The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Processing of High Efficiency Silicon Solar Cells
Jaakko Härkönen
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium S4 at Helsinki University of Technology on the 9th of November 2001 at 12 o'clock noon.
Dissertation in PDF format (ISBN 951-22-5695-9) [5464 KB]
Dissertation is also available in print (ISBN 951-22-5680-0)
Abstract
Fabrication technology of high efficiency silicon solar cells has been studied in this work. Process development work has been carried out since 1997 within a project "Development of high-efficiency low-cost silicon solar cells", which was funded by TEKES, Fortum Advanced Energy Systems and Okmetic Ltd. Co - operation with photovoltaic research group of Fortum Surface Chemistry has been very close during the project. Target of this project is to demonstrate by low cost processing technologies, the feasibility of the fabrication of solar cells with a conversion efficiency as high as possible.
Three different solar cell configurations and their processing technologies are discussed in this content. The solar cells processed by industrially feasible methods on the low cost multicrystalline silicon wafers are the main focus of this work. Solar cells made of single crystalline silicon are studied in order to reveal the capability of the fabrication process in scope of the conversion efficiency. The third cell technology is the devices made by Rapid Thermal Processing of silicon wafers. That topic has been studied because of its possible potential for excellent manufacturability.
Processing of the solar cells has been carried out in the clean room facilities of Microelectronics Center at HUT. In addition to device processing, a special issue in this project has been characterization of metallic impurities and defects in multicrystalline silicon material.
Minimization of unwanted impurities and defects as well as understanding their interactions is necessary when processing high performance devices. Process induced contamination sources has been charted by μPCD (microwave Photoconductive Decay) and SPV (Surface Photovoltage) measurements.
Other special issues in this thesis are investigation of passivation properties of PECVD grown Si3N4 films, optimization of emitter diffusion and Cr/Cu front contact metallization.
During three years, several hundreds of single and multicrystalline silicon wafers have been processed to solar cells. Best conversion efficiencies were 15,1 % (mc-Si), 16,4 % (c-Si) and 14,5 % (RTP mc-Si).
Keywords: solar cells, multicrystalline silicon, silicon processing, lifetime
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© 2001 Helsinki University of Technology
Last update 2011-05-26