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2D materials have garnered significant research attention due to their unique electrical and optical properties. Various photodetectors (PDs) based on 2D materials have been demonstrated to possess a high photoresponse, achieve specific light detection, and construct flexible devices. Among these, photoelectrochemical‐type (PEC) PDs are attracting increasing attention due to their facile fabrication processes, self‐powered capability, and high sensitivity. Compared with transitional solid‐state PDs based on 2D materials, research on 2D material‐based PEC PDs is still in its initial stages but exhibits promising potential for various applications. This paper comprehensively reviews recent advancements in 2D material‐based PEC PDs. The 2D materials for PEC PDs are first classified, and then the synthesis methods employed for their fabrication are briefly summarized. Later, the performance and performance optimization strategies of various 2D material‐based PEC PDs are discussed. Finally, the challenges and opportunities for developing high‐performance 2D material‐based PEC PDs are highlighted. [ABSTRACT FROM AUTHOR]

Out-of-plane ferroelectricity with a high transition temperature in ultrathin films is important for the exploration of new domain physics and scaling down of memory devices. However, depolarizing electrostatic fields and interfacial chemical bonds can destroy this long-range polar order at two-dimensional (2D) limit. Here we report the experimental discovery of the locking between out-of-plane dipoles and in-plane lattice asymmetry in atomically thin In_{2}Se_{3} crystals, a new stabilization mechanism leading to our observation of intrinsic 2D out-of-plane ferroelectricity. Through second harmonic generation spectroscopy and piezoresponse force microscopy, we found switching of out-of-plane electric polarization requires a flip of nonlinear optical polarization that corresponds to the inversion of in-plane lattice orientation. The polar order shows a very high transition temperature (∼700  K) without the assistance of extrinsic screening. This finding of intrinsic 2D ferroelectricity resulting from dipole locking opens up possibilities to explore 2D multiferroic physics and develop ultrahigh density memory devices.

The optical synaptic device is a novel nonvolatile memory device that combines optical sensing function with synaptic plasticity to simulate the basic biomimetic behaviors of the human visual system. It shows a great potential application in artificial vision. However, most of the current optical synaptic devices are either structurally special or complex, which are quite difficult to prepare especially for mass production. In this work, a submillimeter single‐crystal Bi2O2Se flake with selenium vacancies (Bi2O2Se‐VSe) grown by physical vapor deposition is presented. Upon the Bi2O2Se‐VSe flake, an optical synaptic device is designed with the persistent photoconductivity (PPC) effect induced by selenium vacancies. The device can simulate the biological synapses with an obvious synaptic plasticity. Moreover, an artificial vision system consisting of a 3 × 4 array of optical synaptic devices has been fabricated. The intensity of the image pattern can keep at a high memory level of 54.64% and 19.31% for 532 and 1060 nm waiting for 400 s after illumination of 100 s, which demonstrates the devices exhibit excellent image sensing, learning, and memory storage. This work opens up a new route for fabricating the optical synaptic device with a simple structure and provides new ideas for studying artificial vision systems. [ABSTRACT FROM AUTHOR]

A wearable sensor capable of directly detecting cytokines in external secretions external to the human body is pivotal for gauging the intensity of the immune response and circumventing inflammatory storms, a significant clinical concern. The detection of low‐concentration cytokines is often hampered due to interference from impurities in secretions. Addressing this challenge, a wearable detection system is developed by integrating a Janus membrane with water auto‐collection/filtering capabilities, and aptamer‐modified graphene field‐effect transistor sensors, enabling the detection of low‐concentration cytokines in undiluted sweat samples. The Janus membrane can automatically filter external secretions and transport them to the sensor surface, effectively eliminating impurity interference and enhancing the sensor's detection capabilities. The device can sensitively detect cytokines (such as TNF‐α, a marker for inflammation and cancer) in undiluted sweat, with a detection range spanning 0.5 to 500 pM, and a detection limit reaching 0.31 pM. The ultra‐flexibility of the sensor is also verified, maintaining stable electrical properties even after enduring up to 50 extreme deformations. These findings indicate that the wearable detection system has the potential to realize low‐concentration cytokines monitoring in the sweat of inflammatory patients, to assist the healthcare system in controlling the body's immune status. [ABSTRACT FROM AUTHOR]

