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Continuous imaging of cardiac functions is highly desirable for the assessment of long-term cardiovascular health, detection of acute cardiac dysfunction and clinical management of critically ill or surgical patients 1 – 4 . However, conventional non-invasive approaches to image the cardiac function cannot provide continuous measurements owing to device bulkiness 5 – 11 , and existing wearable cardiac devices can only capture signals on the skin 12 – 16 . Here we report a wearable ultrasonic device for continuous, real-time and direct cardiac function assessment. We introduce innovations in device design and material fabrication that improve the mechanical coupling between the device and human skin, allowing the left ventricle to be examined from different views during motion. We also develop a deep learning model that automatically extracts the left ventricular volume from the continuous image recording, yielding waveforms of key cardiac performance indices such as stroke volume, cardiac output and ejection fraction. This technology enables dynamic wearable monitoring of cardiac performance with substantially improved accuracy in various environments. Innovations in device design, material fabrication and deep learning are described, leading to a wearable ultrasound transducer capable of dynamic cardiac imaging in various environments and under different conditions.

Organic–inorganic hybrid perovskites have electronic and optoelectronic properties that make them appealing in many device applications 1 – 4 . Although many approaches focus on polycrystalline materials 5 – 7 , single-crystal hybrid perovskites show improved carrier transport and enhanced stability over their polycrystalline counterparts, due to their orientation-dependent transport behaviour 8 – 10 and lower defect concentrations 11 , 12 . However, the fabrication of single-crystal hybrid perovskites, and controlling their morphology and composition, are challenging 12 . Here we report a solution-based lithography-assisted epitaxial-growth-and-transfer method for fabricating single-crystal hybrid perovskites on arbitrary substrates, with precise control of their thickness (from about 600 nanometres to about 100 micrometres), area (continuous thin films up to about 5.5 centimetres by 5.5 centimetres), and composition gradient in the thickness direction (for example, from methylammonium lead iodide, MAPbI 3 , to MAPb 0.5 Sn 0.5 I 3 ). The transferred single-crystal hybrid perovskites are of comparable quality to those directly grown on epitaxial substrates, and are mechanically flexible depending on the thickness. Lead–tin gradient alloying allows the formation of a graded electronic bandgap, which increases the carrier mobility and impedes carrier recombination. Devices based on these single-crystal hybrid perovskites show not only high stability against various degradation factors but also good performance (for example, solar cells based on lead–tin-gradient structures with an average efficiency of 18.77 per cent). A solution-based lithography-assisted epitaxial-growth-and-transfer method is used to fabricate single-crystal hybrid perovskites on any surface, with precise control of the thickness, area and chemical composition gradient.

Despite the impressive development of metal halide perovskites in diverse optoelectronics, progress on high-performance transistors employing state-of-the-art perovskite channels has been limited due to ion migration and large organic spacer isolation. Herein, we report high-performance hysteresis-free p-channel perovskite thin-film transistors (TFTs) based on methylammonium tin iodide (MASnI 3 ) and rationalise the effects of halide (I/Br/Cl) anion engineering on film quality improvement and tin/iodine vacancy suppression, realising high hole mobilities of 20 cm 2 V −1 s −1 , current on/off ratios exceeding 10 7 , and threshold voltages of 0 V along with high operational stabilities and reproducibilities. We reveal ion migration has a negligible contribution to the hysteresis of Sn-based perovskite TFTs; instead, minority carrier trapping is the primary cause. Finally, we integrate the perovskite TFTs with commercialised n-channel indium gallium zinc oxide TFTs on a single chip to construct high-gain complementary inverters, facilitating the development of halide perovskite semiconductors for printable electronics and circuits. Progress on high-performance transistor employing perovskite channels has been limited to date. Here, Zhu et al. report hysteresis-free tin-based perovskite thin-film transistors with high hole mobility of 20 cm 2 V –1 S –1 , which can be integrated with commercial metal oxide transistors on a single chip.

