高效率色溫可調變有機發光二極體

摘要照明的光色，對人體的生理與心理，有極大的影響；白天工作，需要明亮的環境，此時，可以使用含有藍光的高色溫光源；入夜之後，明亮的光線，尤其當中的藍光，會顯著抑制退黑激素的分泌；若仍有照明需求時，應使用低或無藍光的低色溫或超低色溫光源，以減低光照對褪黑激素分泌的影響。有機發光二極體（Organic Light-Emitting Diode, OLED）可藉由染料的選用與元件的結構設計，使其發光光色具有像自然光般的光色與色溫變化，以提供人們更高品質的照明光源。本研究使用螢、磷發光染料混合元件，並在兩個發光層間插入一載子調製層(carrier modulation layer)，開發出一高效率且色溫調整範圍涵蓋1,900K到2,900K之OLED。所製備的元件分成三部分探討。第一發部分，探討第一發光層主體（3P-T2T）與共主體（TPD-15）材料的比例，對於元件色溫變化與效率的影響。在此部分研究中，當第一發光層的主體材料與共主體材料比例為1:1時，電壓由3V調整至6V時，色溫由6,202K變化至14,339K，而當主體材料與共主體材料比例在3:1時，在相同條件下，色溫則從1,758K變化至2,708K。在1,000 cd/m2的亮度下，後者的電流效率為29.2 cd/A，功率效率為28.8 lm/W，是前者的4.36倍與4.65倍。這是因為共主體材料TPD-15的電洞傳輸性佳，適當添加有助提升元件效率，但當其在第一發光層中濃度過高時（3P-T2T：TPD-15=1:1），則容易將電洞傳遞至第二發光層，使結合區往藍色螢光材料所在第二發光層偏移，讓元件發光效率變低。在第二部分，探討天藍光藍色染料Ide-102與藍光染料DSB對於元件色溫變化與效率的影響。結果發現，使用的兩種藍光染料都可使元件的色溫沿黑體輻射曲線移動；元件從3V到6V的色溫變化分別為1,758K到2,708K（Ide-102）與1,750K到2,436K（DSB）；在1,000 cd/m2下之電流效率分別為29.2 cd/A與26.9 cd/A，功率效率分別為28.8 lm/W與26.7 lm/W。此結果說明，第二發光層的藍色染料，也影響了元件的發光特性，而第二發光層使用天藍色染料Ide-102在光電特性與色溫跨度有較佳的結果。第三部分中，研究了改變載子調製層的組成、與第一、第二發光層的相對厚度，對元件色溫變化、光電特性與壽命的影響。結果顯示，在第一發光層厚度60 Å/載子調製層30 Å/第二發光層厚度210 Å時，元件在3V到6V的電壓調變下，色溫會從1,881K變化到2,843K，且變化貼近黑體輻射曲線，此兩光色相對應的褪黑激素抑制程度（Melatonin Suppression Sensitivity, MSS）為 1.29%與7.38%，而相對應的視網膜最大可忍受之曝照極限值（Maximum Permissible Exposure, MPE）為57,853秒與3,938秒；同時，在1,000 cd/m2亮度下的色溫、電流效率、功率效率和自然光譜相似指數（Spectrum Resemblance Index, SRI）分別為1,892K、40.3 cd/A、40.0 lm/W和82.2；此元件在100 mA/cm2定電流（初始亮度為21,461 cd/m2）下之壽命半衰期為25.08小時。此元件特性良好的結果可歸因於：第一與第二發光層的厚度分配合宜、以及選用合適的載子調製層的成份，因而達到有效將激子分配在兩個發光層中，使得染料有效地放光。總括而言，本研究利用螢、磷混和元件並藉由兩種材料組成的載子調製層製造出了高效率、長壽命、高光質且色溫調整範圍在1,900K~2,900K的OLED元件，是一適合全天候使用的高品質照明光源。

