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For optimum performance of solar cells featuring a locally contacted rear surface, the metallization fraction as well as the size and distribution of the local contacts are crucial, since Ohmic and recombination losses have to be balanced. In this work we present a set of equations which enable to calculate this trade off without the need of numerical simulations. Our model combines established analytical and empirical equations to predict the energy conversion efficiency of a locally contacted device. For experimental verification, we fabricate devices from float zone silicon wafers of different resistivity using the laser fired contact technology for forming the local rear contacts. The detailed characterization of test structures enables the determination of important physical parameters, such as the surface recombination velocity at the contacted area and the spreading resistance of the contacts. Our analytical model reproduces the experimental results very well and correctly predicts the optimum contact spacing without the use of free fitting parameters. We use our model to estimate the optimum bulk resistivity for locally contacted devices fabricated from conventional Czochralski-grown silicon material. These calculations use literature values for the stable minority carrier lifetime to account for the bulk recombination caused by the formation of boron-oxygen complexes under carrier injection

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1 Introduction The emitter of crystalline silicon solar cells is usually formed in mass production by flowing POCl 3 through a furnace, which creates a phosphorussilicate glass (PSG) layer at the surfaces of the p-type wafers, from where phosphorus diffuses into the silicon. Only very recently has the phosphorus concentration in the PSG layer been measured [1]. It is firstly substantially higher than the solubility of P in Si, and secondly it changes only slightly with POCl 3 flow or other process parameters such as temperature. In this paper, a consequence of these recent findings is identified: the high flow of P into Si causes a far larger amount of (extrinsic) Shockley-Read-Hall (SRH) recombination than (intrinsic) Auger recombination. This implies that todays emitters are not Auger limited, but are instead SRH limited, and explains the large discrepancies between measured and simulated saturation current densities, J 0e , observed persistently over the last two decades in industrially fabricated Si solar cells. This clarification correlates strongly with recent cell efficiency improvements by reducing inactive phosphorus