Distinguishing triplet energy transfer and trap-assisted recombination in multi-color organic light-emitting diode with an ultrathin phosphorescent emissive layer

Abstract

Articles you may be interested inEnhanced efficiency and reduced roll-off in nondoped phosphorescent organic light-emitting devices with triplet multiple quantum well structures Appl. Phys. Lett. 97, 083304 (2010) (Ir(ppz) 3 ) to distinguish the contribution of the emission from the triplet exciton energy transfer/diffusion from the adjacent blue phosphorescent emitter and the trap-assisted recombination from the narrow band-gap emitter itself. The charge trapping effect of the narrow band-gap deep-red emitter which forms a quantum-well-like structure also plays a role in shaping the electroluminescent characteristics of multi-color organic light-emitting diodes. By accurately controlling the position of the ultrathin sensing layer, it is considerably easy to balance the white emission which is quite challenging for full-color devices with multiple emission zones. There is nearly no energy transfer detectable if 7 nm thick Ir(ppz) 3 is inserted between the blue phosphorescent emitter and the ultrathin red emitter. V C 2014 AIP Publishing LLC. [http://dx

Highly Photoluminescent Nonconjugated Polymers for Single-Layer Light Emitting Diodes

“…Although devices with the highest Ir content (13 mol %) were the brightest, plotting power and current efficiency (Figure B) with respect to luminance clearly indicates that devices containing copolymers with 6 mol % Ir outperform those with more (13 mol %) and less (1 mol %) Ir, where maximum current efficiencies were 3.6, 2.2, and 1.7 cd/A for 6, 13, and 1 mol % emissive copolymer layers, respectively (Table S4). Device optimization at 6 mol % dopant likely occurs as a result of a compromise between exciton generation (by either charge trapping or exciton hopping) that is efficient at low Ir doping (e.g., 1 mol %), and triplet–triplet annihilation, which occurs readily at higher Ir doping (e.g., 13 mol %). − The discrepancy between optimal PLQY, which was highest for low Ir doping (∼1 mol %), and device performance (6 mol %) likely arises from barriers to charge injection/transport that is alleviated by additional Ir, as evidenced from a drop in turn-on voltage. The shallower HOMO energy level for Ir-2C-MA relative to M6-MA indicates that hole injection/transport improves for devices with more Ir (6 mol %), while too much Ir (13 mol %) leads to unwanted aggregate-induced quenching effects.…”

Recent progress on organic light-emitting diodes with phosphorescent ultrathin (<1nm) light-emitting layers

“…It was demonstrated when the thickness of the spacer layer (Ir(ppz) 3 ) increased to 7 nm, there was nearly no energy transfer detectable from blue phosphorescent emitter and red UEML. This indicates that a critical thickness value of 7 nm is extremely important for manipulating the energy transfer between different emitters on either side of the spacer layer, and further realizes high device performance ( Xue et al., 2014 ).

Figure 4 Dynamic diagrams of charge carriers and excitons and corresponding EL spectra (A–D) Schematic diagram of dynamic of charge carriers and excitons and the corresponding EL spectra at 100 mA cm −2 for devices with deep-red phosphorescent UEML of Ir(piq) 3 inserted into different positions of electron blocking layer Ir(ppz) 3 .

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Figure 4 Dynamic diagrams of charge carriers and excitons and corresponding EL spectra (A–D) Schematic diagram of dynamic of charge carriers and excitons and the corresponding EL spectra at 100 mA cm −2 for devices with deep-red phosphorescent UEML of Ir(piq) 3 inserted into different positions of electron blocking layer Ir(ppz) 3 . Reproduced with permission ( Xue et al., 2014 ), Copyright, AIP Publishing.

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“…It was demonstrated when the thickness of the spacer layer (Ir(ppz) 3 ) increased to 7 nm, there was nearly no energy transfer detectable from blue phosphorescent emitter and red UEML. This indicates that a critical thickness value of 7 nm is extremely important for manipulating the energy transfer between different emitters on either side of the spacer layer, and further realizes high device performance (Xue et al, 2014).…”

Doping-free white organic light-emitting diodes without blue molecular emitter: An unexplored approach to achieve high performance via exciplex emission

“…On the other hand, since the triplet energy (T 1 ) of m-MTDATA (2.6 eV) is higher than that of exciplexes, m-MTDATA can prevent the diffusion of excitons. 25 And the critical thickness of the exciton-blocking layer with high T 1 can be $7 nm, 33 indicating that few triplets can be harvested via the diffusion process in W14. As a result, the orange intensity is decreased with the increasing thickness of m-MTDATA by the above two factors (tunneling and diffusion).…”