Chalcogenide semiconductors via electrodeposition from ionic liquids


CALL: 2011

DOMAIN: MS - New Functional and Intelligent Materials and Surfaces


LAST NAME: Steichen



HOST INSTITUTION: University of Luxembourg

KEYWORDS: electrodeposition, ionic liquids, photovoltaics, chalcogenide, semiconductor, CIGS, thin film solar cells

START: 2011-12-01

END: 2013-11-30


Submitted Abstract

The main objective of the project is to demonstrate that the use of ionic liquids (IL) as deposition solvents can improve the electrodeposition process and the properties of chalcogenide compound semiconductors. ILs consist of a variety of organic cation-anion combinations, which present a large palette of optimization possibilities of the electrodeposition conditions. ILs exhibit intrinsically interesting properties, like a negligible vapour pressure, high thermal stability, and a large electrochemical window. The negligible vapour pressure and high thermal stability gives the opportunity to deposit at temperatures in excess of those possible in aqueous solution, allowing the deposition of more crystalline compound semiconductor films. The large electrochemical window allows the deposition of elements previously very difficultly or impossible to achieve in water, such as gallium. By changing the chemical composition of the IL, the adsorption of the solvent and the speciation of the metal ions will change, giving deposits with different morphology.Chalcogenide compound semiconductors such as Cu(In,Ga)Se2 (CIGS) are normally prepared in a two stage process, firstly the electrodeposition of a precursor containing all the metals with or without the chalcogen, and secondly an post-annealing in a chalcogen atmosphere between 300-500 °C to form the device quality semiconductor. Two hypotheses on the electrodeposition from ionic liquids for the fabrication of chalcogenide compound semiconductor thin films will be investigated:1) The electrodeposition from ionic liquids improves the structural and opto-electronic properties of the chalcogenide semiconductor materials.a) deposition temperature. By increasing the deposition temperature (T>150 °C), the crystallinity, as well as the defect structure of the as-deposited chalcogenide semiconductors can be improved. The need of post-annealing can be diminished or even eliminated.b) chemical composition of the ionic liquid. By modifying the chemical composition of the IL, the speciation and adsorption behaviour change, resulting in Ga-containing metal/metal alloy precursors with different morphology. The influence of the precursor on the annealed CIGS absorber layers will be investigated. 2) The electrodeposition from new cationic metal complex ionic liquids will enhance the rate of electrodeposition of chalcogenide semiconductor precursors.The synthesis of new cationic metal complex ionic liquids (M-IL) will be realised. Indium- and gallium-containing ILs will be synthesised. This allows an increase of the metal concentration in the bulk and at the electrochemical interface during the electrodeposition process. The electrodeposition rate of the metal precursor layer is enhanced and allows the development of a new, low-cost and rapid electrodeposition-annealing process for CIGS solar cell fabrication.

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