Presentation is loading. Please wait.

Presentation is loading. Please wait.

Speaker :陳永祈 Report Date : 10 月 24 日 Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting.

Similar presentations


Presentation on theme: "Speaker :陳永祈 Report Date : 10 月 24 日 Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting."— Presentation transcript:

1 Speaker :陳永祈 Report Date : 10 月 24 日 Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting Diodes (OLED) Keigo Sato, Katsuyuki Shizu, Kazuaki Yoshimura, Atsushi Kawada, Hiroshi Miyazaki, and Chihaya Adachi Phys. Rev. Lett. 110, (2013) Published June 10, 2013

2 Outline Introduction Experiment method Result and discussion summary

3 Introduction

4 Organic luminescent materials are widely used in various consumer products such as highlighters, detergents. zh.wikipedia.org In addition to their use as chemical products, recen t development of organic materials from a new perspective has opened up a novel possibility for their use in optoelectronic devices. ex : display 螢光筆 有機基板顯示器

5 zh.wikipedia.org LED In particular, the luminescence and unique semiconducting characteristics of organic materials can be combined, leading to the rapid development of organic semiconductor devices such as organic light emitting diodes (OLEDs) 可撓性 OLED OLED 電視

6 OLEDs possess attractive features such as 1. high EL efficiency. 2. high contrast. 3. low weight and low cost. 4. It possess the flexible of charactertistic. η EQE ≈20% cck1616tw.pixnet.net OLED 無論是顏色對比度或者是發光強度 都比 LCD 來得好

7 分子放光的方式可以有兩種: 電致發光 光致發光

8 After extensive study of OLEDs for the past 20 years, electroluminescent(EL, 電致發光 ) materials have usually been classified by one of two mechanisms, fluorescence( 螢光 ) or phosphorescence( 磷光 ), where radiative decay occurs from singlet or triplet excited states, respectively.

9 Electroluminescent( 電致發光 ) : 當電子和電洞在發光層內 “ 相遇 “ 時, 就會產生激子,因而放光 η out :內部產生的激子數與外部流動的電子數之比值 η S :單重激子數與總激子數的比值 k S :單重激子的輻射速率 J :電流密度 d :發光層的厚度 e :電荷量

10 Spin multiplicity : 2S + 1 S1S1 T1T1 S 1 : Singlet excited state ( 單重激發態 ) T 1 : Triplet excited state ( 三重激發態 ) 2S+1=1 S=0 2S+1=3 S=1 χ 00 =1/√2(|↑↓> ― |↓↑>) χ 10 =1/√2(|↑↓> + |↓↑>) χ 11 =|↑↑> χ 1-1 =|↓↓> *激子也可以叫做是激發態 !!!

11 k r : the fluorescence decay rate k p : the phosphorescence decay rate k np : the nonradiative decay rate from the T 1 excited state k ISC : the intersystem crossing rate 螢光 電洞注入電子注入 磷光 三重態激子 單重態激子 τ = ~10 1 s τ = ~10 -8 s

12 Photoluminescent(PL, 光致發光 ) : Photoluminescent materials have usually been classified by one of two mechanisms, fluorescence or phosphorescence, where radiative decay occurs from singlet or triplet excited states, respectively. S1S1 S0S0 S1S1 T1T1 Intersystem crossing T1T1 S0S0 光致發光 螢光磷光

13 Energy State( 能階 ) S1S1 S0S0 T1T1 S 1 : Singlet excited state T 1 : Triplet excited state S 0 : Singlet ground state HOMO LUMO 2S+1=1 S=0 2S+1=3 S=1 電子的躍遷是否發生, 取 決於 state 與 state 之間的偶合 程度 HOMO : highest occupied molecular orbital ( 最高電子佔據軌域 ) LUMO : lowest unoccupied molecular orbital ( 最低電子未佔據軌域 ) S0S0 S1S1

14 k r : the fluorescence decay rate k p : the phosphorescence decay rate k np : the nonradiative decay rate from the T 1 excited state k ISC : the intersystem crossing rate 螢光 磷光 τ = ~10 -8 s τ = ~10 1 s 受光激發

