Triplet-triplet Annihilation Process Research Articles

Exploring charge generation and separation in tandem organic light-emitting diodes based on magneto-electroluminescence

5,6,11,12-tetraphenylnaphthacene (rubrene) exhibits resonant energy properties (E S1,rub ≈ 2E T1,rub), resulting in rubrene-based organic light-emitting diode (OLED) devices that undergo the singlet fission (STT) process at room temperature. This unique process gives rise to a distinct magneto-electroluminescence (MEL) profile, differing significantly from the typical intersystem crossing (ISC) process. Therefore, in this paper, we investigate charge generation and separation in the interconnector, and the mechanism of charge transport in tandem OLEDs at room temperature using MEL tools. We fabricate tandem OLEDs comprising green (Alq3) and yellow (Alq3:rubrene) electroluminescence (EL) units using different interconnectors. The results demonstrate that all devices exhibited significant rubrene emission. However, the MEL did not exhibit an STT process with an increasing magnetic field, but rather a triplet–triplet annihilation (TTA) process. This occurrence is attributed to direct carrier trapping within doped EL units, which hinders the transport of rubrene trapped charges, consequently prolonging the lifetime of triplet excitons (T1,rub). Thus, the increased T1,rub concentration causes TTA to occur at room temperature, causing the rapid decrease of MEL in all devices under high magnetic fields. In devices where only the TTA process occurs, the TTA increases with the increasing current. Consequently, the high magnetic field of devices A–C is only related to TTA. Notably, there exists a high magnetic field TTA of device D in the Alq3/1,4,5,8,9,11-Hexaazatriphenylene-hexacarbonitrile interconnector regardless of the current. This occurs because both EL units in the device emit simultaneously, resulting in the triplet-charge annihilation process of Alq3 in the high magnetic field of the MEL. Moreover, the rapid increase in MEL at low magnetic field across all devices is attributed to the ISC between Alq3 polaron pairs. This entire process involves Förster and Dexter energy transfer. This article not only provides novel insights into charge generation and separation in the interconnector but also enhances our understanding of the microscopic mechanisms in tandem OLED devices.

Scintillation properties of lithium-6 salicylate-loaded liquid scintillators.

The limited availability of conventional 3He proportional counters provides impetus for developing novel neutron detectors. As a candidate, lithium-6-loaded liquid scintillators with neutron/gamma pulse shape discrimination (n-γ PSD) capabilities have been developed. However, the trade-off relationship between the 6Li-loading amount and scintillation light yield is a significant problem. This is because 6Li-loading involves the addition of non-luminescent materials, which cause non-radiative relaxation of the excited states. Therefore, aiming to reduce non-radiative relaxation, we chose lithium-6 salicylate (6LiSal), which shows fluorescence in the visible light region, as a chemical for 6Li-loading. In this study, we analyzed the photoluminescence/scintillation properties based on the Förster resonance energy transfer and investigated the optimal content for obtaining a high light yield. By maximizing the sequential energy transfer from the solvent (toluene) to the phosphor (POPOP), a high light yield 6Li-loaded liquid scintillator (4220 photons per MeV under gamma-ray irradiation) with a 6Li concentration of approximately 0.1 wt% was developed. Thermal neutron events were successfully detected with a light yield of 3970 photons per neutron, which is more than three times higher than those of other organic scintillators. In addition, focusing on the triplet-triplet annihilation process and further optimizing the component for the n-γ PSD, the thermal neutron and gamma-ray events were successfully separated. The developed high light yield 6Li-loaded liquid scintillators show n-γ PSD capabilities and can be promising candidates as alternative detectors to the 3He proportional counter.

Unraveling Triplet Formation Mechanisms in Acenothiophene Chromophores.

The evolution of molecular platforms for singlet fission (SF) chromophores has fueled the quest for new compounds capable of generating triplets quantitatively at fast time scales. As the exploration of molecular motifs for SF has diversified, a key challenge has emerged in identifying when the criteria for SF have been satisfied. Here, we show how covalently bound molecular dimers uniquely provide a set of characteristic optical markers that can be used to distinguish triplet pair formation from processes that generate an individual triplet. These markers are contained within (i) triplet charge-transfer excited state absorption features, (ii) kinetic signatures of triplet-triplet annihilation processes, and (iii) the modulation of triplet formation rates using bridging moieties between chromophores. Our assignments are verified by time-resolved electron paramagnetic resonance (EPR) measurements, which directly identify triplet pairs by their electron spin and polarization patterns. We apply these diagnostic criteria to dimers of acenothiophene derivatives in solution that were recently reported to undergo efficient intermolecular SF in condensed media. While the electronic structure of these heteroatom-containing chromophores can be broadly tuned, the effect of their enhanced spin-orbit coupling and low-energy nonbonding orbitals on their SF dynamics has not been fully determined. We find that SF is fast and efficient in tetracenothiophene but that anthradithiophene exhibits fast intersystem crossing due to modifications of the singlet and triplet excited state energies upon functionalization of the heterocycle. We conclude that it is not sufficient to assign SF based on comparisons of the triplet formation kinetics between monomer and multichromophore systems.

