順式二苯乙烯/芴螺旋體衍生之雙極型混成體於有機電激發光二極體和染料敏化太陽能電池材料之應用

Spirally Configured cis-Stilbene/Fluorene Hybrids as Ambiplor Templates for Organic Light Emitting Diode and Dye-Sensitized Solar Cell Applications

蘇湋盛(Wei-Sheng Su)

指導教授 ： 陳建添

國立清華大學/理學院/化學系/碩士(2014年)

摘要

一、順式二苯乙烯/芴螺旋體衍生之雙極型混成體於有機電激發光二極體之應用

有機電激發光二極體在過去幾年已對下一代全彩面板顯示器和固態照明進行深入的研究。然而，電洞與電子不平衡的載子傳輸速率一直是影響元件效率較差的其中一個重要因素。因此，我們成功合成以順式二苯乙烯/芴螺旋混成體系統為核心架構，在C3及C7位置接上相同或不同取代的推拉電子基團，以合成一系列具有電洞傳輸型 (HT-type)、電子傳輸型 (ET-type) 和雙極型 (ambipolar)的藍光、天藍光和藍綠光材料，應用於有機電激發光二極體上。這一系列的材料其玻璃轉換溫度可達120-167 oC，且熱裂解溫度皆高於400℃，擁有不錯的熱穩定性質。此外，我們所開發的材料擁有較為平衡的電洞和電子傳輸速率，其中藍綠光材料N-STIF-P(O)Ph2在電場7.3 105 V/cm下，其電洞傳遞速率為6.510-6 cm2/Vs，電子傳遞速率為5.110-6 cm2/Vs，是為一個良好的雙極性螢光發光材料，應用在單層元件有優越的效率表現 (元件結構：ITO/PEDT:PSS/ N-STIF-P(O)Ph2/LiF/Al)，其元件的驅動電壓為2.5 V，在電流密度20 mA/cm2下的放光效能為3.29 cd/A；功率效能為2.84 lm/W；外部量子效率為1.28%，最大亮度在電流密度為5,611 mA/cm2 (操作電壓: 8.5 V) 下竟可高達7,3359 cd/m2 ，而CIE則座落於(0.21, 0.47)。在主體材料方面，以具有電子傳輸型 (ET-type) 的深藍光材料P(O)Ph2-STIF-P(O)Ph2作為主體材料，摻雜季昀教授所開發的紅光客體材料OS1 (元件結構：ITO/PEDT:PSS/NPB /TCTA/ P(O)Ph2-STIF-P(O)Ph2: 10 wt% OS1/3TPYMB/LiF/Al)，其紅色磷光元件最大放光效能(Max. Current efficiency)達到22.2 cd/A；最大功率效能(Max. Power efficiency)達到23.3 lm/W；最大外部量子效率(EQE)達到16%，最大亮度在電流密度為1,759 mA/cm2 (操作電壓: 10 V) 下可達2,9602 cd/m2，而CIE則座落於(0.63, 0.36)，與一般相關文獻的結果相符合，因此，P(O)Ph2-STIF-P(O)Ph2是一個良好的電子傳輸型 (ET-type) 的主體材料。在有機電激發白光的元件(WOLEDS)上，以主體材料Cbz-STIF-P(O)Ph2摻雜0.4%的橘黃光材料rubrene (元件結構： ITO/PEDT:PSS/NPB /TCTA/ Cbz-STIF-P(O)Ph2: 0.4 wt% Rubrene/TPBI/LiF/Al)，其元件效能在操作亮度為1,000 cd/m2下，放光效能(Current efficiency) 為11.3 cd/A；功率效能 (Power efficiency) 為4.23 lm/W；外部量子效率 (EQE) 為3.62%，最大亮度在電流密度為1,719 mA/cm2 (操作電壓: 14.5 V) 下可達到87,800 cd/m2，CIEx,y色度座標為(0.45, 0.48)，與理想白光光源的(0.33, 0.33)，有36-45%的差距，但從肉眼來看已接近白光光源，同時整體元件效能也達到最佳且最為穩定的狀態。接著，我們嘗試以日本Adachi教授所開發的熱活化型延遲螢光 (Thermally activated delayed fluorescence, TADF)的相同元件結構作為藍光元件，其主體材料為DPEPO，選用Cbz-STIF-cbz作為TADF的客體材料 (元件結構：ITO/PEDOT:PSS/NPB/TCTA/CzSi/DPEPO: 10 wt% Cbz-STIF-cbz/DPPS/BmPyPB/LiF/Al)。雖然沒有觀察到TADF的現象發生於Cbz-STIF-cbz，然而在藍色螢光元件的效能表現還算出色。其元件的驅動電壓為4.1 V，最大亮度在電流密度為538 mA/cm2 (操作電壓: 13.5 V) 下可達2,778 cd/m2，而最大放光效能(Max. Current efficiency)為2.5 cd/A；最大功率效能(Max. Power efficiency)為2.19 lm/W；最大外部量子效率(EQE)達到3.81%，而CIE則座落於(0.15, 0.07)。最後，我們使用高效率且為雙極型材料的N-STIF-CN作為綠、黃和紅光PHOLED的電子傳輸層材料，相較於一般常用的電子傳輸層材料(例如：Alq3, TPBI, BmPyPB等)，可明顯提升元件效能和壽命的表現。其中在綠光PHOLED上，採用業界的元件規格，在不加入電洞阻擋層的情況下，相對於業界採用的ET-01在綠色磷光元件效能增加率(PE: +29%; CE: +29%; EQE: +28% @1,000 cd/m2)。壽命測試方面，在初始亮度為1,000 cd/m2下，N-STIF-CN的元件半衰壽命約為210小時，非常接近ET¬-01的元件半衰壽命的270小時，顯示N-STIF-CN是相當具有潛力的電子傳輸層材料應用於PHOLED上。

