High‐Efficiency Blue‐Emission Crystalline Organic Light‐Emitting Diodes by Engineering Thermally Activated Delayed Fluorescence Nanoaggregates

A crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a powerful strategy to develop high‐performance crystalline OLEDs that can combine the advantages of both crystalline and high‐exciton‐utilization‐efficiency light emitting materials. Here a CHM‐NA structure blue‐emission crystalline OLED is developed, which employs a thermally activated delayed fluorescence (TADF) material. The CHM‐TADFNA OLED is proved to efficiently manage exciton distribution by engineering nanoaggregates. The device exhibits a remarkable EQE up to 10.4% and achieves the characteristics of rapid turn‐on, and fast ramping of luminance and current density, resulting in an enhanced photon output and a lower series‐resistance Joule‐heat loss ratio, indicating a competitive pathway to future blue‐emission OLEDs.


Introduction
Organic crystalline materials exhibit an inherently long-range ordered molecular arrangement, which facilitates aligned dipole orientation and high carrier mobility, [1,2] making them particularly suitable for the fabrication of advanced organic optoelectronic devices. [3,4]7][8][9][10][11][12][13][14][15] Compared to traditional high-EQE DOI: 10.1002/aelm.20230061618][19][20][21][22][23][24] These high-performance C-OLEDs employ weak epitaxy growth (WEG) method, [25,26] which is capable of fabricating crystalline thin films in a continuous, flat and controlled manner, enabling various novel structures of crystalline OLEDs(C-OLEDs). [22,23] crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a strategy that combines fixed crystallized host material and various highexciton-utilization-efficiency guests.[27] Guest material nanoaggregates can grow on surface of ordered crystalline thin film, thereby leaving relatively flat areas where further growth of crystalline thin films can occur.Therefore, CHM-NA structure can offer both the advantages of crystallized and high-efficiency materials, i.e., CHM can provide a channel of high carrier mobility while amorphous nanoaggregates emitters can achieve efficient luminescence.As a consequence of spin statistics, conventional blue fluorescent emitters only can harvest singlet excitons and, therefore suffer from an internal quantum efficiency (IQE) of 25%.[28,29] Conversely, thermally activated delayed fluorescence (TADF) materials possess a small ∆E ST (energy gap between lowest triplet (T 1 ) and singlet (S 1 ) excited states) and therefore can converse triplet excitons into singlet excitons by the reverse intersystem crossing (RISC) process to achieve ≈100% IQE.[30][31][32] Nevertheless, TADF materials have been rarely used in crystalline thin film OLEDs. Varius luminescence mechanisms and device structures can be achieved by engineering the CHM-NA route, including material components, layer geometries, nanoaggregate sizes, etc.The application of CHM-NA strategy will therefore provide more options and a greater probability of fabricating highefficiency C-OLEDs by combining TADF materials.
In this work, a high-efficiency blue-emission OLED based on CHM-NA structure was fabricated, consisting of fluorescent CHM and blue TADF nanoaggregates (TADF-NA).Due to the high carrier mobility generated by CHM and TADF nanoaggregates, the device can attain high-performance blue-emission (CIE (0.15, 0.20)) through the full utilization of excitons.Apart from a low turn-on voltage of 2.7 V (@ 1 cd m −2 ), the device achieves a maximum EQE of up to 10.4%, a maximum power efficiency of 20.0 lm W −1 and a maximum current efficiency of 17.9 cd A −1 , which are the highest values among blue crystalline OLEDs.[35][36] It is also possible to control exciton recombination regions as well as heterojunction effects between CHM and nanoaggregates by modifying TADF nanoaggregate with different morphologies, demonstrating the potential of CHM-TADFNA OLEDs in the future.

