Organic light-emitting diodes (OLEDs) inherently suffer from severe optical losses, with most generated photons confined by total internal reflection. To mitigate these losses, conventional light-extraction methods rely on complex, energy-intensive fabrication using non-biodegradable materials. Thus, this study presents an eco-friendly and biocompatible strategy that combines poly(butylene adipate-co-terephthalate) (PBAT) as a biodegradable template with carboxymethyl cellulose and tannic acid (ECO-UV) films. Templates and films were fabricated through a simple, low-temperature, solution-based replication process without lithography or vacuum processes, forming irregularly distributed microstructures that enhance light scattering and suppress internal reflection. The OLEDs incorporating the ECO-UV film exhibited up to 36

In this study, electrically degraded Blue TADF materials were investigated using spectroelectrochemistry(SEC) and fitting simulations. Electrical stability was examined by analyzing absorption properties after electrical degradation.

The accurate evaluation of energy levels is essential for optimizing the performance of organic light-emitting diode (OLED) materials. In this study, we systematically analyzed the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of small organic molecules widely used in various layers of OLED devices using cyclic voltammetry (CV). These molecules include the thermally activated delayed fluorescence (TADF) emitters 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN). To maximize measurement reliability, we conducted optimization studies across various environmental parameters, such as sweep direction, scan rate, material concentration, solvent, and working electrode type. As a result, we established analytical conditions that ensured a stable potential window tailored to the characteristics of the solvent and electrode, while minimizing background current interference. In particular, we successfully performed negative CV scans, which had previously been challenging to measure reliably due to various technical difficulties. This is significant, as it provides an effective and practical method for the independent and intuitive evaluation of the LUMO levels of organic materials solely through optimized electrochemical CV analysis.

Spontaneous orientation polarization (SOP) in organic molecules is used in organic light-emitting diodes (OLEDs) and induces an internal electric field that facilitates charge injection and transport; however, excessive interfacial charge accumulation can lead to exciton quenching and efficiency loss. In particular, exciton-polaron quenching (EPQ) is significant in devices employing a polar electron-transport layer (ETL), where the SOP-induced field drives a carrier imbalance. Therefore, how the polaron distribution within the emitting layer (EML) changes with the SOP and how it interacts with excitons must be understood to improve device efficiency. In this study, we investigated these relationships by controlling the ETL polarity and the exciton formation position in OLEDs. Displacement current measurements, electroluminescence spectroscopy, and transient electroluminescence analysis revealed that polarons accumulated near the EML/ETL interface when a positively polarized ETL was used. Pronounced exciton quenching occurred only when the exciton recombination zone was located near a polaron-rich region near the EML/ETL interface. These findings demonstrate that the spatial decoupling of the exciton formation region from the polaron accumulation zone effectively suppresses EPQ, providing a universal design strategy for enhancing the efficiency and stability of OLEDs.

Growing interest in organic nonvolatile memories based on electric field-driven charge storage highlights the need for optimized polymeric tunnelling layers (TLs). Yet, no academic standards exist, hindering technological progress. An underlying question concerns how molecular properties translate into macroscopic device characteristics. Here, we argue that the electrical characteristics of organic charge-trap memories (CTMs) are determined by the cross-relational organization of the physicochemical properties of polymeric TLs, and therefore, design needs to target relations rather than isolated properties. In the analysis, the low-k polymer of intrinsic microporosity, poly(DFBP-TTSBI-DFBP-BHPF)-co-poly(DFBP-BHPF) (P(DTDB-DB)), based on complementary nanofactors, exhibited a balanced set of properties in terms of Fowler-Nordheim tunnelling, dielectric constant, field-effect mobility, trap density, and leakage. The memory window, on/off ratio, and data retention characteristics of the CTM with a P(DTDB-DB) TL were superior to those of CTMs using conventional polymer dielectrics as TLs, and multibit operation was further demonstrated in a low-voltage device incorporating the P(DTDB-DB) TL. Lastly, detailed insights are presented, underscoring the essential role of polymeric TLs in organic CTMs and the potential of balance-oriented multi-nanofactor engineering.

This study examines the effects of the thickness and structure of a silver (Ag) interlayer on the performance of phosphorescent red-emitting transparent organic light-emitting diodes (TOLEDs). Inserting an Ag interlayer enabled the top emission of TOLEDs to be enhanced by 1.4–3.1, resulting in a ten-fold decrease in bottom-to-top ratios from 7.6 to 0.76. We show that an extra thin Ag interlayer with a carefully constructed structure could optimize TOLEDs’ top emission by altering their microcavities. The top emission enhancement was verified by comparing the forward emission of devices with and without Ag interlayers. Thus, the TOLEDs with Ag interlayers displayed more balanced light emissions.

