Structural Optimization and Temperature-Dependent Electrical Characterization of GaAs Single-Junction Solar Cells

Abstract

This paper reports the structural optimization and the temperature-dependent electrical characterization of GaAs single-junction solar cells (SJSCs) based on the p+-n-n+ junction structure. First, the effects of the p+-Al0.9Ga0.1As window layer were investigated using illuminated current density-voltage (LJ−V) and photoreflectance measurements to determine the optimal structure of the SJSC. In addition, the thickness and the doping concentration of different layers, such as the p+-GaAs emitter and the n-GaAs base layers, were optimized, leading to the maximum efficiency (η = 21.53%). These results show that the device performance can be improved further when compared to the world record (η = 28.8%). Second, the capacitance-voltage (C−V) and the dark J−V characteristics of a GaAs SJSC with the optimal structure were investigated over the temperature range from 100 to 300 K. As the temperature was increased, both the junction capacitance at zero voltage (Cj0) and the carrier concentration in the active region (Nd) increased while the depletion width (W) and the built-in potential (Vbi) decreased due to purely thermal effects. Among the SC parameters obtained from the dark J−V curves, the ideality factor (n) decreased from 4.38 to 1.70 and the reverse saturation current density (J0) increased from 6.05 × 10 −12 to 4.26 × 10 −10 A/cm2 with increasing temperature. These values at 300 K were similar to those simulated theoretically and reported previously for high-quality GaAs junction diodes.