Architecture of CHM-TADFNA OLEDs
A CHM with high carrier mobility results in rapid formation of excitons, and it plays a pivotal role in determining exciton properties where nanoaggregates are located. [20]As shown in Figure 1a, nanoaggregates can grow concurrently with CHM, indicating that engineering nanoaggregates can be realized by modifying the growth process.For the fabrication of the CHM layers, an indium tin oxide (ITO) anode coated with a 40 nm thick poly (3,4ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer served as a flat substrate for epitaxial film growth as well as a hole injection layer (HIL).The following growth of crystalline thin films was performed by a vacuum deposition technique, weak epitaxy growth (WEG) method, [25] which allows precise control of crystalline thin-film thickness.The molecular configurations used in the device are shown in Figure 1b.A 7 nm thick 2,5-di([1,1′-biphenyl]−4-yl)thiophene (BP1T) inducing layer was first fabricated, then a continuous crystalline needle/stripe-like 2-(4-(9H-carbazol-9-yl)phenyl)−1-(3,5difluorophenyl)−1H-phenanthro [9,10-d]imidazole (2FPPICz, [20] basic parameters are shown in Table S1, Supporting Information) layer was formed on top.Both layers can form flat polycrystalline layers.In addition to working as an inducing layer, the rod-like BP1T can also be a hole transport layer (HTL) and electron blocking layer (EBL) resulting from its proper energy level and hole transport ability. [37]Due to the fact that 2FPPICz layers possess good crystallinity and can maintain crystalline form when their domains come into contact and fuse, the crystalline BP1T and 2FPPICz layers are the foundation of the next CHM-NA emission layers.Blue TADF portions, bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS), [38] can form ellipsoid-shaped nanoaggregates on the surface of the crystalline 2FPPICz host matrix, whose size and morphology can be controlled by varying the evaporated speed and temperature.Afterward, the 2FPPICz host will be able to expand along the gap between nanoaggregates, ensuring continuity while contacting the 2FPPICz below.It can be imagined that the relationship between nanoaggregates and CHM can be engineered by managing their proportion in order to realize various kinds of emitters and exciton recombination regions.Moreover, to set one layer of CHM with nanoaggregates as one module, the emitting layer can be randomly assembled by modules of any thickness or color range, thereby fabricating various kinds of devices.In this work, the emitting layer consisted of four identical modules, after which grown amorphous electron transport layer (ETL) of 40 nm 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPb), electron injection layer of 1 nm LiF, and cathode of 150 nm Al.The molecular structures used are shown in Figure 1b.

Characterization of CHM-TADFNA films
It has been mentioned above that high carrier mobility can be achieved in high-crystallinity thin films.WEG is an effective method that can control the thickness of crystalline thin films accurately, after which nanoaggregates can be grown.Consequently, CHM and nanoaggregate morphologies can be administrated and combined arbitrarily by varying the evaporation rate and temperature.The nominal deposition thickness (NDT) of nanoaggregates is defined as 0.5, 1.0, 2.0, and 3.0 nm, though the geometries of nanoaggregates cannot be simply described based on this parameter.Figure 2a-d illustrates 3D atomic force microscopy (AFM) images of nanoaggregates of different NDT.Combining the AFM images in Figure S1a-d (Supporting Information), it is demonstrated that CHM can grow as flat surfaces, while nanoaggregates tend to adhere to crystal boundaries and arrange themselves in a regular pattern.The increase in NDT will result in an increase in their height and diameter, which is evident from 3D AFM measurements that the bright yellow nanoaggregates expand in proportion to their width and height.Figure 2e-h further illustrates AFM images of 5 nm 2FPPICz CHM including DMAC-DPS nanoaggregates.After CHM has been evaporated on nanoaggregates, the crystal domain is still clear, indicating that 2FPPICz CHM can grow on the aperture between nanoaggregates and continue to crystallize in later processes.Figure 2i demonstrates the out-of-plane X-ray diffraction (XRD) patterns of crystalline inducing layer BP1T, crystalline epi-taxy layer 2FPPICz, and CHM layer containing nanoaggregates, respectively.In accordance with previously reported BP1T and 2FPPICz results, [20] the green and purple solid lines correspond to the peak positions of those structures, while the blue line of the CHM-TADFNA structure has similar characteristic peaks without any new peaks, exhibiting that the crystallinity of CHM is not affected.The root-mean-square (RMS) surface of their roughness also increases in accordance with NDT of nanoaggregates, resulting from the fact that the height of nanoaggregates will exceed the CHM when the NDT is more than 0.5 nm and affect the surface of CHM.A quantitative comparison of the relationship between thickness and morphology characteristics was performed by selecting ten nanoaggregates randomly and estimating their scale information.According to Figure S2a-d (Supporting Information), cross-section profiles of nanoaggregates of different sizes were shown.Due to the space constraints, the graph only shows four representative particles and other more detailed information is provided in Table S2 (Supporting Information).Based on the average and variance analysis, nanoaggregates grow in a uniform and homogeneous manner and are widely distributed and proportioned over the flat CHM. Figure S3a-d (Supporting Information) also presents the ratio of the vertical projection area of nanoaggregates of different sizes on the crystalline thin film.A summary of the calculated average is shown in Figure 2j, which clearly illustrates the growth process of nanoaggregates.Nanoaggregates can be considered as clusters of atoms or molecules that form nanoscale structures.

