Abstract
In this study, we investigated the effects on the characteristic changes in OLED devices of using self-assembled monolayers with different functional groups as the hole injection layer, resulting in changes in their performance. Thus, we confirmed that it is possible to control the wetting properties, surface roughness, and work function of the indium tin oxide (ITO) surface by introducing self-assembled monolayers (SAMs). The contact angle measurements confirmed that the substrate surface contact angle tended to increase with SAM deposition. In addition, AFM measurements confirmed that the substrate surface roughness tended to decrease when SAM was deposited on the surface. Finally, it was confirmed through the work function measurement results that the work function increased when the ITO surface was modified by SAM. Furthermore, compared to OLEDs using only the ITO anode, the SAM-modified device showed a higher current density (359.68 A/cm2), improved brightness (76.8 cd/cm2), and a smaller turn-on voltage (7 V). This approach provides a simple route for fabricating organic light-emitting diode applications.
Highlights
Organic light-emitting diodes (OLEDs) are self-illuminating displays that illuminate when an electrical current is applied
This study investigated the effects of using self-assembled monolayers (SAMs) with different functional groups as the hole injection layer on the characteristic changes in OLED devices that can lead to changes in their performance
The contact angle measurement results for indium tin oxide (ITO), F3SAM, F10SAM, TTPS, and TTNS were 50.2◦, 71.7◦, 98◦, 68.9◦, and 85.9◦, respectively, and an increase in the surface contact angle was observed with SAM deposition
Summary
Organic light-emitting diodes (OLEDs) are self-illuminating displays that illuminate when an electrical current is applied. The large differences in work function values between the organic film and ITO create a huge energy barrier that leads to a high turn-on voltage and low efficiency for OLED devices [7]. Many researchers have investigated methods to reduce the large injection barrier between the ITO and hole transfer material (HTM) Some of these include the use of Dipyrazino[2,3-f:20,30-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT–CN) [8], poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) [9,10], and copper(ii) phthalocyanine (CuPc) [11]. The function of the deposited surface can vary depending on the type of functional groups that are introduced [15] With these advantages, SAMs can be applied in many different fields [16,17,18,19,20]. In this study, trimethoxyphenylsilane (TTPS) and trimethoxy(naphthalene-2-yl)silane (TTNS) with the terminal functional group as the benzene ring, along with heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F10SAM) and 3,3,3trifluoropropyl) trimethoxysilane (F3SAM) with a trifluoromethyl group were used as sample hole injection layers to determine their effects on the properties of OLED devices
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