Nickel Oxide Hole Injection/Transport Layers for Efficient Solution-Processed Organic Light-Emitting Diodes

Solution-processed nickel oxides (s-NiO_<i>x</i>) are used as hole injection and transport layers in solution-processed organic light-emitting diodes (OLEDs). By increasing the annealing temperature, the nickel acetate precursor fully decomposes and the s-NiO_<i>x</i> film shows larger crystalline grain sizes, which lead to better hole injection and transport properties. UV–ozone treatment on the s-NiO_<i>x</i> surface is carried out to further modify its surface chemistry, improving the hole injection efficiency. The introduction of more dipolar species of nickel oxy-hydroxide (NiO­(OH)) is evidenced after the treatment. Dark injection–space charge limited (DI–SCL) transient measurement was carried out to compare the hole injection efficiency of s-NiO_<i>x</i> and poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) hole injection layers (HIL). The UV–ozone treated s-NiO_<i>x</i> shows significantly better hole injection, with a high injection efficiency of 0.8. With a p-type thin film transistor (TFT) configuration, the high-temperature annealed s-NiO_<i>x</i> film shows a hole mobility of 0.141 cm² V^–1 s^–1, which is significantly higher compared to conventional organic hole transport layers (HTLs). Because of their improved hole injection and transport properties, the solution-processed phosphorescent green OLEDs with NiO_<i>x</i> HIL/HTL show a maximum power efficiency of 75.5 ± 1.8 lm W^–1, which is 74.6 + 2.1% higher than the device with PEDOT:PSS HIL. The device with NiO_<i>x</i> HIL/HTL also shows a better shelf stability than the device with PEDOT:PSS HIL. The NiO_<i>x</i> HIL/HTL is further compared with PEDOT:PSS HIL/<i>N</i>,<i>N</i>′-Di­(1-naphthyl)-<i>N</i>,<i>N</i>′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) HTL in the thermal-evaporated OLEDs. The device with NiO_<i>x</i> HIL/HTL shows a comparable efficiency at high electroluminescence (EL) intensities

High-Performance <i>n</i>‑Type Organic Transistor with a Solution-Processed and Exfoliation-Transferred Two-Dimensional Crystalline Layered Film

High-performance <i>n</i>-type organic field-effect transistors (OFETs) based on 2-dimensional (2D) crystalline layered films of the novel dicyanodistyrylbenzene (DCS) derivative (2<i>Z</i>,2′<i>Z</i>)-3,3′-(1,4-phenylene)­bis­(2-(3,5-bis­(trifluoromethyl)­phenyl)­acrylonitrile) (CN-TFPA) were fabricated using a simple solution process. The OFETs showed electron mobilities of up to 0.55 cm² V^–1 s^–1, which was attributed to the appropriate electron affinity and dense molecular packing in the well-ordered 2D terrace structure. Because of the easy exfoliation capabilities of the CN-TFPA 2D crystalline layers, 2–10 CN-TFPA molecular monolayers could be successfully transferred onto the substrates, enabling the fabrication of ultrathin OFET devices with an active layer thickness of ∼30 nm

Tailor-Made Highly Luminescent and Ambipolar Transporting Organic Mixed Stacked Charge-Transfer Crystals: An Isometric Donor–Acceptor Approach

We have rationally designed a densely packed 1:1 donor–acceptor (<b>D</b>–<b>A</b>) cocrystal system comprising two isometric distyrylbenzene- and dicyanodistyrylbenzene-based molecules, forming regular one-dimensional mixed stacks. The crystal exhibits strongly red-shifted, bright photoluminescence originating from an intermolecular charge-transfer state. The peculiar electronic situation gives rise to high and ambipolar p-/n-type field-effect mobility up to 6.7 × 10^–3 and 6.7 × 10^–2 cm² V^–1 s^–1, respectively, as observed in single-crystalline OFETs prepared via solvent vapor annealing process. The unique combination of favorable electric and optical properties arising from an appropriate design concept of isometric <b>D</b>–<b>A</b> cocrystal has been demonstrated as a promising candidate for next generation (opto-)­electronic materials

Tailor-Made Highly Luminescent and Ambipolar Transporting Organic Mixed Stacked Charge-Transfer Crystals: An Isometric Donor–Acceptor Approach