關鍵字

有機發光二極體； OLED ；載子調製層；高效率；高光質；色溫可調

並列摘要

Abstract The color of the light can significantly impact humans’ physical and mental health. The color temperature of cool white light may be desired where daily work is conducted. Lighting sources, especially with blue light, could enormously suppress the secretion of the melatonin after dusk. To minimize the risk of suppression of lighting for melatonin secretion, it is advised to opt for a light with lower color temperature or without the blue light. A high-quality and demanding organic light-emitting diode (OLED) can change its emissive colors and color temperature similar to natural lighting, i.e., the color temperature ranging from 1,900 to 3,000K, by selecting suitable emitting materials and a well-designed device structure. This study presents a desired device using a mix of fluorescent and phosphorescent emitting dyes system and adding a carrier modulation layer in-between. The study result is divided into three sections shown as follows.. First, we discuss the effects of the ratio between the host (3P-T2T) and co-host (TPD-15) on efficiency and color temperature of the devices. The color temperature changes from 6,202K to 14,339K as the ratio of the first emitting layer between the host (3P-T2T) and co-host (TPD-15) is 1:1, and driving voltage is increased from 3V to 6V. It changes from 1,758K to 2,708K at the same voltage range as the ratio was 3:1. At 1,000 cd/m2, the current efficacy is 29.2 cd/A, and the power efficacy is 28.8 lm/W, which is 3.36 times and 3.65 times stronger than the former one. The reason to produce better outputs is that the co-host material TPD-15 has better characteristics of hole transport. It is likely to transfer electricity through the hole transport of the second emitting layer, as the ratio of the first emitting layer is higher than expected (3P-T2T: TPD-15=1:1). This would cause less efficiency of the device because the electricity in connected area is shifted to the second emitting layer where the blue fluorescent material is located. Second, we discuss the effect of sky blue dyes Ide-102 and blue dyes DSB on the variety of color temperature and efficiency. The results show that the color temperature of the device using these two blue dyes moves along the black-body radiation. When the driving voltage of the device increases from 3V to 6V, the color temperature changes from 1,758K to 2,708K (Ide-102) and 1,750K to 2,436K (DSB) correspondently, when luminosity is 1,000 cd/m2, current efficiency is 29.2 cd/A and 26.9 cd/A, the power’s efficacy is 28.8 lm/W and 26.7 lm/W respectively. This result demonstrates that the blue dyes in the second emitting layer also affects the emitting characteristics of the device. The use of sky blue dyes Ide-102 in the second emitting layer has better results in terms of photoelectric characteristics and color temperature. Third, we studied the change of the relative thickness of the first and second emitting layers, and the composition of the carrier modulation layer. Moreover, the influence of these two variables on the color temperature change, photoelectric characteristics and life of the component is observed.The results show that when the thickness of the first emitting layer is 40 Å, the carrier modulation layer is 30 Å. Furthermore, the thickness of the second emitting layer is 230 Å, the color temperature of the device will change from 1,781K to 2,903K under voltage change from 3V to 6V, and the change is close to the black-body radiation. The Melatonin Suppression Sensitivity (MSS) of these two light colors is 1.29% and 7.38%, and the corresponding Maximum Permissible Exposure (MPE) is 52,675 seconds and 4,462 seconds. In addition, the color temperature, the current efficiency, power efficacy and Spectral Resemblance Index (SRI) at 1,000 cd/m2 are 1,892K, 37.2 cd/A, 36.9 lm/ W and 82.2 respectively and the half-life of this device is 28.75 hours at a constant current driving of 100 mA/cm2 ( the initial luminance is 26,078 cd/m2). The favorable characteristics of this device can be attributed to the thickness distribution of the first and second emitting layers and the composition of the appropriate carrier modulation layer. As a result, the excitons are effectively distributed in the two emitting layers so that the material emits light effectively. Lastly, the study confirms that a device composed of fluorescent and phosphorescent dyes as carrier modulation layer result in an OLED device of high efficiency. Its features of high efficiency, better lumens depreciation, high lighting quality and range of color temperature from 1,900K~2,900K can be a light source for all year round.