Proton-beam-induced defect levels in $CuInSe2$ thin-film absorbers: An investigation on nonradiative electron transitions

Electron nonradiative relaxation through the proton-irradiation-induced defects in $CuInSe2$ solar cell material were investigated by using a piezoelectric photothermal spectroscopy (PPTS). Among the observed three peaks at 1.01, 0.93, and $0.84eV$⁠, it was concluded that the peak at $0.84eV$ was due to the proton-irradiation-induced defect. This is because this peak appeared after irradiation with the proton energy of $0.38MeV$ and the fluence of $1×1014cm−2$⁠. The peaks at 1.01 and $0.93eV$ were attributed to free band-edge exciton and intrinsic defect level, respectively. The intensities for the latter two peaks were not affected by the irradiation. Since the irradiation defect was clearly observed at room temperature, we concluded that the PPTS technique was a very sensitive tool to study the defect level in the irradiated semiconductor thin-film solar cell structures.