Ultra-high-power-efficiency organic light-emitting diodes based on a hot-exciton-assisted exciplex (HEAE) system

Abstract

Power efficiency (PE) is crucial for evaluating the performance of organic light-emitting diodes (OLEDs) as it directly reflects their photoelectric conversion efficiency. Featuring a low injection barrier, exciplexes show higher potential than single compounds in the fabrication of high-PE OLEDs, but their poor efficiencies hinder their development. Here, we introduce a novel hot-exciton-assisted exciplex (HEAE) strategy, in which hot-exciton materials used as donors enhance the efficiency of exciplex systems via recovering exciton energy. As a result, the novel exciplex system-based OLED shows an external quantum efficiency (EQE) of 19.0%, which is twice that of a conventional exciplex-based OLED. Moreover, using the novel exciplex as the host of four multiple resonance-emitters, sensitized fluorescence OLEDs with narrow emissions achieve high EQEs of up to 40.5% and a new breakthrough PE exceeding 230 lm W⁻¹. These results prove that hot-exciton materials are excellent candidates for achieving high-performance exciplexes, providing valuable insights into the rational design of low-power-consumption OLEDs.

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New concepts

In this manuscript, we demonstrate a new strategy that using hot-exciton materials as donors to recover the excitons energy and transfer to exciplex, so that the external quantum efficiency (EQE) of the new-type exciplex is enhanced two-fold compared to the conventional exciplex. Exciplexes offer high power efficiencies (PEs) due to the small energy level barriers between the emitting and adjacent functional layers. Unfortunately, severe exciton quenching in exciplexes hinders the EQEs of exciplex-based OLEDs. Herein, a hot-exciton material, which harnesses triplet excitons via the reverse intersystem crossing from the high-lying triplet excitation states (T_n, n ≥ 2) to the lowest singlet excitation state, is selected to enhance the EQE of exciplexes. As a result, an OLED based on the novel exciplex achieved an EQE of 19.0% and a PE of 82.1 lm W⁻¹—a twofold improvement over the OLED based on conventional exciplexes. Finally, applying the novel exciplex as a sensitized host, a series of narrowband OLEDs were fabricated, achieving an EQE of up to 40.5% and a record-breaking PE of over 230 lm W⁻¹, which is one of the highest PE values reported to date.

Introduction

Organic light-emitting diodes (OLEDs) are widely used in the fields of display and illumination due to their unique advantages of flexibility, high resolution, and low power consumption.^1,2 As consumers are becoming increasingly environmentally conscious, their demands for low-power-consumption electronic products are increasing. In general, the power consumption of an OLED is described by its power efficiency (PE, η_P), which is related to external quantum efficiency (EQE, η_EQE), average photon energy (Ē), and driving voltage (U), as follows:with the same Ē, a higher PE can be obtained by increasing the EQE and decreasing the U of the OLED. By using the heavy-atom effect or reverse intersystem crossing (RISC) process in a single molecule, EQE can be enhanced to 20–40%; however, it is difficult for a single molecule to simultaneously achieve a low U and high EQE due to energy level barriers between the emitting material layer (EML) and adjacent functional layers, generally resulting in a bad carrier injection in OLEDs. Therefore, OLEDs with PE ≥ 200 lm W⁻¹ are still rare.

Instead of the donor and acceptor being concentrated within a single molecule, an exciplex is a novel luminescent system formed through intermolecular charge transfer (ICT) between the donor and acceptor molecules. Typically, donors are hole-dominant and inject/transport materials, while acceptors are electron-dominant and inject/transport materials, resulting in small energy level barriers between the EML and adjacent functional layers. OLEDs based on exciplexes generally exhibit low driving voltages and operational current densities.³ Therefore, exciplexes are ideal candidates as emitters or hosts for obtaining OLEDs with a low U.^4,5 However, it is still hard for exciplexes to obtain a high PE value due to the severe exciton quenching that results in a low EQE in exciplex-based OLEDs.⁶

