Critical Role of High‐Lying Triplet States for Efficient Excitons Utilization in High‐Performance Non‐Doped Deep‐Blue Fluorescent and Hybrid White Organic Light‐Emitting Diodes

Abstract

For organic light‐emitting diodes (OLEDs), the characteristics of high‐lying excited states of pure organic materials significantly affect the utilization of triplet excitons, which are critical in the process of electroluminescence. Herein, two novel molecules, PT‐1 and PT‐2, with deep‐blue emission are obtained, which exhibit nearly identical photophysical behavior in the photoluminescence process. However, the remarkable distinction in the characteristics of the high‐lying triplet excited states between PT‐1 and PT‐2 leads to a significant difference in the electroluminescence performance. Moreover, the non‐doped OLED based on PT‐1 exhibits maximum external quantum efficiency (ηext) of 6.63% with a low efficiency roll‐off. In addition, the authors employ PT‐1 as the phosphorescent host materials to fabricate two‐color hybrid white OLEDs (WOLEDs), from which they can realize the transformation from warm‐white to quasi‐white light by tuning the thickness of emission layer, with maximum ηext and power efficiency (ηp) of 23.93%/84.37 lm W−1 and 10.49%/33.96 lm W−1, respectively. These results deeply demonstrate the effects of high‐lying excited states on electroluminescence and facilitate the preparation of functional OLEDs.

Recent progress in imidazole based efficient near ultraviolet/blue hybridized local charge transfer (HLCT) characteristic fluorophores for organic light-emitting diodes

“…9). 90 These fluorophores had similar photophysical properties; however, there was a significant difference in the characteristics of the high-lying triplet excited state between PT-1 23 and PT-2 24 , leading to a noteworthy difference in the EL performance. Specifically, the PT-1 23 fluorophore can capture triplet excitons more efficiently; thus, it exhibits outstanding EL performance (Fig.…”

Improving the optoelectronic properties of blue hybridized local and charge-transfer emitters via rational utilization of intramolecular hydrogen bonds

“…[7][8][9] However, blue OLEDs still lag behind their green and red counterparts because of their intrinsically wide energy gap. [10][11][12] The current commercial green and red OLEDs are fabricated from organic-metal phosphorescent complexes; however, such materials are not suitable for manufacturing blue OLEDs because of their short operational lifetime and/or unsatisfactory color purity. 13 Thus, the development of efficient pure organic blue fluorophores is crucial for the production of full-color OLEDs.…”

Geometric Signatures as Important Factors to Control the Photo-Stabilities of the Phosphorescent Pd(II)/Pt(II) Complexes: A Case Study

“…For instance, Pt(II) and Pd(II) complexes can be regarded as phosphorescent emitters in the field of OLEDs. Over the past decades, substantial progress has been made in the development of high-performance Pt(II) and Pd(II) complexes as a result of extensive research within the academic and industrial communities, which has enabled phosphorescent OLEDs to become a main component in state-of-the-art displays as well as in next-generation solid-state lighting [ 1 , 2 , 3 , 4 , 5 ]. Secondly, as a consequence of their efficient intersystem crossing derived from metal-to-ligand charge transfer (MLCT), Pt(II) and Pd(II) complexes have been developed as popular candidates [ 6 , 7 ].…”