Basic parameters of a three-layer electrorefining process for solar grade silicon

Solar grade silicon for the production of solar cells is currently supplied as off-grade material that does not meet the requirements of the semiconductor industry. This high-purity silicon is produced by the so-called Siemens process, a cost and energy-intensive production process. Consequently, the costs of solar cells remain comparatively high as up to now, there is no industrial production route that directly yields solar grade silicon. Hence, the main task of this thesis is the identification of basic parameters of a three-layer electrorefining process for the production of solar grade silicon at a targeted working temperature of 1450 °C. In the experimental part, the necessary materials for the three layers of anode, electrolyte and cathode are designed because the entire process has to be created. Moreover, a suitable refractory material for the three-layer system and appropriate electrode materials for contacting both the anode and the cathode are identified. Electrochemical measurement techniques such as linear sweep voltammetry, cyclic voltammetry and chronoamperometry are furthermore used to determine different electrochemical properties of the investigated layers. In order to evaluate the potential of the three-layer electrorefining of silicon, electrochemical measurements in the corresponding two-layer systems of anode-electrolyte and electrolyte-cathode are carried out as well. It is hereby proven that the ohmic drop over the interfaces is comparatively small and hence that a flow of electrical current is almost unhampered possible. Consequently, a mass transport of silicon ions from anode to cathode and subsequently an electrolytic refining process seems feasible. A validation of this process in a larger scale is undertaken by the industrial partner of the project. Up to now, the obtained results are promising and it is likely that this electrolytic production route can become an alternative process for a cheaper provision of solar grade silicon for the manufacturing of solar cells.