Development of solution processable vertical organic light-emitting transistors / Mohd Arif Mohd Sarjidan

Mohd Arif , Mohd Sarjidan (2019) Development of solution processable vertical organic light-emitting transistors / Mohd Arif Mohd Sarjidan. PhD thesis, Universiti Malaya.

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Abstract

Display technology is shifting from liquid crystal display (LCD) to active matrix organic light emitting diode (AMOLED) due to many advantages of AMOLED such as better image quality, high viewing angle and flexible in design. However, the backplane thin-film transistor (TFT) issue have hindered the AMOLED to offer a competitive price compare to that of the LCD. Because of this, the vertical organic light emitting transistor (VOLET) was introduced, in which the combination function of charge modulation and light emission can solve the backplane issue. Unfortunately, the suggested solution only focuses on using sophisticated and expensive equipment which will not reduce the fabrication cost of the device. This PhD thesis addresses this issue by developing solution processable VOLET. This PhD thesis begins with understanding the fabrication processes and device characteristics of two type of devices; the static induction transistor (SIT) and Schottky barrier (SB) based VOLET. The simple solution process technology was used to fabricate the organic active layer, which also acts as an emissive layer. In the initial work, both devices show transistor behavior in which current density and luminance brightness were modulated by varying the gate voltage. It is also found that the principle mechanism of the two devices is different between each other. In order to gain more understanding of device physics of the VOLET, a thermally evaporated silver-sourced device has been fabricated as the control. The theoretical study involving Fowler-Nordheim (FN) tunneling and space charge limited current (SCLC) models are used to quantitatively analyze the experimental results and explain the device physics of the VOLET. In addition, a simple approach has been introduced to measure the mobility of the VOLET. The main research work focuses on utilizing a solution processable silver nanowires (AgNWs) as source electrode in the VOLET fabrication. The analysis on this novel device showed similar behavior as the silver-Display technology is shifting from liquid crystal display (LCD) to active matrix organic light emitting diode (AMOLED) due to many advantages of AMOLED such as better image quality, high viewing angle and flexible in design. However, the backplane thin-film transistor (TFT) issue have hindered the AMOLED to offer a competitive price compare to that of the LCD. Because of this, the vertical organic light emitting transistor (VOLET) was introduced, in which the combination function of charge modulation and light emission can solve the backplane issue. Unfortunately, the suggested solution only focuses on using sophisticated and expensive equipment which will not reduce the fabrication cost of the device. This PhD thesis addresses this issue by developing solution processable VOLET. This PhD thesis begins with understanding the fabrication processes and device characteristics of two type of devices; the static induction transistor (SIT) and Schottky barrier (SB) based VOLET. The simple solution process technology was used to fabricate the organic active layer, which also acts as an emissive layer. In the initial work, both devices show transistor behavior in which current density and luminance brightness were modulated by varying the gate voltage. It is also found that the principle mechanism of the two devices is different between each other. In order to gain more understanding of device physics of the VOLET, a thermally evaporated silver-sourced device has been fabricated as the control. The theoretical study involving Fowler-Nordheim (FN) tunneling and space charge limited current (SCLC) models are used to quantitatively analyze the experimental results and explain the device physics of the VOLET. In addition, a simple approach has been introduced to measure the mobility of the VOLET. The main research work focuses on utilizing a solution processable silver nanowires (AgNWs) as source electrode in the VOLET fabrication. The analysis on this novel device showed similar behavior as the silver- sourced device. More interestingly, the efficiency of the device is 10 times higher compared to that of thermally evaporated Ag-soured VOLET, which is due to high exciton formation and recombination. The study is continued with a demonstration of SIT based VOLET by using AgNWs gate. This could be the simplest technique to fabricate the VOLET. The use of AgNW as source and gate electrode has never been investigated prior to this study reported and this study has shown to some extent an improvement in the performance of the VOLET. Therefore, the research indicates that if a similar source and gate are used in VOLET with other high-efficient emissive materials, it could further enhance the performance of the device. Thus, this study provides a great insight and fundamental study for future development of low-cost display panel.

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