Realizing high electroluminescence dissymmetric factor and high external quantum efficiency at the same time is challenging in light-emitting diodes with direct circularly polarized emission. Here, we show that high electroluminescence dissymmetric factor and high external quantum efficiency can be simultaneously achieved in light-emitting diodes based on chiral perovskite quantum dots. Specifically, chiral perovskite quantum dots with chiral-induced spin selectivity can concurrently serve as localized radiative recombination centers of spin-polarized carriers for circularly polarized emission, thereby suppressing the relaxation of spins, Meanwhile, improving the chiral ligand exchange efficiency is found to synergistically promote their spin selectivity and optoelectronic properties so that chiroptoelectronic performance of resulting devices can be facilitated. Our device simultaneously exhibits high electroluminescence dissymmetric factor ( R : 0.285 and S : 0.251) and high external quantum efficiency ( R : 16.8% and S : 16%), demonstrating their potential in constructing high-performance chiral light sources. He et al. report spin-LEDs based on chiral perovskite quantum dots which act as localized spin-selective units and radiative recombination centers simultaneously. Ultrasonic treatment assisted ligand exchange enables spin-LEDs with peak efficiency of 16.8% and dissymmetry factor of 0.285.

Continuous monitoring of the central blood pressure waveform from deeply embedded vessels such as the carotid artery and jugular vein has clinical value for the prediction of all-cause cardiovascular mortality. However, existing non-invasive approaches, including photoplethysmography and tonometry, only enable access to the superficial peripheral vasculature. Although current ultrasonic technologies allow non-invasive deep tissue observation, unstable coupling with the tissue surface resulting from the bulkiness and rigidity of conventional ultrasound probes introduces usability constraints. Here, we describe the design and operation of an ultrasonic device that is conformal to the skin and capable of capturing blood pressure waveforms at deeply embedded arterial and venous sites. The wearable device is ultrathin (240 μm) and stretchable (with strains up to 60%), and enables the non-invasive, continuous and accurate monitoring of cardiovascular events from multiple body locations, which should facilitate its use in a variety of clinical environments. An ultrasonic and stretchable device conformal to the skin that captures blood pressure waveforms at deeply embedded arterial and venous sites enables the continuous monitoring of cardiovascular events.

Acquiring real-time spectral information in point-of-care diagnosis, internet-of-thing, and other lab-on-chip applications require spectrometers with hetero-integration capability and miniaturized feature. Compared to conventional semiconductors integrated by heteroepitaxy, solution-processable semiconductors provide a much-flexible integration platform due to their solution-processability, and, therefore, more suitable for the multi-material integrated system. However, solution-processable semiconductors are usually incompatible with the micro-fabrication processes. This work proposes a facile and universal platform to fabricate integrated spectrometers with semiconductor substitutability by unprecedently involving the conjugated mode of the bound states in the continuum (conjugated-BIC) photonics. Specifically, exploiting the conjugated-BIC photonics, which remains unexplored in conventional lasing studies, renders the broadband photodiodes with ultra-narrowband detection ability, detection wavelength tunability, and on-chip integration ability while ensuring the device performance. Spectrometers based on these ultra-narrowband photodiode arrays exhibit high spectral resolution and wide/tunable spectral bandwidth. The fabrication processes are compatible with solution-processable semiconductors photodiodes like perovskites and quantum dots, which can be potentially extended to conventional semiconductors. Signals from the spectrometers directly constitute the incident spectra without being computation-intensive, latency-sensitive, and error-intolerant. As an example, the integrated spectrometers based on perovskite photodiodes are capable of realizing narrowband/broadband light reconstruction and in-situ hyperspectral imaging.

Perovskite thin‐film transistors (TFTs) simultaneously possessing exceptional carrier transport capabilities, nonvolatile memory effects, and photosensitivity have recently attracted attention in fields of both complementary circuits and neuromorphic computing. Despite continuous performance improvements through additive and composition engineering of the channel materials, the equally crucial dielectric/channel interfaces of perovskite TFTs have remained underexplored. Here, it is demonstrated that engineering the dielectric/channel interface in 2D tin perovskite TFTs not only enhances the performance and operational stability for their utilization in complementary circuits but also enables efficient synaptic behaviors (optical information sensing and storage) under an extremely low operating voltage of −1 mV at the same time. The interface‐engineered TFT arrays operating at −1 mV are then demonstrated as the preprocessing hardware for neuromorphic visions with pattern recognition accuracy of 92.2% and long‐term memory capability. Such a low operating voltage provides operational feasibility to the design of large‐scale‐integrated and wearable/implantable neuromorphic hardware. Engineering the dielectric/channel interface in 2D tin perovskite thin‐film transistors (TFTs) not only enhances the performance and operational stability for their utilization in complementary circuits but also enables efficient synaptic behaviors under −1 mV. The interface‐engineered TFT arrays are demonstrated as the preprocessing hardware for neuromorphic visions with pattern recognition accuracy of 92.2% and long‐term memory capability.

