Pure organic room temperature phosphorescence (RTP) materials are considered as potential
candidates for replacing precious metal-based complexes to fabricate highly efficient organic light
emitting devices (OLEDs). However, for reported RTP materials, low photoluminescence quantum
yields (PLQYs) in thin film state seriously impede their applications in OLEDs. On the other hand, how
using normal organic fluorescence materials to fabricate OLEDs with an internal quantum efficiency
(IQE) over 25% remains a great unaddressed issue beyond the thermally activated delayed fluorescence
(TADF) sensitization approach. Here, we establish a strategy to construct highly efficient OLEDs based
on pure organic RTP material sensitized fluorescence emitter. The key point for our strategy is that
benzimidazole-triazine molecules (PIM-TRZ), 2,6-di(phenothiazinyl)naphthalene (β-DPTZN) and
5,6,11,12-tetraphenylnaphthacene (rubrene) were screened as host, phosphor sensitizer and fluorescent
emitter, respectively. Detail photophysical characterizations demonstrate that the host material PIMTRZ with unique RTP nature is critical for achieving phosphor sensitizing process. As an organic RTP
compound, the singlet and triplet state energy levels of β-DPTZN perfectly match with those of PIMTRZ, resulting in the formation and lasting existence of phosphor’s excitons in emitting layer. The large
overlap between the absorption spectrum of rubrene and PL spectrum of PIM-TRZ:10% β-DPTZN film
can facilitate the Förster energy transfer from the triplet β-DPTZN to the singlet rubrene and the finally
displayed fluorescence is derived from singlet excited states of rubrene. The perfect collocation of host,
phosphorescent sensitizer and fluorescent emitter in the emitting layer promise the predominant
performance of the devices with external quantum efficiency (EQE) of 15.7%. The PLQY of emitting
layer is 60.3%, and therefore about 90% carrier injection induced excitons are harvested for light
emission. We present a new strategy to fabricate efficient fluorescent devices by employing ingenious
combination of host, phosphorescent sensitizer and fluorescent emitter, which is significant to the
development of OLEDs.<br>
Eco‐Friendly and Highly Efficient Light‐Emission Ferroelectric Scintillators by Precise Molecular Design (Adv. Funct. Mater. 35/2021)
