Phosphine Oxide Linkage Manipulating Trinuclear Iridium(III) Complex for High‐Efficiency Bilayer Nondoped Organic Light‐Emitting Diodes

Abstract

A conventional approach to construct efficient PH neat films is combining host and phosphor moieties in single molecules. [7] In this case, phosphorescent emitting cores were encapsulated in host-featured peripheral carrier-transporting groups, [8] dendrons [9] or polymeric skeletons, [10] therefore protected from intermolecular interaction induced collisional quenching by steric effect of functional groups. Wang et al. reported a square-planar Pt 3+ complex, whose vacuum-evaporated non-doped PH OLED (PHOLED) achieved a maximum η EQE of 31%. [11] However, only few solution-processed non-doped PHOLEDs can realize η EQE close to 20%, among which Wang et al. reported a small-molecular Ir 3+ complex with an impressive η EQE of 18.5%. [12] Therefore, the separation by peripheral groups seems not essential for constructing high-efficiency phosphors for non-doped devices. In opposite, the highest occupied (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of the peripheral groups should be deeper and shallower than those of emitting cores, respectively, to confine charge and exciton on the latter, therefore, complicated stacks involving in multiple hole (HTL) and electron transporting layers (ETL) were commonly adopted. [13] Furthermore, energy transfer from peripheral groups to emitting cores leads to energy loss, decreasing the power efficiency of the devices. [14] Actually, Wang and Ding et al. have demonstrated the self-host feature of aliphatic chain-linked multinuclear Ir 3+ complexes. [15] Nevertheless, since triplet quenching is still mainly induced by molecular collision, optimizing intermolecular interactions is still crucial for developing high-efficiency non-doped PHOLEDs. Herein, we demonstrate another effective "linkage manipulation" strategy to develop solution-processable phosphors. An Ir 3+ complex Ir(PBI) 3 (PBI = 1,N-diphenyl benzimidazole) is employed as phosphorescent core, which was linked with triphenylphosphine oxide (TPPO) to form mononuclear Ir(PBI) 2 PBIPO, binuclear [Ir(PBI) 2 ] 2 DPBIPO, and trinuclear [Ir(PBI) 2 ] 3 TPBIPO. The incorporation of TPPO linkage hardly changes single-molecular emission profiles and peak wavelengths, but induces the gradual increase of photoluminescence quantum yield (PLQY, η PL), from 76% of TPPO-free Ir(PBI) 3 to 92% of [Ir(PBI) 2 ] 3 TPBIPO, corresponding to a 50% improved PH rate constant. More importantly, tetrahedral configuration of TPPO linkage destroys the symmetry of Ir 3+ cores in the multinuclear complexes, therefore effectively suppresses triplet quenching. [Ir(PBI) 2 ] 3 TPBIPO Developing high-efficiency nondoped phosphorescence (PH) organic lightemitting diodes (OLEDs) by solution processing is still a big challenge, due to high demand on quenching suppression ability of phosphors. Here, phosphine oxide (PO) linkage is incorporated between Ir 3+ complexed cores of a trinuclear phosphorescent emitter named [Ir(PBI) 2 ] 3 TPBIPO. The emission spectra of single-molecular [Ir(PBI) 2 ] 3 TPBIPO is identical to its mononuclear congeners, but its ...

Combining molecular encapsulation and an AIE strategy to construct an efficient blue TADF polymer for solution-processed multilayer white OLEDs

“…[1][2][3][4][5][6][7] To further enhance the competitiveness of OLEDs, reducing the fabrication cost is an urgent problem to be solved. [8][9][10][11][12][13][14][15] Thermally activated delayed fluorescence (TADF) polymers have become an attractive class of material for fabricating OLEDs with cost-efficient solution-processibility technology due to their good film-forming ability and intrinsic 100% exciton harvest through a reverse intersystem crossing (RISC) process. [16][17][18][19][20] After great efforts from scientists, various TADF polymers have been successfully realized by means of main-chain or side-chain strategies, where the TADF units are embedded in a p-conjugated polymer backbone or connected to a polymer backbone via nonconjugated aliphatic chains, respectively.…”

Developing Efficient Dinuclear Pt(II) Complexes Based on the Triphenylamine Core for High-Efficiency Solution-Processed OLEDs

“…This process is accelerated by the rapid development of phosphorescent organometallic complexes − because transition metal-based complexes can fully utilize both the singlet and triplet excitons formed upon charge recombination in a device to theoretically achieve 100% internal quantum efficiency and thereby significantly enhance the device performance. , To date, most of the phosphorescent complexes have been developed with one metal center, which may result from one of the reasons that the synthetic procedure of mononuclear complexes is relatively simpler. However, more recently, phosphorescent complexes containing two or more metal centers, i.e., multinuclear complexes, have drawn increasing interest because their structural configurations and properties are more diverse and highly tunable, which will offer them more opportunities in various applications. − For example, the incorporation of the second Pt­(II) center could effectively promote the T 1 state to couple with higher-lying singlet states via spin–orbit coupling, leading to higher photoluminescence yields (PLQYs) of resultant dinuclear Pt­(II) complexes and thereby outstanding electroluminescence (EL) performance. − …”