Broadband, sensitive, and spectrally distinctive photodetectors show great applications in multifunction optoelectronic devices, which usually integrate multiple photodetectors for distinguishing different spectra. Recently, UV‐induced photocurrent polarity‐switching in individual photoelectrochemical photodetectors (PEC PDs) has been demonstrated by tuning the interfacial physical/chemical processes. However, broadband and spectrally distinctive PEC PDs are still scarce. Here, mosaic t‐Se/InSe heterojunctions are used for designing broadband and spectrally distinctive PEC PDs. Mosaic t‐Se/InSe photoelectrodes are fabricated by one‐step electrochemical deposition with annealing treatment. t‐Se/InSe self‐powered PEC PDs show a broadband photoresponse from UV to near‐infrared (NIR). The photocurrent is negative for UV‐visible spectra and turns positive under NIR irradiation. The light‐induced photocurrent polarity‐switching originates from the competition of different redox reactions at the t‐Se/InSe photoelectrode/electrolyte interface. The responsivity is −22.5, −10.93, −4.18, and 2.48 mA W−1 for 365, 525, 630, and 850 nm light, respectively, exceeding most spectrally distinctive solid‐state PDs. The boosted photoresponse of t‐Se/InSe is attributed to the synergistic effect of stronger light absorption, faster carrier transport, and accelerated interfacial charge transfer. Moreover, the devices show great potential for applications in encrypted optical communications. This work provides a way for designing broadband and spectrally distinctive PEC PDs and demonstrates their potential applications. [ABSTRACT FROM AUTHOR]

Photoelectrochemical‐type ultraviolet photodetectors (PEC UV PDs) with simple fabrication processes and high sensitivity have attracted ever‐growing attention. However, the self‐powered performance of PEC UV PDs is still unsatisfying. Herein, the SnO2 nanosheet array (NSA) photoanodes are fabricated and their good self‐powered UV detection capability is demonstrated. The 3D structure of SnO2 NSA not only improves the interfacial charge transfer and carrier transport but also enhances UV absorption. Therefore, the self‐powered SnO2 NSA‐based PEC UV PDs exhibit excellent performance with an ultrahigh responsivity of 207.12 mA W−1, an excellent UV–visible rejection ratio (R254/R455 of 3395), a fast response time (25 ms), and good stability under 254 nm illumination, demonstrating one of the recorded‐high‐performance in the recently reported PEC UV PDs. This work provides more options for developing high‐performance PEC UV PDs. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) synaptic devices have attracted great attention in the field of NIR vision sensors due to their highly parallel sensing and memory functions, which emulate the basic biomimetic behaviors of the human visual system. However, it is a great challenge for the 2D material to achieve NIR light response and integration, which obstructs the progress of NIR synaptic devices. Hence, a two‐terminal NIR synaptic device based on a multilayer MoSe2 moiré superlattice is reported. The moiré structure dominated by interlayer excitons significantly enhances the interlayer coupling of multilayer MoSe2, resulting in a narrower band gap nearly to that of bulk to achieve NIR light response and broadband absorption from 240 nm to 1700 nm. The existence of Se vacancies in MoSe2 moiré superlattice makes the device show the fundamental synaptic performance. Furthermore, a 10×10 integrated retinal morphologic device array is constructed. Under the 100 s light pulse stimulation of 1060 nm, the pattern obtained after attenuation of 50 s still has a memory level of 14.84%, reflecting the excellent storage function under NIR illumination. This research opens up a new avenue for the realization of NIR artificial retina and bionic eye based on 2D materials. [ABSTRACT FROM AUTHOR]