Abstract

The origin of efficiency-lifetime trade-off in triplet–triplet fusion (TTF) type blue fluorescent organic light-emitting diodes (OLEDs) was investigated and the device structure to resolve the issue was developed. The efficiency and lifetime were simultaneously improved in the blue OLEDs by developing a multilayer hole transport stack which can adjust carrier densities and recombination zone in the emitting layer (EML). It was found that electron leakage from EML and high spatial density of excitons in the vicinity of the electron blocking layer for high TTF rates by narrow recombination zone are the detrimental factors for efficiency-lifetime trade-off. A multilayer hole transport stack employing a deep highest occupied molecular orbital hole transport layer and an electron blocking layer combined with an appropriate hole blocking layer simultaneously improved the power efficiency by 16% at 500 cd/m² and lifetime by almost 100% (from 73 h up to 145 h). In addition, the low efficiency in the low luminance region was also completely controlled, resulting in negligible efficiency variation in the entire luminance range.

Graphic Abstract

抽象的

研究了三重态-三重态融合（TTF）型蓝色荧光有机发光二极管（OLED）的效率-寿命折衷的起源，并开发了解决该问题的器件结构。通过开发可以调节载流子密度和发光层（EML）中复合区的多层空穴传输堆栈，可以同时提高蓝色OLED的效率和寿命。已经发现，由于狭窄的复合区，对于高TTF速率，EML中的电子泄漏和激子在电子阻挡层附近的高空间密度是效率-寿命折衷的不利因素。²和几乎100％的使用寿命（从73小时到145小时）。另外，还完全控制了低亮度区域中的低效率，导致整个亮度范围内的效率变化可忽略不计。

图形摘要