In this study, the charge injection and accumulation characteristics of thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) comprising a 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4Cz-IPN) emitter were measured before and after device degradation. To investigate the degradation-induced spontaneous orientation polarization (SOP) characteristics of the OLED, the charge carrier dynamics and operational stability of pristine and aged devices were compared using impedance spectroscopy (IS). Capacitance-voltage (C-V) and capacitance-frequency (C-F) analyses revealed the presence of negative interfacial charges induced by the spontaneous alignment of the TADF-emitting and electron-transport layers. Equivalent resistance-capacitance (R-C) circuit simulations quantitatively reproduced the experimental C-F curve and determined the relaxation frequency, confirming that aged devices have a higher resistance and reduced interfacial charges. The changes in charge accumulation at the interfaces and their associated electrical characteristics were evaluated to understand their impact on the lifetime and operational stability of the device. A significant decrease in the luminous efficiency was observed in the aged devices, which was attributed to reduced charge injection and transport into the emitting layer.

Abstract This study analyzes the optical properties and device stability of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN), representative carbazole-based thermally activated delayed fluorescence emitters, with a focus on their polaron states using spectroelectrochemical (SEC) analysis. The oxidation and reduction potentials of each material were determined by cyclic voltammetry. Furthermore, the absorption spectra obtained from SEC measurements are deconvoluted via Gaussian fitting to clearly distinguish the absorption characteristics of each material in both the neutral and polaron states. The results show that in their polaron states, both 4CzIPN and 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene exhibit enhanced absorption in the short- and long-wavelength regions compared with their neutral forms, resulting in spectral overlap with their photoluminescence spectra. Notably, stability evaluations using single-charge devices (electron- and hole-only devices) reveal a decrease of more than 10% in the photoluminescence intensity of the 4CzIPN-based hole-only device. This degradation is attributed to the absorption of excitation light (385 nm) by positive polarons, leading to the simultaneous generation of excitons from both the neutral molecules and positive polarons. Overall, the results demonstrate that SEC analysis enables the rapid assessment of emitter polaron characteristics prior to device fabrication and provides important guidelines for the design of highly efficient and stable thermally activated delayed fluorescence devices.

Stretchable and conformable on-skin sensors have emerged as a key technology for real-time physiological monitoring, interactive human-machine systems, and soft robotics applications. However, conventional sensors are often based on synthetic polymers with poor biodegradability and limited biocompatibility, raising concerns about environmental sustainability and long-term skin contact. In this study, we report a multifunctional, biodegradable, and stretchable sensing platform based on a NaCl-treated carboxymethyl cellulose (CMC)/tannic acid (TA) hybrid film to overcome these limitations. We present a unique combination of material simplicity, biocompatibility, and multifunctional performance. The resulting films exhibit excellent stretchability (up to 300

In this study, we fabricated a bio-microlens array (MLA) film for use in organic light-emitting diodes (OLEDs) to ensure their structural stability in wet biological environments. The film was prepared by imprinting an MLA structure onto a gelatin/chitosan-based bioderived material. Gelatin/chitosan-blended hydrogels are promising candidates for fabricating biocompatible light-extraction films because of their optical transparency and skin-mimicking mechanical properties that minimize the mechanical mismatch with biological tissues. However, their inherent superhydrophilicity poses a challenge in maintaining the morphology of the light-extraction structures when exposed to wet biological environments. To overcome these limitations, a gelatin/chitosan-based optical film with enhanced structural stability and mechanical durability was fabricated by inducing covalent bonding via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) crosslinking. This chemical modification effectively protected the MLA structure against hydration-induced swelling. Consequently, the film yielded a low Young’s modulus that emulates human skin stiffness characteristics, and maintained stable light-extraction structures by suppressing deformation under wet conditions, thereby achieving 31

We devised an eco-friendly and facile external film strategy that simultaneously enhances light extraction and mitigates ultraviolet (UV)-induced degradation in organic light-emitting diodes (OLEDs). To this end, we developed a milk-derived casein (CA)–tannic acid (TA) composite external-light-extraction film, referred to as a CATA film. CA was employed as a film-forming matrix, while TA promoted the formation of a crosslinked structure and imparted UV-protective functionality through its UV-absorbing characteristics. The film was fabricated via a simple process using deionized water as the sole solvent. Additionally, a microlens array (MLA) structure was replicated on the surface of the CATA film to enhance external-light-extraction efficiency by modifying the propagation path of light and thereby alleviating total internal reflection. Among the CATA MLA films with different TA concentrations, the CATA_0.5 film yielded a 57.8% enhancement in electroluminescence intensity compared with the reference device. Furthermore, owing to the UV-absorbing capability of TA, the UV-induced reduction in the current density of OLEDs was suppressed by 71.2%. These results indicate that bio-derived CATA MLA films can simultaneously improve the optical performance of OLEDs and suppress UV-induced photodegradation. Moreover, this study demonstrated a design strategy for an eco-friendly UV-protective external-light-extraction film that can be applied through external attachment without modifying the device architecture.

