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Recombination and optical properties of wet chemically polished thermal oxide passivated Si surfaces

: Schwab, C.; Wolf, A.; Graf, M.; Wöhrle, N.; Greulich, J.; Kühnhold, S.; Kästner, G.; Biro, D.; Preu, R.


IEEE Journal of Photovoltaics 3 (2013), Nr.2, S.613-620
ISSN: 2156-3381
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Oberflächen - Konditionierung; Passivierung; Lichteinfang; Industrielle und neuartige Solarzellenstrukturen

Silicon solar cells typically feature textured surfaces on the front side to increase light absorption. An unwanted side effect of the texture is an increase in surface recombination compared with smoother surfaces. On the rear side of the solar cell, light absorption is not an issue; therefore, planar surfaces are used to decrease surface recombination. In processing, a planar surface can be achieved by wet chemical single-side etching of previously textured surfaces, resulting in a smoothed rear surface. This study investigates surface passivation of these chemically polished surfaces in dependence on the degree of smoothness. Surface passivation is achieved by thin thermally grown silicon oxides. Special focus is set on injection dependence and the influence of postmetallization annealing. Measured optical properties of different surfaces are compared with different optical simulation models. Finally, recombination and optical properties are connected to solar cell performance of fabricated passivated emitter and rear cells.