrication of Superhydrophobic Surfaces by Dislocation-Selective Chemical Etching on Aluminum, Copper, and Zinc Substrates. J. Am. Chem. Soc. 21, 9007-9009 (2005).
- Echlin, P. . Handbook of Sample Preparation for Scanning Electron Microscopy and X-Ray Microanalysis. , (2011).
- Flegler, S. L., Heckman, J. W., Klomparens, K. L. . Scanning and Transmission Electron Microscopy: An Introduction. , (1993).
- O’Donnell, M. Z. R. How To Minimize Measurement Errors In Solar Cell Testing. Solar Industry Magazine. , (2011).
- Grätzel, M. Dye-sensitized solar cells. J. Photochem. Photobiol. C: Photochem. Rev. 4, 145-153 (2003).
- Green, M. A., Emery, K., Hishikawa, Y., Warta, W., Dunlop, E. D. Solar cell efficiency tables (version 46). Prog. Photovolt. Res. Appl. 23, 805-812 (2015).
- Shockley, W., Queisser, H. J. Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Phys. 32, 510-519 (1961).
- Snaith, H. J. Estimating the Maximum Attainable Efficiency in Dye-Sensitized Solar Cells. Adv. Funct. Mater. 20, 13-19 (2010).
- Jeng, M. -. J., Wung, Y. -. L., Chang, L. -. B., Chow, L. Particle Size Effects of TiO2 Layers on the Solar Efficiency of Dye-Sensitized Solar Cells. Int. J. Photoenergy. 2013, 9 (2013).
- Song-Yuan, D., Kong-Jia, W. Optimum Nanoporous TiO2 Film and Its Application to Dye-sensitized Solar Cells. Chin. Phys. Lett. 20, 953-955 (2002).
- Baglio, V., Girolamo, M., Antonucci, V., Aricò, A. S. Influence of TiO2 Film Thickness on the Electrochemical Behaviour of Dye-Sensitized Solar Cells. Int. J. Electrochem. Sci. 6, 3375-3384 (2011).
- Ito, S., et al. High-Efficiency Organic-Dye- Sensitized Solar Cells Controlled by Nanocrystalline-TiO2 Electrode Thickness. Adv. Mater. 18, 1202-1205 (2006).
- Ito, S., Kalyanasundaram, K. . Dye sensitized solar cells. , 251-266 (2010).
- Tsai, J., Hsu, W., Wu, T., Meen, T., Chong, W. Effect of compressed TiO2 nanoparticle thin film thickness on the performance of dye-sensitized solar cells. Nanoscale Res Lett. 8, 1-6 (2013).
- Shin, I., et al. Analysis of TiO2 thickness effect on characteristic of a dye-sensitized solar cell by using electrochemical impedance spectroscopy. Curr. Appl. Phys. 10, 422-424 (2010).
- Brus, L. Electronic wave functions in semiconductor clusters: experiment and theory. J. Phys. Chem. 90, 2555-2560 (1986).
- Jung, S., et al. All-Inkjet-Printed, All-Air-Processed Solar Cells. Adv Energy Mater. 4, 1-9 (2014).
- Cherrington, R., Hughes, D. J., Senthilarasu, S., Goodship, V. Inkjet-Printed TiO2 Nanoparticles from Aqueous Solutions for Dye-Sensitized Solar Cells (DSSCs). Energy Technology. 3, (2015).
