Analytic Efficiency Optimization of Solar Cells under Light Concentration in the Framework of the Single-Diode Model

Abstract

Herein, concentrating solar cells are modeled with two recombination active contacts and a recombination active light absorber in the framework of the one-diode model. The two contacts and the absorber contribute to a lumped series resistance and to a lumped recombination current. It is proven that varying the light concentration can be interpreted as iso-selectivity scaling of the cell's resistance and the cell's recombination. As a consequence of that, the optimal efficiency of a concentrator cell is found at maximum combined selectivity of the two contacts and the absorber. Herein, analytic formulas are derived that calculate the optimal contact areas and the optimal light concentration level for achieving an optimum efficiency. The resulting formulas express the efficiency in terms of the selectivities of each contact and the selectivity of the absorber. These equations are used to calculate the optimum contact area fractions and the optimum light concentration level for Si solar cells of various material qualities with screen-printed Al-doped contacts and n-type poly-Si contacts on oxide. The efficiency results of the novel analytic and a conventional numeric optimization agree to the expected level of accuracy.