Solution-processed white OLEDs with power efficiency over 90 lm W⁻¹ by triplet exciton management with a high triplet energy level interfacial exciplex host and a high reverse intersystem crossing rate blue TADF emitter

Abstract

Solution-processed white organic light-emitting diodes (WOLEDs) have shown much lower device efficiency than vacuum-deposited counterparts, due to the lack of triplet exciton management in single-emissive-layer device structure, which will induce...

Achieving Efficient Solution‐Processed Blue Narrowband Emitting OLEDs with Small Efficiency Roll‐Off by Using a Bulky TADF Sensitizer with High Reverse Intersystem Crossing Rate

“…The electroluminescent properties of the sensitizer were investigated first by fabricating the solution‐processed devices without the MR‐TADF emitter based on the structure of ITO/poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (50 nm)/poly(9‐vinylcarbazole) (PVK) (15 nm)/mCP: 5 t BuCzTRZ (30 nm)/2‐phenyl‐4,6‐bis(3‐(triphenylsilyl)phenyl)‐1,3,5‐triazine (mSiTRZ) (12 nm)/2,4,6‐tris(3′‐(pyridin‐3‐yl)biphenyl‐3‐yl)‐1,3,5‐triazine (TmPPPyTz) (55 nm)/LiF (1 nm)/Al (150 nm) (Figure S6, Supporting Information). [ 55 ] The 5 t BuCzTRZ devices achieve the best performance at the doping concentration of 20 wt%. The maximum EQE is 23.9% (60.6 cd A −1 ), which slowly decreases to 22.3% at 1000 cd m −2 with a small efficiency roll‐off of 6.7% (Figure S8 and Table S4, Supporting Information).…”

“…The maximum EQE is 23.9% (60.6 cd A −1 ), which slowly decreases to 22.3% at 1000 cd m −2 with a small efficiency roll‐off of 6.7% (Figure S8 and Table S4, Supporting Information). However, the EQE of 5 t BuCzTRZ is lower than that of 5CzTRZ (28.1%), [ 55 ] which could be ascribed to the lower PLQY of 5 t BuCzTRZ.…”

Interplay between Singlet and Triplet Excited States in Interface Exciplex OLEDs with Fluorescence, Phosphorescence, and TADF Emitters

“…[ 38 ] The PL spectrum is notable redshifted relative to either of the constituent molecules (Figure S2, Supporting Information), and the large Stokes shifts demonstrate the formation of interface exciplex of CDBP/B4PyPPM. [ 39 ] By doping the CDBP/B4PyPPM exciplex host with Coumarin 6, Ir(ppy) 2 acac and 4CzPN as the emitter (5.0 wt.%), the PL spectra of all emitter‐doped films show emission entirely from the emitter with the peak position at 520 nm, indicating that the energy transfer from exciplex host to emitters is efficient ( Figure a–c). Meanwhile, the change in the absorption spectrum of all the emitter‐doped films is negligible, indicating that the exciplex is still the light absorber at the excitation wavelength (200–400 nm) and subsequently transfers its energy to the emitters.…”

Roles of Molecular Spatial Arrangement in Exciton Energy Transfer in Organic Light-Emitting Diodes: A Theoretical Study

“…11,18−20 So, TADF materials have been regarded as more promising materials for OLEDs after Adachi synthesized them, 10 and TADF materials have been reported extensively in recent years. 21−24 Generally speaking, it is a consensus that TADF emitters are often co-doped with host materials 25−27 in most OLED devices to reduce triplet−triplet annihilation 15,28 and suppress concentration quenching. 29 The host materials are beneficial in dispersing TADF molecules to improve the performance of devices.…”

“…PH materials utilize triplet excitons by enhanced spin–orbital coupling between the lowest triplet excited state (T 1 ) and the ground state (S 0 ) with the help of the poisonous metals, ,, which are pollutants. Unlike PH materials, TADF materials successfully solve this problem via reverse intersystem crossing from T 1 to the lowest singlet excited state (S 1 ) under the thermal activation to make triplet excitons utilized efficiently. ,− So, TADF materials have been regarded as more promising materials for OLEDs after Adachi synthesized them, and TADF materials have been reported extensively in recent years. − Generally speaking, it is a consensus that TADF emitters are often co-doped with host materials − in most OLED devices to reduce triplet–triplet annihilation , and suppress concentration quenching . The host materials are beneficial in dispersing TADF molecules to improve the performance of devices.…”