Miwa Takuya, Kubo Shosei, Shizu Katsuyuki, Komino Takeshi, Adachi Chihaya, Kaji Hironori
Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.
Sci Rep. 2017 Mar 21;7(1):284. doi: 10.1038/s41598-017-00368-5.
Improving the performance of blue organic light-emitting diodes (OLEDs) is needed for full-colour flat-panel displays and solid-state lighting sources. The use of thermally activated delayed fluorescence (TADF) is a promising approach to efficient blue electroluminescence. However, the difficulty of developing efficient blue TADF emitters lies in finding a molecular structure that simultaneously incorporates (i) a small energy difference between the lowest excited singlet state (S) and the lowest triplet state (T), ΔE , (ii) a large oscillator strength, f, between S and the ground state (S), and (iii) S energy sufficiently high for blue emission. In this study, we develop TADF emitters named CCX-I and CCX-II satisfying the above requirements. They show blue photoluminescence and high triplet-to-singlet up-conversion yield. In addition, their transition dipole moments are horizontally oriented, resulting in further increase of their electroluminescence efficiency. Using CCX-II as an emitting dopant, we achieve a blue OLED showing a high external quantum efficiency of 25.9%, which is one of the highest EQEs in blue OLEDs reported previously.
全彩色平板显示器和固态照明光源需要提高蓝色有机发光二极管（OLED）的性能。利用热激活延迟荧光（TADF）是实现高效蓝色电致发光的一种很有前景的方法。然而，开发高效蓝色TADF发光体的困难在于找到一种分子结构，该结构同时具备以下条件：（i）最低激发单重态（S）和最低三重态（T）之间的能量差ΔE较小；（ii）S与基态（S）之间具有较大的振子强度f；（iii）S的能量足够高以实现蓝色发射。在本研究中，我们开发了满足上述要求的名为CCX-I和CCX-II的TADF发光体。它们表现出蓝色光致发光和高三重态到单重态的上转换产率。此外，它们的跃迁偶极矩呈水平取向，从而进一步提高了它们的电致发光效率。使用CCX-II作为发光掺杂剂，我们实现了一种蓝色OLED，其外部量子效率高达25.9%，这是此前报道的蓝色OLED中最高的外量子效率之一。
