Abstract
Herein, we confirm the performance difference according to the structure of self-assembling monolayer (SAM) and investigate the characteristics of the indium tin oxide (ITO) surface when ITO substrates are deposited by (3,3,3-trifluoropropyl)trimethoxysilane (F-3SAM) and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-10SAM) having different chain lengths with trifluoromethyl group as terminal functional group, as well as SAM benzoic acid (BA) and 2-naphthoic acid (NA) with benzene ring forms. Through these, it is possible to control the wetting properties, surface roughness, and work function of the ITO surface. Wetting characteristics, average roughness, and changes in work function of the ITO surface were characterized by contact angle measurement, atomic force microscopy (AFM), and UV photoelectron spectroscopy (UPS). The measured contact angles were 41.1°, 82.25°, and 118° for the bare ITO, NA, and F-10SAM, respectively, the average roughnesses of the SAM-modified surfaces were 1.377, 1.033, and 0.838 nm for the bare ITO, NA, and F-10SAM, respectively. The work function of the ITO surface modified with NA and F-10SAM increased from 0.21 and 0.36 eV to 5.01 and 5.16 eV, respectively. As a result, the surface properties of ITO were better for aliphatic SAM than for aromatic ring SAM.
Highlights
An organic light emitting diode (OLED) is a self-luminous device that emits light when current flows through it
The self-assembled monolayer (SAM) formation proceeds according to the following steps: first, a low-density layer is formed, which shows fluidity due to low surface coverage; an intermediate-density layer is formed, which shows fluidity due to low surface coverage; an intermediate-denlayer comprising an uneven condensation of molecules develops; after the degree of sity comprising uneven condensation of molecules develops;onafter the deSAMlayer coverage reachesan a threshold value, these molecules alignthen horizontally the surface; gree of coverage reaches a threshold value, these molecules align horizontally the when the SAM achieves a high density on the surface, a rearrangement of theon surface; when the achieves a high density on the surface, a rearrangement of molecules occurs along the vertical direction, forming a well-aligned SAM [8]
These results indicate that the indium tin oxide (ITO) interface had a higher contact angle when the When C1 has a value between 0 and 1, θ1 is the contact angle of bare ITO, and θ2 is the aliphatic alkyl chain length was increased than when the number of aromatic rings was contact angle of the ITO surface modified by F-10SAM in the above equation, the quantiincreased
Summary
An organic light emitting diode (OLED) is a self-luminous device that emits light when current flows through it. In the emissive layer electrons and holes meet to form excitons that recombine, emitting light To facilitate this basic luminescence principle, OLEDs have a structure comprising a multi-layered organic thin film stacked between an anode and a cathode. The multilayer structure is advantageous in terms of luminous efficiency and lowering the driving voltage by reducing the energy barrier when the difference in work function decreases between the organic materials. Many studies have reported that the work function between ITO and the HTM can be controlled, which reduces the energy barrier between ITO and organic materials to facilitate hole injection, thereby lowering the luminous efficiency and driving voltage [10,15]. The ITO substrates are deposited by (3,3,3-trifluoropropyl)trimethoxysilane (F-3SAM) and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-10SAM) (having different chain lengths, with a trifluoromethyl group as the terminal functional group) and benzoic acid (BA) and 2-naphthoic acid (NA) (with benzene ring forms), and the corresponding characteristics of the ITO surfaces are examined
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