Engineering Nanoaggregates to Manage Excitons and Device Performance
In order to study the impact of morphology on device characteristics, we further fabricated four devices of the same CHM-TADFNA structure that have different thicknesses of nanoaggregates.The device structure and energy levels are shown in Figure S4 (Supporting Information).The performance of CHM-TADFNA devices is shown in Figure 3a-d.As the morphology of TADF-NAs of different NDT shows significant differences, the device performance is expected to also change prominently.However, the four devices exhibit comparable current densities, although the device with an NDT of 3.0 nm exhibits a relatively low current density.Based on our previous study, [27] it was demonstrated that the CHM is the pathway for hole transportation.On the other hand, electrons are directly injected from the cathode due to the deep LUMO of DMAC-DPS nanoaggregates.Once both the holes and electrons are present in the region of the nanoaggregates, they can combine and form excitons.Consequently, the NDT of nanoaggregates will not have a severe effect on current density.Even though the devices have similar current densities, their operating voltages, turn-on voltages, and electroluminescent (EL) spectrums also exhibit similar characteristics, however, the maximum EQEs of each device are 6.3%, 7.8%, 6.4%, and 5.9%, respectively, indicating a non-monotonic trend.As the CHM-NA devices possess similar mechanisms, the distinction may be attributed to the change in the distribution of excitons brought by the morphology change of nanoaggregates.To investigate the distribution of excitons in devices of different NDT of nanoaggregates, we insert ultrathin long wavelength phosphor layer Ir(tptpy) 2 acac with NDT of 0.06 nm into the middle position of different nanoaggregates regions (Region 1, 2, 3 and 4) of CHM-TADFNA devices with different NDTs of nanoaggregates.The PL spectrum of the inserted phosphor layer is shown in Figure S5 (Supporting Information), which exhibits a characteristic peak of ≈565 nm.The intensities of Ir(tptpy) 2 acac as a function of the position can be calculated and represent the concentration of excitons. [39,40]The detailed inserting positions, EL spectrums of corresponding devices, and calculated ratios of the orange peak to the blue peak in spectrums are shown in Figure .S6 (Supporting Information) and the background colors of Figure S6c,e,g,i (Supporting Information) are also determined by the intensity, where the deep orange color signifies a high concentration of excitons while a pale-yellow color denotes a low concentration.The maximum intensity ratios of the four probe devices exhibit different characteristics.Due to the small proportion of nanoaggregates in devices with NDT of 0.5 nm, the exciton recombination zone tends to have characteristics more similar to CHM, which is found near the electron transport layer, given that 2FPPICz is a p-type semiconductor.Excitons predominantly accumulate in Regions 3 and 4 of the EML, with maximum peak value at Region 4. As for devices with NDT of 1.0, 2.0, and 3.0, they exhibit higher exciton concentration in Region 3, as the proportion of nanoaggregates increases, due to the bipolar nature of DMAC-DPS nanoaggregates.With the increase of NDT, the impact of DMAC-DPS nanoaggregates becomes apparent, resulting in an obvious leftward shift in the distribution of exciton recombination zones.Moreover, as the NDT continuously increases and the exciton recombination zone leftward shifts, exciton concentrations will therewith leftward shift to front area.While the peak concentration remains in Region 3, the exciton concentration keeps rising in Region 2 and declining in Region 4. Consequently, a device with proper NDT, i.e., NDT of 1.0 nm, can achieve comparable exciton densities in Regions 2, 3, and 4, leading to an expanded exciton recombination zone and promoting a more uniform distribution of excitons, which is crucial