Solution-processed Phosphorescent Organic Light-emitting Devices Research Articles

Strategy to improve the efficiency of solution-processed phosphorescent organic light-emitting devices by modified TADF host with tert-butyl carbazole

A new bipolar host material t3Cz-SO was designed and synthesized by introducing tert-butyl carbazole unit to the peripheral of parent TADF units. The calculated triplet energy and ΔEST of t3Cz-SO are 2.85 and 0.11 eV, respectively. Moreover, t3Cz-SO exhibited excellent film-forming ability and morphological stability, which are suitable for the fabrication of solution-processed OLEDs. The FIrpic-based device host with t3Cz-SO achieved low turn-on voltage of 3.5 V and high power efficiency of 16.5 lm W−1, which is almost ten times higher than the unmodified parent TADF molecule. This study shows that the introduction of tert-butyl carbazole unit to the periphery of small molecular TADF emitter is an effective method for the development of efficient electroluminescent materials.

Universal polymeric hosts adopting cardo-type backbone prepared by palladium-free catalyst with precisely controlled triplet energy levels and their application for highly efficient solution-processed phosphorescent organic light-emitting devices

A series of polymeric hosts with cardo-type backbone have been successfully developed with cheap palladium-free catalyst through controlling the special orientation of different monomers. By engineering the configuration of polymer backbones with different number and kind of the functional groups attached to the monomers, the triplet energy-levels (ETs) of these new polymeric hosts can be precisely controlled from 1.92 to 2.83 eV. Importantly, the functional groups on the monomers can afford improved and balanced charge carrier injection/transporting ability to these polymeric hosts. In addition, these polymeric hosts can show good thermal property with decomposition temperatures (Td) higher 410 °C and glass transition temperatures (Tg) higher than 170 °C. Benefitting from all these advanced properties, solution-processed phosphorescent organic light-emitting devices (PhOLEDs) based on these polymeric hosts can show impressive electroluminescence (EL) performances. The optimized blue device B2 possesses a maximum luminance efficiency (ηL) of 25.5 cd A−1, corresponding to a power efficiency (ηP) of 19.9 lm W−1 and an external quantum efficiency (ηext) of 11.3%. The maximum ηL, ηP and ηext for the optimized green device G2 are 66.9 cd A−1, 62.8 lm W−1 and 19.5%, respectively, while EL efficiencies of the optimized red device R2 can reach 11.0 cd A−1, 9.4 lm W−1 and 15.5%. All of the promising EL data achieved by these polymeric hosts show their great potential application in developing high performance polymer-based OLEDs.

Triphenylamine-functionalized iridium(III) complexes for near-infrared phosphorescent organic light emitting diodes

With the aim of enhancing the efficiency of near infrared (NIR) organic light-emitting devices (OLEDs), two new triphenylamine-functionalized NIR iridium(III) complexes by covalently attaching the functional moieties (tBu and F) complexes (tBuTPA-BTz-Iq)2Irpic and (FTPA-BTz-Iq)2Irpic were designed and synthesized (TPA = triphenylamine; BTz = benzotriazole; Iq = isoquinoline). It was found that compared to their parent iridium complex (TPA-BTz-Iq)2Irpic, the addition of either butyl or fluorine groups into the ligand play an important role in improving the optophysical and electroluminescent characteristics. In solution-processed phosphorescent OLEDs, the (tBuTPA-BTz-Iq)2Irpic-based devices achieved a maximum external quantum efficiency (EQEmax) of 0.66% at 716 nm, while the (FTPA-BTz-Iq)2Irpic-based devices achieved an EQEmax of 0.48% at 710 nm. The EQEmax level is 2.28 or 1.65 times higher than that in the (TPA-BTz-Iq)2Irpic-based devices (0.29% at 712 nm), respectively.

Highly efficient solution-processed phosphorescent organic light-emitting devices with double-stacked hole injection layers

In this paper, solution-processed nickel oxide (NiOx) is used as hole-injection layers (HILs) in solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). Serious exciton quenching is verified at the NiOx/emitting layer (EML) interface, resulting in worse device performance. The device performance is significantly improved by inserting a layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) between the EML and NiOx. The solution-processed blue PhOLED with the double-stacked NiOx/PEDOT:PSS HILs shows a maximum current efficiency of 30.5 cd/A, which is 75% and 30% higher than those of the devices with a single NiOx HIL and a PEDOT:PSS HIL, respectively. Improvement of device efficiency can be attributed to reducing exciton quenching of the PEDOT:PSS layer as well as the electron blocking effect of the NiOx layer.

Near-IR Emitting Iridium(III) Complexes with Heteroaromatic β-Diketonate Ancillary Ligands for Efficient Solution-Processed OLEDs: Structure-Property Correlations.

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.

A Donor–Acceptor-type Host Material for Solution-processed Phosphorescent Organic Light-emitting Devices Showing High Efficiency

Abstract The solution-processable host material, 3,3′-[bis(9-phenylcarbazol-3-yl)]benzophenone (BCzBP), containing donor-type phenylcarbazole units and an acceptor-type benzophenone unit was synthesized. BCzBP showed a high excited triplet energy level and a high photoluminescence quantum efficiency with tris[2-(4-tolyl)pyridine]iridium ([Ir(mppy)3]) as a dopant, and a high glass-transition temperature. Solution-processed green phosphorescent OLEDs were fabricated with BCzBP. The device with BCzBP as a host showed comparable efficiencies to those of the corresponding device with 4,4′-bis(N-carbazolyl)biphenyl (CBP) as a host. At the same current density, the device with BCzBP showed a longer device lifetime than that with CBP, due to the high thermal stability and the bipolar nature of the host compound, BCzBP.

Nanoscale heterogeneity and light-emission dynamics in solution-processed phosphorescent organic light-emitting devices

Spatial and temporal heterogeneities observed by optical microscopy in the electroluminescence of polymer-based light-emitting diodes doped with phosphorescent iridium complexes are associated with biased voltage-dependent nanoscale structural relaxation of the host polymer matrix.