Dimers or Solid‐State Solvation? Intermolecular Effects of Multiple Donor–Acceptor Thermally Activated Delayed Fluorescence Emitter Determining Organic Light‐Emitting Diode Performance

Abstract

Organic light‐emitting materials exhibiting thermally activated delayed fluorescence (TADF) show great promise for improving display applications. Recently, intermolecular effects between emitting molecules have been given more attention, revealing strong solid‐state solvation or aggregation induced changes of sample performance. Implications of this on device performance are not yet fully covered. In this work, a thorough investigation of a novel TADF emitter, methyl 2,3,4,5,6‐penta(carbazol‐9‐yl)benzoate (5CzCO2Me), is provided. Steady‐state emission spectra reveal a luminescence redshift with increasing emitter concentration in a small molecule host. In all investigated concentrations, the emission profile remains the same; thus, the redshift is attributed to the solid‐state solvation effect. The highest photoluminescence quantum yield (PLQY) is achieved in the 20 wt% sample, reaching 66%. The best organic light‐emitting diode (OLED) in terms of current–voltage–luminance and external quantum efficiency (EQE) parameters is the device with 60 wt% emitter concentration, reaching maximal EQE values of 7.5%. It is shown that the emitter transports holes and that charge‐carrier recombination does not take place on the bandgap of the host, but rather, a mixed host–guest concentration‐dependent recombination is seen. The hole‐transporting properties of 5CzCO2Me allow for a new dimension in tuning the device performance by controlling the emitter concentration.

Spiro donor–acceptor TADF emitters: naked TADF free from inhomogeneity caused by donor acceptor bridge bond disorder. Fast rISC and invariant photophysics in solid state hosts

“…Most telling is that we observe dual emission from monomeric and this red species simultaneously at high loading, but only from the monomeric species at low loading, again clearly showing that the red shifted species is not a result of 'solid state solvatochromism' (oxymoron) but is an excimer state. 38 Further, the FWHM of the ACRSA emission band in 1% wt loading film (100 nm) (Fig. S3, ESI †) is much narrower to that of 10% wt loading films (150 nm) (Fig.…”

Management of Multi‐Energy‐Transfer Channels and Exciton Harvesting for Power‐Efficient White Thermally Activated Delayed Fluorescence Diodes

“…[29] Transient PL decay characterization of two emitters in doped 4′-bis(carbazol-9-yl)biphenyl (CBP) film was investigated to verify the TADF property (Figure 2d). At room temperature, two films were measured on different scale (100 ns and 50 µs), [30,31] the prompt (τ p ) and delayed (τ d ) lifetimes are 27.6 ns and 13.7 µs for DPPZ-DMAC, while 35.5 ns and 4.47 µs for DPPZ-2DMAC, as shown in Figure S9 (Supporting Information). The specific PL data of transient analysis of emitters based on CBP are shown in the Table S3 (Supporting Information).…”

Electron-withdrawing Group Modified Carbazolophane Donors for Deep Blue Thermally Activated Delayed Fluorescence OLEDs

“…S7, ESI †). However, l PL of both emitters are about 20 nm red-shifted at around 456 nm in these two host matrices, suggesting stronger aggregation 30,31 (Fig. 4 and Fig.…”