Non‐Doped Blue AIEgen‐Based OLED with EQE Approaching 10.3 %

AbstractAggregation‐induced emission (AIE) luminogens (AIEgens) are attractive for the construction of non‐doped blue organic light‐emitting diodes (OLEDs) owning to their high emission efficiency in the film state. However, the large internal inversion rate (kIC(Tn)) between high‐lying triplet levels (Tn) and Tn‐1 causes a huge loss of triplet excitons, resulting in dissatisfied device performance of these AIEgens‐based non‐doped OLEDs. Herein, we designed and synthesized a blue luminogen of DPDPB‐AC by fusing an AIEgen of TPB‐AC and a DMPPP, which feature hot exciton and triplet‐triplet annihilation (TTA) up‐conversion process, respectively. DPDPB‐AC successfully inherits the AIE feature and excellent horizontal dipole orientation of TPB‐AC. Furthermore, it owes smaller kIC(Tn) than TPB‐AC. When DPDPB‐AC was applied in OLED as non‐doped emitting layer, an outstanding external quantum efficiency of 10.3 % and an exceptional brightness of 69311 cd m−2 were achieved. The transient electroluminescent measurements and steady‐state dynamic analysis confirm that both TTA and hot exciton processes contribute to such excellent device performance. This work provides a new insight into the design of efficient organic fluorophores by managing high‐lying triplet excitons.

Non-Doped Blue AIEgen-Based OLED with EQE Approaching 10.3 .

Aggregation-induced emission (AIE) luminogens (AIEgens) are attractive for the construction of non-doped blue organic light-emitting diodes (OLEDs) owning to their high emission efficiency in the film state. However, the large internal inversion rate (kIC (Tn) ) between high-lying triplet levels (Tn ) and Tn-1 causes a huge loss of triplet excitons, resulting in dissatisfied device performance of these AIEgens-based non-doped OLEDs. Herein, we designed and synthesized a blue luminogen of DPDPB-AC by fusing an AIEgen of TPB-AC and a DMPPP, which feature hot exciton and triplet-triplet annihilation (TTA) up-conversion process, respectively. DPDPB-AC successfully inherits the AIE feature and excellent horizontal dipole orientation of TPB-AC. Furthermore, it owes smaller kIC (Tn) than TPB-AC. When DPDPB-AC was applied in OLED as non-doped emitting layer, an outstanding external quantum efficiency of 10.3 % and an exceptional brightness of 69311 cd m-2 were achieved. The transient electroluminescent measurements and steady-state dynamic analysis confirm that both TTA and hot exciton processes contribute to such excellent device performance. This work provides a new insight into the design of efficient organic fluorophores by managing high-lying triplet excitons.

Effect of Conductive Polymers PEDOT:PSS on Exciton Recombination and Conversion in Doped-Type BioLEDs.

Although the effect of the conductive polymers PEDOT:PSS on the electroluminescence performance of doped-type organic light-emitting diodes (OLEDs) has been studied, the process of PEDOT:PSS regulation of exciton recombination region and concentration within the deoxyribonucleic acid (DNA)-based doped-type BioLEDs is still obscure. In this study, we fabricated Bio-devices with and without PEDOT:PSS using varying spin-coating speeds of PEDOT:PSS. The Alq3:Rubrene-based BioLEDs achieve higher luminance (44,010 cd/m2) and higher luminance efficiency (8.1 cd/A), which are increased by 186% and 478%, respectively, compared to the reference BioLEDs without PEDOT:PSS. Similarly, the maximum luminance and efficiency of blue TCTA:TPBi exciplex-type BioLEDs are increased by 224% and 464%. In particular, our findings reveal that with an increasing thickness of PEDOT:PSS, the region of exciton recombination shifts towards the interface between the emitting layer (EML) and the hole transport layer (HTL). Meanwhile, the concentration of singlet exciton (S1,Rub) and triplet exciton (T1,Rub) increases, and the triplet-triplet annihilation (TTA) process is enhanced, resulting in the enhanced luminescence and efficiency of the devices. Accordingly, we provide a possible idea for achieving high performance doped-type BioLEDs by adding conductive polymers PEDOT:PSS, and revealing the effect of exciton recombination and conversion in BioLEDs given different PEDOT:PSS thicknesses.

