Surface passivation schemes for high-efficiency n-type Si solar cells

An effective passivation on the front side boron emitter is essential to utilize the full potential of solar cells fabricated on n‐type silicon. However, recent investigations have shown that it is more difficult to achieve a low surface recombination velocity on highly doped p‐type silicon than on n‐type silicon. Thus, the approach presented in this paper is to overcompensate the surface of the deep boron emitter locally by a shallow phosphorus diffusion. This inversion from p‐type to n‐type surface allows the use of standard technologies which are used for passivation of highly doped n‐type surfaces. Emitter saturation current densities (J0e) of 49 fA/cm2 have been reached with this approach on SiO2 passivated lifetime samples. On solar cells a certified conversion efficiency of 21.7% with an open‐circuit voltage (Voc) of 676 mV was achieved. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) The Letter reports on surface passivation of n‐type Si solar cells. As it is more difficult to achieve a low surface recomination velocity on highly doped p‐type surfaces, the presented aproach is to overcompensate the surface of the deep boron emitter locally by a shallow phosphorus diffusion. This inversion from p‐ to n‐type allows the use of standard technologies for the passivation of highly doped n‐type surfaces.