Organic Light‐Emitting Diodes Based on a Columnar Liquid‐Crystalline Perylene Emitter

Abstract

Liquid crystalline materials possess great potential as emitters in organic light‐emitting diodes (OLEDs) due to their self‐assembling property, which may lead to anisotropic films and improved charge transport. Here, the key photophysical properties of the columnar liquid crystalline emitter perylene‐3,4,9,10‐tetracarboxylic tetraethyl ester (PTCTE) are investigated and the material is implemented into OLEDs. It is found that vacuum‐deposited PTCTE films exhibit preferential horizontal orientation of the transition dipole moment. Embedding the emitter into different host materials leads to increased photoluminescence quantum yield but reduces molecular orientation compared to the neat film. OLEDs containing PTCTE doped into an exciplex‐forming co‐host achieve very high luminance exceeding 10 000 cd m−2 at 5.7 V, which is among the best performances of OLEDs based on columnar liquid crystalline emitters reported so far.

Identification of the Key Parameters for Horizontal Transition Dipole Orientation in Fluorescent and TADF Organic Light‐Emitting Diodes

“…The figure was made using data from 53 separate reports that include EQE max and emitter orientation data on 124 materials systems. [ 20,22–24,37–85 ] While there is no correlation between EQE max and anisotropy across all data, it is clear that the highest efficiency in TADF‐ and non‐TADF‐based systems, respectively, is reached at low anisotropy factors.…”

“…Mater. 2021, 33, 2100677 [38,41,42,52,56,61,[67][68][69]74,93,110,112] The color coding corresponds to the color of the symbols plotted in Figure 10.…”

“…Figure11. Molecular structure of the emitters included in this section [38,41,42,52,56,61,[67][68][69]74,93,110,112]. The color coding corresponds to the color of the symbols plotted in Figure10.…”

Controlling the Emitter Orientation in Solution-processed Films through Introduction of Mesogenic Groups within a Multi-resonance Thermally Activated Delayed Fluorescence Emitter

“…further investigated the TDM orientation of the LC emitter perylene-3,4,9,10-tetracarboxylic tetraethyl ester (PTCTE), when doped in different host materials. 21 The TDM of PTCTE shows preferential horizontal orientation (72% horizontal) as a 2 wt% doped TCTA:TPBi film but with a low FPL of 14%; however, the orientation is isotropic in a TCTA:B3PYMPM film (FPL of 13%). 21 As a result, the OLEDs based on PTCTE/TCTA:B3PYMPM exhibited very low EQEmax below 0.3% at λEL of 550 nm, while for device based on PTCTE/TCTA:TPBi showed an improved EQEmax of 0.8% at λEL of 580 nm.…”

“…19 It is possible to infer the average orientation of the TDMs within a film, 4 which is done typically by either angle-resolved photoluminescence (ARPL) or variable-angle spectroscopic ellipsometry (VASE) studies. [19][20][21] Yokoyama's fundamental work on small molecule orientation in vacuum-deposited films has demonstrated that to minimize the surface energy, the ''first'' layer of the molecules deposited on the interface adopts a horizontal orientation, but then the molecules can quickly undergo surface diffusion until the orientation is fixed by successively overlaying molecules. 2 Indeed, the orientation of the TDM in vacuum-deposited films is influenced by not only the intrinsic anisotropy of the emitter molecule, 22 but also the temperature of the substrate, 23 and the intermolecular interactions within the emissive layer.…”