Thermally Activated Delayed Fluorescence in Commercially Available Materials for Solution-Process Exciplex OLEDs

Abstract

Organic light-emitting diodes (OLEDs) have developed rapidly in recent years. Thermally activated delayed fluorescent (TADF) molecules open a path to increase exciton collection efficiency from 25% to 100%, and the solution process provides an alternative technology to achieve lower cost OLEDs more easily. To develop commercial materials as exciplex hosts for high-performance and solution-processed OLEDs, we attempted to use 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine (TAPC), poly(9-vinylcarbazole) (PVK), N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB), and poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (Poly-TPD) as the donors and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (POT2T) as the acceptor to obtain the TADF effect. All donors and the acceptor were purchased from chemical suppliers. Our work shows that excellent TADF properties and high-efficiency exciplex OLEDs with low turn-on voltage and high luminance can be achieved with a simple combination of commercial materials.

White vertical organic permeable-base light-emitting transistors obtained by mixing of blue exciton and orange interface exciplex emissions

“…The obtained EL spectrum was very similar to the PL spectrum of exciplex TAPC:PO-T2T. 17 The observed EL proved that electrons can pass through the permeable base. Fig.…”

Solution-processed high efficiency OLED harnessing a thermally cross-linked hole-transporting layer and exciplex-forming emission layer

“…17 For example, Tseng and coworkers demonstrated the use of a TAPC : PO-T2T blend as the emitting layer (EML) with efficient green exciplex emission to fabricate a solution-processed device with EQE max of 7.1%. 18 Though solution-processed technologies for OLEDs are still under development, this promising method presents potential benefits over the mainstream physical vapor deposition, such as the exclusion of expensive vacuum equipment, effective material utilization efficiency, and scalable and uniform large-area film production on flexible substrates. 19 Typically, solution processes involve the coating of functional material solutions onto (indium tin oxide) ITO-treated substrates, followed by drying the layer to obtain films.…”

High-PLQY and Efficient Upconverted Fluorescence of the TAPC/PBD Exciplex with Fluorescent Guests

“…13,14 Thanks to their efficient energy harvesting mechanism, exciplex-based TADF materials have rapidly grown into star materials in the field of organic light-emitting diodes (OLEDs). 8,15,16 Recently, further improvements in device stability and quantum efficiency have been achieved by introducing small amounts of fluorescent guests into D−A exciplex hosts. 17−19 The rapid long-range Forster resonance energy transfer (FRET) process from 1 EX to the singlet states of fluorescent guests ( 1 EM) reduces the nonradiative energy loss, thereby improving OLED performance.…”

“…Besides single-component chromophores, multicomponent molecular solids have also been developed owing to their interesting novel characteristics induced by multifunctional collective effects among different components. , For example, an exciplex composed of the designed donor (D) and acceptor (A) in which the energy splitting Δ E ST between singlet ( 1 EX) and triplet ( 3 EX) states can be very small to facilitate the room temperature reverse intersystem crossing (RISC) process leads to available thermally activated delayed fluorescence (TADF) and thus significantly improves fluorescence quantum efficiency. , Thanks to their efficient energy harvesting mechanism, exciplex-based TADF materials have rapidly grown into star materials in the field of organic light-emitting diodes (OLEDs). ,, Recently, further improvements in device stability and quantum efficiency have been achieved by introducing small amounts of fluorescent guests into D–A exciplex hosts. − The rapid long-range Förster resonance energy transfer (FRET) process from 1 EX to the singlet states of fluorescent guests ( 1 EM) reduces the nonradiative energy loss, thereby improving OLED performance. − …”