for enhancing the EQE.As a consequence, engineering nanoaggregates, can manage the exciton distribution and improve the performance of devices, which has the potential to fine-tune emitting colors.Moreover, the CHM-TADFNA structure offers a substantial improvement in device performance when compared to the conventional doping approach.Figure S7 (Supporting Information) presents an emitter layer of 2FPPICz doped with 10 wt% DMAC-DPS, which primarily displaying the spectrum of 2FPPICz and a maximum EQE of ≈2%.The low EQE observed in the crystal-doped device can be attributed to the low triplet energy level of 2FP-PICz (T 1 = 2.47 eV).In contrast, the relatively high EQE of CHM-TADFNA supports the previously mentioned observation that excitons can directly form within the nanoaggregate emitters.Although the loss of triplet excitons remains inevitable, the EQE has experienced a considerable enhancement compared to conventional doping.Another totally amorphous OLED with the same structure as CHM-TADFNA OLED was also fabricated (marked as Device AR).Since nanoaggregates are only capable of forming on crystal surfaces, amorphous OLEDs only have a repeating alternate growth of 1.0 nm DMAC-DPS and 5.0 nm 2FPPICz layers, which do not have the same morphology as crystalline OLEDs.The comparison of these two kinds of devices is shown in Figure S8 (Supporting Information).As shown in Figure S8 (Supporting Information), compared to the Device AR (turn-on voltage of 3.0 V and an increment voltage (∆V) of 2.0 V from 1 to 1000 cd m −2 ), the CHM-TADFNA device shows a lower turn-on voltage (2.7 eV), faster brightness climb as the driving voltage increases (∆V of 1.6 V).
To further determine the distinctions in the working mechanisms between the engineered CHM-TADFNA structure and the conventional doping method, several reference films and OLEDs were prepared for transient photoluminescence (PL) and electroluminescence (EL) analysis.Several crystalline thin films of similar structures apart from different EMLs were fabricated, including 2FPPICz (marked as Film 1); and 2FPPICz: DMAC-DPS series containing 5, 10, and 20 wt% doping concentration (marked as Film 2, 3, and 4, respectively); CHM-TADFNA series, containing nanoaggregates of NDTs of 0.5, 1.0, 2.0, and 3.0 nm (marked as Film 5, 6, 7, and 8, respectively); and DMAC-DPS (marked as Film 9).The EL OLEDs shared similar structures, ITO/PEDOT: PSS (40 nm)/BP1T (7 nm) /EML/BmPyPb (40 nm)/LiF/Al.These included: C-OLED with 2FPPICz as the emitter (marked as Device ①); C-OLEDs with 2FPPICz: DMAC-DPS as the emitters containing 5, 10, and 20 wt% doping concentration (marked as Devices ②, ③, and ④, respectively); and C-OLEDs with CHM-TADFNA as the emitter, containing nanoaggregates of 0.5, 1.0, 2.0, and 3.0 nm (marked as Devices ⑤, ⑥, ⑦, and ⑧, respectively).Figure 4a shows the transient PL of these thin films, by monitoring the emission peak at 471 nm (the dominant emission peak of CHM-TADFNA film).Film 7 has a higher ratio of delayed parts than Film 1 and Film 3, indicating a more efficient TADF effect due to emitters in CHM-TADFNA structure, explaining the higher EQE.However, the short lifetime inferred the fluorescence component is still in dominance.In contrast, Figure 4b shows the transient EL decay curves of these OLEDs, where Device ⑦ appears to have a delayed component, while Devices ① and ③ show a fast decay characteristic.The PL and EL decay curves for doped and nanoaggregate series are shown in Figure S9a-d (Supporting Information).The increase of the doping concentration evidently increases the lifetime and the ratio of the delayed part (Figure S9a, Supporting Information), which means the more 2FPPICz proportion will reduce the lifetime and the ratio of the delayed part.It can be said that the more energy transfer process from DMAC-DPS to 2FPPICz happened, and the upconverted process of DMAC-DPS subsequently declined, which made a waste of triplet excitons.Conversely, the