Photoluminescence Properties of Sodium Incorporated in CuInSe2 Thin Films

Abstract

CuInSe₂ films with Cu/In ratios of m=0.83–0.99 have been deposited on glass substrates by the co-evaporation method using a bi-layer process. The effects of sodium in these films have been investigated by comparing the electrical and optical properties of the films with and without the Na₂Se incorporation. Two donor-acceptor pair emissions, [D, A]_α at 0.89–0.94 eV and [D, A]_β at 0.84–0.87 eV, were typically observed in the photoluminescence spectra. The relative intensity of [D, A]_α to [D, A]_β was found to depend strongly on both the Cu/In ratio and Na incorporation. For the films with m=0.94, [D, A]_α was predominantly observed regardless of Na incorporation. For m≤0.90, [D, A]_β became dominant for the films without Na, while [D, A]_α remained as the dominant emission for the films with Na. A correlation between the prominence of [D, A]_α and resistivities below 2×10³ Ω· cm was found, suggesting a reduced compensation by suppressed Se vacancy donors due to the presence of Na.