Various strategies have been proposed to address this problem and to improve the efficiency of exciplexes, in which introducing additional RISC channels to recover the energy of excitons recombined on donors or acceptors has become a feasible solution.⁷ For example, Zhang et al. applied a thermally activated delayed fluorescence (TADF) material named MAC as the donor of exciplexes, preparing OLEDs with an excellent EQE of 17.8% and a PE of 45.5 lm W⁻¹.⁸ Considering that hot-exciton materials feature rapid high-lying RISC channels, they are also ideal candidates for assisting exciplexes in recovering exciton energy via additional RISC channels. Unfortunately, only a few exciplex systems containing hot-exciton materials have been reported, in which hot-exciton materials have not yet been used as donors. A comprehensive investigation into the potential of exciplex systems containing hot-exciton materials is urgently needed.^9,10 Considering that the lowest triplet (T₁) state of hot-exciton materials is generally LE-dominated, it is speculated that the spin–orbit coupling (SOC) effect occurs when the locally excited triplet states (³LE) of hot-exciton materials are adjacent to the CT-dominated singlet (¹CT) and triplet (³CT) states of exciplexes.^11–13

Herein, we developed a hot-exciton-assisted exciplex (HEAE) system, which exhibited a high EQE and a wide exciton recombination area. Three hot-exciton materials—2MCz-CNMCz, 2t-2MCz-CNMCz, and 4t-2MCz-CNMCz—were used as donors, and they were combined with 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) to construct exciplexes H1, H2, and H3, respectively. Owing to the high-lying RISC channels of the three hot-exciton materials, the energy of excitons recombined on the donor was recovered and transferred to the exciplex through the Förster resonance energy transfer (FRET) process (Fig. 1). Consequently, OLEDs based on H1 showed green emissions with twice the maximum EQE of conventional exciplexes. By introducing a third component to fine-tune the horizontal dipole orientation (Θ_‖) of H1, the maximum EQE and PE were enhanced to 19.0% and 82.1 lm W⁻¹, respectively. Magneto-electroluminescence (MEL) curves demonstrated that the RISC originated from the SOC effect and was regulated via the peripheral tert-butyl groups on hot-exciton materials. The detection of exciton recombination regions in H1-based OLEDs confirmed a wide exciton recombination area of exciplex H1. Therefore, exciplex H1 was applied as a sensitized host of four multiple-resonance TADF (MR-TADF) emitters. As a result, four sensitized devices with maximum EQEs of 37.7%, 40.5%, 30.7%, and 33.4% and PEs of 232.8, 223.5, 176.6, and 203.6 lm W⁻¹ were designed. These results confirm that an efficient conversion of electrically generated excitons into luminescence occurs in the HEAE system, providing an effective method for obtaining OLEDs with high PEs.

Fig. 1 Mechanisms of the HEAE system and a conventional exciplex system under an electric field. ISC is intersystem crossing, IC is internal conversion, and F is fluorescence.

Results

Design and evaluation of hot-exciton materials

Blue-violet materials with high T₁ levels are commonly selected as donors or acceptors to prevent reverse energy transfer when constructing exciplexes, and carbazole derivatives featuring wide band gaps, excellent hole transport, and molecular planarity are ideal donor candidates.¹⁴ The reported hot-exciton carbazole derivative 2MCz-CNMCz with a high T₁ energy of 2.69 eV, a high hole mobility of 2.8 × 10⁻³ cm² V⁻¹ s⁻¹, and an exciton utilization rate of 77.1% was chosen as the donor in this work, and its hot-exciton behavior is further demonstrated in Fig. S1 and Table S1.¹⁵ Tert-butyl groups with varying numbers and substitution patterns were incorporated into 2MCz-CNMCz. On one hand, the tert-butyl substituents exhibited minimal perturbation to the π-conjugation of the molecular skeleton, thereby preserving near-ultraviolet emission characteristics and hot-exciton properties. On the other hand, sterically bulky tert-butyl groups were strategically introduced at the para or meta positions to modulate the intermolecular interactions between the donor and acceptor, enabling the screening of optimal exciplex compositions. Furthermore, the incorporation of the tert-butyl groups was employed to investigate their effects on the charge carrier transport properties of the corresponding exciplexes and the influence of the T₁ state of hot-exciton materials on the SOC effect. Here, two tailor-made molecules, 2t-2MCz-CNMCz and 4t-2MCz-CNMCz, were designed and synthesized. Their specific synthesis routes are described in the Supporting Information (Fig. S2–S9 and Table S2).