decay curves of nanoaggregates series show obvious delayed components and exhibit approximate characteristics.Both Devices ⑤ and Devices ⑥ as well as Devices ⑦ and ⑧ showed nearly identical curves, indicating that the CHM-TADFNA structure may be able to reserve the majority of triplet excitons through its TADF effect.In addition, to further confirm the mechanism, PL spectrums of the films were measured (Figure 4c).The board peak can be attributed to the overlapping of the peaks of 2FPPICz and DMAC-DPS.Both series are shown in Figure S10 (Supporting Information), and their PL spectra are analogical in their concentration dependence, while the nanoaggregates series exhibits a stronger peak intensity of DMAC-DPS compared to the doped series.anwhile, the PLQYs of both series are also shown in Table S3 (Supporting Information).In comparison with doped films, DMAC-DPS molecules in nanoaggregates contact one another closely more than 2FPPICz, resulting in sufficiently high PLQY values.Higher PLQYs imply a reduction of nonradiative deactivation pathways, which can contribute to a lower non-radiative voltage loss. [41]Additionally, in CHM-TADFNA structures, the PL peaks of DMAC-DPS are significantly stronger than those of conventionally doped ones with comparable concentrations, which may account for the higher EQE in devices.As compared to the EL results in CHM-TADFNA OLEDs (Figure 3c), the PL spectrum exhibits a clear component of 2FPPICz.However, the EL results of the doped OLEDs exhibit a significant peak of 2FP-PICz (Figure S8c, Supporting Information).As a consequence, CHM-TADFNA appears to employ a different mechanism.The EL of the CHM-TADFNA structure exhibits a dominant emission peak of DMAC-DPS emitter while that of doped C-OLED exhibits dominant emission peak of 2FPPICz.The formation of the exciton must take place at a different location, otherwise, they would not exhibit such significant differences.Based on the EL spectrum, exciton formation of a doped device must majorly occur in the CHM, whereas it does not happen in a CHM-TADFNA device.If CHM did not work as transport channel rather than emission center in CHM-NA route, the EL spectrum of CHM-TADFNA would have also shown an obvious portion of 2FP-PICz.However, in fact, it not happened.This reveals that the excitons will form directly within the nanoaggregate regions, avoiding the unexpected energy transport process of triplet excitons from DMAC-DPS to 2FPPICz to the maximum extent possible.Hereto, a schematic diagram of the working mechanism can be described in Figure 4d.Excitons will directly form on the nanoaggregates region, after which the triplet excitons can be harvested by RISC and ISC process.The novel structure can provide an alternative for systems that use high energy level dopant emitters, despite some inevitable energy transfer from DMAC-DPS to 2FPPICz.In CHM-NA route, the high mobility CHM works major as transport channel rather than emission center.The top parts of nanoaggregates exposed out of the film surface can facilitate the direct injection of electrons from the electron transport layer into nanoaggregates. [27]At the same time, the hole carriers injected from the anode pass through the high mobility BP1T/2FPPICz crystalline layers and then encounter the electrons at DMAC-DPS nanoaggregates.It should be noted that the CHM-TADFNA structure system can be expanded to include TADF materials, further enhancing the utilization of excitons.Furthermore, additional dopants may be added to reuse the triplet excitons wasted in 2FPPICz CHM.Although we currently use 2FPPICz as host matrix at present to expand the crystalline route to many material systems, a crystalline host matrix with higher triplet energy level will be useful to eliminate the energy transfer from TADF guest to crystalline host.In the future, we are confident that we will be able to select a more ficient crystalline matrix and eliminate the unnecessary energy transfer process.

