THE THIN FILMS OF Alq3, DCM, AND ITS DERIVATIVES REFRACTIVE INDEX MANIPULATION

Ivan Karbovnyk, B. Turko, V. Vasil’yev, A. Kostruba, O. Kushnir

Abstract


Organic compounds such as tris(8-hydroxyquinolinato) aluminum (Alq3), dicyanomethylene pyran (DCM), and its derivatives are of great interest for research because of their wide range of applications. They are used in lasers, organic light-emitting diodes (OLEDs), sensors (including explosive detectors), logic gates, sensitized dyes for solar cells, and more. In practical devices, a "host-guest" system is often employed, like Alq3:DCM, as DCM itself exhibits low emission intensity due to strong intermolecular interactions. To enhance the efficiency of OLEDs, it is necessary to reduce the refractive index of thin film layers, which can increase the OLED quantum efficiency by up to 30%. Some researchers use the oblique angle deposition method to manipulate the refractive index of Alq3 films, and achieving a change of 0.3. The authors of the paper investigated the effectiveness of this method for DCM, its derivatives and Alq3:DCM films.

Thin films of DCM and its derivatives, as well as Alq3:DCM films, were fabricated using vacuum deposition techniques both perpendicularly and at an oblique angle (10° to the vapor stream). The refractive index was determined by ellipsometry at a wavelength of 632.8 nm, which corresponds to a helium-neon laser.

The study found that by employing oblique angle deposition for the organic films of DCM, DCM-5, DCM-18, Alq3:DCM (10 wt.% DCM), and Alq3:DCM-5 (10 wt.% DCM-5), refractive indices could be manipulated within the range of 0.05 to 0.18 at a wavelength of 632.8 nm.

The larger size of organic molecules in the films we studied is associated with the reduced impact of the technology on the refractive index. During the adsorption of the evaporated substance on a substrate positioned at an oblique angle relative to the vapor flow, islands are formed, which shade a portion of the substrate and hinder the vapor flow from entering shaded areas. This effect results in an ordered, porous, and columnar growth of the film. However, the efficiency of such ordering diminishes as the molecule size increases.

Key words: dicyanomethylene pyran, derivatives of dicyanomethylene pyran, tri-(8-hydroxyquinoline) aluminum, ellipsometry, refractive index, oblique angle deposition, thin films.


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DOI: http://dx.doi.org/10.30970/eli.23.9

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