Direct detection of carrier traps in Si solar cells after light-induced degradation

Abstract

In solar cells fabricated from boron-doped Cz-Si wafers minority and majority carrier traps were detected by deep level transient spectroscopy (DLTS) after so-called "light-induced degradation" (LID). The DLTS signals were detected from mesa-diodes with the full structure of the solar cells preserved. Preliminary results indicate metastable traps with energy levels positioned at EV + 0.37 eV and EC - 0.41 eV and apparent carrier capture cross-sections in the 10-17-10-18 cm2 range. The concentration of the traps was in the range of 1012-1013 cm-3. The traps were eliminated by annealing of the mesa-diodes at 200 °C. No traps were detected in Ga-doped solar cells after the LID procedure or below the light protected bus bar locations in B-doped cells.