Photon Output Characteristic
The final optimized structure and performance of CHM-TADFNA device, ITO/PEDOT: PSS (40 nm)/BP1T (7 nm) /EML/BmPyPb (10 nm)/ BmPyPb : LiCO 3 (10 nm)/LiCO 3 /Al, are shown in Figure 5a-e.It exhibits an impressive maximum EQE of 10.4%, which is the first time that a blue crystal device can achieve EQE up to 10%, a relatively low turn-on voltage of 2.7 V (@ 1 cd m −2 ), a maximum power efficiency of 20.0 lm W −1 and a maximum current efficiency of 17.9 cd A −1 .The device shows a luminance of 1000 cd m −2 at 3.9 V, and the ∆V (the difference between V on and V 1000 ) is only 1.2 V, which is far less than the original amorphous devices. [38,43]able 1 presents comparisons between the CHM-TADFNA OLED and other representative blue amorphous OLEDs with high EQE whose CIE y are close but less than 0.20, including TADF, [33] triplet-triplet annihilation (TTA), [34] and phosphorescent (Phos.)materials. [35]An InGaN/GaN [36] blue LED device is shown as well.The CHM-TADFNA OLED exhibits the lowest ∆V, indicating a rapid climb at low driving voltages, due to the high carrier mobility CHM and fast formation of excitons.As Figure 6a shows, luminance of the CHM-TADFNA OLED also has the quickest increase, and has the largest brightness at the same voltage, inferring the advantage of low operation voltages.Current density shows similar characteristics (Figure 6b), and CHM-TADFNA OLED exhibits the same rapid growth trend at low voltages.The instantaneous slope of J-V curves at 1000 cd m −2 was defined as Slope 1, which represents the areal differential conductance.As conductance has a positive correlation to mobility, the advantages brought by high-mobility CHM are apparent.Slope 2 and Slope 3 were defined as the instantaneous slope of log (V)-J at 10 cd m −2 and the average slope of that at 10 to 1000 cd m −2 .And Figure 6c shows the corresponding curves.To mitigate the effects of human visual perception and appraise the luminous performance of OLEDs, the number of emitted photons per unit time and unit area (N) is utilized.N can be calculated from the formula, where e represents the elementary charge, and J is the current density.Figure 5d shows the comparison of V with semi-log emitted photons (N) characteristics.Compared to amorphous OLEDs, CHM-TADFNA OLEDs show demonstrable superior performance.Slope 4 and slope 5 were defined as the instantaneous slope of V-semi-log N at 10 cd m −2 and the average slope of that at 10 to 1000 cd m −2 .As N increases with EQE and conductance, the higher value of CHM-TADFNA OLED has uncontroversial enhanced efficient photon output.Meanwhile, the input power, series-resistance joule heat losses, and their ratios were also calculated and shown in Table 1.Those smaller values of CHM-TADFNA OLED further proved the efficient emission and fast formation of excitons, which brings an enhanced increase in device performance compared to conventional doping route.

Morphological Stability of CHM-TADFNA Thin Films
[46][47][48][49] As shown in Figures S11and S12 and Note S1 (Supporting Information), the CHM-TADFNA thin films show extraordinary stability up to 100 h in an atmospheric environment (Condition 1, 25°C, 50-60% humidity, without encapsulation).At a heated condition (Condition 2, 60°C, pressure of 300 pa), the morphology still can be maintained for 1 h.In contrast, amorphous thin films of reference structures in same conditions showed evident phase separation within 5 h and "large aggregates" within 20 min, respectively.Additionally, although a typical material system of MADN: DSA-Ph (3 wt%) was used to fabricate a long-lifetime blue OLED (T 1/2 = 46 000 h), [50] it shows evident molecular aggregates and "pinholes" within 20 h at Condition 1 and 20 min at Condition 2. [27] These results demonstrated superior stability of the CHM-TADFNA thin film and their potential in realizing OLED with high operational stability.

