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Electron leakage is one of the most critical factors for the degradation of blue fluorescent organic light‐emitting diodes (FOLEDs), as it occurs when electrons injected from the cathode flow to an electron‐blocking layer (EBL) without being entirely consumed within an emissive layer (EML). To address this issue, this study introduces the concept of an electron leakage‐pathway (ELP). Anthracene core materials, used as hosts for blue FOLEDs were doped in the EBL to prevent its direct damage to the EBL molecules by constructing the ELP. This study shows that using an anthracene core with high bond dissociation energy (BDE) in the anionic state as the ELP is the most effective way to increase the lifetime of the FOLED, demonstrating over 400 h. of LT90 (the time taken for the luminance to decrease to 90% of its initial value), which corresponds to an increase of 33% compared to the lifetime without the ELP. Remarkably, under a commonly used brightness level of 500 cd m−2 in smartphones, an LT50 of over 10 000 h was obtained. Ultimately, this study outlines a strategy for increasing the lifetime of blue FOLEDs through simple modifications to the device structure, without requiring the development of EBL materials or complex device engineering. [ABSTRACT FROM AUTHOR]

Metal–halide perovskite nanocrystals (NCs) have emerged as suitable light‐emitting materials for light‐emitting diodes (LEDs) and other practical applications. However, LEDs with perovskite NCs undergo environment‐induced and ion‐migration‐induced structural degradation during operation; therefore, novel NC design concepts, such as hermetic sealing of the perovskite NCs, are required. Thus far, viable synthetic conditions to form a robust and hermetic semiconducting shell on perovskite NCs have been rarely reported for LED applications because of the difficulties in the delicate engineering of encapsulation techniques. Herein, a highly bright and durable deep‐blue perovskite LED (PeLED) formed by hermetically sealing perovskite NCs with epitaxial ZnS shells is reported. This shell protects the perovskite NCs from the environment, facilitates charge injection/transport, and effectively suppresses interparticle ion migration during the LED operation, resulting in exceptional brightness (2916 cd m−2) at 451 nm and a high external quantum efficiency of 1.32%. Furthermore, even in the unencapsulated state, the LED shows a long operational lifetime (T50) of 1192 s (≈20 min) in the air. These results demonstrate that the epitaxial and hermetic encapsulation of perovskite NCs is a powerful strategy for fabricating high‐performance deep‐blue‐emitting PeLEDs. [ABSTRACT FROM AUTHOR]

Multimaterial emission layer (EML) with host and dopant is known for its advantages in efficiency and lifetime for organic light‐emitting diodes (OLEDs). However, as the compositions and the mixing ratio in the EML diversify, complex device physics and photophysics and complicated fabrication processes become challenging issues. Herein, a new concept to integrate exciton donor (host) and acceptor (dopant) into a single emitting molecule is suggested. 9‐(8,9,10,11‐Tetradeuterospiro[benzo[de]anthracene‐7,9′‐fluoren]‐2'‐yl)‐9H‐carbazole (SBAF‐Cz) and 8,9,10,11‐tetradeutero‐N‐(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐N‐phenylspiro[benzo[de]anthracene‐7,9′‐fluoren]‐3‐amine (FPA‐SBAF) are used as host and dopant, respectively. By integrating two units, 8,9,10,11‐tetradeutero‐2′‐(9H‐carbazol‐9‐yl)‐N‐(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐N‐phenylspiro[benzo[de]anthracene‐7,9′‐fluoren]‐3‐amine (FPA‐SBAF‐Cz) is synthesized, and photophysical and electrical properties are characterized. Density functional theory and experimental results consistently reveal that SBAF‐Cz and FPA‐SBAF are photophysically and electrically independent. The electrical properties of FPA‐SBAF‐Cz behave independently, while the photophysical properties are the sum of those of SBAF‐Cz and FPA‐SBAF, which is attributed to the zero radius of intramolecular energy transfer (ZRIET) between donor and acceptor in FPA‐SBAF‐Cz. The single‐component blue OLED with FPA‐SBAF‐Cz exhibits a maximum external quantum efficiency of 4.18%, which is higher than those of OLEDs with SBAF‐CZ:FPA‐SBAF multicomponent EMLs. Surprisingly, the device lifetime to 50% decrease from initial luminance is 114 h in FPA‐SBAF‐Cz OLED, which is 2.2 times longer than that of SBAF‐Cz:FPA‐SBAF OLEDs. [ABSTRACT FROM AUTHOR]