The photoluminescence (PL) properties of 2t-2MCz-CNMCz and 4t-2MCz-CNMCz were evaluated (Fig. S10 and Tables S3–S5). Based on the onset energies of fluorescence and phosphorescence spectra at 77 K in toluene, the S₁ and T₁ energy levels were estimated to be 3.29 and 2.68 eV for 2t-2MCz-CNMCz and 3.32 and 2.77 eV for 4t-2MCz-CNMCz, corresponding to the large energy gap (ΔE_S1–T1) values of 0.61 and 0.55 eV, respectively. The large ΔE_S1–T1 values exclude the TADF mechanism of 2t-2MCz-CNMCz and 4t-2MCz-CNMCz. Natural transition orbital simulation confirmed that the T₁ states of both 2t-2MCz-CNMCz and 4t-2MCz-CNMC were LE-dominated (Fig. S11 and Tables S6, S7). Based on the energy level distributions of the singlet and triplet states, hot-exciton channels were presumed to exist in 2t-2MCz-CNMCz and 4t-2MCz-CNMC (Fig. S12 and S13).¹⁶ Upon the incorporation of the tert-butyl groups, the excited-state distributions and properties of 2t-2MCz-CNMCz and 4t-2MCz-CNMC remained largely unchanged, and hot-exciton channels were preserved. In addition, the carrier transport abilities of 2MCz-CNMCz, 2t-2MCz-CNMCz, and 4t-2MCz-CNMCz were investigated by fabricating electron-only and hole-only devices. All three molecules exhibited hole carrier mobilities (μ_h) at magnitudes of 10⁻³∼10⁻⁴ cm² V⁻¹ s⁻¹ and electron carrier mobilities (μ_e) at a magnitude of 10⁻⁴ cm² V⁻¹ s⁻¹, and all three molecules exhibited a μ_h value higher than their μ_e value, indicating that all of them were appropriate for constructing a donor (Fig. S14).

Generation and photophysical properties of exciplexes

Herein, three hot-exciton molecules—2MCz-CNMCz, 2t-2MCz-CNMCz, and 4t-2MCz-CNMCz—were employed as donors to form exciplexes (H-type exciplex for short) with the high-triplet (T₁ = 3.0 eV) material PO-T2T as the acceptor, yielding exciplexes H1, H2, and H3, respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of 2MCz-CNMCz, 2t-2MCz-CNMCz, and 4t-2MCz-CNMCz were −5.35 and −2.28 eV, −5.11 and −2.01 eV, and −5.13 and −2.02 eV, respectively, matching the HOMO (−7.5 eV) and LUMO (−3.5 eV) of PO-T2T (Fig. S16).¹⁷ To conduct a systematic investigation of the proposed concept, five conventional donor molecules—including carbazole and triphenylamine derivatives (mcp, mCBP, TcTa, TAPC, and Tris-PCz)—were also selected to form conventional exciplexes (C-type exciplex for short) with PO-T2T, as shown in Fig. 2, named C1, C2, C3, C4, and C5, respectively.^18–22 The PL properties of all donor–acceptor mixtures were evaluated in films using an optimized ratio of 40 wt% donor to 60 wt% acceptor. All mixtures showed broad absorption tails extending to 600 nm, attributed to intermolecular CT transitions. The H1, H2, and H3 films exhibited green emissions, which were clearly distinct from the spectra of either donor or PO-T2T (Fig. S17), confirming the formation of the exciplex. With increasing steric bulk of the tert-butyl groups, the spectra of H1–H3 exhibited a progressive blue shift, indicating a weakened intermolecular CT characteristic. Transient PL decay curves for the H1, H2, and H3 films revealed typical biexponential decay profiles comprising prompt (τ_P) and delayed (τ_D) components, further confirming exciplex generation (Fig. 2b). The k_RISC values evaluated by transient PL decay curves for the H1, H2, and H3 films were 1.5 × 10⁵, 1.8 × 10⁵, and 1.0 × 10⁵ s⁻¹, respectively. Temperature-dependent transient PL decay data of the H1, H2, and H3 films revealed that the ratio of delayed fluorescence increased as the temperature increased (Fig. S18). The photoluminescence quantum yield (PLQY) values of the H1, H2, and H3 exciplex films were 37.4%, 44.9%, and 38.8%, respectively. All H-type and C-type exciplex films showed long-lived phosphorescence emissions when the temperature dropped to 77 K (Fig. S19). As shown in Table 1, the H1, H2, and H3 exciplexes showed ΔE_S1–T1 values of 0.23, 0.26, and 0.27 eV, respectively. As shown in Fig. 2c, the energy levels of the ³LE states of hot-exciton materials are located between the ¹CT and ³CT states of exciplexes. It is speculated that the SOC effect could be generated in the H-type exciplexes, which is beneficial for promoting the RISC process.

