AIE‐active Emitters and Their Applications in OLEDs

As a solid-state lightening technology, organic light-emitting diode (OLED) has experienced a rapid progress in last few decades, and numerous emitters with different photophysical mechanisms have been designed and applied in this area. Organic emitters play an important role in deciding the OLEDs' performance not only from the molecule structures but also from the aggregated states. Currently, the aggregation-induced emission (AIE) property has attracted tremendous attentions due to its significant advantage of enhanced solid emission, which can be applied for nondoped OLEDs through facile process, with both high efficiency and low cost. Till now, numerous AIE emitters have been applied in OLED devices, therefore, in this review, we mainly demonstrate the emitters based on AIE property integrated with different photophysical mechanisms and their applications in OLED devices. So far, most of AIE emitters are traditional fluorescent. Due to the facile molecule design, the traditional fluorescent AIE emitters have covered wide range of spectrum, from blue to green and red, and even the white OLEDs based on these emitters have been fabricated. However, due to the theoretical external quantum efficiency (EQE) limitation of 5% for traditional AIE-active emitters-based OLEDs, AIE property has been combined with other high exciton utilizing efficiency (EUE) photophysical mechanisms to prepare highly efficient emitters for OLED devices. Among these emitters, the aggregation-induced phosphorescent emissive (AIPE) emitters with both AIE property and phosphorescent emission were developed first, but with only few cases regarding the emitters were reported. The aggregation-induced delayed fluorescence (AIDF) and hybridized local and charge transfer (HLCT)-AIE materials have seen a rapid development, with both numerous emitters and high EQE efficiency reported in comparison to their non-AIE-active counterparts. Finally, we give the outlook about the development of novel AIE emitters and OLED research.