Siddiqui Qamar T, Awasthi Ankur A, Bhui Prabhjyot, Parab Pradnya, Muneer Mohammad, Bose Sangita, Agarwal Neeraj
School of Chemical Sciences, UM-DAE, Centre for Excellence in Basic Sciences, University of Mumbai Santacruz (E) Mumbai 400098 India
Department of Chemistry, Aligarh Muslim University Aligarh India.
RSC Adv. 2019 Dec 4;9(69):40248-40254. doi: 10.1039/c9ra08227a. eCollection 2019 Dec 3.
Materials showing white light emission have found applications in a variety of solid state devices especially in display technology. For white light emission, doping of red (R), green (G) and blue (B) emitters in a host matrix is commonly practised. However, finding RGB emitters of similar stability with homogenous doping is challenging. Furthermore, such devices suffer from color purity in the long run. Small organic light emitters, capable of colour tuning and having a broad emission spectrum are in high demand as they provide colour stability, reproducibility, a simple device geometry and high efficiency. Recently, it has been shown that the efficiency of OLEDs can be enhanced by employing thermally activated delayed fluorescence (TADF) materials. Here, we designed and synthesised a xanthone-carbazole based D-A-D material (Xan-Cbz) for TADF properties. Blue TADF emission, in neat thin films, at 470 nm was observed and further investigated by studying delayed fluorescence and lifetime measurements. In addition, a blend of Xan-Cbz with NPD shows exciplex emission at 525 nm in thin film. OLEDs based on Xan-Cbz were fabricated using several device configurations. OLEDs having the device configuration ITO/PEDOT:PSS/NPD/Xan-Cbz/Bphen/LiF-Al showed a luminance of 1.96 × 10 Cd m (at a current density of 50 mA cm) and at ∼6 V. Electroluminescence showed the features of both neat emission (470 nm) of Xan-Cbz and its exciplex (525 nm) with NPD. Further, colour tuning was observed as a function of applied voltage and the ratio of light intensity ( / ) of neat and exciplex emission was found to decrease with increasing voltage. Greenish-blue emission (CIE coordinates: 0.202, 0.382) from Xan-Cbz OLEDs was obtained. Xan-Cbz showed its neat emission (at 470 nm) in ITO/PEDOT:PSS/CBP/Xan-Cbz/Bphen/LiF-Al and pure exciplex emission (at 525 nm) in ITO/PEDOT:PSS/NPD:Xan-Cbz/Bphen/LiF-Al device configurations. Thus in this article we showed blue TADF emission, exciplex emission and voltage dependent color tuning in OLEDs based on a small organic emitter.
发出白光的材料已在各种固态器件中得到应用，尤其是在显示技术领域。对于白光发射，通常会在主体基质中掺杂红色（R）、绿色（G）和蓝色（B）发光体。然而，要找到具有相似稳定性且能均匀掺杂的RGB发光体具有挑战性。此外，从长远来看，此类器件存在颜色纯度问题。能够进行颜色调节且具有宽发射光谱的小型有机发光体需求很大，因为它们具有颜色稳定性、可重复性、简单的器件几何结构和高效率。最近，研究表明采用热激活延迟荧光（TADF）材料可以提高有机发光二极管（OLED）的效率。在此，我们设计并合成了一种基于呫吨酮 - 咔唑的D - A - D材料（Xan - Cbz）以实现TADF特性。在纯薄膜中观察到了470 nm处的蓝色TADF发射，并通过研究延迟荧光和寿命测量进行了进一步研究。此外，Xan - Cbz与NPD的混合物在薄膜中于525 nm处显示出激基复合物发射。基于Xan - Cbz的OLED采用了几种器件结构进行制造。具有ITO/PEDOT:PSS/NPD/Xan - Cbz/Bphen/LiF - Al器件结构的OLED在50 mA cm的电流密度下，于约6 V时显示出1.96×10 Cd m的亮度。电致发光显示出Xan - Cbz的纯发射（470 nm）及其与NPD的激基复合物（525 nm）的特征。此外，观察到颜色随施加电压而调节，并且发现纯发射与激基复合物发射的光强度比（/）随电压增加而降低。从Xan - Cbz OLED获得了绿蓝色发射（CIE坐标：0.202，0.382）。Xan - Cbz在ITO/PEDOT:PSS/CBP/Xan - Cbz/Bphen/LiF - Al器件结构中显示出其纯发射（470 nm），在ITO/PEDOT:PSS/NPD:Xan - Cbz/Bphen/LiF - Al器件结构中显示出纯激基复合物发射（525 nm）。因此，在本文中我们展示了基于小型有机发光体的OLED中的蓝色TADF发射、激基复合物发射以及电压依赖性颜色调节。
