Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light‐Emitting Diodes Based on a Single Emissive Layer

Abstract

White organic light‐emitting diode (WOLED) technology has attracted considerable attention because of its potential use as a next‐generation solid‐state lighting source. However, most of the reported WOLEDs that employ the combination of multi‐emissive materials to generate white emission may suffer from color instability, high material cost, and a complex fabrication procedure which can be diminished by the single‐emitter‐based WOLED. Herein, a color‐tunable material, tris(4‐(phenylethynyl)phenyl)amine (TPEPA), is reported, whose photoluminescence (PL) spectrum is altered by adjusting the thermal annealing temperature nearly encompassing the entire visible spectra. Density functional theory calculations and transmission electron microscopy results offer mechanistic understanding of the PL redshift resulting from thermally activated rotation of benzene rings and rotation of 4‐(phenylethynyl) phenyl)amine connected to the central nitrogen atom that lead to formation of ordered molecular packing which improves the π–π stacking degree and increases electronic coupling. Further, by precisely controlling the annealing time and temperature, a white‐light OLED is fabricated with the maximum external quantum efficiency of 3.4% with TPEPA as the only emissive molecule. As far as it is known, thus far, this is the best performance achieved for single small organic molecule based WOLED devices.

Single‐Molecular White‐Light Emitters and Their Potential WOLED Applications

“…Most importantly, due to the lack of efficient and stable deep blue emitters, the general characteristic of voltage‐dependent CIE chromaticity coordinates in multilayered WOLEDs would result in an unstable emission color of the devices . Therefore, a single‐molecular system, which is white‐light emissive, would be an ideal material to develop a highly efficient WOLED with less phase separation, more simple device structure and stable emission color . To date, there are some review articles on the white‐light generation from a single phase, in which multifunctional molecules are used to assemble the white‐light emissive supramolecules or nanostructures .…”

Centimeter-scale hole diffusion and its application in organic light-emitting diodes for reducing efficiency roll-off and enhancing operation lifetime

“…However, these accumulated holes can form polarons and can quench excitons via excitonpolaron annihilation leading to decreased efficiency and operation lifetime [15][16][17][18][19][20][21][22][23][24] . It can be seen that in either scenario, both efficiency and operation lifetime are harmfully affected.…”

Research progress of full electroluminescent white light-emitting diodes based on a single emissive layer

“…4 . For example, in some organic molecules 16 , 38 such as triphenylamine derivatives, thermally activated rotation in the molecular structure leads to the enhancement of π–π stacking and electronic coupling, which thereby results in a redshift in some molecules. In some crystals, the lattice distortion-induced self-trapping state can also promote the coexistence of multicolour centres and has attracted much attention for some perovskite emitters in recent years, such as Cs 2 Ag 0.60 Na 0.40 InCl 6 , δ -CsPbI 3 , and CsCu 2 I 3 26 , 28 , 29 .…”

“…Li, X. et al reported a small molecule, tris(4-(phenylethynyl)phenyl) amine (TPEPA), with the characteristic adjustable photoluminescence (PL) spectrum covering almost the entire visible-light band, which was controlled by annealing temperature (Fig. 6d ) 16 . When the annealing temperature is reached, the benzene ring and bis(phenylethylnyl)benzene in the organic molecular structure rotate, which changes the energy level and forms different species that emit blue, green, and red colours (Fig.…”

“…Here, we summarise the performance of some SEL–WLEDs that include broad-spectrum emitters, which are generally materials that possess the coelectroluminescence of multicolour centres (e.g., triphenylamine derivatives, CsPbCl 3 : Sm 3+ , δ -CsPbI 3 , and CsCu 2 I 3 ), as shown in Table 1 . In the last two decades, following the development of OLEDs, some copolymers and small molecules have been developed for SEL–WOLEDs 16 , 38 , 48 , 49 , 61 . Single-emitting layers formed by spin coating (SC) or vacuum thermal evaporation (VTE) have been proven to achieve multicolour coemission and high brightness.…”