Fig. 2 Photophysical properties of exciplexes. (a) Molecular structure of compounds used in this study. (b) UV-vis absorption spectra (left), PL spectra (middle), and transient PL decay curves (right) of the exciplex films at room temperature. (c) Energy levels of exciplexes and donors.

Table 1 Photophysical characteristics of exciplexes considered in this study

Exciplex	λabs^a (nm)	λmax^a (nm)	PLQY^a (%)	τP^b (ns)	τD^b (µs)	Rdelayed^c (%)	kRISC^c (× 10^6 s^−1)	ES1/ET1/ΔES1T1^d (eV)
a Characteristic absorption peaks, emission peaks, and photoluminescence quantum yield (PLQY) in a nitrogen environment of the exciplex films.b Fitting from the transient PL decay curves of the exciplex films.c Deduced from PLQY and transient PL decay curves.d Determined from the onset of PL and phosphorescence spectra in films at 77 K.
H1	352	521	37.4	16.6	33.8	79.7	0.2	2.68/2.45/0.23
H2	354	514	44.9	22.6	140.0	91.1	0.2	2.76/2.50/0.26
H3	352	507	38.8	22.0	160.1	90.3	0.1	2.80/2.53/0.27
C1	328	475	39.3	44.0	4.5	88.7	2.0	2.92/2.87/0.05
C2	343	476	39.6	43.7	3.8	87.9	2.1	2.92/2.92/0.00
C3	335	542	20.8	55.1	1.2	72.4	4.4	2.58/2.57/0.01
C4	282	562	13.1	59.8	1.5	84.4	3.1	2.48/2.46/0.02
C5	309	535	12.8	47.8	1.4	82.2	4.0	2.57/2.57/0.00

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Electroluminescent performances of exciplexes

