High-Triplet-Energy Dendrons: Enhancing the Luminescence of Deep Blue Phosphorescent Iridium(III) Complexes

Lo, Shih‐Chun; Harding, Ruth E.; Shipley, Christopher P.; Stevenson, Stuart G.; Burn, Paul L.; Samuel, Ifor D. W.

doi:10.1021/ja903157e

Cited by 189 publications

(116 citation statements)

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“…The blue phosphorescent dendrimer [122] with the molecular structure shown in Figure 6.1c was deposited on top of the charge transport layer by spin-coating.…”

Section: Device Architecturementioning

confidence: 99%

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Active channel field-effect transistors: Towards high performance light emitting transistors

Tandy¹

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This thesis describes the study of the development and device physics of organic field-effect transistors and organic light-emitting field-effect transistors. Using chemical and physical properties of organic semiconductors such as light emission, multi-functional devices, or "Active Channel Field-Effect Transistors" can be created. This thesis first describes the creation of basic ambipolar FETs before building on this knowledge to develop ambipolar as well as hole-dominated light emitting field-effect transistors.Ambipolar FETs using a diketopyrrolopyrrole-based copolymer were first investigated in this thesis. When gold electrodes were used, the devices could transport only holes. The charge injection was altered by changing the contacts to aluminium. The devices then were able to conduct both electrons and holes with maximum electron and hole mobilities of order 10 −4 cm 2 V −1 s −1 and 10 −3 cm 2 V −1 s −1 respectively.Light-emitting field-effect transistors were first studied using the model emissive polymerSuper Yellow. Charge injection was studied by altering the electron-injecting contact. Materials used included the low work function metals Ca, Ba and Sm, the inorganic salt Cs 2 CO 3 and the organic material TPBi. Ambipolar devices were created using a neat Super Yellow layer. Electron and hole mobilities in these devices were both of the order of 10 −4 cm 2 V −1 s −1 . The maximum external quantum efficiency was 1.2 ± 0.2 % with a Sm electron-injecting contact, however this occurred at a brightness of less than 1 cd m −2 . A maximum brightness of 43 ± 9 cd m −2 was obtained using a Cs 2 CO 3 -Ag electron-injecting contact in electron accumulation mode. At this brightness, the external quantum efficiency was 0.19 ± 0.04 %.Unipolar devices were also fabricated by adding high mobility charge transport layer of PBTTT underneath the Super Yellow. Since PBTTT had a hole mobility that was orders of magnitude greater than the charge carrier mobilities of Super Yellow, charges were transported in the PBTTT, and recombined within the Super Yellow layer. Super Yellow acted as an emissive layer only. Using this bilayer device architecture, a maximum brightness of 100 ± 4 cd m −2 was obtained with a Ca electron-injecting contact. An external quantum efficiency of 0.04 ± 0.01 % was achieved at the maximum brightness.In order to improve the external quantum efficiency of LEFETs, phosphorescent materials were chosen for use as the emissive layer. A co-evaporated layer of the iridium complex Ir(ppy) 3 in a host of CBP was initially used in the devices. Charge injection was studied by using either a Ba or a TPBi/Ba electron-injecting contact. 4Devices were first fabricated using PBTTT as a hole-dominated charge transport layer.Using a TPBi/Ba electron-injecting contact, the maximum brightness achieved was 200 ± 40 cd m −2with an external quantum efficiency of 0.18 ± 0.01 % at the maximum brightness. Devices were then fabricated using a charge transport layer of DPP-DTT to create ambipolar devices. Electron and ...

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“…The blue phosphorescent dendrimer [122] with the molecular structure shown in Figure 6.1c was deposited on top of the charge transport layer by spin-coating.…”

Section: Device Architecturementioning

confidence: 99%

“…A blue phosphorescent dendrimer previously reported in OLEDs [122] gave a maximum EQE of 3.9 %. The reported OLED brightness reached a maximum of 200 cd m −2 .…”

Section: Introductionmentioning

confidence: 96%

Active channel field-effect transistors: Towards high performance light emitting transistors

Tandy¹

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“…Using an especially rigid set of dendrons a solution quantum yield of 94% was obtained, which is substantially higher than that of the isolated complex (27%). 70 The enhanced quantum yield was attributed to a reduction in the non-radiative rate by steric crowding and reduced intermolecular interactions.…”

Section: Ir(ptz) 3 -A Family Of Blue Phosphorescent Iridium Complexesmentioning

confidence: 99%

“…70,[124][125][126] Generally though, a small amount of the phosphorescent dye is doped into a host matrix, the purpose of which is to provide (i) charge transport and (ii) prevent intermolecular interactions between emitting phosphors. So as to make the back transfer of energy from guest to host unfavourable, the LUMO and triplet energy levels of the host should have a higher higher energy than the guest.…”

Section: Guest:host Blended Films For Phosphorescent Oledsmentioning

confidence: 99%

“…4 To date, the best phosphorescent materials for OLEDs are based on iridium(III) complexes. 19,53,70,215 Ligand modification has been used to tune the emission colour, 51 but it is not possible to predict the photoluminescence quantum yields (PLQYs) of the resultant metal complexes. 19,99 The subtle effect played by spin-orbit coupling (SOC) in enabling phosphorescence, has been inadequately studied in this respect, which makes it difficult to understand the relationship between ligand substitution and the radiative rate of phosphorescence.…”

Section: Introductionmentioning

confidence: 99%

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