Investigation of thin aluminium films on the rear of monocrystalline silicon solar cells for back surface field formation

The trend to thinner crystalline silicon wafers in the production of silicon solar cells instigates a re-evaluation of the back surface field (BSF) formation. Aluminium layers, whose thickness is typically over 10 /spl mu/m, are commonly used for BSF formation. Such thick films, however, cause sever...

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Published inConference Record of the Twenty-Ninth IEEE Photovoltaic Specialists Conference, 2002 pp. 118 - 121
Main Authors Hartley, O.N., Russell, R., Heasman, K.C., Mason, N.B., Bruton, T.M.
Format Conference Proceeding
LanguageEnglish
Published Piscataway NJ IEEE 2002
Subjects
Aluminum
Applied sciences
Crystallization
Energy
Exact sciences and technology
Natural energy
Photovoltaic cells
Photovoltaic conversion
Production
Semiconductor films
Silicon
Solar cells. Photoelectrochemical cells
Solar energy
Surface morphology
Surface structures
Surface texture
Thick films
Crystalline material
Silicon solar cells
Back surface
Aluminium
Thin film
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Summary:The trend to thinner crystalline silicon wafers in the production of silicon solar cells instigates a re-evaluation of the back surface field (BSF) formation. Aluminium layers, whose thickness is typically over 10 /spl mu/m, are commonly used for BSF formation. Such thick films, however, cause severe warping on thin solar cells (<250 /spl mu/m). This study investigates the use of thin Al films of between 0.1 and 2.0 /spl mu/m and focuses on the aluminium/rear surface structure after sintering in a mixed nitrogen and oxygen gas atmosphere at temperatures between 820/spl deg/C and 995/spl deg/C. It is shown that the rear surface morphology has a strong influence on the reaction of Al with Si. Secondary electron and focused ion beam microscopy reveal that thin Al layers form Al islands on smooth surfaces but the Al agglomerates at the apex of pyramids when the surface is textured. In both cases the Al dissolves the Si rear surface inhomogeneously. The structural results are correlated with electrical measurements of laser grooved buried contact solar cells. The correlation shows increasing short circuit current with increasing Al film thickness. The results are used to explain deviations of the standard theory of the Al:BSF formation when using thin Al films.
ISBN:9780780374713
0780374711
ISSN:1060-8371
DOI:10.1109/PVSC.2002.1190470