Hole mobility characterizations of DNA biopolymer and its application in organic optoelectronic devices

DNA生物高分子之電洞遷移率特性分析及 其在有機光電元件之應用

林庭宇

指導教授 ： 洪毓玨

國立清華大學/電機資訊學院/光電工程研究所/博士(2014年)

摘要

As deoxyribonucleic acid (DNA) has attracted increasing research attention, the unique biochemical properties and easy availability have become great advantages of making DNA
competitive and widely used. Owing to the intrinsic hydrophilic property of DNA, extra procedures are required to modify the DNA molecules. In this work, various surfactants were used to modify the DNA molecules for compatibility in organic process. The detailed syntheses and characterizations of these DNA biopolymers are described in Chapter 2. Fouriertransform infrared spectroscopy (FTIR) spectra, ultraviolet-visible (UV-VIS) spectroscopy spectra, surface morphology, and thermal stability of DNA biopolymers were also measured.

The electrical properties and charge transport behavior of these DNA biopolymers are major parameters for the design of DNA-based optoelectronic devices. We characterized the conductivities and hole mobilities of DNA biopolymers in Chapter 3. The I-V characterizations of these DNA-based biopolymers exhibited a positive correlation between the
concentration of surfactant and material conductivity as the stoichiometric ratio of DNABTMA from 1:1 to 1:10. In the hole mobility measurement, a positive molecular weight
dependence was found in DNA-CTMA with 2000 and 200 base pairs. Besides, the hole mobilities of the DNA biopolymers increased at temperature from 253 to 303 K. We observed
that the mobility first exhibited a negative dependence on the applied fields and gradually increased with electric field (when E > 2105 V/cm) above 273 K. Gaussian disorder model (GDM) was utilized to describe the transport mechanisms of charges in these DNA biopolymers. Such characterization results are informative for the employment of DNA biopolymers in optoelectronic applications.

Due to the metallic affinity of DNA molecules, we developed a phototriggered process to synthesize a DNA-nanoparticle biopolymer. Silver nanoparticles (Ag NPs) were formed via
a photochemical synthesis using Irgacure-2959 ((1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one)) (I-2959). I-2959 produced ketyl radicals upon UV irradiation
and the radicals then functioned as reducing agents to reduce silver ions, leading to the formation of Ag NPs. These DNA-based biopolymers combined with Ag NPs were employed as functional layers in the color tunable organic light emitting devices (OLEDs). When incorporating such nanocomposite into OLEDs, a color tunable property was achieved by varying the UV radiation time in the formation process of nanoparticles. The hole mobility of the DNA-CTMA/Ag NP (deoxyribonucleic acid-cetyltrimethylammonium/silver nanoparticle)
biopolymer was affected by the UV irradiation process, resulting in the shift of the recombination zone. We also applied the concept of negative electric field dependency of the biopolymer in the color tunable OLEDs by tuning the driving voltage. The materials formed by Ag NPs embedded in DNA-based biopolymer were proved to be able to provide a facile way to tune the hole mobility of DNA biopolymers, which are promising for the applications in various DNA-based optoelectronic devices.

Furthermore, these DNA-based biopolymers combined with Ag NPs were also integrated into the memory devices. The device exhibited write-once read-many-times (WORM) memory
behavior and nonvolatile property. Through tuning the Ag NPs content by external doping process in the DNA-based biopolymer film, the electronic devices are capable of
exhibiting write-once read-many-times (WORM) memory effect, rewritable memory effect, and conductor behavior. These controllable electrical properties and nonvolatile electrical bistable switching effects of these devices can be attributed to hole trapping in the Ag NPs of the DNA-based biopolymer matrix. The operation cycles of the device with fairly good accuracy can be further achieved by improving the distribution of the Ag NPs under magnetic
stirring. The demonstration of the DNA-CTMA-Ag NPs memory device implies the potential to use DNA-based biopolymer for high capacity and low-cost storage element in
future electronics.

關鍵字

高分子材料 ； 導電率 ； 電洞遷移率 ； 有機發光二極體元件 ； 有機記憶體元件

參考文獻

Society for Optics and Photonics, 2011.

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