二、順式二苯乙烯/芴螺旋體衍生之雙極型混成體於染料敏化太陽能電池之應用

我們成功合成以順式二苯乙烯/芴螺旋混成體為主體π-核心模板，藉由在C3位置接上雙甲苯基胺作為電子予體，在C7位置接上不同取代的受體型之π-橋體，以合成具有D-π-π-A-A系統的染料N-STIF-T-BTD-CA和具有D-π-A-π-A系統的染料N-STIF-BTD-T-CA。這一系列染料其最大的UV吸收波長在470-523 nm之間，而莫耳吸收係數則為20,801-21,690 M-1 cm-1。在元件效率方面，表現最好的材料為染料N-STIF-BTD-T-CA，在AM 1.5標準太陽光照射下元件效率(η)最大可達4.26 % (Voc = 643 mV, JSC = 8.81 mA/cm2, FF = 0.74); 而光電轉換效率(IPCE)在400-550 nm的吸收範圍中，染料N-STIF-BTD-T-CA的光電轉換效率 (IPCE) 可達到49.3%。

關鍵字

有機電激發光二極體 ； 雙極性 ； 主體材料 ； 客體摻雜物 ； 電子傳輸層材料 ； 染料敏化太陽能電池 ； 順式二苯乙烯/芴

並列摘要

1.Spirally Configured cis-Stilbene/Fluorene Hybrids as Ambiplor Templates for Organic Light Emitting Diode Applications

