# Electro-Optic Properties of High-Efficiency Organic Electronics with the Addition of An Interlayer
## 1 Introduction  
Organic light-emitting diodes (OLEDs) are light-emitting devices subject to ongoing research. They are structured in several layers of organic materials. When an electric field is applied to the cathode, light is emitted as the electrons generated at each pole meet the holes [1]. Except for special cases, OLED devices have an inherent ability to emit light even on the surface of materials given the presence of thin films of such structures, thus allowing the production of more flexible designs compared to conventional light-emitting devices, with a multitude of advantages, ranging from higher color expression to wider viewing angles than conventional devices [2]. Current OLED displays consist of a hole injection layer (HIL), hole transport layer (HTL), emissive layer (EML), electron transport layer (ETL), and electron injection layer (EL), as well as a layer that assists in the efficient transport of holes and electrons via the addition of an interlayer and a layer in which the electrons and holes meet to produce light emission [3]. Self-emitting organic materials emit light upon application of electricity based on \"electroluminescence\". The excitation state is temporarily unstable and the return to the 'ground state' is immediate, since electrons seek to find a stable state. As electrons return from the excited state to the ground state, the energy level decreases back to the original level, when the reduced energy is emitted in the form of light. The most-applied material used as the anode in the fabrication of OLED devices at present is indium tin oxide (ITO) on a glass substrate for transparent electrodes [4]. ITO is a type of transparent conducting oxide material composed of indium oxide (In\({}_{2}\)O\({}_{3}\)) and tinoxide (SnO\({}_{2}\)). ITO is widely used in the fabrication of displays, electronic paper, OLED, architecture, solar cells, and protective coatings due to its electrical conductivity, optical transparency, excellent substrate adhesion, high-temperature resistance, ability to form thin films, and chemical resistance to moisture [5]. [PERSON] et al. reported the HTL of an OLED device could be modified to improve performance by reducing the driving voltage, which was the first work to modify the device's interlayer. [PERSON] et al. achieved quantum efficiency (1% photon/electron), luminance efficiency (1.5 \(\mathrm{\SIUnitSymbolMicro m}\)/W), and brightness (\(>\)1000 \(\mathrm{cd}\mathrm{/}\mathrm{m}^{2}\)) at driving voltages less than 10 volts in 1987 [6]. Additionally, the light emitting layer was doped with other substances in 1989, which increased efficiency by more than two fold compared to the previous work done at driving voltages less than 10 volts [7]. Significant improvement in electron injection was achieved by introducing a thin LiF film and reducing the electronic barrier of the organic/AI interface layer, further improving the efficiency of the device [8]. In recent years, there has been intensive research into the modification of the inner layer of the device, aiming to create high-brightness, high-efficiency, low-power, and commercial technologies. The most well-known studies on the HIL layer involve using materials such as PEDOT:PSS, 2-TNATA, MoOx [9; 10] and SAM, while those on the HTL layer report on the use of TCTA, TPD, and m-MTDATA [11]. The two layers act to improve the efficiency of hole injection to the subsequent layer by increasing the highest occupied molecular orbital (HOMO) level [12]. Self-assembled monolayers (SAMs) are organic monolayers with an intrinsic nanostructure that are formed at phase boundaries [13]. They are advantageous in inducing a change in the substrate, as the SAM film coating on the surface of an existing solid material may provide lubrication or prevent oxidation [14]. Based on these characteristics, SAMs have been actively and continuously studied since their first introduction by [PERSON] and [PERSON] in 1946 [15].