Enhancement of Förster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

Abstract

Fluorescence/phosphorescence hybrid white organic light-emitting devices (WOLEDs) based on double emitting layers (EMLs) with high color stability are fabricated. The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence (TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone (DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate) ((tbt) 2 Ir(acac)). Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline (Bphen) and 1,3,5-tris(2-Nphenylbenzimidazolyl) benzene (TPBi) are selected as the electron transporting layer (ETL), and the thickness of yellow EML is adjusted to optimize device performance. The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l'Eclairage (CIE) coordinates variation of (0.017, 0.009) at a luminance ranging from 52 cd/m 2 to 6998 cd/m 2 . The TPBi-based device yields a high efficiency with a maximum external quantum efficiency (EQE), current efficiency, and power efficiency of 10%, 21.1 cd/A, and 21.3 lm/W, respectively. The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer, so that Förster energy transfer (FRET) from DMAC-DPS to (tbt) 2 Ir(acac) is dominant, which is beneficial to keep the color stable. The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

Exploring plasmons weakly coupling to perovskite excitons with tunable emission by energy transfer

“…The Dexter energy transfer (DET) is thought to be energy transfer as a result of exchanging electrons at an electron cloud overlap. [29] It (also called Dexter electron exchange) is a fluorescence quenching mecha-nism in which an excited electron is transferred from one molecule (a donor) to a second molecule (an acceptor) via a non-radiative path. This process requires a wavefunction overlap between the donor and acceptor, which means it can only occur at short distances, typically within 1 nm.…”

“…Another type of nonradiative energy transfer is the direct exchange of electrons between two molecules, involving the overlap of electron clouds or the contact of molecules. [29] This process, called Dexter energy transfer (DET), is different from FRET and is suitable for long-range energy transfer with an intermolecular distance of 5 nm to 10 nm. [30] It is only suitable for short-range energy transfer with intermolecular distances within 1.5 nm.…”

Recent progress on organic light-emitting diodes with phosphorescent ultrathin (<1nm) light-emitting layers

“…In this respect, a sky-blue TADF emitter DMAC-DPS first caught the eye of researchers because of its high T 1 level (2.9 eV) and PLQY (0.88) in neat film. In addition, DMAC-DPS also exhibits a broad emission spectrum with a full width at half maximum of about 80 nm ( Wang et al., 2017 ; Zhao et al., 2017 ). Thus, in 2017, Yu et al.…”

Luminescent properties of thermally activated delayed fluorescence molecule with intramolecular π – π interaction between donor and acceptor

“…Great progress has been made in the last three decades on the development of organic light-emitting diodes (OLEDs). [1][2][3][4] As the third generation of OLEDs, the thermally activated delayed fluorescence (TADF) materials have received extensive attention in recent years [5][6][7][8][9][10] since the pioneering work was performed by Adachi and co-workers in 2012. [11][12][13] TADF materials are pure organic molecules which are cheaper than phosphorescence materials and will not cause environment pollution.…”