Digital noise spectroscopy system and its application to solar cells

A creative combination of hardware and software has produced a new digital noise spectroscopy system. It provides a low cost, user-friendly, rapid, non-destructive and non-invasive capability to acquire noise spectra. Thorough testing showed that the system has a very low noise floor (3×10^-17 V²/Hz), as well as a broad frequency range (1 to 10⁵ Hz). The system has been applied to survey solar cells with a variety of materials and geometries. In particular, we acquired noise spectra from (a) single junction Si and GaAs solar cells and (b) triple-junction solar cells that were heavily irradiated with 3 MeV protons. The results should make it possible to determine characteristics of solar cells, for example, trap densities, from the spectra. Later work will compare noise spectroscopy with normal means of characterizing solar cells.