We have rationally designed a densely packed 1:1 donor–acceptor (<b>D</b>–<b>A</b>) cocrystal system comprising two isometric distyrylbenzene- and dicyanodistyrylbenzene-based molecules, forming regular one-dimensional mixed stacks. The crystal exhibits strongly red-shifted, bright photoluminescence originating from an intermolecular charge-transfer state. The peculiar electronic situation gives rise to high and ambipolar p-/n-type field-effect mobility up to 6.7 × 10^–3 and 6.7 × 10^–2 cm² V^–1 s^–1, respectively, as observed in single-crystalline OFETs prepared via solvent vapor annealing process. The unique combination of favorable electric and optical properties arising from an appropriate design concept of isometric <b>D</b>–<b>A</b> cocrystal has been demonstrated as a promising candidate for next generation (opto-)­electronic materials

Design and Testing of Safer, More Effective Preservatives for Consumer Products

Preservatives deter microbial growth, providing crucial functions of safety and durability in composite materials, formulated products, and food packaging. Concern for human health and the environmental impact of some preservatives has led to regulatory restrictions and public pressure to remove individual classes of compounds, such as parabens and chromated copper arsenate, from consumer products. Bans do not address the need for safe, effective alternative preservatives, which are critical for both product performance (including lifespan and therefore life cycle metrics) and consumer safety. In this work, we studied both the safety and efficacy of a series of phenolic preservatives and compared them to common preservatives found in personal care products and building materials. We quantified antimicrobial activity against Aspergillus brasiliensis (mold) and Pseudomonas aeruginosa (Gram negative bacteria), and we conducted a hazard assessment, complemented by computational modeling, to evaluate the human and environmental health impacts of these chemicals. We found that octyl gallate demonstrates better antimicrobial activity and comparable or lower hazards, compared to current-use preservatives. Therefore, octyl gallate may serve as a viable small-molecule preservative, particularly in conjunction with low concentrations of other preservatives that act through complementary mechanisms

Design and Testing of Safer, More Effective Preservatives for Consumer Products

Preservatives deter microbial growth, providing crucial functions of safety and durability in composite materials, formulated products, and food packaging. Concern for human health and the environmental impact of some preservatives has led to regulatory restrictions and public pressure to remove individual classes of compounds, such as parabens and chromated copper arsenate, from consumer products. Bans do not address the need for safe, effective alternative preservatives, which are critical for both product performance (including lifespan and therefore life cycle metrics) and consumer safety. In this work, we studied both the safety and efficacy of a series of phenolic preservatives and compared them to common preservatives found in personal care products and building materials. We quantified antimicrobial activity against Aspergillus brasiliensis (mold) and Pseudomonas aeruginosa (Gram negative bacteria), and we conducted a hazard assessment, complemented by computational modeling, to evaluate the human and environmental health impacts of these chemicals. We found that octyl gallate demonstrates better antimicrobial activity and comparable or lower hazards, compared to current-use preservatives. Therefore, octyl gallate may serve as a viable small-molecule preservative, particularly in conjunction with low concentrations of other preservatives that act through complementary mechanisms

Conductivity Enhancement of Nickel Oxide by Copper Cation Codoping for Hybrid Organic-Inorganic Light-Emitting Diodes

We demonstrate a Cu­(I) and Cu­(II) codoped nickel­(II) oxide (NiO_<i>x</i>) hole injection layer (HIL) for solution-processed hybrid organic-inorganic light-emitting diodes (HyLEDs). Codoped NiO_<i>x</i> films show no degradation on optical properties in the visible range (400–700 nm) but have enhanced electrical properties compared to those of conventional Cu­(II)-only doped NiO_<i>x</i> film. Codoped NiO_<i>x</i> film shows an over four times increased vertical current in comparison with that of NiO_<i>x</i> in conductive atomic force microscopy (c-AFM) configuration. Moreover, the hole injection ability of codoped NiO_<i>x</i> is also improved, which has ionization energy of 5.45 eV, 0.14 eV higher than the value of NiO_<i>x</i> film. These improvements are a consequence of surface chemical composition change in NiO_<i>x</i> due to Cu cation codoping. More off-stoichiometric NiO_<i>x</i> formed by codoping includes a large amount of Ni vacancies, which lead to better electrical properties. Density functional theory calculations also show that Cu doped NiO model structure with Ni vacancy contains diverse oxidation states of Ni based on both density of states and partial atomic charge analysis. Finally, HyLEDs of Cu codoped NiO_<i>x</i> HIL have higher performance comparing with those of pristine NiO_<i>x</i>. The current efficiency of devices with NiO_<i>x</i> and codoped NiO_<i>x</i> HIL are 11.2 and 15.4 cd/A, respectively. Therefore, codoped NiO_<i>x</i> is applicable to various optoelectronic devices due to simple sol–gel process and enhanced doping efficiency