Comparative study of GaAs and CdTe solar cell under low-intensity light irradiance was carried out to study the cell device performance in response to the changed light irradiance intensity. For highly efficient GaAs solar cell, the series R-S, and the shunt R-P resistance were found to be low/high enough to have almost undetectable negative effect on the cell device performance at low-intensity light irradiance. The robust diode parameters guaranteed good cell performance at low-intensity light irradiance. An ideal logarithmic function was established to describe the variation of cell efficiency with light irradiance intensity for GaAs solar cell. For CdTe polycrystalline solar cell, the relatively large series resistance Rs and small shunt resistance R-P, compared to that of the GaAs solar cell, significantly decreased the cell fill factor. With increased light illumination intensity, both the diode ideality factor A and the reverse saturation current density J(o) were increased due to the high density of interface states at the CdS/CdTe junction. The comparative study and conclusions drawn in this work provide device fabrication improvement direction for the CdTe solar cell. (C) 2017 Elsevier Ltd. All rights reserved.