Non‐approximative Kinetics of Triplet‐Triplet Annihilation at Room Temperature: Solvent Effects on Delayed Fluorescence

AbstractThe molecular processes taking place during triplet‐triplet annihilation (TTA) in solvents at room temperature are examined in detail. Special attention is paid to modelling of the nonlinear kinetic reactions. Using time‐ and spectrally resolved spectroscopy of DPA and Pt/Pd‐OEP based sensitizer and annihilators, it is shown how the kinetic of parameters, such as the triplet energy transfer (TET) and TTA of the rate‐reactions, can be simulated, measured and fitted, without approximations, using a numerical scheme. Studies of DPA in the solvents DMSO, THF and toluene at room temperature revealed that viscosity/diffusion together with the excited triplet lifetime of the annihilator are the most crucial parameters for high TTA induced delayed fluorescence. From an analysis of the experimentally determined rates an efficiency of 16–40 % was determined for the combined TET and TTA processes using THF, DMSO and toluene as solvents. (DPA=9,10‐diphenylanthracene, OEP=2,3,7,8,12,13,17,18‐octaethyl‐21H,23H‐porphyrin)

Triplet–Triplet Annihilation Enhanced Deep‐Blue Organic Light‐Emitting Diodes by Naphtho[1,2‐d]imidazole‐Isomer Derivatives with Spin–Orbit Coupling

AbstractThe utilization of triplet excitons is of great importance for organic light‐emitting diodes (OLEDs). Triplet–triplet annihilation (TTA) is one of the effective tactics to achieve high efficiency deep‐blue organic electroluminescence emitters by converting two triplet excitons into one singlet exciton. Whereas, in addition to the 25% electrogenerated singlet excitons, the proportion of radiative singlet excitons (RSE) produced by the TTA process is usually only 15%; thus the total radiative excitons are 40%. In this study, ≈35% of RSE is achieved by the TTA process (total 60%) with two deep‐blue emitters based on the isomeric naphthoimidazole (NI) unit and anthracene bridge. As a result, non‐doped OLEDs based on the two NI derivatives as emitting layers achieve maximum external quantum efficiencies of 10.9% and 11.2% with an identical deep‐blue emission peak of 452 nm, which are the best TTA OLEDs with a Commission Internationale de l'Eclairage chromaticity Y coordinate below 0.15. Theoretical and experimental results demonstrate that the TTA process can be improved owing to the efficient spin–orbit interactions, even though the energy levels of the triplet pairs are higher than the calculated second triplet excited states.

Geometric Signatures as Important Factors to Control the Photo-Stabilities of the Phosphorescent Pd(II)/Pt(II) Complexes: A Case Study.

Operation lifetime, as an important parameter, determines the performance of phosphorescent organic light-emitting diodes (OLEDs). Unveiling the intrinsic degradation mechanism of emission material is crucial for improving the operation's lifetime. In this article, the photo-stabilities of tetradentate transition metal complexes, the popular phosphorescent materials, are explored by means of density functional theory (DFT) and time-dependent (TD)-DFT, aiming to illustrate the geometric signatures as important factors to control the photo-stabilities. Results indicate that for the tetradentate Ni(II), Pd(II), and Pt(II) complexes, the coordinate bonds of the Pt(II) complex exhibit stronger strength. It seems that the strengths of coordinate bonds are closely related to the atomic number of the metal center in the same group, which could be attributed to the various electron configurations. The effect of intramolecular and intermolecular interactions on ligand dissociation is also explored here. The large intramolecular steric hindrance and strong π-π interaction between the Pd(II) complexes caused by aggregation could effectively raise the energy barriers of the dissociation reaction, leading to an unfeasible reaction pathway. Moreover, the aggregation of Pd(II) complex can change the photo-deactivation mechanism as compared to that of monomeric Pd(II) complex, which is favored for avoiding the TTA (triplet-triplet annihilation) process.