Organic light-emitting diodes (OLEDs) employing electron-transport layers (ETLs) with substantial spontaneous orientation polarization (SOP) can exhibit a giant surface potential (GSP), which produces polarization-induced interfacial charge (IC) and influences charge injection. In this study, we investigate the threshold-voltage (Vth) increase in aged OLEDs employing an 1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene (OXD-7) ETL with a GSP. Electrical aging was accompanied by an increase in Vth delayed hole injection, and a decrease in the estimated polarization-induced interfacial charge obtained from capacitance–voltage (C–V) measurements. To examine the role of localized charge trapping, a hole-trap device was fabricated by introducing TAPC into a 5-nm-thick region of the OXD-7 ETL adjacent to the emitting layer. The hole-trap device reproduced electrical characteristics similar to those observed in the aged devices, including delayed hole injection and increased Vth. C–V and displacement-current measurements, together with bias-dependent photoluminescence analysis, support an association between localized charge trapping and an apparent weakening of the polarization-related electrostatic contribution to hole injection. These findings suggest a degradation pathway that is particularly relevant to OLEDs employing ETLs with a GSP and highlight the importance of controlling localized charge trapping in such layers to maintain stable charge-injection characteristics during operation.

In this study, two novel blue phosphorescent organic light-emitting diode (B-PhOLED) host materials were developed, namely 5,10-diphenyl-15-(4-(triphenylsilyl)phenyl)-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (DIINCz-Si) and 5-phenyl-12-(4-(triphenylsilyl)phenyl)-5,12-dihydroindolo[3,2–a]carbazole (INCz-Si). Both compounds are silane-based indolocarbazole derivatives that exhibit excellent thermal stability, with decomposition temperatures exceeding 390 °C and reaching up to 427 °C. It was demonstrated that the high triplet energies and well-aligned energy levels of these compounds facilitated efficient energy transfer to the blue dopant. These characteristics contributed to superior charge balance and low turn-on voltage in the fabricated devices. Consequently, B-PhOLEDs fabricated using these hosts achieved a maximum external quantum efficiency of 22%, a current efficiency of 41 cd/A, and a luminous efficiency of 43 lm/W. These results demonstrate that the proposed hosts possess enhanced efficiency and reduced roll-off characteristics, combined with high thermal stability, rendering them highly suitable for use in B-PhOLED applications.

Sustainable memory devices that combine reliable multilevel data storage, stable synaptic-weight modulation, and environmentally responsive degradability are increasingly needed for next-generation Internet of Things, wearable, and data-centric electronics, where rapid device replacement cycles continue to intensify electronic-waste concerns. Charge-trapping memory transistors offer an attractive platform for this purpose owing to their multilevel memory operation through modulation of trapped charge density and excellent retention characteristics, both of which are essential for preserving programmed conductance states in neuromorphic computing. However, previously reported biodegradable and bio-derived memory and synaptic transistors have mainly been limited in their practical neuromorphic applicability because of write-once-read-many behavior, insufficient retention, or unbalanced rewritable operation. Therefore, biodegradable and eco-friendly charge-trapping memory transistor platforms that integrate electrically rewritable non-volatile memory operation with balanced synaptic-weight modulation remain largely unexplored for their applicability to practical memory and neuromorphic computing systems. Here, we report a biodegradable charge-trapping memory transistor based on an optimized blended charge-trap layer composed of carboxymethyl cellulose sodium salt (CMC), a biodegradable polymer, and tannic acid (TA), a plant-derived polyphenolic molecule. CMC and TA exhibit charge-trapping behavior with different dominant tendencies toward electron and hole trapping, respectively, enabling their bias-dependent trapping contributions to be balanced by controlling the blending ratio. The optimized CMC (88%):TA (12%) charge-trap layer, combined with a tunneling layer, enables repetitive and well-balanced electrical program/erase operation, stable retention with a memory on/off current ratio exceeding 103 for 1000 s, and improved transistor switching characteristics. The resulting stable multilevel conductance modulation supports reversible potentiation and depression, which are implemented as synaptic weights in a hardware neural-network simulation for handwritten-digit recognition, achieving an accuracy comparable to the ideal software system. Moreover, the biodegradable charge-trap layer undergoes water-triggered dissolution in deionized water, leading to rapid loss of device integrity after immersion. These findings represent a significant step toward biodegradable charge-trapping memory transistors that simultaneously enable stable non-volatile retention, balanced synaptic-weight modulation, and environmentally responsive degradability for sustainable neuromorphic electronics.

