Radiative recombination properties of near-stoichiometric CuInSe2 thin films

The properties of electronic defects and their relation to structural defects are of high relevance for CuInSe2 photovoltaic absorbers. Here, we use Raman scattering and steady-state photoluminescence to study the intrinsic optoelectronic properties of near-stoichiometric CuInSe2 samples with a lateral composition gradient around the Cu saturation point. Apart from a well-known shallow defect band at 0.97 eV, we also observe a deep defect band at 0.8 eV, which is not discernable in photoluminescence spectra at lower temperatures. The preparation of a laterally graded sample with a very precise relative composition range by in situ process control allows for a measurement of a significant decrease of the photoluminescence emission yield at the Cu-poor/Cu-rich transition on a very narrow composition scale. Possible assignments of the bands to structural point defects are discussed.