Efficient solution-processed OLEDs featuring deep-blue triplet-triplet annihilation emitter based on pyrene derivative

Achieving high efficiency deep-blue organic light-emitting diodes (OLEDs) with a CIEy < 0.08 is still terribly urgent yet challenge. Herein, we designed and synthesized a novel blue triplet-triplet annihilation (TTA) emitter with a fan-shape torsional molecular structure, namely TbuPyB, which is based on benzene as core and three tert-butylpyrene as arm. The photophysical, electrochemical and electroluminescent performances of TbuPyB were systematically investigated. Intense deep-blue/blue emissions peaked at 413 and 472 nm are observed in the 7 wt% doped 1,3-bis(N-carbazolyl)benzene (mCP) thin film and neat film, accompanied by absolute photoluminescence (PL) quantum yield (PLQY) of 66.3% and 74.8%, respectively. Contributed by the TTA process, the solution-processed non-doped device exhibits blue emission peak at 470 nm with an impressive EQE of 10.65% and a CIE coordinates of (0.15, 0.20) at the voltage of 7.8 V. In contrary, at the 7 wt% dopant concentration, an outstandingly 57 nm violet-shifted deep-blue emission at 413 nm with an EQE of 6.87% and a CIE coordinates of (0.15, 0.06) was achieved in the doped device. These results schedule a novel avenue for designing highly efficient deep-blue emitter in the solution processable OLEDs.

Anthracene derivatives with hot exciton and TTA process for high-efficiency organic light-emitting diodes

Organic fluorophores with unique photophysical properties that converting the triplet excitons to singlet excitons, are desired to improve the efficiencies of organic light-emitting diodes (OLEDs). Here, two new anthracene-based emitters pipdAnCz and pipdAnTPA, with proper donor and acceptor substituents are designed and synthesized. The theoretical calculation and experimental results demonstrate that both pipdAnCz and pipdAnTPA possess hot exciton and triplet-triplet annihilation (TTA) characteristics, which can convert the triplet excitons to singlet excitons from the high-lying triplet energy levels (Tn) and the lowest triplet energy level (T1) respectively. Due to its relative higher photoluminescence quantum yields (PLQYs), the pipdAnTPA based non-doped device achieved a maximum external quantum efficiency (EQEmax) of 6.43% with an exciton utilization efficiency (EUE) of 72%. Further device physics study reveal that the hot exciton process is the dominant mechanism, assisted by TTA process, to convert the triplet excitons, especially for the pipdAnTPA based device.

Harvesting Triplet Excitons in High Mobility Emissive Organic Semiconductor for Efficiency Enhancement of Light-Emitting Transistors.

Organic light-emitting transistors (OLETs), a kind of highly integrated and minimized optoelectronic device, demonstrate great potential applications in various fields. The construction of high-performance OLETs requires the integration of high charge carrier mobility, strong emission, and high triplet exciton utilization efficiency in the active layer. However, it remains a significant long-term challenge, especially for single component active layer OLETs. Herein, the successful harvesting of triplet excitons in a high mobility emissive molecule, 2,6-diphenylanthracene (DPA), through the triplet-triplet annihilation process is demonstrated. By incorporating a highly emissive guest into the DPA host system, an obvious increase in photoluminescence efficiency along with exciton utilization efficiency results in an obvious enhancement of external quantum efficiency of 7.2times for OLETs compared to the non-doped devices. Moreover, well-tunable multi-color electroluminescence, especially white emission with Commission Internationale del'Eclairage of (0.31, 0.35), from OLETs is also achieved by modulating the doping concentration with a controlled energy transfer process. This work opens a new avenue for integrating strong emission and efficient exciton utilization in high-mobility organic semiconductors for high-performance OLETs and advancing their related functional device applications.

Recent Advances in Triplet–Triplet Annihilation-Based Materials and Their Applications in Electroluminescence

Efficient and stable blue organic light-emitting devices (OLEDs) represent one of the most important components in future solid-state lighting and full color displays. Although red and green OLEDs have been successfully commercialized, it remains challenging to realize blue OLEDs showing high efficiency and high stability simultaneously, restricting their commercialization. Triplet–triplet annihilation (TTA)-based materials have been emerging as a new category of electroluminescent or host materials with promising potential for highly efficient and stable blue devices due to their appealing photophysical properties (e.g., ability to generate emissive singlet excited states through TTA process, high photoluminescence quantum yield, ease of molecular design, etc.). Recently, research on TTA-based materials toward high-performance blue OLEDs has received an increasing attention. In this review, recent research advances on the molecular design strategies, photophysical properties of TTA-based materials (both blue emitters and host materials), mechanism of TTA-based electroluminescence, as well as their OLED applications are presented comprehensively. Moreover, potential perspectives with future research opportunities in this field are also described. We believe that the emerging TTA-based materials will bring more opportunities for developing a large family of novel photofunctional materials showing appealing and tunable photophysical properties, thus providing new opportunities for high-efficiency and stable blue electroluminescence in the future.