Herein, we report the development of highly stable red phosphorescent organic light-emitting diodes (PhOLEDs) that exhibit stable light emission and low efficiency roll-off under high-brightness operation. Typical applications of PhOLEDs include smart phones, TVs, tablets, and automotive displays. Two new acceptor-type host materials, 6-phenyl-3,9-bis(3-(pyridin-3-yl)phenyl)benzo[k]phenanthridine (PBPyP-BPH) and 3-(3,5-di(pyridin-3-yl) phenyl)-6-phenylbenzo[k]phenanthridine (DPyP-BPH) were designed and synthesized based on a highly rigid benzophenanthridine core. Owing to this structural rigidity, the two hosts demonstrated excellent thermal stability with high 5 % weight loss temperatures (Td,5 %) of 403 degrees C for PBPyP-BPH and 395 degrees C for DPyP-BPH. These high thermal transition temperatures ensure device reliability for automotive applications, even under harsh driving conditions. When utilized in a bipolar mixed-host system with a thermally stable donor, 4,4 ',4 ''-tri(Ncarbazolyl)triphenylamine (TCTA), the developed red PhOLEDs (doped with Bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) [Ir(MDQ)2(acac)], TCTA: PBPyP-BPH and TCTA: DPyP-BPH, achieved high maximum external quantum efficiencies (EQEs) of 17.9 and 17.2 %, respectively with significantly suppressed efficiency roll-offs. These results demonstrate that securing high thermal stability through molecular design, combined with controlling charge balance via device structure optimization, is an effective strategy for realizing high-performance red PhOLEDs.

We propose a novel vertical capacitive humidity sensor capable of transducing the resistance variation of a humidity-sensitive material into a corresponding capacitance change. The proposed hydroxyethyl cellulose-based vertical structure expands the distribution of electric flux lines as the humidity increases, thereby overcoming the challenges of high output resistance at low humidity and the resultant incompatibility with commercial circuitry. The RC equivalent circuit model demonstrates that the effective length of the electric flux lines from the top-electrode edge increases with humidity, and the small inter-electrode spacing inherent in our design ensures amplified capacitance change. Over 10%–90% relative humidity, the capacitance change increased from 5 pF for the conventional interdigitated-electrode sensor to 114 pF for the vertical sensor, representing a 23-fold enhancement. Furthermore, we confirmed compatibility of the design with a wide range of humidity-sensitive conductive materials, indicating practical applicability of the proposed sensor design across a broad range of applications.

This study demonstrates the performance of a hydroxyethyl cellulose (HEC) charge trap layer for p-type organic thin-film transistor memory. The HEC charge trap transistor memory (HEC-TM) shows conventional charge trapping characteristics; that is, positive and negative threshold voltage (Vth) shifts after the application of a positive and negative bias, respectively. As the time and amplitude of the gate bias increases, Vth shift increases gradually and saturates. Because the electron trap is relatively more dominant than the hole trap in the hydroxyl group of HEC, a larger shift in Vth and longer memory retention appears when a positive voltage is applied rather than a negative voltage. HEC-TM is immersed and the HEC charge trap layer (HEC-CTL) is dissolved sufficiently with deionized water to validate its water degradability. HEC-TM is expected to be utilized as a biodegradable short-term transistor memory device.

This review discusses the studies from pioneering groups that advanced the use of impedance spectroscopy (IS) and equivalent circuit techniques to investigate operational mechanisms in organic electronics.

Developing advanced materials that balance stretchability, conductivity, and biocompatibility is essential for next-generation stretchable devices. This study reports a highly conductive and stretchable hydrogel engineered from polyvinyl alcohol (PVA) and xanthan gum (XG) using a dual cross-linking method followed by sodium persulfate treatment. The optimized hydrogel exhibited exceptional mechanical robustness, achieving a tensile strength of 1.31 MPa, elongation at break of 410.2%, and toughness of 3.16 MJ/m3. Concurrently, it demonstrated superior electrical performance with an ionic conductivity of 5.23 S/m and minimal electrical hysteresis, making it ideal for dynamic applications. Its utility as a wearable wireless sensor was confirmed by accurately tracking diverse human motions, with machine learning models classifying these movements with 84.91% accuracy. Furthermore, the hydrogel demonstrated potential for sustainable energy generation via the hydrovoltaic effect, producing a peak power density of 20.62 mu W/m2 from salinity gradients. This work presents a versatile PVA/XG hydrogel platform with significant promise for wearable electronics, human-machine interfaces, and osmotic energy harvesting. The combination of excellent mechanical properties, high conductivity, and demonstrated functionalities highlights its potential for cutting-edge technological applications.