We analyzed the degradation mechanism by deteriorating the exciplex host‐based phosphorescent organic light‐emitting diodes (PhOLEDs) while repeatedly applying voltages in the range of several nA to mA. To identify the most significant degradation factors represented by bleaching, quenching, and charge imbalance, the degradation process was described from various perspectives by the capacitance (C)‐voltage (V) curves (CV), and magneto‐electroluminescence (MEL). Comparing the MEL of the non‐doped and the doped devices, the bleaching of the dopant was confirmed as degradation progressed. Since the highest occupied molecular orbital (HOMO) of the dopant aligns with that of the hole‐transporting layer, the injected holes are easily trapped. As a result, the trap‐induced Shockley‐Read Hall recombination became dominant. Thus, it was identified that the bleaching of the dopant itself acts as the major degradation factor. [ABSTRACT FROM AUTHOR]

A highly efficient anthracene‐based 5‐(4‐(10‐phenylanthracen‐9‐yl)phenyl)‐5H‐benzofuro[3,2‐c]carbazole (ATDBF) with nearly 100% exciton utilization efficiency is developed for highly efficient nondoped blue organic light‐emitting diodes (OLEDs) through inter‐ and intramolecular triplet exciton up‐converting mechanisms. The ATDBF emitter opens hybridized hot excitons, triplet–triplet fusion (TTF), and mixed TTF/hot exciton channels for triplet exciton to singlet exciton conversion. The molecular design adopting a benzofuro[3,2‐c]carbazole (BFCz) donor manages the singlet and triplet excited states for hybridized triplet exciton up‐conversion mechanisms, which enable a high external quantum efficiency (EQE) of 7.93% in the ATDBF blue device with color coordinates of (0.15, 0.06). This is one of the best efficiencies of the nondoped blue OLEDs with a y color coordinate below 0.06. [ABSTRACT FROM AUTHOR]

An electroplex is an excited state charge transfer complex formed between a donor molecule and an acceptor molecule upon electrical excitation. Since the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of electroplex is small likewise exciplex, the energy difference between the singlet and the triplet charge transfer (1CT and 3CT) states can be very small, which facilitate the conversion of triplet excitons into singlet excitons by the assistance of thermal energy and the emission as delayed fluorescence. However, in contrast to exciplex, the detailed analysis of the reverse intersystem crossing (RISC) from 3CT to 1CT and the exciton‐related annihilation processes in electroplex OLEDs have been rarely reported. In this talk, the magnetic field effects (MFEs) on the electroplex host using 2,2'‐di(9H‐carbazol‐9‐yl)‐1,1'‐biphenyl (oCBP) and 9‐(4,6‐bis(3‐(triphenylsilyl)phenyl)‐1,3,5‐triazin‐2‐yl)‐9H‐carbazole (DSiCzTrz) were investigated. Temperature‐dependent MFE measurements revealed that RISC channel co‐exists with the intersystem crossing (ISC) channel and triplet‐polaron quenching process prevails in the electroplex EML. It was also found that 3CT excitons behave as charge scattering sites. [ABSTRACT FROM AUTHOR]

In phosphor-sensitized-fluorescent organic light-emitting diodes (PSF-OLEDs), triplet excitons generated in the emitting layer (EML) are harvested by the sensitizer and the excitonic energy is efficiently transferred to the fluorescent dopant molecules. Since a phosphorescent sensitizer is typically doped at around 10 wt.%, the sensitizer not only affects cascade energy transfer but also electrical transporting in the PSF-OLEDs. However, the electrical role of phosphorescent metal complex molecules in the EML is unclear. In this study, we report the impact of the phosphorescent sensitizer on the electrical properties of PSF-OLEDs. Through a comprehensive analysis using impedance spectroscopy in conjunction with current density (J)-voltage (V)-luminance (L) properties of the PSF-OLED, it was revealed that 10 wt.% phosphorescent sensitizer forms an electron transporting pathway inside the EML. Thus, the sensitizer molecules transform a unipolar single host into a bipolar mixed host. In other words, the phosphorescent sensitizer is an n-type host in the PSF-OLEDs. As a result, the charge balance and the operating voltage were simultaneously and significantly improved in the PSF-OLEDs. [ABSTRACT FROM AUTHOR]

