F. Rousseau

Role of reactive species in processing materials at laboratory temperature by spray plasma devices

Processing the aerosol of metal salts in non-equilibrium plasma represents a promising technique that combines the advantages of spray pyrolysis with the high reactivity of plasmas at nearlaboratory temperature in order to produce mixed-oxides and perovskite materials. The aim of this paper is to describe the principles of this new technique and to present the various applications and latest developments. This technique’s capacity to deposit various mixed metal oxides with precise stoichiometry is demonstrated. It is shown that oxidant plasma species play a key role in the chemical transformation of starting materials into oxides at laboratory temperature, while the configuration of the reactor determines the morphology and texture of the deposited layers. Two different reactor configurations are presented. The porous layers of LaxSr1−xMnO3 as the cathode for fuel cells were synthesised in a wave shock reactor configuration, while nanostructured ZnO-Al layers to form a transparent conductive cathode for photovoltaic cells were deposited in the spray plasma reactor of the latest generation for this technique. The experimental results emphasise the role of plasma species in the rate of chemical reactions and in the chemical composition of the deposited layers.

Study of a low power plasma reactor for the synthesis of doped and undoped zinc oxide used as the window layer in CIGS solar cells

The Low Power Plasma Reactor is an original process which allows a rapid deposition of ZnO thin films with calibrated thickness. The deposition is performed by the spraying of an aqueous precursor solution in cold plasma. The final optimizations allow high average growth rates reaching 0.6 nm/s. Characterization of films (XRD, FTIR, Transmittance, resistivity measures) reports the expected crystallinity, composition, the needed transparency and a calculated optical gap value ranging between 3.2-3.3 e V. The resistivity of layers was studied to be decreased in order to improve the electric properties of thin films. The performances of Cu(In,Ga)Se2 solar cells with a plasma sprayed intrinsic ZnO (i-ZnO) layer showed efficiencies around 15% (equivalent value with classic sputtered i-ZnO).