Effect of Organic Binders of TiO<sub>2</sub> Pastes in the Photoanodes of Cost-Effective Dye Sensitized Solar Cells Fabrication

Research Article

Austin Chem Eng. 2016; 3(5): 1042.

Effect of Organic Binders of TiO2 Pastes in the Photoanodes of Cost-Effective Dye Sensitized Solar Cells Fabrication

Valsaraj D1,2, Subramaniam MR², Baiju G² and Kumaresan D2,3*

¹Department of Electrical & Electronics Engineering, Amrita School of Engineering, Coimbatore 641112, Amrita Vishwa Vidyapeetham, Amrita University, India

²Department of Chemical Engineering and Materials Science, Amrita School of Engineering, Coimbatore 641112, Amrita Vishwa Vidyapeetham, Amrita University, India

³CoE–AMGT, Amrita School of Engineering, Coimbatore 641112, Amrita Vishwa Vidyapeetham, Amrita University, India

*Corresponding author: Duraisamy Kumaresan, Department of Chemical Engineering and Materials Science, Amrita School of Engineering, Coimbatore 641112, Amrita Vishwa Vidyapeetham, Amrita University, India

Received: September 09, 2016; Accepted: October 06, 2016; Published: October 10, 2016


A simple method of preparation of screen printable TiO2 paste from commercial anatase TiO2 nanopowder using two different organic binders i.e. polyvinylpyrrolidone and ethyl cellulose was tested, to study the effect of organic binders on their TiO2 films used as photoanodes in dye sensitized solar cells. In this study, TiO2 films made from the TiO2 paste with ethyl cellulose binder showed an improved power conversion efficiency of 4.47% over the TiO2 paste with polyvinylpyrrolidone binder producing power conversion efficiency of 3.59%, in their respective DSSC photoanodes. Also, the electrochemical impedance studies revealed a better charge transfer dynamics with reduced recombination processes for the DSSC photoanode made from TiO2 paste with ethyl cellulose binder. These results show a superior photovoltaic performance for the TiO2 paste with ethyl cellulose binder made by the simple method introduced in this work, which can open up options for the large-scale production of TiO2 pastes useful to the manufacturing of cost-effective DSSCs.

Keywords: Dye-sensitized solar cells; TiO2 nanopowder; TiO2 pastes; Organic binders; Photovoltaic performance


In recent years, dye-sensitized solar cells (DSSCs) have showed enormous potential over the conventional silicon solar cells as inexpensive solar cells due to the surpassing power conversion efficiency (~13%) and their ease of fabrication. Also, the low-cost of fabrication of DSSCs has made them very attractive to the researches related to the device performance enhancement and on integrating the DSSCs in to domestic products [1-3]. Usually, DSSCs are made by the sandwich of mesoscopic TiO2 film anode, an electrolyte and a metal (platinum) coated cathode. Among these components, the techniques used for TiO2 film deposition on transparent conducting oxide (TCO) are critical to the fabrication of highly efficient DSSCs, together with the mesoscopic TiO2 film typically coated by a monolayer of high molar extinction co-efficient dye molecules to extend the visible light absorption of anode [4]. Moreover, for the fabrication of high performance DSSC, coating of nano-sized highly porous TiO2 film on TCO plays a significant role. Consequently, TiO2 nanoparticles used for the fabrication of DSSCs expected to have a particle diameter of about 20 – 25 nm, which makes the long wavelengths of visible light to penetrate the TiO2 film easily. And to improve the light scattering, an additional layer of particle diameter around 400nm is introduced on top of the smaller size nanoparticles layer. Generally, TiO2 nanomaterials exist in rutile, brookite and anatase crystalline phases. The most utilized phase of TiO2 in DSSC application is anatase phase. Brookite phase exists only in ore form and due to smaller surface area, lower fermi level and larger crystallite size rutile phase is not favorable to the DSSC applications. Therefore, the maximum efficiency achieved in DSSC fabricated with the thin film of anatase TiO2 nanoparticles which are mostly synthesized via hydrothermal method. And for the above mentioned reasons, anatase phase TiO2 film preparation adoptable to the screen printing technique for printing the uniform thickness TiO2 layer on top of fluorine doped tin oxide (FTO) coated glass has been widely preferred.

For the industrial scale manufacturing of inexpensive DSSC, screen printing of TiO2 layer on top of FTO or polymer surface is one of the widely used technologies. The applications of TiO2 paste also covers areas including gas sensors, Gamma – radiation sensors, corrosion resistance, and microwave absorption and so on [5-7]. Since titanium dioxide is nontoxic and eco-friendly, it has also found a wide variety of applications in health care products, cosmetics and paints. The main factor which influences the screen printing is the characteristics and quality of TiO2 paste. The preparation of TiO2 paste with controllable nanoparticles size via hydrothermal method takes minimum of 28 hrs to complete and follows a lengthy procedure. A lengthy procedure of TiO2 paste making may not fit industrially due to the economic constraints and the slow processes. So, to achieve an easy TiO2 paste preparation with comparable efficiency as that of nanoparticles, several methods are tried using commercially available nanopowder (P25, Degussa) [8].

