Remote Steric Effect as a Facile Strategy for Improving the Efficiency of Exciplex-Based OLEDs

Abstract

This work reports a new strategy of introducing remote steric effect onto the electron donor for giving the better performance of the exciplex-based organic light-emitting device (OLED). The bulky triphenylsilyl group (SiPh) was introduced onto the fluorene bridge of 4,4'-(9H-fluorene-9,9-diyl)bis(N,N-di-p-tolylaniline) (DTAF) to create remote steric interactions for increasing the possibility of effective contacts between electron-donating chromophores and acceptor molecules, rendering the resulting exciplex to have a higher photoluminescence quantum yield (PLQY). The green exciplex device based on DSDTAF:3N-T2T (1:1) as an emitting layer exhibits a low turn-on voltage of 2.0 V, high maximum efficiencies (13.2%, 42.9 cd A, 45.5 lm W), which are higher than the device employed DTAF (without SiPh groups) (11.6%, 35.3 cd A, 41.3 lm W) as donor under the same device structure. This strategy was further examined for blue exciplex, where the EQE was enhanced from 9.5% to 12.5% as the electron acceptor PO-T2T mixed with a tert-butyl group substituted carbazole-based donor (CPTBF) as the emitting exciplex in device. This strategy is simple and useful for developing high performance exciplex OLEDs.

Tricomponent Exciplex Emitter Realizing over 20% External Quantum Efficiency in Organic Light‐Emitting Diode with Multiple Reverse Intersystem Crossing Channels

“…Therefore, the evidently improved Φ PL of DBT-SADF:PO-T2T:CDBP is actually ascribed to the better upconversion of triplet excitons with three RISC channels and prove the feasibility of our strategy to improve the exciton utilization of exciplex emitters. Moreover, to the best of our knowledge, this is the first report with an EQE over 20% for the OLEDs based on exciplex emitters at room temperature (Figure 4; Table S2, Supporting Information), [1,2,[4][5][6][7][8][9][10][11][12][13][14][17][18][19][20][21]30,31,[46][47][48] thus our novel strategy of tricomponent exciplexes will provide a valuable approach for further development of exciplex emitters. As the mixing ratios of exciplexes would change their charge balance and affect the device performance, [13,14] the carrier transporting properties of four exciplexes were carefully investigated.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Formed between electron-donating (D) and electron-accepting (A) molecules, group reported an exciplex-based TADF-OLEDs by employing a bipolar constituting molecule, and achieved a maximum EQE of 15.4%. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Formed between electron-donating (D) and electron-accepting (A) molecules, group reported an exciplex-based TADF-OLEDs by employing a bipolar constituting molecule, and achieved a maximum EQE of 15.4%.…”

“…The lower-energy exciplex could be beneficial due to the energy transfer between two exciplexes. [1,2,[4][5][6][7][8][9][10][11][12][13][14][17][18][19][20][21]30,31,[46][47][48] The outstanding performance of the DBT-SADF:PO-T2T:CDBP-based OLEDs not only demonstrates that introducing multiple RISC channels can effectively improve the exciton utilization of exciplex emitters, but also proves the superiority of our novel tricomponent exciplex strategy for further development of exciplex emitters. According to our novel strategy, two tricomponent exciplex emitters, 13AB ((1,3-bis(9,9dimethylacridin)) benzene):PO-T2T ((1,3,5-triazine-2,4,6-triyl) tris(benzene-3,1-diyl) tris(diphenylphosphine oxide)):CDBP (4,4′-bis(9-carbazolyl)-2,2′-dimethylbiphenyl) and DBT-SADF Energy transfer diagrams of the conventional bicomponent TADF exciplexes, TADF-assistant bicomponent TADF exciplexes, and novel tricomponent TADF exciplexes (blue: conventional constituent material, orange: single-molecule TADF emitter).…”

“…With these completely separated frontier molecular orbitals, exciplexes naturally have extremely small energy gaps (ΔE ST s) between their lowest singlet and triplet (S 1 and T 1 ) energy levels. [1][2][3][5][6][7][8][9][10][11][12][13][14][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] As the exciplexes can realize the balanced charge transport and suppress the triplet-triplet annihilation by upconvert triplet excitons to singlet excitons, the OLEDs using exciplexes as the hosts have realized remarkable progress till now. Besides, as the constituting D and A materials are generally capable of hole-and electron-transporting properties, respectively, exciplexes would possess bipolar transporting properties, and even reach a charge-transporting balance by adjusting the mixing ratio between D and A, which would be helpful to further simplify the structures and lower the driving voltages for OLEDs.…”

A Novel Sterically Bulky Hole Transporter to Remarkably Improve the Lifetime of Thermally Activated Delayed Fluorescent OLEDs at High Brightness

“…Thus, HTLs should have deep I p to suppress unfavorable intermolecular interaction such as the low‐energy charge‐transfer (CT) complex or exciplex formation in TADF OLEDs. From the viewpoint of chemical structure, sterically bulky materials are very promising because these can significantly reduce the intermolecular π–π stacking interactions . Furthermore, the bond dissociation energy (BDE) of the materials should be considered for the long operation lifetime.…”