OLEDs with different EMLs were designed and fabricated with the structure shown in Fig. 3: ITO (90 nm)/HATCN (5 nm)/TAPC (50 nm)/TcTa (5 nm)/EML (20 nm)/PO-T2T (50 nm)/LiF (1 nm)/Al (120 nm); here, HATCN, TAPC, and TcTa were 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile, 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane, and tris(4-(9H-carbazol-9-yl)phenyl)amine, which were used as hole injection, hole transport, and exciton blocking layers, respectively. The EMLs included the H-type exciplexes (devices H1, H2, and H3) and C-type exciplexes (devices C1, C2, C3, C4, and C5). The EL properties of all exciplexes were evaluated with an optimized ratio of 40 wt% donor to 60 wt% acceptor (Figure S20 and Table S8). Devices H1–H3 showed turn-on voltages (V_on) of 2.2, 2.2, and 2.3 V, and devices C1–C5 showed V_on values of 2.8, 2.4, 2.2, 2.2, and 2.2 V, respectively. Devices H1, H2, and H3 exhibited green emissions with peak emission wavelengths (λ_EL) of 532, 532, and 526 nm and maximum EQEs of 13.5%, 11.6%, and 10.0%, respectively. For devices C1–C5, λ_EL values were 528, 528, 546, 572, and 560 nm, and maximum EQEs were 6.9%, 5.7%, 7.4%, 4.3%, and 6.3%, respectively. Notably, devices H1–H3 demonstrated maximum EQEs 2–3 times higher than those of devices C1–C5. This improvement was attributed to the hot-exciton channels in the donor materials, which recovered the energy of excitons captured by the donor molecules and transferred it to the exciplex. In addition, improving the Θ_‖ of exciplexes has been proven to boost the optical outcoupling efficiency (η_out) of devices.^23,24 By incorporating an inert material DPEPO ([2-(diphenylphosphino)phenyl]ether oxide) as a spacer (Fig. S21 and Table S9) into the exciplex H1 at different ratios, the Θ_‖ of H1 improved from 54.6% to 66.7%, resulting in a substantial increase in η_out from 25.8% to 34.3% (Fig. S21 and Table S9). The participation of DPEPO in exciplex formation was excluded (Fig. S22 and Table S10). However, the incorporation of spacers impeded carrier transport in EMLs and increased the V_on of devices. Consequently, device D1 with moderate spacers (EML composed of 50 wt% exciplex H1 and 50 wt% DPEPO) maintained a green emission (λ_EL of 526 nm) and achieved a maximum EQE of 19.0% and a PE of 82.1 lm W⁻¹.

Fig. 3 Electroluminescent performances of exciplexes. (a) Device structure. (b) EL spectrum of devices at 10 mA cm⁻². (c) EQE–luminance characteristics of devices. (d) Interactions of the donor and acceptor with different numbers of spacers. (e) EL spectrum at 10 mA cm⁻². (f) EQE–luminance–PE plot.

Exciton dynamics and charge carriers of exciplexes

To explore the effect of introducing tert-butyl on the H-type exciplexes, magnetic field effects at different current densities were measured (Fig. S23 and Table S11). As shown in Fig. 4a, under an external magnetic field, the MEL line shapes of devices H1, H2, and H3 increased continuously. The maximum half-widths of the MEL curves of devices H1, H2, and H3 were larger than those caused by hyperfine interaction (HFI) (<10 mT), indicating that magnetic field effects were governed by the SOC effect.^25,26 Therefore, the low-lying ³LE state of hot-exciton materials was confirmed to promote the SOC effect of exciplexes. MEL curves at different current densities were fitted by the Δg factor model, and the fitted curves were completely consistent with the data obtained from the measurements.²⁷ The fitting constant (C) values of devices H1, H2, and H3 were 0.135, 0.122, and 0.100, respectively. A smaller C value suggested a larger SOC effect. Herein, the SOC effect in the H-type exciplexes was effectively enhanced by introducing the tert-butyl groups in donors. Nonetheless, the carrier transport abilities of hot-exciton materials were reduced after the introduction of tert-butyl (Fig. S14), further affecting the carrier transport properties of H-type exciplexes (Fig. S24) and resulting in lower EQEs of devices H2 and H3 than that of device H1.

Fig. 4 Exciton dynamics and charge carrier evaluation of exciplexes. (a) MEL curves of devices H1, H2, and H3 at 5 mA cm⁻². (b) PL spectra of the H1 film and the absorption and PL spectra of TBRb in toluene solution. (c) Plot of the relative intensity of TBRb versus position and voltage, in which the position is the distance from TBRb to the TcTa layer.

