The distributed series resistance problem in solar cells

Abstract

In the classical literature on solar cells, the distributed sheet resistance of the emitter layer of a photovoltaic cell is treated by introducing an effective lumped series resistor. This model enables the fill factor loss for moderate sheet resistances to be calculated in a reliable way. For important sheet resistances, however, the lumped resistor model predicts a fill factor of 25%, a value much smaller than the real value. In the present paper a model is developed, which predicts a fill factor of around 36% for extreme values of the sheet resistance, i.e. a value much closer to accurate computer calculations and to experimental measurements. As a second advantage, the model yields the correct asymptotic behaviour for the forward current, i.e. an exp( qV 2akT ) law, whereas the lumped resistor model wrongly suggests a linear I( V) law for V → +∞.