Efficient solid-state infrared-to-visible photon upconversion on atomically thin monolayer semiconductors.

Upconverting infrared light into visible light via the triplet-triplet annihilation process in solid state is important for various applications including photovoltaics, photodetection, and bioimaging. Although inorganic semiconductors with broad absorption and negligible exchange energy loss have emerged as promising alternative to molecular sensitizers, currently, they have exclusively suffered from low efficiency and contained toxic elements in near-infrared (NIR)-to-visible upconversion. Here, we report an ultrathin bilayer film for NIR-to-visible upconversion based on atomically thin two-dimensional (2D) monolayer semiconductors. The atomic flatness and strong light absorption of 2D monolayer semiconductors enable ultrafast energy transfer and robust NIR-to-visible emission with a high upconversion quantum yield (1.1 ± 0.2%) at modest incident power (260 mW cm-2). Increasing layer thickness adversely quenches the upconversion emission, highlighting the 2D advantage. Considering the whole library of 2D semiconductors, the facile large-scale production and the ultrathin solid-state architecture open a new research field for solid-state upconversion applications.

Cover Feature: Triplet‐triplet Annihilation Dynamics of Naphthalene (Chem. Eur. J. 40/2022)

Triplet–triplet annihilation (TTA)-based photon upconversion involves the fusion of two non-emissive triplet excited states into one singlet excited state. The TTA process in naphthalene is found to be mediated by conical intersection between the T1T1 and S1S0 states. The coupling of an optical cavity to a naphthalene dimer results in an increase in the efficiency of TTA-assisted photon upconversion process. More information can be found in the Research Article by M. Gudem and M. Kowalewski (DOI: 10.1002/chem.202200781).

Triplet-triplet Annihilation Dynamics of Naphthalene.

Triplet‐triplet annihilation (TTA) is a spin‐allowed conversion of two triplet states into one singlet excited state, which provides an efficient route to generate a photon of higher frequency than the incident light. Multiple energy transfer steps between absorbing (sensitizer) and emitting (annihilator) molecular species are involved in the TTA based photon upconversion process. TTA compounds have recently been studied for solar energy applications, even though the maximum upconversion efficiency of 50 % is yet to be achieved. With the aid of quantum calculations and based on a few key requirements, several design principles have been established to develop the well‐functioning annihilators. However, a complete molecular level understanding of triplet fusion dynamics is still missing. In this work, we have employed multi‐reference electronic structure methods along with quantum dynamics to obtain a detailed and fundamental understanding of TTA mechanism in naphthalene. Our results suggest that the TTA process in naphthalene is mediated by conical intersections. In addition, we have explored the triplet fusion dynamics under the influence of strong light‐matter coupling and found an increase of the TTA based upconversion efficiency.

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

Some peculiarities of triplet excitations dynamics in organic macromolecules and crystals

Spectral properties of polymer macromolecules in the optical energy range and relation of these properties to the chemical structure and energy levels system of polymers were examined. The nature of optical centers of the macromolecules with π-electron systems localized on separate groups (so-called chromophores) was analyzed. It was stressed that such vitally important biopolymers as DNA and RNA belong to this type of polymers. It was shown that in synthetic and biological macromolecules with pendant aromatic groups, the triplet excitons meet and annihilate with the very high probability due to large lifetime and one-dimensional motion. The presented results prove that efficiency of triplet-triplet annihilation processes (at the used excitation power) is higher than efficiencies of other electronic processes. Consideration of this fact in the kinetic equation for triplet excitons in macromolecule leads to inverse square root dependence of phosphorescence intensity on the macromolecule length. At the same time, for three-dimensional molecular crystals of stilbene and para-terphenyl, the intensity of the delayed fluorescence is less dependent on the size of the granules compared to the dependence of the delayed fluorescence intensity on the length for one-dimensional macromolecules.

