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We verify a fast and simple analytical model for locally contacted rear surface passivated solar cells by three dimensional numerical simulations. For low level injection conditions the analytical model shows good agreement with the numerical results. For intermediate injection levels and for the injection dependent bulk lifetime in oxygen contaminated silicon, the present analytical model deviates from the numerical results. The accordance clearly improves when including injection dependent recombination and conductance in the analytical model. For intermediate to high injection levels, it is crucial to implement additional corrections for injection effects, being emphasised by the low recombinative front side and bulk material of the device structure investigated in this work. When accounting for these deviations from low level injection, analytical modelling turns out being a fast way to predict the optimum contact spacing as well as the electrical parameters of locally contacted rear surface passivated solar cells even for intermediate injection conditions

Double side collecting silicon solar cells such as the emitter wrap through and the both sides contacted and collecting concept are one possibility to maintain high efficiencies even on low lifetime material. To investigate the intrinsic advantages and limitations of this concept we use the solution of the continuity equation under low level injection conditions for a double side collecting (n + pn + ) and a single side collecting (n + pp + ) solar cell. In general, compared to the single side collecting structure, the double side collecting structure yields the highest advantages concerning the roduct of the short circuit current density and the open circuit voltage Jsc·Voc on highly doped material with diffusion lengths in the range of half the cell thickness. A realistic calculation of the fill factor of such devices is done using two dimensional numerical simulations. It is shown that a major reduction of the fill factor is caused by laterally varying voltage induced non-generation losses and ohmic losses, both caused by the majority carrier flow in the base. Electro- and photoluminescence images verify and illustrate the lateral voltage distribution under different illumination levels and terminal voltages.