Significance of bias light spectral composition for accurate measurement of silicon solar cell spectral response

To determine solar cell spectral response (SR) at working illumination conditions, measurements of the signal generated by a modulated spectral beam imposed on a DC short circuit current due to white light bias with different irradiances are typically used. In practice the bias light source does not usually simulate the sun's spectrum. However the effect of the spectral composition of the bias light on the SR measurements is not known. The goal of this work is to find empirical evidence of the effect of the bias light spectrum on measured Si solar cell SR. The bifacial solar cell samples used for this study can be characterized by: significant dependence of SR on injection level, and different spatial distribution of bulk recombination centers. The sources of bias light were chosen based on their spectral composition which controls the depth distribution of carriers generation during SR measurements. An incandescent halogen lamp with a variable power supply voltage with/without optical neutral filters and ∼ 617 nm light emitting diodes were used. As the measurements show, the spectrum of the white bias light emitted by a tungsten filament of color temperature in the range 2400 – 3900 K is not a critical factor in SR measurements. However, use of highly absorbed bias light can result in a different SR compared to that measured with white light bias.