In this study, a commonly available TiO2 nanopowder (Sigma Aldrich, USA) is converted into paste in lesser time when compared to the hydrothermal method. A faster and easier procedure makes the industrial manufacturing of DSSC more easy and rapid, without compromising the performance and quality. So, we have prepared the TiO2 pastes by following a simple method with different binders and tested their photovoltaic performances, and also studied the influence of dispersion agent with the best performing paste made from commercially available TiO2 powder. The paste preparation doesn’t involve any sophisticated equipments and the overall paste preparation has been completed in less than 6 hours. In contrast, the paste preparation using laboratory made nanoparticles requires trained hands and well equipped machineries. Moreover, the commercially available TiO2 nanopowder based paste provides almost similar performance throughout and high reliability regardless of number of batches of the TiO2 paste prepared.



Commercial TiO2 nanopowder (Anatase) was procured from Sigma-Aldrich, USA. Ethyl cellulose powder (18-22 cps) was purchased from Loba Chemie, India. Polyvinylpyrrolidone was purchased from Himedia, India. Fluorine doped tin oxide (FTO) glass slides (12-14 ohm/sq) were purchased from Dyesol Corporation, Australia. Commercial N719 dye (4- tertbutylpyridine, cis di(thiocyanato)-N, N’-bis (2,2’ bipyridyl- 4-carboxylic acid-4’- tetrabutylammonium carboxylate) ruthenium (II) were procured from Dyesol Corporation, Australia. Adhesive film (Surlyn, Meltronix 1170-25PF) was purchased from Solaronix, Switzerland.

Preparation of screen-printable TiO2 pastes

Different type of TiO2 pastes were prepared using commercially available TiO2 nanopowder by varying different organic binder concentrations. Then their TiO2 films adhesion and performance were tested. Based on the literature, the widely known two organic binders ethyl cellulose, and polyvinyl pyrrolidone were selected for this study and compared with the TiO2 paste made without binder.

Preparation of TiO2 paste without binder: In the beginning, anatase TiO2 powder was mixed with few drops of DI water and ethanol thoroughly. Then, the mixture was crushed in an agate mortar until it converts as viscous state [9] by following the detailed procedure given below:

TiO2 powder was taken in a crucible and heated at 400°C for 30 minutes to remove the absorbed moisture and impurities. 2mL ethanol was then added to 1 gram TiO2 powder drop wise in an agate mortar followed by constant grinding, until the mixture turns in to a smooth white viscous paste. This mixture was then ultrasonicated for an hour and kept for magnetic stirring up to 12 hours at a speed of 300 rpm to obtain a homogenous, viscous paste. This paste was then used for TiO2 doctor blading/screen printing on substrates.

Polyvinyl pyrrolidone as binder: TiO2 powder was taken in a crucible and heated up to 400°C for 30 minutes to remove the absorbed moisture and organic impurities. Then the powder was mixed with polyvinylpyrrolidone (PVP) in different concentrations. Polyvinylpyrrolidone (PVP), also commonly called polyvidone or povidone, is a water-soluble binder extracted from the monomer N-vinylpyrrolidone. Therefore, at the outset TiO2 films were made using TiO2 paste with different concentrations of poly(vinylpyrrolidone) as a binder to understand the effect of PVP. Then, Triton X-100, acetic acid and ethanol were used in different stages of the TiO2 paste preparation. The amount of each chemical used for making the TiO2 paste with different PVP concentrations was followed as per the literature procedure [10]. TiO2 powder mixed with PVP in different proportions was crushed using 2mL of ethanol in an agate mortar for 20min to avoid aggregation. After that, 0.2mL of acetic acid was added. Triton X-100 was used as a dispersing agent; subsequently ethanol was used to dilute the mixture. After thorough mixing, the mixture was concentrated by heating on the hotplate to obtain a viscous paste [10,11].

As shown in the Figure 1 the photovoltaic properties of TiO2 films in DSSC photoanode are usually influenced by the methods of TiO2 paste made. PVP was used as a binder to regulate the viscosity of the paste, inhibit the aggregation of TiO2 nanopowder and improve the mechanical stability and continuity of the sintered film. An optimal paste composition, suitable for superior dye adsorption to improve the DSSC performance was obtained. Even though PVP enables good adhesion of paste on the FTO, the dye absorption was found to be poor, because the film was forming non-porous surfaces in several places after the sintering.