Furthermore, an orange fluorescence emitter, 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb), was used as a detector to explore carrier recombination in device H1.²⁸ As shown in Fig. 4b, the absorption of TBRb closely overlapped with the PL emission of the exciplex H1, indicating efficient FRET from H1 to TBRb. An ultrathin (0.2 nm) layer of TBRb was inserted into the EML of device H1 at various positions, and the relative emission intensity of TBRb was recorded to plot a relative intensity–position–voltage graph. The relative emission intensity of TBRb was distributed across the entire EML during different operating voltages (2.2–8 V), demonstrating a wide exciton recombination area within the exciplex H1.

Sensitization performance of the exciplex H1

Owing to the high efficiency and wide exciton recombination area, the exciplex H1 was further used as a sensitized host. MR-TADF emitters with narrow full-width at half maximum (FWHM) show great potential for ultrahigh-definition OLED displays.²⁹ However, the slow RISC process hinders the development of MR-TADF emitters.³⁰ Here, using MR-TADF as the terminal emitter and materials with the exciplex H1 as sensitizer resulted in OLEDs with both ultrahigh PE and narrow emission by transferring energy from the sensitizers to the emitter.³¹ In this work, we proposed the HEAE-sensitized fluorescence (HESF) concept, which includes the HEAE system as a host and a fluorescent dopant. As shown in Fig. 5, exciton energy was transferred from the HEAE system to dopants via FRET using a low dopant concentration of 1 wt% to avoid dopant exciton quenching caused by Dexter energy transfer (DET).

Fig. 5 Sensitization performance of OLEDs based on the exciplex H1 as the host. (a) Mechanism of HESF. (b) Absorption spectra of four MR-TADF materials in toluene solution (10⁻⁵ M) and PL spectra of the H1 film. (c) Transient PL lifetime of the four sensitized films. (d) EL spectra of the devices at 10 mA cm⁻². (e) EQE–luminance–PE plot of devices. (f) Plot of the emission peak wavelength–PE–EQE of green and orange OLEDs (red star represents OLEDs with PEs over 220 lm W⁻¹).

Four MR-TADF materials with high PLQYs and narrow-emission spectra—BN2, BN3, tCzphB-Ph, and tCzphB-Fl—were doped into H1 as terminal emitters.^32,33 The absorption spectra of the four dopants overlapped well with the PL spectrum of H1, and the sensitized films exhibited λ_EL values at 543, 565, 525, and 537 nm with FWHM values of 43, 40, 30, and 31 nm, respectively (Fig. S25). As shown in Fig. 5b, the energy transfer processes in the sensitized films were investigated through transient PL measurements. The four sensitized films exhibited different delayed lifetimes with H1, indicating an efficient FRET from H1 to the dopants. Devices were fabricated with the same configuration mentioned above using EMLs of H1, such as H1 : 1 wt% BN2 (device S1), H1 : 1 wt% BN3 (device S2), H1 : 1 wt% tCzphB-Ph (device S3), and H1 : 1 wt% tCzphB-Fl (device S4). As shown in Table 2 and Fig. S26, devices S1–S4 showed low V_on values of 2.1, 2.1, 2.2, and 2.2 V, respectively. Devices S1–S4 exhibited single peaks at λ_EL of 544, 568, 526, and 534 nm, respectively. The spectra of the four sensitized devices showed a slight broadening with FWHM values of 46, 42, 33, and 33 nm, respectively, due to the high polarity of PO-T2T. Fortunately, devices S1–S4 achieved excellent maximum EQEs of 37.7%, 40.5%, 30.7%, and 33.4% and record-breaking PE values of 232.8, 223.5, 176.6, and 203.6 lm W⁻¹, respectively (Fig. 5f and Table S12). Such high EQE and PE values demonstrated the potential and advantages of the HEAE system.

