Clean Technology 2009

Electrostatic Printing og Nano-Particles for Photovoltaic Applications.

R.H. Detig
Elextrox, US

Keywords: electrostatic coating, nano-particles, liquid toners


ELECTROSTATIC PRINTING OF NANO PARTICLES FOR PHOTO-VOLTAIC APPLICATIONS; BY: Electrox Corporation I INTRODUCTION: The new generation of solar cells will be either a dyed inorganic cell ( the dye sensitized solar cell, DSSC; or the polymer PV cell, or hybrids combinations of the two. These can be printed, for the most part like documents from a copy machine or laser printer. A typical Xerox Docutek high volume copier produces documents for 2.5 cents per page, less the cost of the paper. There is a huge manufacturing cost saving opportunity here! The two important 3rd generation technologies for solar cells are the dye sensitized cells and the polymer cells. II Dye Sensitized Solar Cells: Dye sensitized cells are now demonstrating efficiencies of 10 % and are expected to reach 15 % by 2015. At least half a dozen firms will introduce cells within the next two years. The dyed cell consists of a transparent cathode coated with a 10 micron layer of TiO2 nano-particles, which is then dyed with an organic dye. A thin layer of an ionic conducting material is placed between this dyed layer and the anode. Initially this was a liquid iodide solution but ionic gel materials, which are printable, have replaced the liquids. Electrostatic printing of thick layers, 10 to 12 microns, of pigment particles, is an ideal task for this technology. If the particles are say 50 nm in diameter, this implies a layer of 400 to 500 particles. To make such a layer, free of mud cracking, using traditional inks is a formidable task. We have printed nano-powders of ZnO and TiO2 dispersed in a non-polar solvent that have as little as 0.1 to o.01% other process burden materials on their surfaces. They can be coated on conductive surfaces like ITO coated glass and polymeric film III Organic Photo Voltaics: This year two American companies are introducing organic photovoltaics panels with 6 % efficiency. These are printed, in air, on light weight flexible films. The next generation of this technology will be the hybrid solar cell, the organic cell with a thin layer of inorganic photo active particles of the cathode. These particles include; TiO2, ZnO, fullerenes, C-80 modified (Tri-Meta Spheres- Luna Nanoworks Inc.), CNT’s, quantum dots and other nano particles. These particles need to be coated or printed in thin layers, even mono-layers but they must be contiguous. For reduced manufacturing costs plasma, CVD, sputtering processes, etc. are not within budget. Electrostatic printing of nano-particles from liquid dispersions, i.e. liquid toners; is a prime candidate to be the dominant technology. APPENDIX I: Electrographic manufacturing technology, i.e. using electric fields to create graphics or images has many advantages over traditional printing or ink jet printing technologies: 1.) Liquid toners have a high fraction of useful material (the metal, glasses, phosphors, etc.) vs. inks of all kinds. Inks typically are in the 25-40% range, of functional fraction materials, while ink jet inks are in the 10% range, toners in the 90+% range. 2.) Toners can handle a broad range of particle sizes (10 nanometers to 1000 micron, 1mm, 10000:1) and densities (1 to 20) 3.) The use of electric fields allows one to “align” long thin particles along the direction of the field. Interesting things can be done with the effect. Long, thin particles can be “chained” or self assembles between two electrodes. This constitutes a high performance field effect transistor or a high surface area chemical sensor, or “sniffer”. 4.) Finally electric fields allow one to produce uniform coatings of both fine particles (50 nano meters) and large heavy particles (50 microns, density of 10.0). This is useful to: 1.) The solar cell industry 2.) The battery, fuel cell electrodes, etc. 3.) Super capacitor electrodes. In other words, we can image nano particles, carbon nanotubes, graphenes, fullerenes (Bucky-balls), etc without the huge burdens associated with traditional inks.
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