High light extraction performance using evanescent waves for top emission OLED applications with thin film encapsulation.

We report high light extraction from the top emission OLED (TEOLED) device structure by improving mainly the waveguide mode loss in the atomic layer deposition processed thin film encapsulation (TFE) layer. A novel structure incorporating the light extraction concept using evanescent waves and the hermetic encapsulation of a TEOLED device is presented here. When the TEOLED device is fabricated using the TFE layer, a substantial amount of generated light is trapped inside the device due to the difference in refractive index (RI) between the capping layer (CPL) and the aluminum oxide (Al2O3) layer. By inserting a low RI layer at the interface between the CPL and Al2O3, the direction of the internal reflected light is changed by the evanescent waves. The high light extraction with the low RI layer is attributed to the presence of evanescent waves and an electric field in the low RI layer. The novel fabricated TFE structure, CPL/ low RI layer/ Al2O3/ polymer/ Al2O3, is reported here. The current efficiency of the fabricated blue TEOLED device using this low RI layer is improved by about 23% and the blue index value is enhanced by about 26%. This new approach for light extraction will be applicable to future encapsulation technology for flexible optoelectronic devices.

Double boron-embedded multiresonant thermally activated delayed fluorescent materials for organic light-emitting diodes.

The subclass of multi resonant thermally activated delayed fluorescent emitters (MR-TADF) containing boron atoms has garnered significant attention in the field of organic light emitting diode (OLED) research. Among boron-based MR-TADF emitters, double boron-embedded MR-TADF (DB-MR-TADF) emitters show excellent electroluminescence performances with high photoluminescence quantum yields, narrow band emission, and beneficially small singlet-triplet energy levels in all the full-color gamut regions. This article reviews recent progress in DB-MR-TADF emitters, with particular attention to molecular design concepts, synthetic routes, optoelectronic properties, and OLED performance, giving future prospects for real-world applications.

Biochar-induced reduction of N2O emission from East Asian soils under aerobic conditions: Review and data analysis.

Global meta-analyses showed that biochar application can reduce N2O emission. However, no relevant review study is available for East Asian countries which are responsible for 70% of gaseous N losses from croplands globally. This review analyzed data of the biochar-induced N2O mitigation affected by experimental conditions, including experimental types, biochar types and application rates, soil properties, and chemical forms and application rates of N fertilizer for East Asian countries. The magnitude of biochar-induced N2O mitigation was evaluated by calculating N2O reduction index (Rindex, percentage reduction of N2O by biochar relative to control). The Rindex was further standardized against biochar application rate by calculating Rindex per unit of biochar application rate (ton ha-1) (Unit Rindex). The Rindex averaged across different experimental types (n = 196) was -21.1 ± 2.4%. Incubation and pot experiments showed greater Rindex than column and field experiments due to higher biochar application rate and shorter experiment duration. Feedstock type and pyrolysis temperature also affected Rindex; either bamboo feedstock or pyrolysis at > 400 °C resulted in a greater Rindex. The magnitude of Rindex also increased with increasing biochar rate. Soil properties did not affect Rindex when evaluated across all experimental types, but there was an indication that biochar decreased N2O emission more at a lower soil moisture level in field experiments. The magnitude of Rindex increased with increasing N fertilizer rate up to 500-600 kg N ha-1, but it decreased thereafter. The Unit Rindex averaged across experimental types was -1.2 ± 0.9%, and it was rarely affected by experimental type and conditions but diminished with increasing biochar rate. Our results highlight that since N2O mitigation by biochar is affected by biochar application rate, Rindex needs to be carefully evaluated by standardizing against biochar application rate to suggest the best conditions for biochar usage in East Asia.

Rice straw cover decreases soil erosion and sediment-bound C, N, and P losses but increases dissolved organic C export from upland maize fields as evidenced by δ13C.

Soil surface with crop residue is effective in reducing soil erosion and carbon (C), nitrogen (N), and phosphorus (P) losses from sloping fields. However, there is a high possibility that surface cover increases export of dissolved organic C (DOC) though relevant field studies under natural rainfall are lacking. In this study, the effects of surface cover with rice (Oryza sativa L.) straw on soil and CNP losses in both dissolved and sediment-bound forms from maize (Zea mays L.) fields were investigated under two fertilization levels (standard and double) × two types of runoff experiments (natural rainfall and artificial irrigation). Changes in soil properties including moisture, temperature, nutrients, and C concentration as well as maize yield were also examined. Surface cover decreased soil and total CNP losses by up to 82% across the experimental plots with some exceptions. However, surface cover increased DOC export in both natural (by 68-82% in total across all events) and artificial (by 3-4 fold) runoff, suggesting that crop residue cover may act as a DOC pollution source of water bodies. The contribution of rice straw to DOC, which was calculated using the δ13C of DOC from covered plots (-24.1 to -28.0‰) and control plots (-19.6 to -25.1‰), was 52.5-95.8%. The concentrations of K2SO4-extractable and microbial biomass C of the soils did not differ between covered and control plots, suggesting that DOC produced from rice straw was not incorporated into the soils, but rather, was washed out with surface runoff in this study. Surface cover increased maize growth and yield, particularly in double fertilization plots, through improved soil moisture, temperature, and nutrient conditions. To take full advantage of surface cover with crop residue, a further study on reducing DOC loss from crop residue needs to be conducted.