Accurate and fast master equation modeling of triplet-triplet annihilation in organic phosphorescent emission layers including correlations

Triplet-triplet annihilation (TTA) in phosphorescent emission layers of modern organic light-emitting diodes compromises their performance and device lifetime. TTA can occur by a F\"orster-type interaction between two triplets, leading to a loss of one of them. The TTA process gives rise to correlations in the positions of the surviving triplets, which complicate its study. These correlations can in principle be accounted for exactly in kinetic Monte Carlo (KMC) simulations, but such simulations are computationally expensive. Here, we present master equation modeling of TTA that accounts for correlations in a computationally efficient way. Cases without and with triplet diffusion, which partly washes out correlations, are considered. We calculate the influence of TTA on transient photoluminescence experiments, where it leads to a deviation from exponential decay, and on steady-state emission efficiency. A comparison with KMC simulations shows that our master equation modeling is an accurate and computationally competitive alternative.

Investigations of microscopic mechanisms in exciplex-based devices with isomers of mCBP and CBP as donors via magneto-electroluminescence

The mCBP and CBP are two kinds of isomers containing carbazole groups and often used as the device hosts for fluorescence and phosphorescence emission. However, there are little studies on the microscopic mechanisms of exciplex-type devices based on mCBP or CBP. In this paper, the isomers of mCBP and CBP are used as donors and the PO-T2T is selected as an acceptor. The two kinds of exciplex-based devices are fabricated according to a mass ratio of 1∶1, which are respectively referred to as device 1 (Dev. 1) and device 2 (Dev. 2). Their magneto-electroluminescence (MEL) curves are measured at different working temperatures and various injection currents. It is found that the low field effects of the MEL curves from Dev. 1 are dominated by the &lt;i&gt;B&lt;/i&gt;-mediated reverse intersystem crossing (RISC) process at room temperature, and as the operational temperature decreases, the MEL line-shapes change gradually from RISC to the intersystem crossing (ISC) process. Conversely, the low field effects of the MEL curves of Dev. 2 are governed by the &lt;i&gt;B&lt;/i&gt;-mediated ISC process at room temperature, and the ISC process first weakens then strengthens with temperature decreasing. The high field effects of the MEL curves of Dev. 1 and Dev. 2 are both dominated by the &lt;i&gt;B&lt;/i&gt;-mediated triplet-charge annihilation (TQA) process at room temperature, but those of Dev. 2 at 20 K present the &lt;i&gt;B&lt;/i&gt;-mediated triplet-triplet annihilation (TTA) process. The completely opposite low-field line-shapes of MEL traces from Dev. 1 and Dev. 2 can be attributed to their different structures of mCBP and CBP, which lead to the higher and lower triplet state exciton energy, respectively. The higher triplet exciton energy of the mCBP donor causes the triplet exciplex energy to be confined effectively, which promotes the RISC process (EX&lt;sub&gt;1&lt;/sub&gt; ← EX&lt;sub&gt;3&lt;/sub&gt;) in Dev.1. Contrarily, the lower triplet exciton energy of the CBP donor causes the triplet exciplex to experience an energy loss process (EX&lt;sub&gt;3&lt;/sub&gt; → T&lt;sub&gt;1&lt;/sub&gt;, CBP) , resulting in the suppressed RISC process in Dev. 2. Consequently, the overlapped effects of the ISC process of polaron pairs and the RISC process of exciplex in Dev. 2 under the action of external magnetic field display the ISC-determined process at room temperature. Moreover, the temperature-dependent change in the microscopic process of Dev. 1 such as the conversion from RISC to ISC is because decreasing temperature is not conducive to the occurrence of the RISC process of exciplex states due to its endothermic property. The low-temperature TTA process occurring in Dev. 2 is due to the suppressed energy loss process of triplet exciplex via the Dexter energy transfer from the triplet exciplex to the triplet exciton of CBP donor. In addition, when the mass ratio of mCBP donor to PO-T2T acceptor varies from 1∶4 to 1∶1 to 4∶1, the RISC process of MEL curves of devices turns stronger and stronger, which is because the devices tend more to balance, favoring the RISC process. A higher external quantum efficiency is obtained in the mCBP:PO-T2T host than in the CBP:PO-T2T host when fluorescent guest material of TBRb is used as a dopant in these two exciplex-based devices, which verifies the importance of the effective confinement of triplet exciplex energy in improving the luminescence efficiency. Note that via the MEL detection technology, the current- and temperature-dependent microscopic processes and their reasonable interpretations and device performances from exciplex-based devices with the isomers of mCBP and CBP as donors have not been reported in the literature. This work provides experimental and theoretical references for fabricating the high-efficiency exciplex-based organic light-emitting devices.