Investigating Sub-bandgap Spectral Effects in GaInP-on-Ge Solar Cells

There is a fundamental understanding in photo-voltaics that sub-bandgap light will not be absorbed in the solar cell and therefore will not affect the power generation. We have shown a novel phenomenon in which sub-bandgap illumination is required for good electrical performance in III-V solar cells on heterosubstrates. We investigate this effect in GaInP cells on Ge substrates with current-voltage measurements under varying spectra and irradiances. This has implications for device characterization, the development of solar cells both on heterosubstrates and for conditions lacking long-wavelength light, and the prediction of device performance under spectra that differ from the test conditions.