White Polymer Light-Emitting Diodes Based on Star-Shaped Polymers with an Orange Dendritic Phosphorescent Core

All-Solution-Processed Multilayered White Polymer Light-Emitting Diodes (WPLEDs) Based on Cross-Linked [Ir(4-vb-PBI)2(acac)]

All-solution-processed multilayered white polymer light-emitting diodes (WPLEDs) are promising candidates for low-cost and large-area flexible full-color flat-panel displays and solid-state lighting. However, it is still challenging to improve their performance. In this work, based on an elegant strategy of orthogonal materials, the utilization of the cross-linked Ir³⁺ polymer film poly(NVK-co-[Ir(4-vb-PBI)₂(acac)]-co-NVK) (NVK = N-vinyl-carbazole; 4-vb-HPBI = 1-(4-vinylbenzyl)-2-phenyl-1H-benzo[d]imidazole; and Hacac = acetylacetone) as the emitting layer (EML) between a hydrophilic polymer film poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole injection layer (HIL) and a hydrophobic polymer film poly(vinyl-PBD) (vinyl-PBD = 2-(4-(tert-butyl)phenyl)-5-(4'-vinyl-[1,1'-biphenyl]-4-yl)-2,5-dihydro-1,3,4-oxadiazole) as the electron transport layer (ETL) led to the successful fabrication of reliable all-solution-processed multilayered WPLEDs. The device exhibits a η_CE^Max of 18.19 cd/A, a η_PE^Max of 8.16 lm/W, and a η_EQE^Max of 9.32% with stable white light (Commission International De L'Eclairage (CIE) coordinates x = 0.269-0.283, y = 0.317-0.330; corrected color temperatures (CCTs) of 7237-8199 K, and CRIs (color rendering indices) of 63-72) under a wide applied-voltage range. Its high performance, especially with record efficiencies among those of reported all-solution-processed WPLEDs, renders cross-linked Ir³⁺ polymers a new platform to all-solution-processed multilayered WPLEDs.

Investigation of Energy Transfer in Star-Shaped White Polymer Light-Emitting Devices via the Time-Resolved Photoluminescence

A series of white polymer light-emitting devices (WPLEDs) were fabricated by utilizing star-shaped white-emission copolymers containing tri[1-phenylisoquinolinato-C2,N]iridium (Ir(piq)₃), fluorenone (FO) and poly(9,9-dioctylfluorene) (PFO) as red-, green- and blue-emitting (RGB) components, respectively. In these WPLEDs, a maximum current efficiency of 6.4 cd·A⁻¹ at 20 mA·cm⁻² and Commission Internationale d’Eclairage (CIE) coordinates of (0.33, 0.32) were achieved, and the current efficiency was still kept to 4.2 cd·A⁻¹ at the current density of 200 mA·cm⁻². To investigate energy transfer processes among the three different chromophores of the star-shaped copolymers in these WPLEDs, the time-resolved photoluminescence (PL) spectra were recorded. By comparing the fluorescence decay lifetimes of PFO chromophores in the four star-like white-emitting copolymers, the efficient energy transfer from PFO units to Ir(piq)₃ and FO chromophores was confirmed. From time-resolved PL and the analysis of energy transfer process, the results as follows were proved. Owing to the star-like molecular structure and steric hindrance effect, intermolecular interactions and concentrations quenching in the electroluminescence (EL) process could also be sufficiently suppressed. The efficient energy transfer also reduced intermolecular interactions’ contribution to the enhanced device performances compared to the linear single-polymer white-light systems. Moreover, saturated stable white emission results from the joint of energy transfer and trap-assisted recombination. This improved performance is expected to provide the star-like white-emitting copolymers with promising applications for WPLEDs.

Polyfluorene-based white light conjugated polymers incorporating orange iridium(iii) complexes: the effect of steric configuration on their photophysical and electroluminescent properties

Owing to large steric hindrance, white light hyperbranched conjugated polymers exhibited the best electroluminescent performance with suppression of triplet–triplet annihilation.

Conjugated Polymer Nanoparticle-Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior

Conjugated polymer nanoparticles based on poly[9,9-bis(2-ethylhexyl)fluorene] and poly[N-(2,4,6-trimethylphenyl)-N,N-diphenylamine)-4,4'-diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2'-bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye-coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle-dye hybrids. It is proposed that the excited state electron transfer from the electron-rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed-electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir-based triplet emitting dye as the guest.