Nanosecond-time-scale delayed fluorescence molecule for deep-blue OLEDs with small efficiency rolloff

Abstract

Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin-orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor-acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance.

Highly Efficient Deep‐Blue OLEDs using a TADF Emitter with a Narrow Emission Spectrum and High Horizontal Emitting Dipole Ratio

“…These k RISC are similar to that of the recently reported TADF emitters using oxygen-bridged boron acceptor, but larger than previously reported blue TADF emitters. [12,20,36,37] k ISC of TDBA-SAF was ten times larger than k RISC , resulting in longer decay lifetime of delayed emission than DBA-SAB.…”

“…reported D–A type deep‐blue‐emitting TADF emitters adopting an oxygen‐bridged boron acceptor unit, which is rigid and has symmetric structure. [ 36,37 ] The FWHM of the emitters was effectively reduced compared to the emitters using a nonrigid and symmetric acceptor unit, indicating that the nitrogen‐bridged or oxygen‐bridged boron structures are promising acceptor units for deep blue TADF emitters. Nevertheless, the efficient deep blue TADF OLEDs with EQEs near 30% and the CIE y coordinate under 0.1 have not been reported yet to our best knowledge.…”

Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

“…Charge-transfer (CT) interactions between electron donors (D) and acceptors (A) are the basis of many functions of p-conjugated molecules and polymers, [1][2][3][4][5][6][7] Recently,thermally activated delayed fluorescence (TADF) polymers [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] with CT emission have attracted much attention because they can convert triplet excitons to singlet ones through reverse intersystem crossing (rISC) process to realize 100 %i nternal quantum efficiency (IQE), [28][29][30][31][32][33][34][35][36][37][38][39][40][41] providing ap romising approach for developing solution-processed OLEDs without use of precious metal complexes.…”

Three‐ and Four‐Coordinate, Boron‐Based, Thermally Activated Delayed Fluorescent Emitters

“…Furthermore, high EQE values up to 20.2% and 18.3% in the TMCz-BO and TMCz-3P devices were retained at 100 cd m −2 , respectively, because of their extremely small delayed fluorescence lifetimes. [84] As described, the rigid and planar-type DBNA acceptor was effective at increasing the EQE of blue and green TADF OLEDs. DBNA-derived TADF emitters also provided device stability (through a fast RISC process) and molecular stability, which demonstrates the potential of the DBNA as an acceptor to develop blue TADF emitters.…”