A Method to Realize Efficient Deep-Red Phosphorescent OLEDs with a Broad Spectral Profile and Low Operating Voltages

Abstract

Organic light-emitting diodes (OLEDs) used as phototherapy light sources require sufficient spectral distribution in the effective wavelength ranges and low operating voltages. Herein, a double emitting layer structure consisting of a red-emitting Ir(piq)2acac and a deep-red Ir(fliq)2acac was designed to generate a broad electroluminescence spectrum. An efficient TCTA:CN-T2T exciplex system was used as the host of the emitting layer, facilitating effective energy transfer from the exciplex host to the red and deep-red phosphors. The materials used in the exciplex host were also used as the carrier transport layers to eliminate the energy barriers and thus increase the current density. The hole injection layer structures were varied to examine the hole injection capabilities and the carrier balance. The resulting optimized phosphorescent OLEDs with a broad spectral profile exhibit a 90% coverage ratio in the target ranges from 630 to 690 nm, together with a high peak efficiency of 19.1% (10.2 cd/A and 13.8 lm/W). The proposed device only needs 5.2 V to achieve a power density of 5 mW/cm2, implying that the device could be driven via two series-connected button cell batteries. These results illustrate the feasibility of our design concepts and demonstrate the realization of a portable and lightweight OLED phototherapy light source.

Perceiving the influence of phenyl-carbazole isomers on sulfone/thioxanthone-based D–A–D hosts: realizing efficient red-phosphorescent OLEDs

“…55 Furthermore, using the same material for both layers could avoid the formation of an energy barrier at the EML and ETL, resulting in smooth electron injection into the EML. 18 Furthermore, the choice of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4′′-tris( N -carbazolyl)triphenylamine (TCTA) was made for the hole transport layers due to their appropriate HOMO levels and adequate triplet energy bandgaps. 47 These levels are conducive to gradual hole transport from the hole injection layer (HIL) to the EML, thus facilitating fluent hole injection.…”

“…11,12 To overcome this hurdle, uniform distribution of red emitters in suitable organic host materials can improve the emission efficiency of OLEDs, and several host materials have been reported. 13–19 Additionally, the selection of host materials with superior charge injection and transport capabilities, along with high thermal and operational stabilities, plays a crucial role in achieving high efficiency. 20–22 Extensive research is urgently needed to achieve highly efficient red PhOLEDs.…”

Highly efficient (EQE > 27%) Yellow OLEDs using spiro[fluorene-9,9′-phenanthren-10′-one]-carbazole-based donor–acceptor–donor host materials

“…Therefore, green-emitting Ir(ppy) 3 was used as the emitter for the host materials MS-CN and MS-OC , while yellow-emitting PO-01 and red-emitting Ir(piq) 2 acac were doped into all synthesized host materials to construct the EML. 28–30 Two commonly used hole-transporting materials, namely, bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4′′-tris( N -carbazolyl)triphenylamine (TCTA), were chosen to form step-wise hole-transport layers (HTLs), aiming to promote smooth hole injection from the HTL into the EML. 31 Moreover, as mentioned above, CN-T2T with appropriate electron transport properties was used as the electron transport layer (ETL).…”

Exciplex forming a Phenyl-Spaced Phenoxazine D–A Cohost for a Highly Efficient Red-Phosphorescent Organic Light-Emitting Diode

“…Since the corresponding triplet energy band gap of these compounds ranges from 2.28 to 2.78 eV, they are considered suitable hosts for a red-emitting Ir(piq) 2 acac emitter to facilitate an effective energy transfer between the host and emitter. 24 Moreover, given the different carrier transport capabilities and the energy band gaps of the target compounds, we carefully regulated the thicknesses of each layer in the materials used to optimize the EL efficiency. As a result, 1,1bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4′,4″tris(carbazol-9-yl)-triphenylamine (TCTA) were combined to form stepwise hole transport layers (HTLs) because of their appropriate HOMO levels.…”