Conclusion
As a novel structure, a crystal matrix host and embedded nanoaggregates have exhibited intriguing advantages.In this work, a TADF material was introduced to form nanoaggregates.It is possible to control exciton distribution and adjust device performance by engineering the nanoaggregate portions.The final optimized blue CHM-TADFNA OLED exhibits a remarkable EQE of up to 10.4%, marking the first instance in which a blue-emission OLED based on crystalline thin film route has been able to attain a level beyond 10%.Due to the high carries mobility of CHM, the CHM-TADFNA OLED also achieves rapid turn-on, rapid increase in luminance, and rapid rise in current density, which results in a high conductance and a lower series-resistance Joule-heat loss ratio, thereby increasing photon output.This work broadens material systems in CHM-NA structure, creating more opportunities for various applications and explorations.

Experimental Section
Materials: To fabricate a CHM-TADFNA device, organic material BP1T was synthesized according to a previous report. [51]2FPPICz was bought from Jilin Yuanhe Electronic Material Company and both materials were purified twice by thermal gradient sublimation before use.DMAC-DPS was bought from Xi'an Polymer Light Technology Corporation.BmPyPb was bought from Luminescence Technology Corporation (Lumetc).These two materials were used as received.
Film and Device Fabrication: The crystalline thin film was manufactured by WEG method. [25,26]Morphologies and crystal structures of crystalline films and nanoaggregates were identified on heavily doped n-type Si/SiO 2 substrates (capacitance per unit area, C i = 10 nF cm −2 ).Quartz substrates were used to investigate photoluminescence and PLQY.Indium tin oxide (ITO) substrates, which had thickness of 180 nm and sheet resistance of 10 Ω were used to manufacture OLEDs and identify transient EL decay curves.ITO substrates were cleaned with detergent first.Then, the Si/SiO 2 , quartz, and ITO substrates were ultrasonically treated for 20 min with acetone, alcohol, and deionized water, respectively.After that, they were all desiccated in high purity nitrogen and dried in a bake oven at 120°C for 30 min.To fabricate OLEDs, ITO was followed and treated with oxygen plasma.PEDOT: PSS (Clevious P VP Al 4083) was then spin-coated on ITO at 4000 rpm for 30 s and baked for 30 min at 120°C.Before fabrication procedure, the Si/SiO 2 , quartz, and ITO substrates were respectively transferred to the vacuum chamber at a pressure of under 10 −4 Pa and grow films.The growth speeds of BP1T and 2FPPICz were approximately both 4-10 Å min −1 on a substrate of temperature of 102°C.Afterward, the substrate was cooled down to 40°C, and the nanoaggregates were then grown at a rate of 10 Å min −1 .Subsequently, the substrate was reheated to 102°C and the CHM and dopants were grown at rates of 4-10 and 0.2-0.5 Å min −1 , respectively.The deposition rates of BmPyPb, LiF, LiCO 3 , and Al were 1-2, 0.05-0.08,0.03-0.06and 10-15 Å s −1 , respectively at room temperature.The film thickness was controlled by a quartz-crystal microbalance.The effective emission area overlapping the area between the ITO and Al electrodes was 4.0 mm × 4.0 mm.
Film and Device Characterization: A SPI 3800/SPA 300 HV (Seiko Instruments Inc., Japan) atomic force microscope with tapping mode was applied to identify the morphologies of films and nanoaggregates.

Figure 1 .
Figure 1.Schematic diagram of CHM-TADFNA OLED.a) Schematic illustration of the device structure.b) Chemical structures of materials.

Figure 6 .
Figure 6.Comparisons of CHM-TADFNA OLED with amorphous thin-film OLEDs.a) Comparison of voltage (V) with semi-log L characteristics.b) Comparison of J-V curves.c) Comparison of V with semi-log J characteristics.d) Comparison of V with semi-log emitted photons (N) characteristics between CHM-TADFNA OLED with representative reported amorphous thin-film OLEDs including InGaN/GaN, TADF, TTA, Phos.Materials.All reference data for comparison are extracted from the corresponding literature.