Optimization of silicon solar cell design for use under concentrated sunlight

Abstract
For efficient operation under concentrated sunlight, solar cells must be optimized in terms of the collection efficiency and series resistance. At low concentrations, collection efficiency is more important, however, series resistance becomes increasingly important at high intensities ultimately limiting the device output. At a given intensity a tradeoff between these properties results in optimum performance. The computations includes losses from recombination, series resistance, contact coverage, and reflection. There are nine design parameters that were optimized; junction depth, thickness of anti-reflecting coating, width of grid strips, width of contact strips, separation of grid strips, length of grid strips, wafer thickness, and doping concentration of both sides of the junction. An optimization computer program was used to find the optimum design by employing a sequential search technique. An example is given for the optimum design of a silicon solar cell operating under an incident intensity of 9 W/cm2with active and total area efficiencies of 12.8 and 11.6 percent. Active area efficiencies as high as 17.8 percent are possible but with lower total area efficiencies. The effect of each of the nine parameters on device performance is presented. The theory was confirmed by fabricating and testing experimental devices. When corrected for temperature, the theory accurately predicts device performance to intensities of 50 suns (5.2 W/cm2).

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