Li Yungui, Van der Zee Bas, Tan Xiao, Zhou Xin, Wetzelaer Gert-Jan A H, Blom Paul W M
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Adv Mater. 2023 Dec;35(49):e2304728. doi: 10.1002/adma.202304728. Epub 2023 Oct 27.
Highly efficient organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters are realized in recent years, but the device lifetime needs further improvement for practical display or lighting applications. In this work, a device design principle is presented by tuning the optical cavity of single-layer undoped devices, to realize efficient and long-lived TADF OLEDs. Extending the cavity length to the second-order interference maximum by increasing the emissive layer thickness broadens the recombination zone, while the optical outcoupling efficiency remains close to that of the thinner first-order devices. Such a device design leads to efficient and stable single-layer undoped OLEDs with a maximum external quantum efficiency of 16%, an LT of 452 h, and an LT of 3693 h at an initial luminance of 1000 cd m , which is doubled compared to the first-order counterparts. It is further demonstrated that the widely-used empirical relation between OLED lifetime and light intensity originates from triplet-polaron annihilation, resulting in an extrapolated LT at 100 cd m of close to 90 000 h, approaching the demands for practical backlight applications.
近年来，基于热激活延迟荧光（TADF）发光体的高效有机发光二极管（OLED）得以实现，但对于实际的显示或照明应用而言，器件寿命仍需进一步提高。在这项工作中，通过调整单层未掺杂器件的光学腔，提出了一种器件设计原则，以实现高效且长寿命的TADF OLED。通过增加发射层厚度将腔长扩展至二阶干涉最大值，可拓宽复合区，而光外耦合效率仍接近较薄的一阶器件。这种器件设计可实现高效且稳定的单层未掺杂OLED，在初始亮度为1000 cd m 时，最大外量子效率为16%，寿命为452小时，寿命为3693小时，与一阶同类器件相比增加了一倍。进一步证明，OLED寿命与光强之间广泛使用的经验关系源于三重态 - 极化子湮灭，在100 cd m 时外推的寿命接近90000小时，接近实际背光源应用的要求。
