Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

The performance of many silicon devices is limited by electronic recombination losses at the crystalline silicon (c-Si) surface. A proper surface passivation scheme is needed to allow minimizing these losses. The surface passivation properties of amorphous hydrogenated silicon (a-Si:H) on monocrystalline Si wafers are investigated here. We introduce a simple model for the description of the surface recombination mechanism based on recombination through amphoteric defects, i.e. dangling bonds, already established for bulk a-Si:H. In this model, the injection-dependent recombination at the a-Si:H/c-Si interface is governed by the density and the average state of charge of the amphoteric recombination centers. We show that with our surface recombination model, we can discriminate between the respective contribution of the two main mechanisms leading to improved surface passivation, which is achieved by (a) the minimization of the density of recombination centers and (b) the strong reduction of the density of one carrier type near the interface by field effect. We can thereafter reproduce the behaviors experimentally observed for the dependence of the surface recombination on the injection level on different wafers, i.e., of both p and n doping type as well as intrinsic. Finally, we are able to exploit the good surface passivation properties of our a-Si:H layers by fabricating flat heterojunction solar cells with open-circuit voltages exceeding 700 mV. © 2007 The American Physical Society

Modulating the field-effect passivation at the SiO2/c-Si interface: Analysis and verification of the photoluminescence imaging under applied bias method

acceptedVersio

Modulating the field-effect passivation at the SiO 2

acceptedVersio

Replacement of Silver in Silicon Solar Cell Metallization Pastes Containing a Highly Reactive Glass Frit: Is it Possible?

AbstractMassive savings in silicon solar cell production could be achieved by replacing the costly Ag in front side metallization pastes against cheaper metals like Ni or Zn. Regarding the attempt to split the metallization process up into a two step process, first printing a paste containing Ni or Zn instead of Ag for contact formation and second printing a conducting paste containing e.g. Cu, this work is restricted to the investigation of the contacting paste. Simple pastes containing only Ni or Zn respectively, rudimentary glass frit, organic binder and solvent were tested on wafers with a low resistivity emitter using various fast firing profiles and annealing. Our first attempts using Ag compatible frits have shown that it is possible to create a contact to Si yet it is significantly worse than with comparable silver pastes. SEM measurements of the contact area after selective metal/glass etch have shown a strong Si etching by the investigated pastes and only insufficient crystallite formation. This explains the reduced open circuit voltage, pseudo fill factor and the high contact resistivity measured on the cells. Our investigations show that it is very hard to exchange Ag by another metal without fundamentally changing the paste formulation and/or the firing conditions