Light scattered or radiated from a material carries valuable information on the said material. Such information can be uncovered by measuring the light field at different angles and frequencies. However, this technique typically requires a large optical apparatus, hampering the widespread use of angle-resolved spectroscopy beyond the lab. Here we demonstrate compact angle-resolved spectral imaging by combining a tunable metasurface-based spectrometer array and a metalens. With this approach, even with a miniaturized spectrometer footprint of only 4 × 4 μm 2 , we demonstrate a wavelength accuracy of 0.17 nm, spectral resolution of 0.4 nm and a linear dynamic range of 149 dB. Moreover, our spectrometer has a detection limit of 1.2 fJ, and can be patterned to an array for spectral imaging. Placing such a spectrometer array directly at the back focal plane of a metalens, we achieve an angular resolution of 4.88 × 10 − 3  rad. Our angle-resolved spectrometers empowered by metalenses can be employed towards enhancing advanced optical imaging and spectral analysis applications. Employing a miniaturized spectrometer that combines a metasurface-based spectrometer array and a metalens, angle-resolved spectral imaging is achieved with a wavelength accuracy of 0.17 nm, spectral resolution of 0.40 nm and angular resolution of 4.88 × 10 −3  rad for a spectrometer with a 4 × 4 μm 2 footprint.

Strain engineering is a powerful tool with which to enhance semiconductor device performance 1 , 2 . Halide perovskites have shown great promise in device applications owing to their remarkable electronic and optoelectronic properties 3 – 5 . Although applying strain to halide perovskites has been frequently attempted, including using hydrostatic pressurization 6 – 8 , electrostriction 9 , annealing 10 – 12 , van der Waals force 13 , thermal expansion mismatch 14 , and heat-induced substrate phase transition 15 , the controllable and device-compatible strain engineering of halide perovskites by chemical epitaxy remains a challenge, owing to the absence of suitable lattice-mismatched epitaxial substrates. Here we report the strained epitaxial growth of halide perovskite single-crystal thin films on lattice-mismatched halide perovskite substrates. We investigated strain engineering of α-formamidinium lead iodide (α-FAPbI 3 ) using both experimental techniques and theoretical calculations. By tailoring the substrate composition—and therefore its lattice parameter—a compressive strain as high as 2.4 per cent is applied to the epitaxial α-FAPbI 3 thin film. We demonstrate that this strain effectively changes the crystal structure, reduces the bandgap and increases the hole mobility of α-FAPbI 3 . Strained epitaxy is also shown to have a substantial stabilization effect on the α-FAPbI 3 phase owing to the synergistic effects of epitaxial stabilization and strain neutralization. As an example, strain engineering is applied to enhance the performance of an α-FAPbI 3 -based photodetector. A method of deposition of mixed-cation hybrid perovskite films as lattice-mismatched substrates for an α-FAPbI 3 film is described, giving strains of up to 2.4 per cent while also stabilizing the metastable α-FAPbI 3 phase for several hundred days.

Recent advances in wearable ultrasound technologies have demonstrated the potential for hands-free data acquisition, but technical barriers remain as these probes require wire connections, can lose track of moving targets and create data-interpretation challenges. Here we report a fully integrated autonomous wearable ultrasonic-system-on-patch (USoP). A miniaturized flexible control circuit is designed to interface with an ultrasound transducer array for signal pre-conditioning and wireless data communication. Machine learning is used to track moving tissue targets and assist the data interpretation. We demonstrate that the USoP allows continuous tracking of physiological signals from tissues as deep as 164 mm. On mobile subjects, the USoP can continuously monitor physiological signals, including central blood pressure, heart rate and cardiac output, for as long as 12 h. This result enables continuous autonomous surveillance of deep tissue signals toward the internet-of-medical-things. A wearable ultrasound patch monitors subjects in motion using machine learning and wireless electronics.