Understanding coordination reaction for producing stable electrode with various low work functions

Metronomic photodynamic therapy for deep organ cancer by implantable wireless OLEDs

Metronomic photodynamic therapy (mPDT) is a method of continuously delivering low-intensity light to a cancer lesion. This approach does not require high-intensity light, enabling the miniaturization of light devices and making them suitable for implantation within the body. However, the application of mPDT to tumors in deep organs such as the liver and pancreas has yet to reach practical implementation. In this study, we developed an mPDT system designed to meet three key requirements deemed essential for practical use: (1) uniform light irradiation throughout the tumor, (2) maintenance of constant light intensity within the body with sufficient operational duration, and (3) avoidance of immunological complications and thermal damage. The newly constructed mPDT system incorporates an ultra-thin organic light-emitting diode (OLED) device and wireless energy transfer technology, allowing it to be designed for implantation in deep organs. In experiments using a rat model of orthotopic hepatoma, the new mPDT system effectively induced widespread cell death deep within the tumor and exhibited high therapeutic efficacy against cancer. This study is the first study to demonstrate that mPDT utilizing a biocompatible and wirelessly powered OLED device has strong anti-tumor effects against parenchymal organ cancers. The findings represent a significant advancement toward the clinical application of mPDT for the treatment of deep organ cancers.

Silver coordination-induced n-doping of PCBM for stable and efficient inverted perovskite solar cells

The bidirectional migration of halides and silver causes irreversible chemical corrosion to the electrodes and perovskite layer, affecting long-term operation stability of perovskite solar cells. Here we propose a silver coordination-induced n-doping of [6,6]-phenyl-C61-butyric acid methyl ester strategy to safeguard Ag electrode against corrosion and impede the migration of iodine within the PSCs. Meanwhile, the coordination between DCBP and silver induces n-doping in the PCBM layer, accelerating electron extraction from the perovskite layer. The resultant PSCs demonstrate an efficiency of 26.03% (certified 25.51%) with a minimal non-radiative voltage loss of 126 mV. The PCE of resulting devices retain 95% of their initial value after 2500 h of continuous maximum power point tracking under one-sun irradiation, and > 90% of their initial value even after 1500 h of accelerated aging at 85 °C and 85% relative humidity.

Efficient and air-stable n-type doping in organic semiconductors

Chemical doping of organic semiconductors (OSCs) enables feasible tuning of carrier concentration, charge mobility, and energy levels, which is critical for the applications of OSCs in organic electronic devices. However, in comparison with p-type doping, n-type doping has lagged far behind. The achievement of efficient and air-stable n-type doping in OSCs would help to significantly improve electron transport and device performance, and endow new functionalities, which are, therefore, gaining increasing attention currently. In this review, the issue of doping efficiency and doping air stability in n-type doped OSCs was carefully addressed. We first clarified the main factors that influenced chemical doping efficiency in n-type OSCs and then explain the origin of instability in n-type doped films under ambient conditions. Doping microstructure, charge transfer, and dissociation efficiency were found to determine the overall doping efficiency, which could be precisely tuned by molecular design and post treatments. To further enhance the air stability of n-doped OSCs, design strategies such as tuning the lowest unoccupied molecular orbital (LUMO) energy level, charge delocalization, intermolecular stacking, in situ n-doping, and self-encapsulations are discussed. Moreover, the applications of n-type doping in advanced organic electronics, such as solar cells, light-emitting diodes, field-effect transistors, and thermoelectrics are being introduced. Finally, an outlook is provided on novel doping ways and material systems that are aimed at stable and efficient n-type doped OSCs.

Unlocking the Full Potential of Electron-Acceptor Molecules for Efficient and Stable Hole Injection

Understanding the hole-injection mechanism and improving the hole-injection property are of pivotal importance in the future development of organic optoelectronic devices. Electron-acceptor molecules with high electron affinity (EA) are widely used in electronic applications, such as hole injection and p-doping. Although p-doping has generally been studied in terms of matching the ionization energy (IE) of organic semiconductors with the EA of acceptor molecules, little is known about the effect of the EA of acceptor molecules on the hole-injection property. In this work, the hole-injection mechanism in devices is completely clarified, and a strategy to optimize the hole-injection property of the acceptor molecule is developed. Efficient and stable hole injection is found to be possible even into materials with IEs as high as 5.8 eV by controlling the charged state of an acceptor molecule with an EA of about 5.0 eV. This excellent hole-injection property enables direct hole injection into an emitting layer, realizing a pure blue organic light-emitting diode with an extraordinarily low turn-on voltage of 2.67 V, a power efficiency of 29 lm W^-1 , an external quantum efficiency of 28% and a Commission Internationale de l'Eclairage y coordinate of less than 0.10.

In situ-formed tetrahedrally coordinated double-helical metal complexes for improved coordination-activated n-doping

In situ coordination-activated n-doping by air-stable metals in electron-transport organic ligands has proven to be a viable method to achieve Ohmic electron injection for organic optoelectronics. However, the mutual exclusion of ligands with high nucleophilic quality and strong electron affinity limits the injection efficiency. Here, we propose meta-linkage diphenanthroline-type ligands, which not only possess high electron affinity and good electron transport ability but also favour the formation of tetrahedrally coordinated double-helical metal complexes to decrease the ionization energy of air-stable metals. An electron injection layer (EIL) compatible with various cathodes and electron transport materials is developed with silver as an n-dopant, and the injection efficiency outperforms conventional EILs such as lithium compounds. A deep-blue organic light-emitting diode with an optimized EIL achieves a high current efficiency calibrated by the y colour coordinate (0.045) of 237 cd A-1 and a superb LT95 of 104.1 h at 5000 cd m-2.

Understanding Interface Dipoles at an Electron Transport Material/Electrode Modifier for Organic Electronics

Interface dipoles formed at an electrolyte/electrode interface have been widely studied and interpreted using the "double dipole step" model, where the dipole vector is determined by the size and/or range of motion of the charged ions. Some electron transport materials (ETMs) with lone pairs of electrons on heteroatoms exhibit a similar interfacial behavior. However, the origin of the dipoles in such materials has not yet been explored in great depth. Herein, we systematically investigate the influence of the lone pair of electrons on the interface dipole through three pyridine derivatives B2-B4PyMPM. Experiments show that different positions of nitrogen atoms in the three materials give rise to different hydrogen bonds and molecular orientations, thereby affecting the areal density and direction of the lone pair of electrons. The interface dipoles of the three materials predicted by the "double dipole step" model are in good agreement with the ultraviolet photoelectron spectroscopy results both in spin-coated and vacuum-deposited films. These findings help to better understand the ETMs/electrode interfacial behaviors and provide new guidelines for the molecular design of the interlayer.

Unravelling the electron injection/transport mechanism in organic light-emitting diodes

Although significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

Understanding the role electron injection and transport in organic light-emitting diodes (OLED) is critical for optimizing device performance. Here, the authors elucidate the electron injection/transport mechanism in OLEDs and identify the cathode/emissive layer energy barrier as the key factor.