Table 2 Device performance of OLEDs

Device	λEL (nm)	Von^a (V)	L^b (cd m^−2)	CEmax^c (cd A^−1)	PEmax^d (lm W^−1)	EQEmax/100/1000^e (%)	CIE (x, y)^f
a Turn-on voltage ≥ 1 cd m^−2.b Maximum luminance.c Maximum current efficiency.d Maximum PE.e Maximum EQE/EQE at 100 cd m^−2/EQE at 1000 cd m^−2.f Commission international de l'Éclairage, recorded at 10 mA cm^−2.
H1	532	2.2	6632	45.3	64.7	13.5/10.0/3.4	0.341, 0.576
H2	532	2.2	4611	38.7	52.9	11.6/8.9/3.2	0.340, 0.572
H3	526	2.3	4275	31.8	43.1	10.0/5.9/2.1	0.300, 0.549
C1	528	2.8	7859	22.3	25.1	6.9/6.5/4.9	0.310, 0.524
C2	528	2.4	7665	18.4	20.6	5.7/5.2/4.2	0.318, 0.533
C3	546	2.2	27460	24.1	30.4	7.4/7.4/7.3	0.402, 0.566
C4	572	2.2	13210	11.4	13.8	4.3/4.3/4.0	0.495, 0.497
C5	560	2.2	26630	18.7	23.1	6.3/6.3/6.1	0.447, 0.534
D0	528	2.3	5168	57.4	78.4	17.6/9.9/2.7	0.325, 0.566
D1	526	2.3	4172	60.1	82.1	19.0/10.0/2.5	0.305, 0.556
D2	522	2.5	3331	52.5	66.0	16.9/6.5/2.0	0.297, 0.542
S1	544	2.1	20620	155.6	232.8	37.7/26.6/12.2	0.336, 0.638
S2	568	2.1	26430	149.4	223.5	40.5/29.9/11.8	0.464, 0.529
S3	526	2.2	19680	123.7	176.6	30.7/24.2/11.7	0.237, 0.703
S4	534	2.2	19160	142.6	203.6	33.4/26.6/12.2	0.279, 0.682

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Conclusion

In summary, the underlying mechanisms by which hot-exciton materials featuring high-lying RISC channels enhance the EQE of exciplexes by recovering exciton energy were revealed. Three hot-exciton materials with high hole mobility were used as donors, and high-performance exciplexes were successfully constructed. PL spectra and the obvious delayed components in transient PL lifetimes confirmed the generation of exciplexes. The EQE and PE of the OLEDs based on the novel exciplexes were significantly higher than those of the OLEDs based on conventional exciplexes. By introducing the exciplex H1 into a highly oriented host, OLED performance further enhanced, achieving an EQE of 19.0%, which was twice the EQE of conventional exciplexes, and a PE of 82.1 lm W⁻¹. In addition, the T₁ state of hot-exciton materials was confirmed to participate in the generation of the SOC effect, and the SOC effects of exciplexes were regulated by introducing tert-butyl groups into the donor material. Considering the commercial demand for narrow emissions, four sensitized devices based on the exciplex H1 were successfully prepared, exhibiting unexpected efficiencies owing to the high EQE and wide exciton recombination area of the exciplex H1. These results proved the feasibility of the HEAE strategy, providing a novel avenue for designing low-power-consumption OLEDs.

Author contributions

J. Lou and J. He contributed equally. Conceptualization: J. Lou, J. He and H. Zhang; methodology: J. Lou, Y. Chen and H. Zhang; investigation: J. Lou, B. Li, and J. He; writing – original draft: J. Lou and H. Zhang; writing – review & editing: H. Zhang and Z. Wang; funding acquisition: Z. Wang and B. Z. Tang; resources: Z. Wang and B. Z. Tang; supervision: Z. Wang and B. Z. Tang.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d6mh00070c.

Acknowledgements

We are grateful for financial support from the National Natural Science Foundation of China (52473173, U25A20569), Natural Science Foundation of Guangdong Province (2022B1515020084), Guangdong Basic and Applied Basic Research Foundation (2023B1515040003), Key Project of Yunnan Provincial Department of Science and Technology (202303AC100021), Independent Research Project of State Key Lab of Luminescent Materials and Devices (SCUT) (Skllmd-2024-10, Skllmd-2025-05), Science and Technology Program of Guangzhou (2023A04J0988) and Key-Area Research and Development Program of Guangdong Province (2024B0101040001).

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