15 螢光和磷光最大的不同就是輻射生命期的長短: 螢光輻射生命期: ~ s 磷光輻射生命期: ~ 10 1 s 奎寧水因吸收紫外光之後而放出螢光 夜明珠所放出的磷光 zh.wikipedia.org/zh-tw

16 The use of phosphorescent iridium 銥 (Ir) complexes overcame the limitation of exciton production efficiency through spin-orbit coupling, resulting in devices with very high external EL efficiency (EQE)of over 20%. In fact, the high EQE of such phosphorescent complexes prompted commercialization of OLEDs. Unfortunately, rare metals such as Ir and Pt are not the ideal choice for OLED emitters. They are unevenly distributed resources, expensive, rather low solubility and produce toxic waste. spin-orbit coupling → = value iridium 銥 (Ir) complexes 的值越大,就越有可能放出磷光

17 To produce OLED emitters without these drawbacks, we recently prepared novel light-emitting materials that realize high efficiency without using rare metal complexes by taking advantage of very efficient thermally activated delayed fluorescence (TADF).

18 螢光 磷光 電子注入電洞注入 受光激發

19 Although some molecules are already known to exhibit TADF, their efficiencies are generally quite low. In the last few years, they have surveyed various candidates as TADF emitters and found the molecules that exhibit significant TADF.

20 ΔE ST = 0.1eV η EQE = 5.3% ΔE ST = 0.06eV η EQE = 11% η EQE = 10% ΔE ST = 0.1eV ΔE ST = 0.24eV η EQE = 0.1% J. Chem. Theory Comput. 2013, 9, 3872−3877 CC2TA ACRFLCN PIC-TRZ SnF 2 OEP >2% considering only the photoluminescence (PL) efficiency of Φ PL = 39% related to conventional fluorescence

21 Recently, they found an advanced molecule with an ultimately small ΔE ST ≈ 0eV, virtually zero gap. They believe that this is the first report on the molecules having zero-gap between the singlet and triplet excited states. An OLED containing this molecule exhibited a high η EQE of 14% ±1% △ E≈0 eV S0S0 S1S1 T1T1

22 In their successive design of TADF molecules, taking advantage of the backbone of PIC-TRZ, they systematically changed the number and position of an indolocarbazole unit through quantum mechanism calculation. PIC-TRZ PIC-TRZ2 Indolocarbazole unit

23 Experiment method

24 計算方法: DFT/PBE0/6-31G(d) Φ i : electron basis function c i : coefficient Ψ : the molecular orbital of wavefunction DFT(Density Function Theoy) PBE0 : 6-31G(d) : A kind of basis set 氫原子的分子軌域 Setting up of parameter during calculation

25 PIC-TRZ PIC-TRZ2 HOMOLUMO HOMO and LUMO are separated incompletely ΔE calc = 0.08eV LUMOHOMO HOMO and LUMO are completely separated ΔE calc = 0.003eV

26 Their goal is to achieve high TADF performance in a solid film, aimed for application in OLEDs, so they focused on host-guest systems. PIC-TRZ2 host guest Dope( 摻雜 )

27 Spectra corresponded well with each other, indicate that the delayed component is caused by TADF. Figures 3(a) and 3(b) show transient PL decay and fluorescence (black line) and delayed fluorescence, 延遲螢光 (red line) spectra of 6 wt %-PIC-TRZ2 doped( 摻雜 ) into a 1,3-bis(carbazol-9-yl)benzene (mCP) host layer at T = 5K. λ = 475nm (S 1 = 2.61 eV)

28 Result and discussion

29 In the case of PIC-TRZ, although we clearly observed the appearance of phosphorescence at low temperature, demonstrating a characteristic emission spectrum with clear vibrational peaks, no such emission spectrum was observed for PIC-TRZ2. at T = 5K 有磷光產生 沒有磷光產生

30 They conclude that the delayed component is related to TADF, and up-conversion occurs in PIC-TRZ2 even at T = 5K, indicating it possesses virtually zero gap.

