以三功能硫氰酸亞銅製作之高效率有機發光二極體

Highly Efficient Organic Light Emitting Diode with Trifunctional Copper(I) Thiocyanate

歐祖豪(Tsu-Hao Ou)

指導教授 ： 周卓煇

國立清華大學/工學院/材料科學工程學系/碩士(2019年)

摘要

有機發光二極體 (Organic Light Emitting Diode, OLED) 具有多項侵入性特
質，如面光源、可撓曲、高對比、廣視角、全彩化、低驅動電壓、節能和超高 顯色指數等優點，被譽為終極的顯示技術。
然而，目前 OLED 的發展，其發光效率仍有很大的進步空間，而改善元件 效率的方式，可透過低的注入能障、載子有效侷限、增加再結合區和有效的激 子產生，以研製出高效率 OLED，進而達到節能之效果。
本研究使用三功能硫氰酸亞銅(copper(I) thiocyanate, CuSCN)，此材料可 同時作為電洞注入、傳輸層(HIL/HTL)和電子侷限層(EBL)，4,4′-Bis(N- carbazolyl)-1,1′-biphenyl (CBP)為主體，摻雜綠色染料 bis[2-(2-pyridinyl-N)-phe- nyl-C](acetylacetonato)iridium(III) [(ppy)2Ir(acac)]，透過濕式製程研製出一高效 率綠光有機發光二極體;在 100 cd/m2 和 1,000 cd/m2 時，元件效率為 51.7 lm/W 和 40.3 lm/W，相較於一般以 PEDOT:PSS 作為電洞注入、傳輸層(HIL/HTL) 元件時，效率為 45.6 lm/W 和 25.1 lm/W，高出 13%和 60%;此外，當亮度由 100 cd/m2 升至 1,000 cd/m2 時，以 CuSCN 作為 HIL/HTL/EBL 的元件，效率下 降 22%;以 PEDOT:PSS 作為 HIL/HTL 的元件，效率則下降 45%;因此，以 CuSCN 作為 HIL/HTL/EBL 的元件時，在高亮度下，效率有更顯著的提升;此 外，當亮度提升時，也可減緩效率滾降。

此元件之高效率及減緩效率滾降，可歸因於 CuSCN 具有(1)較 PEDOT:PSS 淺的最低未填滿分子軌域(lowest unoccupied molecular orbital, LUMO)(-1.8eV)，施加電壓增強時，有效將電子侷限在發光層，與電洞再 結合，產生更多的激子;(2)較 PEDOT:PSS 深的最高填滿分子軌域(highest occupied molecular orbital, HOMO)(-5.5eV)，促進電洞注入發光層，提升電 子與電洞於發光層形成激子的機率;(3)較 PEDOT:PSS 高的可見光穿透率， 能有效提升出光效率;(4)減少薄膜表面粗糙度，降低元件漏電流機率。

關鍵字

有機發光二極體 ； 硫氰酸亞銅 ； 電洞注入層 ； 電洞傳輸層 ； 電子侷限層

並列摘要

Organic Light Emitting Diode (OLED) has many disruptive characteristics, such as surface light source, flexible, high contrast, wide viewing angle, full color, low driving voltage, energy saving and ultra-high color rendering index. , known as the ultimate display technology.
However, the development of OLEDs still has a lot of space for improvement in luminous efficiency, and the way to improve device power efficiency can be achieved through low injection energy barrier, effective carrier limitation, increased recombination zone and effective exciton generation. To develop high-efficiency OLEDs to achieve energy savings.
In this study, Trifunction copper (I) thiocyanate (CuSCN) was used as a hole
injection, transporting layer (HIL/HTL) and electron Blocking layer (EBL), 4,4'-Bis
(N-carbazolyl)-1,1'-biphenyl (CBP) as the host, doped with green dye bis[2-(2-
pyridinyl-N)-phenyl-C](acetylacetonato)iridium(III) [(ppy)2Ir (acac)], a high-
efficiency green organic light-emitting diode was developed through a wet process;
The power efficacies for the CuSCN based devices are found to be 51.7 and 40.3
lm/W at 100 and 1000 cd/m2, respectively, which are 13 and 60% higher than the PE-
DOT:PSS based counterparts, when PEDOT:PSS is used as a hole injection and
transporting layer (HIL/HTL), the power efficiency is 45.6 lm/W and 25.1 lm/W; In

addition, when the brightness is increased from 100 cd/m2 to 1,000 cd/m2, with CuSCN as the HIL/HTL/EBL device, the efficacy is reduced by 22%; with PEDOT:PSS as the HIL/HTL device, the efficacy is reduced by 45%; Therefore, CuSCN is used as the HIL/HTL/EBL In the case of high-brightness, the efficiency is more significantly improved; In addition, when the brightness is increased, the efficiency roll-off can also be slowed down.
The high efficacy of this device and the mitigating efficacy roll-off are attributable to the fact that CuSCN has (1) lower unoccupied molecular orbital (LUMO) (-1.8 eV), which is shallower than PEDOT:PSS. Effectively confine the electrons to the emissive layer and recombine with the holes to generate more excitons with applied voltage enhancement; (2) the highest occupied molecular orbital (HOMO) (-5.5eV) deeper than PEDOT:PSS , promoting the injection of holes into the emissive layer, increasing the probability of electrons and holes forming excitons in the emissive layer; (3) higher visible light transmittance than PEDOT:PSS, which can effectively improve light extraction efficacy; (4) reducing film surface roughness degree, reduce the probability of device leakage current.

並列關鍵字

Organic Light Emitting Diode ； Copper(I) Thiocyanate ； Hole injection layer ； Hole transporting layer ； Electron blocking layer

參考文獻

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