臺灣博碩士論文加值系統

Localized surface plasmon resonance generated by gold nanoparticles have been doped into the hole transport layer to enhance the luminance of the organic light emitting diode device. However, the mechanism of luminance enhancement and device properties are still under debate. Some research reported that the luminance enhancement comes from electrical characteristics improvement, but another report that it comes from localized surface plasmon resonance effect induced by gold nanoparticles. In this work, we synthesize 12 nm of gold nanoparticles incorporated into hole transport layer in the organic light-emitting device by mixing solutions directly with volume percent concentration variations. The luminance and efficiency reach 35% and 28% optimum enhancement, respectively, at 15 volume percent doping concentration. Interestingly, the electrical characteristics are also showing improvement that influences the charge balance properties of the device. By combining both of mechanism, the enhancement in both luminance and efficiency explained clearly. This evidence brings the improvement of device performance with the easiest method to incorporate gold nanoparticles.

Recommendation letter from the thesis advisor
Oral defense committee certification
Preface and Acknowledgements iii
English Abstract v
Table of Contents vi
List of Figures viii
List of Tables xi
Chapter 1 Introduction 1
1.1. Background 1
1.2. History 3
1.3. State-of-the-art 4
1.4. Motivation 9
1.5. Thesis framework 10
Chapter 2 Theoretical and Literature Review 11
2.1. Fundamental principle of OLED 11
2.1.1. OLED device structure 11
2.1.2. Carrier injection 13
2.1.3. Carrier transport 15
2.1.4. Recombination process 17
2.2. Localized Surface Plasmon Resonance (LSPR) 17
2.3. Metal nanoparticles enhanced fluorescence 23
2.3.1. Fluorescence process 23
2.3.2. Electronic transition process 23
2.3.3. Energy transfers mechanism 26
Chapter 3 Experimental and Measurement Details 29
3.1. Materials 29
3.1.1. Substrate and anode layer 29
3.1.2. Hole transport layer (HTL) 29
3.1.3. Emitting layer (EML) 30
3.1.4. Electron injection layer (EIL) 30
3.1.5. Cathode layer 31
3.1.6. Passivation 31
3.2. Device fabrication 31
3.2.1. Anode patterning 32
3.2.2. Device fabrication processes 33
3.3. Device Measurement 38
Chapter 4 Result and Discussion 40
4.1. Gold Nanoparticles Characteristics 40
4.2. OLED Device Characteristics 43
4.2.1. Electrical characteristics 43
4.2.2. Luminance characteristics 45
4.2.3. Devices efficiency 47
4.3. The Proposed Mechanism 48
4.3.1. Current injection 48
4.3.2. Localized surface plasmon resonance 53
Chapter V Conclusion 56
Bibliography 57


List of Figures
Figure 1.1. The latest breakthrough from OLED technology:
OLED77W7P©
flexible wallpaper TV from LG Display and
Lenovo Cplus© wearable smartphone have been released to
the market ................................................................................. 3
Figure 2.1. A simply OLED device structure............................................ 12
Figure 2.2. Two kinds of charges injection processes (a) thermionic
emission, and (b) tunneling process ............................................ 14
Figure 2.3. Fowler-Nordheim tunneling analysis for different energy
barrier height............................................................................... 14
Figure 2.4. Log J - log V curve of SCLC transport properties on the
organic layer. ............................................................................... 16
Figure 2.5. Collective oscillation of electrons in metal nanoparticles
influenced by applied external electric field ............................... 18
Figure 2.6. Optical properties of metal nanoparticles as response to
external electric field (a) scattering cross-section and (b)
absorption cross-section spectra ................................................. 20
Figure 2.7. Finite-difference time-domain (FDTD) simulation of 100 nm
Ag-sphere with incident electric field along x-axis..................... 21
Figure 2.8. Various local–electric–fields produced around metal
nanoparticles due to plasmonic effect (a) near–field (b) far–field,
(the incident applied electric field is along the z-axis). .............. 22
Figure 2.9. An example of Jablonski diagram of a molecule with their
electronic states and vibrational states, also the transition related
to the absorption and emission.................................................... 24
Figure 2.10. The enhancement of electron transition rate on the
fluorescence under the metal nanoparticles influences............... 26
Figure 3.1 Chemical structure of PEDOT:PSS. ....................................... 30
Figure 3.2 Chemical structure of PFO:F8BT........................................... 31
Figure 3.3 (a) the metal mask used for patterning the ITO anode,.......... 33
Figure 3.4 sample devices inside the chamber while O2 plasma treatment.
..................................................................................................... 34
Figure 3.5 (a) the PEDOT:PSS and Au nanoparticles solutions (b) the
mixing process in the ultrasonic bath.......................................... 34
Figure 3.6 the process while spin-coating (a) before and (b) after put the
filter to the injector (c) when dropping the solution onto the
surface of the sample. .................................................................. 35
Figure 3.7 the thermal evaporation machine to do cathode film
deposition..................................................................................... 36
Figure 3.8 the full device structure of OLED. .......................................... 38
Figure 3.9 the electrical and optical measurement machine ................... 39
Figure 3.10 field emission transmission electron microscope ................. 39
Figure 4.1. (a) Transmission electron microscopy (TEM) picture of selfsynthesized
gold nanoparticles by modified Frens method (the
scale bar is 20 nm), the inset of the picture is the size distribution
of gold nanoparticles calculated from TEM picture.................... 41
Figure 4.2. The absorption spectrum of 12 nm gold nanoparticles......... 42
Figure 4.3. J – V curves, the linear current density characteristics depend
on the applied voltage.................................................................. 43
Figure 4.4. Semi- log scales of J – V curves, the log scale of current
density depends on the linear scale of applied voltage. .............. 44
Figure 4.5. The luminance characteristic of gold nanoparticles doped
devices.......................................................................................... 46
Figure 4.6. The efficiency of light emitted related to the current injected
into the devices ............................................................................ 47
Figure 4.7. The energy level diagram of undoped OLED device used as
reference....................................................................................... 49
Figure 4.8. Potential barrier height analysis by fitting with Fowler -
Nordheim formula in “hole-only” device.................................... 51
Figure 4.9. The spectra match between absorption of 12 nm Au
nanoparticles with the electroluminescence of PFO in the OLEDs
device. .......................................................................................... 53
Figure 4.10. The mechanism of luminance enhancement induced by local
near-field generated from LSPR effect. ....................................... 55


List of Tables
Table 1.1. Several works have done by the methods which incorporated of
gold nanoparticles dispersed on the top of ITO anode. ............. 5
Table 1.2. Several works have done by the methods which incorporated
gold nanoparticles blend with the hole transport compound in hole
transport layer inside the OLED device. ........................................ 9

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