VP Disp IPA 2730 X A New AEROXIDE® Fumed Titania Dispersion for Dye-sensitized Solar Cell Manufacture

Unlike solid state devices where the photo- collector and charge carrier functions are performed by one material (crystalline silicon metal), DSSCs separate the two functions. Fundamental to DSSCs is a tailor-made sub-pigmentary titania, used as raw material for the porous electrode.2 And key to the fabrication of an efficient porous electrode is screen-printing of inks or pastes from commercially available tita-nia powders, such as AEROXIDE® TiO2 P 25 fumed titania, that achieve near transpar-ent layers without cracking or peel-off from the semi-conductive glass substrate.3

Along with this careful macroscopic con-trol of the titania layers, the processing must also be watchful that material prop-erties such as surface area, pore size dis-tribution, and pore volume, crucial to the overall achievable solar light conversion efficiency, are not damaged.4

AEROXIDE® TiO2 P 25, well known for its high chemical purity and well defined physico-chemical properties such as sur-face area and unique phase structure, is widely used as a raw material for DSSCs.

However, handling AEROXIDE® Fumed Metal Oxides such as AEROXIDE® TiO2 P 25 requires sophistication due to the fineness and fluffy nature of the powder; so prod-ucts that simplify the incorporation of AEROXIDE® into a formulation or process technology clearly bring the potential of DSSC solar energy conversion that much closer to widespread commercial success.

To address such challenges, Evonik has added a new product to its broad portfolio of AERODISP® dispersions: VP Disp IPA 2730 X – the first dispersion of fumed titania in an organic solvent.

Dye-sensitized solar cells (DSSCs) increasingly attract academic and commercial interest as regenerative low-cost alternatives to conventional solid state devices. It has also been speculated that the DSSC approach has the potential to be a lower cost alterna-tive to conventional solar cells.1

Dye-sensitized Solar Cell configuration

A New AEROXIDE® Fumed Titania Dispersion for Dye-sensitized Solar Cell Manufacture

Glass

Glass

TCOPlatinum

Electrolyte

Dye

TCO

TiO2

VP Disp IPA 2730 X

By using an advanced dispersing techno-logy with equipment that imparts 1000 times the shear energy as standard disper-sion equipment, we are able to manufac-ture extremely fine particle metal oxide dispersions. These mondisperse, stable dispersions are identified by an extra “X” at the end of the product name.

VP Disp IPA 2730 X is a low viscosity dispersion, filled with 30 wt% fumed titania, in isopropanol, and as such it is recommended to be used as the titania source (master-batch) for the production of titania pastes.

Advantages for Titania Paste ProducersWhen making pastes of titania, including AEROXIDE® TiO2 P 25, solvents (water and alcohols) often induce the particles to aggregate thus yielding non-reproducible results in long-term experiments. One factor, critical to overcoming this tendency and allowing the development of titania pastes for the mass production of DSSCs, is the narrow particle size distribution offered with VP Disp IPA 2730 X. The following experiments demon-strate the benefits:

Application ExampleGeneral Conditions – The rheology of the titania dispersions was adjusted with ethylcellulose (ETHOCEL™ 45). The resulting “pastes” were applied with a doctor blade to a glass plate, dried at room tem-perature and sintered at 500°C for ca. 1 hour. All samples exhibited good adhesion to the substrate. Resulting dry film thickness was approximately 12 µm.

Extremely Fine Dispersions by Unique Dispersion Technology

Sample 1 Paste composition – 20% AEROXIDE® TiO2 P 25 with standard dispersion tech-nology (Rotor/Stator):

Sample 2 Paste composition – 20% Fumed titania from VP Disp IPA 2730 X and simple mixing (no dispersion required).

AEROXIDE® TiO2 P 25, dispersed with standard dispersion technology. Typical results may include: • Opaque films • Large pores and a less dense layer • Aggregation of particles

VP Disp IPA 2730 X leads to dramatically improved film properties: • Dense, very regular layers • Narrow pore size distribution • High transparency

Figure 2 exhibits the shift toward a very narrow pore size distribu-tion seen for a paste made with VP Disp IPA 2730 X vs. starting with AEROXIDE® TiO2 P 25 powder:

Figure 2Comparison of pore size distributions ......between sample 1 and sample 2

2,5

2,0

1,5

1,0

0,5

0 1 10 100 1000

Pore Diameter/nm

Sample1 Sample2

Diff

eren

tial P

ore

Vol/

ml/

g*dl

ogD

To further investigate the advantages of starting with VP Disp IPA 2730 X, please contact Evonik in order to initiate the sampling process. Free samples in 500 ml packaging are available at your regional contact.

Please note: Developmental products are labeled with the prefix VP. While currently purchasable in commercial quantities, future avail-ability should be verified.

References:

1. Michael Grätzel, “Review: Dye-sensitized solar cells,” J. Photochemistry and Photobiology C: Photochemistry Reviews, 4 (2003) 145-1532. Anders Hagfeldt, Gerrit Boschloo, Licheng Sun, Lars Kloo, and Henrik Pettersson, “Dye-Sensitized Solar Cells,” Chemical Reviews, 110 (2010) 6595-66633. Hongyan Bi, Liang Qiao, Jean-Marc Busnel, Valerie Devaud, Baohong Liu, and Hubert H. Girault, “TiO2 Printed Aluminum Foil: Single-Use Film for a Laser Desorption/Ionization Target Plate,” Anal. Chem. 81 (2009) 1177-11834. Wei Shao, Feng Gu, Chunzhong Li, and Mengkai Lu, “Highly Efficient Dye-Sensitized Solar Cells by Using a Mesostructured Anatase TiO2 Electrode with High Dye Loading Capapcity,” Ind. Eng. Chem. Res. 49 (2010) 9111-9116

Characteristic physico-chemical data

Properties and test methods Unit Value

TIO2-contentbased in ignited material

wt.% 30±1

ViscosityMeasured according to DIN EN ISO 3219 at a shear rate of 100s-1

mPa s ≤ 1000

Mean aggregate sized-50 value

nm≤ 100

Density20°C g/cm3 1.14

The data represents typical values (no product specification)

DisclaimerThis information and any recommenda-tions, technical or otherwise, are present-ed in good faith and believed to be cor-rect as of the date prepared. Recipients of this information and recommendations must make their own determination as to its suitability for their purposes. In no event shall Evonik assume liability for damages or losses of any kind or nature that result from the use of or reliance upon this information and recommenda-tions. EVONIK EXPRESSLY DISCLAIMS ANY REPRESENTATIONS AND WAR-RANTIES OF ANY KIND, WHETHER EXPRESS OR IMPLIED, AS TO THE AC-CURACY, COMPLETENESS, NON-IN-FRINGEMENT, MERCHANTABILITY AND/OR FITNESS FOR A PARTICU-LAR PURPOSE (EVEN IF EVONIK IS AWARE OF SUCH PURPOSE) WITH RESPECT TO ANY INFORMATION AND RECOMMENDATIONS PROVID-ED. Reference to any trade names used by other companies is neither a recom-mendation nor an endorsement of the corresponding product, and does not im-ply that similar products could not be used. Evonik reserves the right to make any changes to the information and/or recommendations at any time, without prior or subsequent notice.

AEROXIDE® is a registered trademark of Evonik Industries or its subsidiaries.

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