ICMCTF2011 Session G3: Atmospheric and Hybrid Plasma Technologies

The use of low-cost, high-volume inkjet printing technologies for the delivery of solution processed photovoltaic materials onto flexible substrates has shown great potential over bulky, rigid silicon technologies and is likely to be at the forefront of revolutionary solar cell manufacturing processes. The main advantages of inkjet printing over other commonly used deposition techniques lie in its high repeatability, pattern flexibility, and roll-to-roll compatibility. The ease of fabrication via low temperature evaporation and/or solution processing opens up a potentially wide market for these energy harvesting and storage devices to be integrated onto or into other applications such as textiles, composite and packaging materials.

However, the use of polymer-based flexible platforms raises some technical challenges related to poor adhesion between the substrates and the deposited materials, as well as the development of conformal, pinhole-free coatings. To overcome these issues, we employed atmospheric plasma technology to functionalize the surface of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) substrates prior to the subsequent coating with ZnO nanorods and CdSe nanoparticles, which act as photosensitive materials. The goal of this work is to investigate the contribution of the He-O₂ and He-H₂O plasma pretreatment step to the surface properties of PEN and PET. Towards this direction, we used contact angle goniometry, x-ray photoelectron spectroscopy and scanning electron microscopy to study the physicochemical changes of the plasma treated polymers. Results show improved hydrophilicity due to the grafting of oxygen-containing groups which are expected to participate in the formation of covalent bonds with the photoactive coatings. Also, we studied the effect of ink-jetting parameters, including drop volume, velocity, frequency, temperature, substrate translational speed, orifice/substrate offset distance, and others, on the microstructure of the deposited photoactive materials on the flexible substrates.

The source operates at a frequency of around 2.45 GHz with a maximum oscillator power of 30 W. The complete source module including electrode, resonator and microwave oscillator has a length of approx. 150 mm and a diameter of approx. 30 mm. The visible afterglow plasma flame has a diameter of approx. 1 mm and a length up to 5 mm. The plasma source works with ambient Air as well as with Oxygen, Argon, Helium, and Nitrogen.

Several procedures of microwave characterization including specialized calibration and de-embedding procedures are presented. Ignition voltages are measured as well as transient microwave plasma impedances during ignition which are important for the design of a stable and efficient oscillator.

Data are presented for several applications, e. g. for the surface activation of polymers. The possibilities of integration in manufacturing processes are discussed.

A focused ICP atmospheric plasma torch has been used for yttrium oxide (Y₂O₃) nanocoating to prolong lifetime of the immersed in a plasma etching chamber parts with the non-flat surfaces like showerheads holes, steps of focusing rings, etc. Although Y₂O₃ has a high melting point our torch can provide for injected nanoparticles enough residential time in a high temperature area to be completely melted , evaporated in and delivered inside of deep holes , trenches and the porous structures. Another application such a torch is developing the nano-structured arrays used for anti-reflective, anti-glare and light capturing surfaces. It is possible using simultaneously with yttrium oxide as precursor nanopowder of silicon oxide or other material with a low resistance to etching plasma to develop the large scale moth’s eye like repetitive arrays nanostructures with cones approximately 200 nm high and 200 nm apart. But it requests a fine focusing of the torch in combination with a precise motion of substrate and one by one injection of two precursors synchronized with motion.

The torch is sustained by two saddle-like ICP antennas with the different frequencies, i.e. 27.12 and 13.56 MHz. Each antenna comprises two or more spiral coils in a mirror position and in series or parallel connection. These coils are distributed with an angular uniformity and envelop a quartz tube of a plasma reactor. Such a design allows generation of a transversal RF field directed normally to axis of this reactor that broaden and lengthen the high temperature area. . A plasma fluid is fixed on the axis due to buoyancy in the centrifugal force field created by a swirling injection of a discharge gas and two sheath gases in clockwise and a counterclockwise directions . .Such a triple vortex stabilization provides intensive flow rotation and the pressure minimum on the axis and prevents approaching of plasma to the quartz tube. Nevertheless, such a torch is highly charged especially in area of a tip causing diffusing of the spot. We have developed a method of compensation of these charges that minimize such a spot. Behavior of an inductively coupled plasma torch with non-axial generation, mechanisms of balancing of saddle-like antenna coupling, dynamic of the vortex stabilization of the plasma fluid and gas focusing will be discussed.

1. Y.Glukhoy, I. Ivanov RF Atmospheric Plasma Systems for Nanopowder Production and Deposition of Nanocrystallines. AVS 53rd International Symposium, San Francisco, California, November , 2006 CA, USA.

2. Y.Glukhoy. Saddle-like ICP Antenna for RF Atmospheric Plasma Processes. AVS 56th International Symposium, San Jose, California, November , 2009 CA, USA.