A high triplet energy host is developed using a silane moiety, 9‐(4‐(triphenylsilyl)dibenzo[b,d]furan‐2‐yl)‐9H‐carbazole (SiDBFCz), is designed through extensive density functional theory (DFT) calculations to obtain appropriate hole and electron injection barriers. The chemical hardness and the charge transport characteristics are comprehensively investigated to realize a bipolar host with high triplet energy over 2.9 eV for deep blue phosphorescent organic light‐emitting diodes (PHOLEDs). The synthesized SiDBFCz clearly exhibits the bipolar characteristics especially with emitter molecules doped. An external quantum efficiency over 19 % without any microcavity optimization is achieved thanks to the good charge balance in the SiDBFCz PHOLED. The device lifetime of the SiDBFCz PHOLED is improved more than 1000 %, compared to the unipolar control devices at an initial luminance of 500 cd m−2. The dramatic enhancement of the operational stability of the deep blue PHOLED is also thoroughly investigated in terms of electrochemical stability of host molecules in charged or excited states. The results clearly indicate that the device lifetime is strongly correlated with the bond dissociation energy and the activation energy for the bond dissociation reaction in triplet excited state. [ABSTRACT FROM AUTHOR]

We report fluorenyl amine-based electron blocking layers (EBLs) N,9,9-triphenyl-N-(4′-(triphenylsilyl)-[1,1′-biphenyl]−4-yl)−9 H-fluoren-2-amine (P-pSi-DPFA), N,9,9-triphenyl-N-(3-(triphenylsilyl)phenyl)−9 H-fluoren-2-amine (P-mSi-DPFA), and N-([1,1′-biphenyl]−4-yl)−9,9-diphenyl-N-(3-(triphenylsilyl)phenyl)−9 H-fluoren-2-amine (BP-mSi-DPFA) that prevent intermolecular interactions with emissive layer (EML). Triplet-triplet fusion (TTF)-based organic light-emitting diodes (OLEDs) use anthracene derivatives as hosts, and due to the electron-rich nature of anthracene core, the recombination zone is predominantly formed at the EBL/EML interface. Therefore, it is important to control the intermolecular interaction between EBL and EML while also having an EBL with suitable hole transport characteristics and an appropriate highest occupied molecular orbital (HOMO) level. We developed TTF-based OLED achieving up to 1489 hours (LT 50 at 500 cd/m2) using P-pSi-DPFA as the EBL, securing hole transport characteristics through a fluorenyl amine core, and preventing unwanted intermolecular interactions with the EML by substituting triphenyl silane into the amine core. • Three newly synthesized EBL materials extended OLED device lifetime significantly. • Experimental and theoretical analyses support EBL materials' effectiveness. • P-pSi-DPFA device achieved an impressive 1489-hour lifetime at 500 cd/m². [ABSTRACT FROM AUTHOR]

• p-host and fluorescent dopant was seamlessly integrated into a single molecule. • Non-conventional exciplex formed between fused p-host and n-host. • ZETPLEX, an extremely efficient energy transfer within fused p-host and n-host. A multi-component emissive layer (EML) composed of a mixture of p- and n-type hosts and a dopant is a widely used structure in organic light-emitting diodes (OLEDs) due to its high efficiency and operational stability. However, multi-component EML devices impose limitations such as difficulty in accurately controlling the mixing ratio and profiles in the manufacturing process, high costs, and complexity in the photophysical properties of the components. In this paper, a p-type host fused with a blue fluorescent dopant, 5,9-di([1,1′-biphenyl]-2-yl)-2′-(9H-carbazole-9-yl)3,7-dimethyl-5,5a,5a1,9,9a,16a-hexahydrospiro[5,9-diaza-16b-boraindeno[2,1-b]naphtho[1,2,3-fg]anthracene-11,9′-fluorene] (DABNA-Spiro-Cz), was designed and successfully synthesized to construct a novel EML structure. Completely fused within DABNA-Spiro-Cz, the p-type host and blue fluorescent dopant can independently perform their respective roles. An exciplex is formed between n-type host and p-type host unit in the DABNA-Spiro-Cz molecule and its energy is effectively transferred to the blue fluorescent dopant unit in DABNA-Spiro-Cz. In other words, a degree of freedom is earned from a conventional 3-component exciplex-dopant system. A high external quantum efficiency of 14.9 % was achieved thanks to " z ero-radius of intramolecular e nergy t ransfer in exci plex (ZETPLEX)" system, which is completely non-conventional and novel. We believe the ZETPLEX mechanism opens a new era of designing emissive materials and paves a new way of constructing a novel EML and device architecture for highly efficient OLEDs. [ABSTRACT FROM AUTHOR]

