Roll-To-Roll Electroplating for Photovoltaic Film Manufacturing

Abstract

A roll to roll system for forming an absorber structure for solar cells on a flexible foil as the flexible foil is advanced through units of the system and by unwrapping from a supply spool and wrapping around a take-up spool. Surface of the flexible foil is first conditioned in a conditioning unit to form an activated surface. A precursor stack including copper, gallium and indium layers is electroplated onto the activated surface by utilizing separate electroplating units for each layers. The precursor layer is reacted with at least one of Se and S in an annealing unit of the system.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to Provisional Application Ser. No. 60 / 862,164 filed on Oct. 19, 2006.FIELD OF THE INVENTION [0002] The present invention relates to methods and apparatus for preparing thin films of Group IBIIIAVIA compound semiconductor films for radiation detector and photovoltaic applications. BACKGROUND [0003] Solar cells are photovoltaic devices that convert sunlight directly into electrical power. The most common solar cell material is silicon, which is in the form of single or polycrystalline wafers. However, the cost of electricity generated using silicon-based solar cells is higher than the cost of electricity generated by the more traditional methods. Therefore, since early 1970's there has been an effort to reduce cost of solar cells for terrestrial use. One way of reducing the cost of solar cells is to develop low-cost thin film growth techniques that can deposit solar-cell-quality absorber materials on larg...

AI Technical Summary

Benefits of technology

[0030] The roll-to-roll processing approach of the present invention offers several advantages. Electrodeposition is a surface sensitive process. Defects in electrodeposited layers mostly originate from the surface they are plated on. Therefore, it is preferable to minimize handling of substrates in an electroplating approach. Surfaces to be plated need to be protected from physical contact, particles etc. that may later cause defectivity in the films deposited on such surfaces. Plating efficiency and the thickness uniformity of electroplated layers are also affected by the condition of the surface they are plated on. For example, electrodeposition of Cu, Ga or In on a chemically active, fresh surface is a much more repeatable process compared to electrodeposition on a surface that may be exposed to air, chemical vapors or, in general, to outside environment for varying amounts of time. In a roll-to-roll process all depositions are done in a controlled environment (enclosure for the roll not shown in figures) and the time between depositions are minimized unlike a batch process that requires several loading and unloading steps to deposit a stack of materials on a base. In the present roll-to-roll process a material, such as Cu is plated on a section of the base. The surface of this plated material is fresh and active after plating and after the water rinse step. Therefore, when section moves into the next plating bath, for example a Ga or In plating bath, within a few seconds or minutes, deposition initiates on this active surface. If the velocity of the foil base is constant, then the Ga or In plating always operates on the same Cu surface in terms of activity. This provides highly repeatable results in terms of thickness and uniformity of the In and Ga layers. Same is true for the Cu layer also.

Problems solved by technology

However, the cost of electricity generated using silicon-based solar cells is higher than the cost of electricity generated by the more traditional methods.

This technique was found to require very high plating current densities resulting in non-uniformities and problems of adhesion to the substrate as discussed in reference publications (Kapur et al., “Low Cost Thin Film Chalcopyrite Solar Cells, Proceedings of 18th IEEE Photovoltaic Specialists Conf., 1985, p.

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