The Influence of Temperature and Frequency on the Optimal Dimensions of the Base of a Quantum Well Photocell (AlGaAs/GaAs)

Abstract

Optimising the thickness of the base is a key parameter in the design of AlGaAs/GaAs heterostructure quantum well solar cells, as it determines the trade-off between the absorption of incident photons and the collection of photogenerated carriers. In this study, the photocurrent density is determined under dynamic conditions as a function of the recombination rate at the junction, for different values of temperature and modulation frequency. An analysis of the behaviour of this quantity during a short circuit, where the photocurrent density tends towards a constant value independent of the recombination rate (Sf), leads by cancelling out its first derivative with respect to the recombination rate to a quadratic equation. Solving this equation yields the analytical expressions for two characteristic recombination rates at the rear surface, denoted (Sb1 and Sb2), the intersection of which defines an inflection point associated with the optimum base thickness. The parametric study of (Sb1 and Sb2) as a function of frequency and temperature thus makes it possible to determine, for each (T, f) pair, the base thickness that provides the best compromise between diffusion and recombination of minority carriers. Based on these results, calibration relationships linking the optimum thickness to temperature and frequency are proposed, providing a useful predictive tool for the design and optimisation of quantum well structures intended for high-efficiency photovoltaic applications.