On the spectral response measurement of multijunction solar cells

This work presents particular aspects dealing with the measurement of the spectral response on multijunction solar cells, a tricky and somewhat complex issue. Here, we demonstrate the development of a facility to measure spectral response (SR) between 300 nm and 1900 nm on III-V solar cells for space applications, particularly oriented to measure large area triple junction (3J) InGaP/GaAs/Ge cells, although it can be utilized to measure other types of devices. The equipment is based on narrowband interference filters and a novel and low cost approach of two dichroic lamps as bias light source, used to select the subcell to be measured using suitable bandpass filters, whereas a simple incandescent halogen lamp is used to generate the monochromatic light beam. The signal is measured on an appropriate resistance inserted in a serial circuit using a lock-in amplifier. Measurement is fully automated, which allows operator independent results. Detailed studies performed on bias spectrum conditions and voltage biasing for these types of cell are showed, as well as a thorough treatment of the uncertainty and measurement error sources. Preliminary SR measurement results demonstrate the good performance of this setup. As an example, the results of the application of this setup to analyze radiation damage induced by 10 MeV protons are shown.