31 The transient PL decay characteristics of PIC-TRZ2 at T = 300 K at Figure (c) Fast PL transient lifetime τ f = 83 ns slow PL decay τ d = 2.7 μs They note that the latterτ d is comparable to that of conventional Ir complexes such as iridium 2-phenylpyridine [Ir(ppy) 3 ] derivatives with τ = 1 ~ 5 μs, indicating that PIC-TRZ2 has comparable transient performance of delayed fluorescence to those of Ir complexes. iridium 2-phenylpyridine

32 They measured the temperature dependence of the radiative decay rate of the delayed fluorescence(k r (TADF)) *阿瑞尼士方程式 (Arrhenius equation) 告訴我們:溫度越高, k r 的反應速率就越快 !

33 To maximize the TADF efficiency of films doped with PIC-TRZ2, they optimized the host materials.

34 PLQE : PL quantum efficiencies Total PLQE : 總放光之效率 Prompt PLQE :放螢光之效率 Delayed PLQE :放延遲螢光之效率 *總放光效率=放螢光之效率+放延遲螢光之效率 學者發現說 PIC-TRZ 摻雜其他不同的 host materials 之後,會有不同大小的發光效率

35 Triplet energy (eV)Φ PL TPT ~24% TAPC2.8758~62% PYD ~47% mCP2.9139~43% DPEPO≈3.149~53% UGH2≈3.557~61% PIC-TRZ2 energy transfer Back energy transfer 學者猜測三重激子會在 TAPAC 分子待上一段 很長的時間,而後再將能量釋放出來,並 轉移至 PIC-TRZ ,使得 PIC-TRZ 的激子數增多, 放光效率因而提升。

36 Triplet excitation energy : host materials > PIC-TRZ2 Triplet excitation energy : host materials < PIC-TRZ2 Transient PL measurements revealed that Energy transfer host materials PIC-TRZ2 → 延遲螢光會發生 Energy transfer → 能量會以非輻射 (nonradiation) 的方式流失, 例如:熱 。因而造成不必要的能量浪費。 當然 ! 這是我們不希望的 !!!

37 if energy transfer occurs readily, we can expect a further enhancement of EQE, suggesting a theoretical maximum of 11.8%. They tried to optimize the device parameters to maximize η EQE due to imperfect triplet exciton confinement.

38 Electron Transport Layer Metal Cathode Light Emitting Polymer Hole Transport Layer ITO Anode device VI TAPAC ITO Anode PYD2 : 6wt % PIC-TRZ2 LiF/Al Cathode TmPyPBi device Vdevice VII (20nm) (45nm) (40nm) LiF/Al Cathode TPBi TAPAC ITO Anode PYD2 : 6wt % PIC-TRZ2 LiF/Al Cathode DPEPO PYD2 : 6wt % PIC-TRZ2 TAPAC ITO Anode

39 TAPAC ITO Anode PYD2 : 6wt % PIC-TRZ2 LiF/Al Cathode TmPyPBi Device VII 雖然本篇 Paper 沒有顯示出 Device I 、 Device II 、 Device III 以及 Device IV 的結構,但唯一能夠確定的是;無論是效率 或著是穩定性都沒有比右邊的三種 Device 來得好 ! 並且效率最大的是 Device VII ?

40

41 Summary : 1. They expect that improved understanding of molecular structures will reveal undeveloped functions that will further enhance OLED performance. 2. While PIC-TRZ2 has nearly zero-gap energy, a rather high f of 60% was obtained. This is because PIC-TRZ2 has appreciable oscillator strength ( 振子強度 ) →, leading to highly efficient TADF. *振子強度的數值越大,兩個 State 之間的躍遷就越容易發生 3. The radiative decay rate of the delayed fluorescence(k r (TADF)) dependence of temperature.


Download ppt "Speaker :陳永祈 Report Date : 10 月 24 日 Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting."

Similar presentations


Ads by Google