The performance of organic electrochemical transistors (OECTs) relies on the interaction between organic semiconductors and ions. Consequently, hydrophilic ethylene glycol (EG) side chains are incorporated into organic semiconductors to improve the channel's capacity to absorb ions. However, the EG substituted organic semiconductors tend to swell when immersed in aqueous electrolytes and exhibit microstructural changes induced by dopant ions. In our research, we introduce an alkyl spacer to create distance between the fullerene and EG chain. This approach is designed to reduce the negative effects of swelling and balance the ion and electron conduction. We conducted an analysis of OECTs using four fullerene derivatives: no alkyl spacer, butyl, hexyl, and octyl spacers. The OECTs based on fullerene derivatives with butyl and hexyl spacers exhibit enhanced transconductance (g_m=11.8 and 19.4 mS) compared to the ones without alkyl spacers. It has also been observed that the butyl and hexyl spacers lead to a more than tenfold increase in volumetric capacitance. Further increasing the alkyl spacer (octyl group) leads to no transistor behavior. Our study uncovers the relationship between alkyl spacers and the performance of OECTs based on fullerene derivatives. This will serve as a guideline for designing n-type small molecules for OECTs. Finally, we showcased the potential of utilizing OECTs based on these fullerene derivatives in cation sensing, which is promising for developing sweat sensors.

Developing emerging technologies in Internet of Things and artificial intelligence requires high-speed, low-power, high-sensitivity, and switchable-functionality strain sensors capable of sensing subtle mechanical stimuli in complex ambience. Resonant tunneling diodes (RTDs) are the good candidate for such sensing applications due to the ultrafast transport process, lower tunneling current, and negative differential resistance. However, notably enhancing sensing sensitivity remains one of the greatest challenges for RTD-related strain sensors. Here, we use piezotronic effect to improve sensing performance of strain sensors in double-barrier ZnO nanowire RTDs. This strain sensor not only possesses an ultrahigh gauge factor (GF) 390 GPa⁻¹, two orders of magnitude higher than these reported RTD-based strain sensors, but also can switch the sensitivity with a GF ratio of 160 by adjusting bias voltage in a small range of 0.2 V. By employing Landauer–Büttiker quantum transport theory, we uncover two primary factors governing piezotronic modulation of resonant tunneling transport, i.e., the strain-mediated polarization field for manipulation of quantized subband levels, and the interfacial polarization charges for adjustment of space charge region. These two mechanisms enable strain to induce the negative differential resistance, amplify the peak-valley current ratio, and diminish the resonant bias voltage. These performances can be engineered by the regulation of bias voltage, temperature, and device architectures. Moreover, a strain sensor capable of electrically switching sensing performance within sensitive and insensitive regimes is proposed. This study not only offers a deep insight into piezotronic modulation of resonant tunneling physics, but also advances the RTD towards highly sensitive and multifunctional sensor applications.

Oxygen vacancies in oxygen evolution cocatalysts (OECs) can significantly improve the photoelectrochemical (PEC) water splitting performance of photoanodes. However, OECs with abundant oxygen vacancies have a poor stability when exposing to the highly-oxidizing photogenerated holes. Herein, we partly fill oxygen vacancies in a MnCo₂O_x OEC with N atoms by a combined electrodeposition and sol-gel method, which dramatically improves both photocurrent density and stability of a BiVO₄ photoanode. The optimized N filled oxygen vacancy-rich MnCo₂O_x/BiVO₄ photoanode (3 at.% of N) exhibits an outstanding photocurrent density of 6.5 mA·cm⁻² at 1.23 V_RHE under AM 1.5 G illumination (100 mW·cm⁻²), and an excellent stability of over 150 h. Systematic characterizations and theoretical calculations demonstrate that N atoms stabilize the defect structure and modulate the surface electron distribution, which significantly enhances the stability and further increases the photocurrent density. Meanwhile, other heteroatoms such as carbon, phosphorus, and sulfur are confirmed to have similar effects on improving PEC water splitting performance of photoanodes.

