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. 2024 Aug 28;15(9):1089.
doi: 10.3390/mi15091089.

Optical Properties and Growth Characteristics of 8-Quinolinolato Lithium (Liq) Nano-Layers Deposited by Gas Transport Deposition

Alexandros Zachariadis  1 , Michalis Chatzidis  1 , Despoina Tselekidou  1 , Olaf Wurzinger  2 , Dietmar Keiper  2 , Peter K Baumann  2 , Michael Heuken  2 , Kyparisis Papadopoulos  1 , Argiris Laskarakis  1 , Stergios Logothetidis  1   3 , Maria Gioti  1
Affiliations

Optical Properties and Growth Characteristics of 8-Quinolinolato Lithium (Liq) Nano-Layers Deposited by Gas Transport Deposition

Alexandros Zachariadis et al. Micromachines (Basel). .

Abstract

Organometallic complexes containing reactive alkali metals, such as lithium (Li), represent a promising material approach for electron injection layers and electron transport layers (EILs and ETLs) to enhance the performance of Organic Light-Emitting Diodes (OLEDs). 8-Quinolinolato Lithium (Liq) has shown remarkable potential as an EIL and ETL when conveyed in very thin films. Nevertheless, the deposition of nano-layers requires precise control over both thickness and morphology. In this work, we investigate the optical properties and morphological characteristics of Liq thin films deposited via Organic Vapor Phase Deposition (OVPD). Specifically, we present our methodology for analyzing the measured pseudodielectric function <ε(ω)> using Spectroscopic Ellipsometry (SE), alongside the nano-topography of evaporated Liq nano-layers using Atomic Force Microscopy (AFM). This information can contribute to the understanding of the functionality of this material, since ultra-thin Liq interlayers can significantly increase the operational stability of OLED architectures.

Keywords: 8-Quinolinolato Lithium; Liq; OLED; OVPD; Spectroscopic Ellipsometry.

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Conflict of interest statement

Authors Olaf Wurzinger, Dietmar Keiper, Peter K. Baumann, and Michael Heuken were employed by the company AIXTRON SE. Author Stergios Logothetidis was employed by the company Organic Electronic Technologies (OET). The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interests.

Figures

Figure 1
Figure 1
Measured (open circles) and fitted (lines) dielectric function of Liq thin films on c-Si.
Figure 2
Figure 2
(a) Calculated bulk dielectric function of Liq, and (b) overlay spectra of Liq PL emission, calculated absorption coefficient, and transmittance (inverted axis to highlight the absorbing properties).
Figure 3
Figure 3
AFM images (5 × 5 μm) of the five (A–E) Liq samples. The white lines indicate a 1 μm scale.
Figure 4
Figure 4
(a) AFM cross-sections of the five (A–E) Liq samples, (b) P2P and RMS roughness values of the samples (inset: numerical data of RMS and P2P), and (c) black-and-white AFM image analysis of samples “A” and “B” for structures with heights greater than 2 nm.
See this image and copyright information in PMC

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