Validated front contact grid simulation for GaAs solar cells under concentrated sunlight

In a common approach, the electric behavior of a solar cell is modeled by dividing it into smaller sub-circuits and solving the resulting network by a circuit simulator. In this paper detailed network simulations are presented for a GaAs single-junction solar cell. All resistive losses and losses influencing the diode saturation currents, such as recombination in the depletion region or at the perimeter are taken into account. With this model the maximum power point of a solar cell can be calculated for one-sun and for higher illumination intensities. The results were validated experimentally using suitable test structures. This includes solar cell devices with varying dimensions, grid finger spacing and lengths. An excellent agreement between theoretical and experimental results was obtained. The network simulation model allows determining the optimum size and concentration ratio at which a solar cell operates at its maximum efficiency. In the case of a GaAs single-jun ction solar cell this global efficiency maximum was found for an area of 1 mm2 and at a concentration ratio of 450 suns. Under these conditions the largest loss mechanisms are the finger shading with 36.1% and the emitter resistance losses with 21.5% of the total power losses