Photoinduced current transient spectroscopy of defect levels in CuInSe2 and CuGaSe2 epitaxial and polycrystalline layers

Abstract

Photoinduced current transient spectroscopy (PITS) was used to study defect level spectra in Cu(In,Ga)Se2 chalcopyrite compounds used as absorbers in solar cells. We show that for CuGaSe2 PITS provides similar results as modulated photocurrent (MPC) spectroscopy, while in the case of CuInSe2 much better results are achieved with PITS due to the lack of background illumination necessary in the MPC. We found four defect levels common for both CuInSe2 and CuGaSe2 (three electron traps with one of them acting as a recombination centre and one very deep hole trap). All those deep levels were observed both in the epitaxial and polycrystalline samples so we attributed them to bulk structural defects.