We investigated the effect of hydrogen doping on characteristics of InGaTiO (IGTO) electrode with high conductivity and transmittance during sputtering process. After hydrogen doping, the 300 nm-thick IGTO:H electrode showed lower sheet resistance of 13.79 Ω/square compared to sheet resistance (69.2 Ω/square) of pure IGTO electrode without change of optical transmittance. In addition, wet etching reaction rate of IGTO:H electrode for patterning process was significantly accelerated after hydrogen doping. Possible explanation for hydrogen doping effect on electrical properties and wet etching process of the IGTO:H electrode was suggested. The doped hydrogen influenced the electrical characteristics through the passivation of dangling bonds and oxygen vacancies. Moreover, it significantly impacts crystalline structure, consequently altering the etching rate. Using patterned IGTO:H electrodes, we fabricated red organic light emitting diodes (OLEDs) to show feasibility of the IGTO:H electrodes. External quantum efficiency and current efficiency of the red OLED with IGTO:H (10%) were higher than IGTO electrode without hydrogen doping, indicating that hydrogen doping is an effective method to improve the film properties and IGTO:H electrode can serve as a prospective transparent anode for both flexible and rigid OLEDs. [Display omitted] • Highly conductive and transparent hydrogen-doped InGaTiO electrodes (IGTO:H). • Possible mechanism of the effect of hydrogen doping on the electrical properties and wet-etching rate of IGTO:H electrode. • IGTO:H electrodes exhibit enhanced electrical and mechanical properties after hydrogen doping. • Transparent IGTO:H electrodes for red organic light emitting diodes. [ABSTRACT FROM AUTHOR]

• Intermolecular interaction between host and deep blue Pt complex utilized in WOLEDs. • By varying the ratio of n-type host, a wide range of colors was achieved. • Highly efficient WOLEDs were realized with a single deep blue Pt(II) complex. Previous studies on white organic light-emitting diodes (WOLEDs) using a single Pt dopant relied on square-planar Pt complexes, exhibiting various emission characteristics due to ligand-centered π-π interactions. However, this approach limits the range of the materials selections to those with excimer or aggregation-induced emission (AIE) properties. In this study, a new method for creating WOLEDs with a single Pt dopant is proposed. We observed the emergence of an intermolecular interaction, specifically the formation of an exciplex due to π-π interaction between the n-host (ET) and the Pt complex, leading to a low-energy yellow emission. By varying the mixing ratio of ET and Pt complex, a spectrum of emissions ranging from pure blue to yellow was achievable. Consequently, we constructed 3-stack tandem devices, leveraging color variations based on the ET:Pt ratio. As a result, we successfully achieved a cool white emission with a Color Rendering Index (CRI) of 66.7, International Commission on Illumination (CIE) coordinates of (0.294, 0.380). Additionally, through optimization of the device structure, external quantum efficiency (EQE) was enhanced from 18.3% to 21.9%. This novel and simple device architecture adjusting intermolecular interaction based on molecular geometry between ET and Pt(II) complex provides a solution to materials limitations in WOLEDs. [ABSTRACT FROM AUTHOR]