Owing to the relatively short hole diffusion length, severe charge recombination in the bulk of bismuth vanadate (BiVO₄) is the key issue for photoelectrochemical water splitting. Herein, we design a nanoporous MoO_3−x/BiVO₄ heterojunction photoanode to promote charge separation. The efficient electron transport properties of oxygen deficient MoO_3−x and the nanoporous structure are beneficial for charge separation, leading to a significantly enhanced PEC performance. The optimized MoO_3−x/BiVO₄ heterojunction photoanode exhibits a photocurrent density of 5.07 mA·cm⁻² for Na₂SO₃ oxidation. By depositing FeOOH/NiOOH dual oxygen evolution cocatalysts to promote surface kinetics, a high photocurrent density of 4.81 mA·cm⁻² can be achieved for PEC water splitting, exhibiting an excellent applied bias photon-to-current efficiency of 1.57%. Moreover, stable overall water splitting is achieved under consecutive light illumination for 10 h. We provide a proof of concept for the design of efficient BiVO₄-based heterojunction photoanodes for stable PEC water splitting.

The emergence of human coronaviruses (HCoVs), especially the current pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), engender severe threats to public health globally. Despite the outstanding breakthrough of new vaccines and therapeutic medicines in the past years, HCoVs still undergo unpredictable mutations, thus demanding more effective diagnostic and therapeutic strategies. Benefitting from the unique physicochemical properties and multiple nano–bio interactions, nanomaterials hold promising potential to fight against various HCoVs, either by providing sensitive and economic nanosensors for rapid viral detection, or by developing translatable nanovaccines and broad-spectrum nanomedicines for HCoV treatment. Herein, we systemically summarized the recent applications of nanoagents in diagnostics and therapeutics for HCoV-induced diseases, as well as their limitations and perspectives against HCoV variants. We believe this review will promote the design of innovative theranostic nanoagents for the current and future HCoV-caused pandemics.

Flexible electronics is the research field with interdisciplinary crossing and integration. It shows the promising advantages of novel device configurations, low-cost and low-power consumption due to their flexible and soft characteristics. Atomic layered two-dimensional (2D) materials especially transition metal dichalcogenides, have triggered great interest in ultra-thin 2D flexible electronic devices and optoelectronic devices because of their direct and tunable bandgaps, excellent electrical, optical, mechanical, and thermal properties. This review aims to provide the recent progress in 2D TMDs and their applications in flexible electronics. The fundamental electrical properties and mechanical properties of materials, flexible device configurations, and their performance in transistors, sensors, and photodetectors are thoroughly discussed. At last, some perspectives are given on the open challenges and prospects for 2D TMDs flexible electronic devices and new device opportunities.

Strong light-matter interactions involved with photons and quasiparticles are fundamentally interesting to access the wealthy many-body physics in quantum mechanics. The emerging two-dimensional (2D) semiconductors with large exciton binding energies and strong quantum confinement allow to investigate exciton-photon coupling at elevated temperatures. Here we report room- temperature formation of Bragg polaritons in monolayer semiconductor on a dielectric mirror through the exciton-Bragg photon coupling. With the negative detuning energy of ~ 30 meV, angle-resolved reflection signals reveal anti-crossing behaviors of lower and upper polariton branches at ±18° together with the Rabi splitting of 10 meV. Meanwhile, the strengthened photoluminescence appears in the lower polariton branch right below the anti-crossing angles, indicating the presence of the characteristic bottleneck effect caused by the slowing exciton-polariton energy relaxation towards the band minimum. The extracted coupling strength is between the ones of weak and distinct strong coupling regimes, where the eigenenergy splitting induced by the moderate coupling is resolvable but not large enough to fully separate two polaritonic components. Our work develops a simplified strategy to generate exciton-polaritons in 2D semiconductors and can be further extended to probe the intriguing bosonic characteristics of these quasiparticles, such as Bose-Einstein condensation, polariton lasing and superfluidity, directly at the material surfaces.

Possessing a valley degree of freedom and potential in information processing by manipulating valley features (such as valley splitting), group-VI monolayer transition metal dichalcogenides have attracted enormous interest. This valley splitting can be measured based on the difference between the peak energies of σ⁺ and σ^- polarized emissions for excitons or trions in direct band gap monolayer transition metal dichalcogenides under perpendicular magnetic fields. In this work, a well-prepared heterostructure is formed by transferring exfoliated WSe₂ onto a EuS substrate. Circular-polarization-resolved photoluminescence spectroscopy, one of the most facile and intuitive methods, is used to probe the difference of the gap energy in two valleys under an applied out-of-plane external magnetic field. Our results indicate that valley splitting can be enhanced when using a EuS substrate, as compared to a SiO₂/Si substrate. The enhanced valley splitting of the WSe₂/EuS heterostructure can be understood as a result of an interfacial magnetic exchange field originating from the magnetic proximity effect. The value of this magnetic exchange field, based on our estimation, is approximately 9 T. Our findings will stimulate further studies on the magnetic exchange field at the interface of similar heterostructures.