Control and passivation of V-Se defect levels in H2Se-selenized CuInSe2 thin films

In this study, we investigated the dominating intrinsic defect levels in Cu InSe2 by means of temperature- and excitation-dependent steady-state photol uminescence (PL. The polycrystalline thin films were prepared by rapid ther mal treatment of metallic alloys in H2Se-Ar. Attention was mainly focused o n the influence of post-growth treatments tin Ar-H-2 and O-2) on the defect structure of these films. The PL spectra of slightly In-rich as-grown film s were dominated by a donor-acceptor pair transition at 0.92 eV. The defect levels are ascribed to V-Cu and V-Se and their activation energies have be en determined to be 45 and 95 meV, respectively. Post-growth treatment in A r-H2 resulted in a shift of these peaks to higher energies and a significan t increase in the intensity. In contrast, annealing in O-2 resulted in a sh ift of the peak to lower energies and to a dramatic reduction in intensity, compared with the as-grown samples. These effects were also found to be re versible. The change of the PL spectra on oxygen and hydrogen annealing is explained by the change of the density of V-Se defects. This is explained b y a model in which oxygen can occupy a V-Se site owing to coordinatively un saturated In at the grain boundaries. The V-Se concentration and therefore the device quality of these CuInSe2 thin films can thus be controlled eithe r by a post-growth annealing step or during the growth process itself.