We developed a one-step simple wet etching process for flexible Ga, Ti co-doped In 2 O 3 (IGTO)/AgPdCu (APC)/IGTO multi-layer electrodes deposited on colorless polyimide (CPI) substrates for flexible bottom emission organic light-emitting diodes (OLEDs). To fabricate OLEDs, the transparent and flexible IGTO/APC/IGTO multilayer electrode with a low sheet resistance of 8.35 Ohm/square and high average transmittance of 82.65 % was directly patterned using a mixed etchant of oxalic acid and nitric acid. For direct patterning of the IGTO/APC/IGTO electrode, wet etching condition was optimized as a function of etch rate, mixture solution ratio, and process temperature. At optimal wet etching condition with oxalic acid of 1 M and nitric acid of 0.79 M at 30 ℃, we successfully patterned the IGTO/APC/IGTO multi-layer without residue by one-step wet etching process. To demonstrate the feasibility of one-step patterned IGTO/APC/IGTO bottom electrode, we fabricated typical bottom emission (OLEDs) on the patterned IGTO/APC/IGTO electrodes. The performance of the flexible OLEDs with the patterned IGTO/APC/IGTO multi-layer electrodes was similar to that of rigid OLEDs with reference ITO electrodes, demonstrating the effectiveness of one-step wet etching as an effective patterning process for flexible IGTO/APC/IGTO multi-layer electrodes. [Display omitted] • Transparent and flexible InGaTiO/AgPdCu/InGaTiO multilayer electrodes. • One-step wet etching of InGaTiO/AgPdCu/InGaTiO multilayer for direct patterning • Outstanding mechanical flexibility of InGaTiO/AgPdCu/InGaTiO multilayer electrodes. • Transparent InGaTiO/AgPdCu/InGaTiO anode for flexible organic light emitting diodes [ABSTRACT FROM AUTHOR]

The pursuit of hybridized local and charge transfer (HLCT) excited state-based emitters is a promising strategy to achieve high external quantum efficiency in blue organic light-emitting diodes (OLEDs). Two isomeric dimethyl-dihydroindenocarbazole-anthracene-phenanthroimidazole-based emissive molecules (PhAnsIn and PhAnoIn) were designed and explored based on the HLCT scheme. All molecules possessed the HLCT excited-state characters, according to the photophysical investigation and density functional theory calculations. Consequently, PhAnsIn and PhAnoIn showed good blue emission with peaks at 457 and 464 nm and photoluminescence quantum yield of 80.6% and 56.5% in neat films, respectively. The fabricated blue OLEDs with PhAnsIn and PhAnoIn as emitters also realized the corresponding blue emission with electroluminescence peaks at 458 and 457 nm, respectively. The nondoped devices based on PhAnsIn and PhAnoIn exhibited maximum external quantum efficiencies of 8.2% and 8.5% with CIE coordinates of (0.14, 0.12) and (0.14, 0.11), respectively. • Hybridized local and charge transfer excited state based blue fluorescence emitter. • High photoluminescence quantum yield of 80.6% in a neat film. • Non-doped blue fluorescence organic light-emitting diodes with external quantum efficiency of 8.2%. [ABSTRACT FROM AUTHOR]

"Hot-exciton" materials exhibiting high-lying reverse intersystem crossing (hRISC) are promising candidates for organic light-emitting diode (OLED) materials owing to their improved exciton utilization efficiency and efficiency roll-off. To investigate the excited-state structure–property relationship in anthracene/benzophenone-based materials, we designed and prepared three anthracene-benzophenone derivatives by varying substituents at peripheral benzophenone units, namely, AnBP-F , AnBP-H , and AnBP-OMe. Systematic investigation of the excited-state properties of these compounds and DFT calculations showed that they have hybridized local and charge-transfer (HLCT) characteristics in their emissive transitions. All prepared compounds were adapted in a non-doped OLED device, which exhibited an external quantum efficiency (EQE) of up to 2.88%. To further study the exciton dynamics in the device, magnetoelectroluminescence was measured, which exhibits the combined characteristics of triplet–triplet annihilation (TTA) and HLCT mechanisms. [Display omitted] • Anthracene/benzophenone-based HLCT emitters were prepared by varying substituents at peripheral benzophenone units. • Substituents help to tune the nature of the excited state. • Non-doped OLEDs achieved EQE max of 2.88%. • Studies on the exciton dynamics of the device indicate that the TTA and HLCT mechanisms concurrently exist. [ABSTRACT FROM AUTHOR]

