Fundamental processes governing operation and degradation in state of the art P-OLEDs

Thermally Activated Delayed Fluorescence in Polymers: A New Route toward Highly Efficient Solution Processable OLEDs

“…EL spectra of P-OLEDs were measured using Ocean Optics USB2000+ spectrometer, and J -V -L characteristics were measured using Minolta CS-200 luminance meter and Keithley 2400 SourceMeter. Device EQE was calculated using P-OLED optical model, [ 11 ] where deviation from Lambertian emission pattern was taken into account. Values of EQE at few current densities were additionally checked by measurements in an integration sphere.…”

“…Details of the model can be found elsewhere. [ 11 ] Emitter alignment was measured by a polarized angular PL technique, similar to that described by Flämmich et al, [ 16 ] giving an average dipole orientation (ratio of parallel vs perpendicularly aligned emitters) of p || : p ⊥ = 2:0.84, indicating a slight alignment beneficial for the outcoupling enhancement compared to an isotropic emitter. Using experimentally measured values of the device EQE (10.0 ± 0.5%) and the delayed EL fraction (73.2 ± 0.7%) observed at V = 3.2 V ( J = 0.008 mA cm −2 ), η PL = 43.6 ± 0.9%, and η PL air = 41 ± 0.8% we fi nd that in order to match Equations ( 2) -( 4) RISC and ISC quantum effi ciencies should be within the range of Φ RISC = 83 ± 7%, and Φ ISC = 8 ± 5%, respectively.…”

“…Such tendency has been reported before and ascribed to the presence of a 3n-π* intermediate state by Dias et al, [ 12 ] and to molecular conformation changes during long transient lifetime of triplet excitons by Hirata et al [ 5b ] Following confi rmation of TADF in our solution processable material, P-OLEDs were fabricated using an intermonomer TADF polymer as LEP in a generic P-OLED structure, consisting of an indium tin oxide (ITO) anode, a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layer, interlayer, LEP, and a shallow work function cathode. [ 11 ] The hole injection layer, interlayer, and LEP were spun from solution, and a cathode deposited by thermal evaporation. A conjugation broken polymeric interlayer (poly(2,5-dihexylbenzene-N -(4-(2-butyl)phenyl)-diphenylamine)) with reasonably high triplet level (T 1 = 2.52 eV) was used to minimize triplet quenching in the TADF emissive layer.…”

“…Excess of triazine units (50%) over amine units (5%) was chosen in order to ensure an electron rich material with RZ location away from the cathode following design rules for high effi ciency fl uorescent polymer organic light-emitting diodes (P-OLEDs) described elsewhere. [ 11 ] To confi rm existence of TADF in our polymeric material we have performed detailed optical characterization of a neatThe improvement of the external quantum effi ciency (EQE) of organic light-emitting devices (OLEDs) remains one of the key challenges in the commercialization of OLED technology. The EQE of traditional fl uorescence-type OLEDs is limited by the formation of up to 75% normally nonemissive triplet excitons for each injected charge pair.…”

The contribution of triplet–triplet annihilation to the lifetime and efficiency of fluorescent polymer organic light emitting diodes

“…[5][6][7][8] In the model devices considered in this study, the primary cause of efficiency loss during electrical stressing has been shown to be the buildup to photoluminescence quenching sites in the emissive layer rather than the decay of the charge injecting contacts. 9 Although there have been some recent reports on the contribution that triplet states can make to the efficiency of a fluorescent small molecule OLED, 10,11 there has been little published research on the consequences of high triplet densities on the operational lifetime of the devices. This paper will report on the effect of triplet-triplet annihilation (TTA) on the device lifetime and efficiency of P-OLEDS.…”