High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present. Here, we report ultrathin films of non-encapsulated layered BiOSe, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ∼0.8 eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000 cm V s is measured in as-grown BiOSe nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition and at the LaAlO-SrTiO interface, making the detection of Shubnikov-de Haas quantum oscillations possible. Top-gated field-effect transistors based on BiOSe crystals down to the bilayer limit exhibit high Hall mobility values (up to 450 cm V s), large current on/off ratios (>10) and near-ideal subthreshold swing values (∼65 mV dec) at room temperature. Our results make BiOSe a promising candidate for future high-speed and low-power electronic applications.

Transparent conductive film on plastic substrate is a critical component in low-cost, flexible, and lightweight optoelectronics. Industrial-scale manufacturing of high-performance transparent conductive flexible plastic is needed to enable wide-ranging applications. Here, we demonstrate a continuous roll-to-roll (R2R) production of transparent conductive flexible plastic based on a metal nanowire network fully encapsulated between graphene monolayer and plastic substrate. Large-area graphene film grown on Cu foil via a R2R chemical vapor deposition process was hot-laminated onto nanowires precoated EVA/PET film, followed by a R2R electrochemical delamination that preserves the Cu foil for reuse. The encapsulated structure minimized the resistance of both wire-to-wire junctions and graphene grain boundaries and strengthened adhesion of nanowires and graphene to plastic substrate, resulting in superior optoelectronic properties (sheet resistance of ∼8 Ω sq(-1) at 94% transmittance), remarkable corrosion resistance, and excellent mechanical flexibility. With these advantages, long-cycle life flexible electrochromic devices are demonstrated, showing up to 10000 cycles.

Non-neutral layered crystals, another group of two-dimensional (2D) materials that lack a well-defined van der Waals (vdWs) gap, are those that form strong chemical bonds in-plane but display weak out-of-plane electrostatic interactions, exhibiting intriguing properties for the bulk counterpart. However, investigation of the properties of their atomically thin counterpart are very rare presumably due to the absence of efficient ways to achieve large-area high-quality 2D crystals. Here, high-mobility atomically thin BiOSe, a typical non-neutral layered crystal without a standard vdWs gap, was synthesized via a facial chemical vapor deposition (CVD) method, showing excellent controllability for thickness, domain size, nucleation site, and crystal-phase evolution. Atomically thin, large single crystals of BiOSe with lateral size up to ∼200 μm and thickness down to a bilayer were obtained. Moreover, optical and electrical properties of the CVD-grown 2D BiOSe crystals were investigated, displaying a size-tunable band gap upon thinning and an ultrahigh Hall mobility of >20000 cm V s at 2 K. Our results on the high-mobility 2D BiOSe semiconductor may activate the synthesis and related fundamental research of other non-neutral 2D materials.

Infrared light detection and sensing is deeply embedded in modern technology and human society and its development has always been benefitting from the discovery of various photoelectric materials. The rise of two-dimensional materials, thanks to their distinct electronic structures, extreme dimensional confinement and strong light–matter interactions, provides a material platform for next-generation infrared photodetection. Ideal infrared detectors should have fast respond, high sensitivity and air-stability, which are rare to meet at the same time in one two-dimensional material. Herein we demonstrate an infrared photodetector based on two-dimensional Bi2O2Se crystal, whose main characteristics are outstanding in the whole two-dimensional family: high sensitivity of 65 AW−1 at 1200 nm and ultrafast photoresponse of ~1 ps at room temperature, implying an intrinsic material-limited bandwidth up to 500 GHz. Such great performance is attributed to the suitable electronic bandgap and high carrier mobility of two-dimensional oxyselenide.

Monolayer Bi2O2Se is a promising post-silicon-era semiconductor candidate because of its simultaneous excellent device performance and high ambient stability.

A new layered oxide semiconductor (Bi2O2Se) is found with excellent electronic properties for promising applications.

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Patterning of high-mobility 2D semiconducting materials with unique layered structures and superb electronic properties offers great potential for batch fabrication and integration of next-generation electronic and optoelectronic devices. Here, a facile approach is used to achieve accurate patterning of 2D high-mobility semiconducting Bi O Se crystals using dilute H O and protonic mixture acid as efficient etchants. The 2D Bi O Se crystal after chemical etching maintains a high Hall mobility of over 200 cm V s at room temperature. Centimeter-scale well-ordered arrays of 2D Bi O Se with tailorable configurations are readily obtained. Furthermore, integrated photodetectors based on 2D Bi O Se arrays are fabricated, exhibiting excellent air stability and high photoresponsivity of ≈2000 A W at 532 nm. These results are one step towards the practical application of ultrathin 2D integrated digital and optoelectronic circuits.