在本論文中主要使用有機/無機材料作為多層結構中的電荷傳輸層，並與無機硒化鎘@硫化鋅/硫化鋅-核/殼型量子點製作反置型量子點電致發光二極體。該元件基本架構為氧化銦錫(ITO)/氧化鋅奈米粒子(ZnO nanoparticles)/量子點(QDs)/CBP/TCTA/NPB/三氧化鉬(MoO3)/鋁(Al)。本實驗中所有元件皆沉積於玻璃基板上，氧化銦錫當作陰極，氧化鋅奈米粒子作為電子傳輸層，綠光發光層材料為溶膠狀量子點，熱蒸鍍有機材料CBP/TCTA/NPB作為多層電洞傳輸層，電洞注入層則為三氧化鉬，最後鍍上鋁來當作陽極。
傳統量子點發光二極體結構大多以無機氧化鋅奈米粒子來當作電子傳輸層，製作於量子點與陰極之間，由於氧化鋅奈米粒子其導電帶與陰極鋁功函數近乎相等，且無機金屬氧化物與有機聚合物相比擁有較高的電子遷移率，因此會有電子注入高於電洞而造成非輻射複合、降低效率的現象。在本實驗中我們採用新式的反置結構來製作量子點發光二極體，以減少電子注入效率，並沉積多層電洞傳輸層來提升電洞注入能力，使元件在8伏特的亮度約提升10倍，而最大效率也提升了2.8倍。接著我們嘗試優化多層電洞傳輸層的厚度來得到最佳的電子-電洞平衡，進而提升元件的亮度與效率，其亮度達到了每平方公尺56617燭光量，電流效率為每安培4.4燭光量。
最後我們嘗試使用半穿透銀電極取代氧化銦錫，相較於氧化銦錫，銀電極具有較低的片電阻與功函數，因此元件的起始光驅動電壓由原本的5.1伏特下降了25.5%至3.8伏特。另外銀薄膜與元件的上電極會形成微共振腔效應，但在本論文中並未明顯觀察到此效應，原因可能為共振腔長度不對或反射層銀電極不夠平整，未來會嘗試使用不同的共振腔長度並修飾銀薄膜表面來完成本實驗。

In this study, the organic/inorganic materials as carrier transport layers in multilayer structure and the gradient core thick-shell CdSe@ZnS/ZnS quantum dots (QDs) were mainly employed to fabricate the inverted electroluminescent quantum dot light-emitting diodes (QD-LEDs).The basic structure of the OLEDs was composed by indium tin oxide (ITO)/ zinc oxide nanoparticles (ZnO NP)/QDs 4,4'-Bis(carbazol-9-yl)biphenyl (CBP)/ Tris(4-carbazoyl-9-ylphenyl)amine (TCTA)/ N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (NPB)/ molybdenum trioxide (MoO3)/ aluminum (Al). All devices were fabricated on the transparent glass substrates. ITO was cathode, ZnO NP was used as electron transport layers (ETLs), QDs were green light-emitting materials, and CBP/TCTA/NPB were multi-hole transport layer (HTL). Moreover, MoO3, and Al were used as hole injection layer (HIL), and anode, respectively.
Traditional structure had made use of ZnO NP to be electron transport layer inserted between QDs and cathode. The hole current density is less than the electron current density due to the higher electron mobility of ZnO NP as well as proper band alignments. The conduction band of ZnO NP is aligned with the Fermi level of Al and the conduction band of the green QDs, and apparently results in low energy barriers for electron injection from the cathode into the EML. All of the above factors result in the non-radiative recombination and low efficiency of the devices. As a result, a novel inverted structure was used to fabricate our QD-LEDs for the purpose of reducing electron injection. Moreover, a multi-layer hole transport layer was developed to reduce the hole injection barrier. Due to the multi-layer hole transport layer in QD-LEDs, the luminance intensity at 8 V and current efficiency would be significantly increased by approximately 10 and 2.8 times, respectively. After that, optimizing individual thickness of hole transport layer could improve electron-hole balance, result in the enhancement of light emitting efficiency. The maximum luminance and current efficiency of the device could reach levels of 56617 cd/m2 and 4.43 cd/A, respectively,
The resonant cavity QLEDs consist of the semi-transparent silver (Ag) thin film as the bottom mirror and Al film as the top mirror was fabricated. Compared to traditional ITO electrode, the sheet resistant and work function of Ag electrode is lower. Therefore, the light turn on voltages of Ag device was 3.8 V which was reduced by 25.5% in comparison with that of 5.1 V for ITO device. However, the microcavity effect was not obviously observed in my experiment. The reason may be that the microcavity length was not correct or the semi-transparent silver thin film was not flat enough. The different microcavity length and modified Ag surface would be used to achieve a resonant cavity quantum dots light-emitting diodes in the future.

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