Mixed-Host Systems with a Simple Device Structure for Efficient Solution-Processed Organic Light-Emitting Diodes of a Red-Orange TADF Emitter

Abstract

Charge balance, concentration quenching, and exciton confinement are the most important factors for realizing the use of thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes. Red-orange organic light-emitting diodes of a TADF emitter 2-[4 (diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA) have been reported by doping in a mixed p-type host system of poly(Nvinylcarbazole) (PVK) and 1,3-bis(N-carbazolyl)benzene (mCP) via solution-processed. We have demonstrated the peak external quantum efficiency of 9.75%, maximum current efficiency of 19.36 cd/A, and power efficiency of 12.17 lm/W along with a CIE coordinate of (0.45, 0.51). The devices were compared with different doping concentrations of TXO-TPA, and a comparative investigation on the effect of the thickness electron transport layer was studied. The results clearly indicated that this solution-processed TXO-TPA device structure is a promising strategy to develop highly efficient but simple OLED structures.

Diluted exciplex concentrations in organic light emitting diodes for blue-shifted spectra and improved efficiency

“…6 A series of high efficiency TADF emitters with blue, green, orange and red emissions had been explored in the past decade. [7][8][9][10] TADF emitters show monomolecular emission with intramolecular charge transfer 11 and the achievement of high efficiency is derived from efficient reverse intersystem crossing (RISC) of triplet excitons due to the small singlet-triplet energy level splitting (DE ST ). 12 Besides, a kind of bimolecular emission 13 in OLEDs, which is known as the exciplex emission, 14 occurring due to the interaction between the donor and acceptor has also attracted attention.…”

“…19 Liang et al developed an electron acceptor of 1-phenyl-1H-benzo[d]imidazole(1,3,5-triazine) (PIM-TRZ) based benzimidazole-triazine to fabricate a series of green exciplexes with di-[4-(N,N-ditolyl amino)-phenyl]cyclohexane (TAPC), 4,4 0 ,4 00tris(N-carbazolyl) triphenylamine (TCTA) and 9,9 0 ,9 00 -triphenyl-9H,9H 0 ,9H 00 -[3,3 0 :6 0 ,3 00 ]-tercarbazole (Tris-Cz) as donors, and finally high maximum EQEs of 21.7%, 19.1% and 18.6% were realized, respectively. 20 [9,1]quinolizino [3,4,5,6,7-defg]acridine (DEX) and a PO-T2T acceptor to form a green exciplex at 520 nm with an EQE of 11.2%. 21 Hu et al achieved a highly efficient yellow exciplex with an emission peak at 566 nm and an EQE of 9.7% by using triazatruxene-based molecules Tr-Tol as the donor and 2,4,6-tris(3-(1H-pyrazol-1-yl)phenyl)-1,3,5-triazine (3P-T2T) as the acceptor, respectively.…”

Effect of a twin-emitter design strategy on a previously reported thermally activated delayed fluorescence organic light-emitting diode

“…The PVK layer is applied to facilitate hole injection from PEDOT:PSS to the emitting layer. Besides, PVK and PPF, possessing high T 1 energies of 3.0 eV [ 41 ] and 3.1 eV [ 42 ], respectively, were inserted to confine the excitons in the emitting layer. PEDOT:PSS, PVK and the emitting layer were fabricated by spin-coating, and the other layers were vacuum-deposited.…”

Insights into Charge Transport in High-Efficiency Green Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with a Single Emitting Layer

“…The OLEDs with 1 and 2 wt % of emitter exhibited V on near 7 V; however, devices based on 5, 8, and 10 wt % of 2PXZ-OXD showed a lower V on of 5 V. Such values of V on are relatively very low taking into account the simple, "one organic" layer device structure, considering ITO/PEDOT:PSS as an optimized anode. 42 A decrease of V on with increasing emitter concentration can be explained by changes in the electrical carrier mobility inside the active layer, allowing a more electrically balanced device and, simultaneously, a possible decrease in the interfacial barriers through a more injected electrical carrier into the TADF emitter. First of all, the L max of devices with the EML containing 5, 8, and 10 wt % of 2PXZ-OXD reached 7456, 7240, and 8061 cd/ m 2 (at 18 V), which are much higher values than those of devices with a lower doping concentration of the emitter.…”