An Overlooked Charge‐Transfer Interaction in the Interfacial Triplet?Triplet Upconversion Process in Blue Organic Light‐Emitting Diodes
An Overlooked Charge‐Transfer Interaction in the Interfacial Triplet?Triplet Upconversion Process in Blue Organic Light‐Emitting Diodes
复制标题
蓝色有机发光二极管界面三重态中被忽视的电荷转移相互作用？三重态上转换过程
DOI：
10.1002/adom.202200704
复制
发表时间：
2022
影响因子：
9
通讯作者：
Adachi Chihaya
中科院分区：
文献类型：
--
作者：
Nguyen Thanh Ba;Nakanotani Hajime;Adachi Chihaya
在传统的基于荧光的有机发光二极管（oled）中，两个低能三重态可以通过三重态-三重态上转换（TTU）产生一个单重态，并导致激子产率超过25%。在大多数情况下，由于这种低能量三重态不会导致OLED严重退化，因此TTU - OLED是迄今为止唯一商业化的蓝色OLED。本文阐明了空穴-输运/发射极-层界面上的电荷-转移（CT）相互作用是显著提高TTU产率的一个被忽视的途径。首先，界面处的小能量偏移使高能CT激子的形成成为可能。其次，发射层中由蒽基团产生的低能量三重态收集了界面三重态CT。第三，由于高密度界面三重态的形成，即使在低电流密度下，界面处的TTU也有助于发射层或蓝色掺杂的电致发光。这一发现强调了CT界面在纯蓝色oled中发挥TTU全部潜力的重要作用。
Two low‐energy triplets can generate one singlet via triplet–triplet upconversion (TTU), and result in an exciton production yield exceeding 25% in conventional fluorescence‐based organic light‐emitting diodes (OLEDs). In most cases, since such low‐energy triplets induce no serious OLED degradation, TTU‐OLEDs are the only commercialized blue OLEDs so far. Herein, it is clarified that the charge‐transfer (CT) interaction at a hole‐transport/emitter‐layer interface is an overlooked pathway to enhance TTU yield significantly. First, a small energy offset at the interface enables the formation of a high‐energy CT exciton. Second, the lower energy triplet state originated from an anthracene moiety in the emitter layer collects the interfacial triplet CT. Third, due to the high‐density interfacial triplets formation, TTU at the interface contributes to the electroluminescence from the emitter layer or blue dopants even at low current density. This finding underlines the important role of the CT interface to exploit the full potential of TTU in pure‐blue OLEDs.