Organic light emitting diodes (OLEDs) have been intensively investigated in the recent years for their potential applications in next generation full-color at panel displays and solid state lighting. However, the recombination efficiency of holes and electrons with unbalanced-charge carriers is one of the key factors for making bad device efficiencies. Therefore, we developed a new class of cis-stilbene/fluorene spiro hybrid systems with hole-transporting, electron-transporting and ambipolar organic fluorescent materials for optoelectronic applications. These types of materials exhibited a stable amorphous glassy state (Tg:120-167 oC) and stable decomposition temperatures (Td: >400 oC). One of the fluorescent materials, N-STIF-P(O)Ph2, had ambipolar charge transport feature with balanced hole and electron mobilities (μh: 6.510-6 cm2/Vs; μe: 5.110-6 cm2/Vs @7.3 105 V/cm). This feature allowed us to utilize N-STIF-P(O)Ph2 successfully in a single-layer device (i.e., ITO/PEDT:PSS/ N-STIF-P(O)Ph2/LiF/Al) with excellent performance. The single layer device emitted bluish green light and showed a turn-on voltage of 2.5 V, a
maximum brightness of 73,359 cd/m2 at 5,611 mA/cm2 (8.5 V), operational current efficiency of 3.29 cd/A, power efficiency of 2.84 lm/W and EQE of 1.28% at 20 mA/cm2 with CIE color coordinates of (0.21, 0.47). Next, we demonstrated red-emitting PhOLED using the P(O)Ph2-STIF-P(O)Ph2 as the electron-transporting type host material and [Os(bpftz)2(PPhMe2)2 , OS1] as red dopant (i.e., ITO/PEDT:PSS/NPB /TCTA/ P(O)Ph2-STIF-P(O)Ph2: 10 wt% OS1/3TPYMB/LiF/Al). This device with highly efficient performance was successfully achieved, with maximum current efficiency of 22.2 cd/A, power efficiency of 23.3 lm/W, EQE of 16%, and a maximum brightness of 29,602 cd/m2 at 1,759 mA/cm2 (10 V) with CIE color coordinates of (0.63, 0.36). And then, we fabricated fluorescent white OLEDs based on 0.4 wt% rubrene-doped Cbz-STIF-P(O)Ph2 (i.e., ITO/PEDT:PSS/NPB /TCTA/ Cbz-STIF-P(O)Ph2: 0.4 wt% Rubrene/TPBI/LiF/Al). This device showed a turn-on voltage of 3.1 V, a maximum brightness of 87,800 cd/m2 at 1,719 mA/cm2 (14.5 V), operational current efficiency of 11.3 cd/A, power efficiency of 4.23 lm/W and EQE of 3.62% at 1,000 cd/m2 with CIE color coordinates of (0.45, 0.48). Compared with the CIE color coordinates of the ideal white light (CIE: 0.33, 0.33), there were 36-45% gaps between our device and ideal WOLED. However, our device was very close to the white light by the naked eye. And this device had already achieved the best performance and the most stable state. And Next, we tried to fabricate blue OLED based on thermally activated delayed fluorescence (TADF) device configuration developed by Prof. Adachi. For this blue OLED, we used the DPEPO as host material and Cbz-STIF-cbz as TADF material (i.e., ITO/PEDOT:PSS/NPB/TCTA/CzSi/DPEPO: 10 wt% Cbz-STIF-cbz/DPPS/BmPyPB/LiF/Al). Although there was no TADF observed in Cbz-STIF-cbz, this was still good device performance for blue OLED. And this device showed a turn-on voltage of 4.1 V, a
maximum brightness of 2,778 cd/m2 at 538 mA/cm2 (13.5 V), maximum current efficiency of 2.5 cd/A, power efficiency of 2.19 lm/W and EQE of 3.81% with CIE color coordinates of (0.15, 0.07). Finally, we used a highly efficient and ambipolar-type material, N-STIF-CN, as electron transporting material for green, yellow and red PHOLEDs. Compared with those devices which used common electron transporting materials (i.e., Alq3, TPBI, BmPyPB, etc.), our devices had further improved the device efficiencies and lifetime. For example, we demonstrated green PhOLED using the industry’s device configuration (i.e., ITO/HAT-CN /HT-01: 3 wt% F4-TCNQ /NPB/ TPBI: 5 wt% Ir(ppy)3/ ETL/ LiF/Al), without any hole blocking layer, N-STIF-CN could further supplant ET-01 which was often used in the industry as superior ET material with improved power efficiency by 29%, current efficiency by 29%, and EQE by 28% at 1,000 cd/m2. And for device lifetime tests, the half-life of N-STIF-CN was 210 hours and it was very close to the half-life of ET-01 which was 270 hours under the initial brightness of 1,000 cd/m2. Therefore, N-STIF-CN was very promising material based electron transporting layer for PHOLEDs.

2.Spirally Configured cis-Stilbene/Fluorene Hybrids as Ambiplor Templates for Dye-Sensitized Solar Cell Applications

A new class of cis-stilbene/fluorene spiro hybrid systems with di-p-tolylamine donor and combined benzothiadiazole (BTD) and thiophene (T) acceptor units at C-3 and C-7, respectively, were synthesized as two novel D-π-π-A-A-featured dye N-STIF-T-BTD-CA and D-π-A-π-A-featured dye N-STIF-BTD-T-CA for dye-sensitized solar cell applications. These two dyes whose maximum absorption wavelength were observed at 470 nm and 523 nm, respectively, and the molar absorption coefficient were observed at 20,801 M-1 cm-1 and 21,690 M-1 cm-1, respectively. The best device performance was D-π-A-π-A-featured dye N-STIF-BTD-T-CA, and it showed a conversion efficiency (η) of up to 4.26% (Voc = 643 mV, JSC = 8.81 mA/cm2, FF = 0.74) under AM 1.5 G conditions. And the best IPCE values achieved 49.3% within the 400–550 nm absorption range.

並列關鍵字

OLED ； ambipolar ； host material ； dopant ； electron transporting material ； DSSC ； cis-Stilbene/Fluorene

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