• Ir(dpbic) 3 works as an intermediate energy carrier (IEC) and p-type host in PhOLEDs. • IEC forms multiple energy transfer channels in PhOLEDs to minimize degradation. • Superbly long lifetime and high efficiency in deep blue phosphorescent OLED for IEC. Despite over two decades of relentless endeavor, the industrial application of blue phosphorescent organic light-emitting diodes (PhOLEDs) has not been realized due to extremely short lifetime. The degradation of PhOLEDs is generally accelerated at high current levels since high triplet energy with long exciton lifetime are mostly concentrated on host molecules and transferred to dopant via slow Dexter energy transfer (DET) processes rather than fast Förster resonance energy transfer (FRET) processes. Herein, we propose a novel device architecture that creates multiple energy transfer channels by employing an Ir-complex intermediate energy carrier (IEC). Unlike exciplex or electroplex, no excitons were generated between the host and the IEC even though the IEC also behaves as a p-type host. The most crucial role of the IEC is to diversify the energy transfer channels. By introducing the IEC in deep blue PhOLEDs, both FRET and DET channels were additionally created between the IEC and the host, and the IEC and the dopant. Consequently, an unprecedentedly long half luminance lifetime of 13,830 h at an initial luminance of 100 cd/m2 was obtained with a high efficiency of 14.4% and CIEy = 0.17. To our best knowledge, the lifetime in our report is the longest with a deep blue phosphorescent Ir complex. [ABSTRACT FROM AUTHOR]

In general, electron transport layer (ETL) in organic light-emtting diodes (OLEDs) consists of single component of electron transporting material (ETM) or a mixture with n-dopant such as 8-hydroxyquinolinolato-lithium (Liq). However, there exists a limit to controlling a wide range of carrier density in OLEDs according to the required characteristics of the devices due to electrically insulating property of Liq. Here, we suggest a universal strategy to construct an efficient ETL. We synthesized two ETMs, diphenyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-amine (An-Ph) and phneyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-pyridin-3-yl-amine (An-Py) that have the same core structures with different polarities in functional groups. The electrical characteristics of electron-only-devices (EODs) were investigated by space charge limited current (SCLC) modeling and impedance spectroscopy analysis. Interestingly, the homostructure type ETL composed of An-Ph and An-Py showed not only superior electron transporting capability, but also the possibility of controlling electron injection and transporting in a wide range compared to the heterostructure type ETL of An-Ph and Liq. Compared to the An-Ph-only EOD, the electron mobility in 75% An-Py-mixed homostructure EOD increased by almost 4 orders of magnitude. Such dramatic variation of electron mobility was achieved thanks to the molecular design strategy to separate charge injection and charge transport regions within a molecule, which consequently induced the giant surface potential (GSP) effect between the ETL/cathode interface. As a result, the external quantum efficiency (EQE) of blue fluorescent and phosphorescent OLEDs with the homostructure ETLs was enhanced by 28.6% and 34%, respectively, compared to that of each control device without manipulating outcoupling effects. [Display omitted] • The anthracene-based electron transporting materials, An-Py and An-Ph with different polarities were designed and synthesized for universal electron transporting layers. • The superior charge injection property was comprehensively investigated with impedance spectroscopy and attributed to the giant surface potential in the ETL. • Compared to Liq-based ETL, the EQE of fluorescent and phosphorescent OLEDs with An-Py and An-Ph ETL was enhanced by 28.6% and 34%, respectively. [ABSTRACT FROM AUTHOR]

Many studies have analyzed the mobility and injection characteristics of charge carriers for organic light-emitting diodes (OLEDs) using hole-only and electron-only devices (HODs and EODs). However, the charge dynamics of a single type of carrier cannot fully represent the characteristics of light-emitting devices such as charge balance, recombination, and efficiency. In this report, we applied the impedance spectroscopy (IS) measurement to operating devices with light-emission. A series of thermally activated delayed fluorescence (TADF) OLEDs with a single or mixed host were fabricated and their electro-optical properties were comprehensively investigated. 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) and 2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) were used for the single host and a mixture of CBP and TPBi (1:1 ratio) was used for the mixed host; 2,4,5,6-Tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN) was used as an emitter. In all the OLEDs, the injection and transporting property of holes and electrons were successfully discriminated from the Bode plots of the modulus. Besides, the recombination properties depending on the type of hosts were also thoroughly understood from capacitance (C)-voltage (V), Re(z)-frequency and Cole-Cole plots. The modulus Bode plot revealed that the voltage of the maximum efficiency coincided with the voltage at which the low frequency (electron) signal merges with the high frequency (hole) signal in the mixed host system. Image 1 • Charge injection and transporting properties in single OLED were investigated by applying impedance spectroscopy measurements. • TADF OLEDs with n-, p-type and mixed host were successfully correlated with charge dynamics in terms of recombination process and efficiency. • Modulus Bode plot revealed the interrelationship between max efficiency and low (electron)/high (hole) frequency signals. [ABSTRACT FROM AUTHOR]