Fly ash and zeolite decrease metal uptake but do not improve rice growth in paddy soils contaminated with Cu and Zn.

Fly ash (FA) and zeolite (Z) are known to reduce bioavailability of metals in soils via immobilization; however, these amendments may not only immobilize metals such as copper (Cu) and zinc (Zn), but also reduce nitrogen (N) and phosphorus (P) availability in the soils via sorption (for N by Z) and precipitation (for P by FA). This study was conducted to evaluate the effects of application of FA and Z (0, 5, and 10% rate) on the availability of nutrients as well as metals in the metal-contaminated soils cultivated with paddy rice (Oryza sativa L.). Both FA and Z reduced Cu and Zn uptake by rice while increasing metal retention in the soils regardless of the application rates. However, reduced uptake of metals did not translate into increase in rice growth, especially at the 10% of amendment rates, due to decreased nutrient uptake as indicated by higher NH4+ and available P concentration in the soils amended with Z and FA, respectively, which inhibited tillering in the early rice growth period and thus reduced biomass accumulation at maturity. Our results suggest that FA and Z may reduce Cu and Zn uptake by rice in the soils contaminated with the metals; however, the availability of N and P is likely to be co-decreased. We suggest that the capacities of FA and Z to immobilize nutrients as well as metals need to be considered prior to using the amendments in metal-contaminated rice paddies.

Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars.

Ammonium (NH4+) is a common form of reactive nitrogen in wastewater, and its discharge to water bodies can lead to eutrophication. This study was conducted to understand NH4+ adsorption mechanisms of pine sawdust and wheat straw biochars in aqueous solutions and the factors affecting NH4+ removal. Biochars were produced by pyrolysing pine sawdust at 300 °C (PS300) and 550 °C (PS550) and wheat straw at 550 °C (WS550). Pseudo-second-order and Redlich-Peterson models best fitted the adsorption data. The PS300 showed the highest NH4+ adsorption capacity (5.38 mg g-1), followed by PS550 (3.37 mg g-1) and WS550 (2.08 mg g-1). Higher H/C and O/C ratios of PS300 (0.78 and 0.32, respectively) indicated the greater presence of functional groups on the biochar's surface as compared to PS550 (0.35 and 0.10, respectively) and WS550 (0.36 and 0.08, respectively), resulting in different NH4+ adsorption through electrostatic interactions. The dominant mechanism for NH4+ adsorption by the biochars was likely chemical bonding and electrostatic interaction of NH4+ with the surface functional groups. Lower pyrolysis temperature resulted in a higher NH4+ adsorption capacity by the pine sawdust biochar. At the same pyrolysis temperature (550 °C), the biochar made with pine sawdust as the feedstock had a higher NH4+ adsorption capacity than biochar made from wheat straw. We conclude that biochars can be efficient absorbents for NH4+ removal from wastewater, and the removal efficiency can be optimised by selecting different feedstocks or the pyrolysis condition for biochar production.

Microcapsule-Type Self-Healing Protective Coating for Cementitious Composites with Secondary Crack Preventing Ability.

A microcapsule-type self-healing protective coating with secondary crack preventing capability has been developed using a silanol-terminated polydimethylsiloxane (STP)/dibutyltin dilaurate (DD) healing agent. STP undergoes condensation reaction in the presence of DD to give a viscoelastic substance. STP- and DD-containing microcapsules were prepared by in-situ polymerization and interfacial polymerization methods, respectively. The microcapsules were characterized by Fourier-transform infrared (FT-IR) spectroscopy, optical microscopy, and scanning electron microscopy (SEM). The microcapsules were integrated into commercial enamel paint or epoxy coating formulations, which were applied on silicon wafers, steel panels, and mortar specimens to make dual-capsule self-healing protective coatings. When the STP/DD-based coating was scratched, self-healing of the damaged region occurred, which was demonstrated by SEM, electrochemical test, and water permeability test. It was also confirmed that secondary crack did not occur in the healed region upon application of vigorous vibration to the self-healing coating.

Microcapsule-Type Organogel-Based Self-Healing System Having Secondary Damage Preventing Capability.

We have developed a novel microcapsule-type organogel-based self-healing system in which secondary damage does not occur in the healed region. A mixture of an organogelator, poor and good solvents for the gelator is used as the healing agent; when the good solvent evaporates from this agent, a viscoelastic organogel forms. The healing agent is microencapsulated with urea-formaldehyde polymer, and the resultant microcapsules are integrated into a polymer coating to prepare self-healing coatings. When the coatings are scratched, they self-heal, as demonstrated by means of corrosion testing, electrochemical testing, optical microscopy, and scanning electron microscopy (SEM). After the healed coatings are subjected to vigorous vibration, it is demonstrated that no secondary damage occurs in the healed region. The secondary damage preventing capability of the self-healing coating is attributable to the viscoelasticity of the organogel. The result can give insight into the development of a "permanent" self-healing system.