Analyzing the effects of laterally varying emitter sheet resistance in combination with contact resistance
In this work the effect of a laterally varying emitter sheet resistance on IV characteristic parameters is analyzed for an industrial like solar cell structure by distributed circuit simulations. The influence of the emitter sheet resistance on contact resistance is considered by an experimentally determined dependence for screen printed contacts on shallow emitters with high surface doping concentration. Production solar cells with flaws in the distribution of the emitter sheet resistance as distinguished from e.g. cell structures with selective emitters are analyzed. In these cases the efficiency of a solar cell with laterally inhomogeneous emitter sheet resistance is decreased compared to the one of a solar cell with laterally homogeneous emitter sheet resistance with the mean value of the distribution. Nevertheless for solar cells with e.g. an emitter inhomogeneity of +/-20% on 20% of the cell area the decrease of efficiency is less than 0.15% relative in case of a moderate dependence between contact resistance and emitter sheet resistance. Hence a laterally inhomogeneous emitter influences the solar cell efficiency primarily by its effect on the contact formation during the firing step. Further effects are negligible.