Spectral response measurement of tandem modules

Abstract

The measurement of the spectral photo current of stacked solar cells using semiconductor materials with a lower bandgap material as the bottom cell and a higher bandgap material as the top cell, like the a-Si/uc-Si tandem solar cell, is needed to conduct high accurate nominal power measurements. The prediction of the annual energy yield of tandem cell concepts also depends on the current matching of the top and bottom cell at standard STC spectra, not only on the STC nominal power. Thus the customers have to know if the optimal current matching is reached at STC AM 1.5 spectra or at a spectrum shifted more to the red or to the blue. The spectral photo current measurement is a standard on the small square centimeter cell area, especially in research labs, mostly using monochromatic light and colored bias light. In this paper we report the successful measurement results of the photocurrent of large area square meter sized tandem modules at wavelength between 400 and 1100nm using 50nm bandpass filters and blue and infrared LED bias light. Additionally a new measurement method is successfully introduced to measure changes of the short circuit current of a tandem modules using a dynamic changing LED bias light together with STC flasher light during a few milliseconds or without flasher light. Analyzing the characteristics of the measured tandem module current within a few milliseconds it can be clearly seen if the module is top or bottom limited, even the degree of mismatch is able to be characterized precisely. Thus the later analysis has the potential to be implemented as a standard measurement procedure within the end test of a tandem module production line. Even existing standard flasher may be adapted, without changing the existing flasher light source, by mounting the additional LED bias light source to perform different characteristics of dynamic bias light.