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Recently, the increasing demand for data-centric applications is driving the elimination of image sensing, memory and computing unit interface, thus promising for latency- and energy-strict applications. Although dedicated electronic hardware has inspired the development of in-memory computing and in-sensor computing, folding the entire signal chain into one device remains challenging. Here an in-memory sensing and computing architecture is demonstrated using ferroelectric-defined reconfigurable two-dimensional photodiode arrays. High-level cognitive computing is realized based on the multiplications of light power and photoresponsivity through the photocurrent generation process and Kirchhoff’s law. The weight is stored and programmed locally by the ferroelectric domains, enabling 51 (>5 bit) distinguishable weight states with linear, symmetric and reversible manipulation characteristics. Image recognition can be performed without any external memory and computing units. The three-in-one paradigm, integrating high-level computing, weight memorization and high-performance sensing, paves the way for a computing architecture with low energy consumption, low latency and reduced hardware overhead.It remains challenging to integrate memory, sensing and computing in one device. Here a compact in-memory sensing and computing architecture based on ferroelectric-defined reconfigurable two-dimensional photodiode arrays has been reported.

Charge-carrier separation is regarded as one of the critical issues of photocatalytic water splitting and could be accelerated by constructing microscopic junctions in photocatalysts. Homojunction photocatalysts consisting of different forms of semiconductor with identical compositions could inherit the advantages of heterojunction-based photocatalysts in charge separation due to the built-in electric field, while omitting the potential drawbacks of interfacial lattice distortion by providing continuous band bonding. Therefore, homojunction-based photocatalysts have recently drawn growing attention in water splitting. In this review, the synthetic approaches to preparing photocatalysts with various homojunction structures including p-n junction, phase junction, and facet junction were introduced, together with a comprehensive analysis and discussion on the latest progress in the application of photocatalytic water splitting. This review work is expected to inspire more related work with promoted research on designing efficient homojunction-based photocatalytic systems for water splitting.

Understanding charge transfer dynamics and carrier separation pathway is challenging due to the lack of appropriate characterization strategies. In this work, a crystalline triazine/heptazine carbon nitride homojunction is selected as a model system to demonstrate the interfacial electron-transfer mechanism. Surface bimetallic cocatalysts are used as sensitive probes during in situ photoemission for tracing the S-scheme transfer of interfacial photogenerated electrons from triazine phase to the heptazine phase. Variation of the sample surface potential under light on/off confirms dynamic S-scheme charge transfer. Further theoretical calculations demonstrate an interesting reversal of interfacial electron-transfer path under light/dark conditions, which also supports the experimental evidence of S-scheme transport. Benefiting from the unique merit of S-scheme electron transfer, homojunction shows significantly enhanced activity for CO 2 photoreduction. Our work thus provides a strategy to probe dynamic electron transfer mechanisms and to design delicate material structures towards efficient CO 2 photoreduction. Here, the authors reveal how interfacial electron migration occurs in S-scheme crystalline carbon nitrides by applying several dynamic in situ characterization and theoretical calculations.

With the further miniaturization and integration of multi-dimensional optical information detection devices, polarization-sensitive photodetectors based on anisotropic low-dimension materials have attractive potential applications. However, the performance of these devices is restricted by intrinsic property of materials leading to a small polarization ratio of the detectors. Here, we construct a black phosphorus (BP) homojunction photodetector defined by ferroelectric domains with ultra-sensitive polarization photoresponse. With the modulation of ferroelectric field, the BP exhibits anisotropic dispersion changes, leading an increased photothermalelectric (PTE) current in the armchair (AC) direction. Moreover, the PN junction can promote the PTE current and accelerate carrier separation. As a result, the BP photodetector demonstrates an ultrahigh polarization ratio (PR) of 288 at 1450 nm incident light, a large photoresponsivity of 1.06 A/W, and a high detectivity of 1.27 × 10 11 cmHz 1/2 W −1 at room temperature. This work reveals the great potential of BP in future polarized light detection. Integrated polarization-sensitive photodetectors are important for sensing applications and optical communication. Here, the authors report the realization of 2D black phosphorus homojunction photodetectors defined by ferroelectric substrates, showing polarization ratios up to 288 and high responsivity in the near-infrared.

Photocatalytic H 2 O 2 synthesis (PHS) via graphite carbon nitride (g-C 3 N 4 ) is a low-carbon and environmentally friendly approach, which has garnered tremendous attention. However, as for the pristine g-C 3 N 4 , the PHS is severely constrained by the slow transfer and rapid recombination of photogenerated carriers. Herein, we introduced cellulose-derived carbon nanofibers (CF) into the homojunction of g-C 3 N 4 nanotubes (MCN) and g-C 3 N 4 nanosheets (SCN). A series of photocatalytic results demonstrate that the embedding of cellulose-derived carbon for MCN/SCN/CF composite catalyst significantly improved the photocatalytic H 2 O 2 generation (136.9 μmol·L −1 ·h −1 ) with 5-holds higher than that of individual MCN (27.5 μmol·L −1 ·h −1 ) without any sacrificial agent. This enhancement can be attributed to the combined effects of the two-step one-electron oxygen reduction reaction (ORR) on conduction band (CB) side and the water oxidation reaction (WOR) on valence band (VB) side. A comprehensive characterization of the mechanism indicates that CF enhances the absorption of light, promotes the separation and migration of photogenerated carriers, and regulates the position of the valence and conduction bands with an effective dual-channel ORR pathway for photo-synthesis of H 2 O 2 . This work provides valuable insights into utilizing biomass-based materials for significantly boosting photocatalytic H 2 O 2 production. Graphical Abstract

Control over carrier type and doping levels in semiconductor materials is key for optoelectronic applications. In colloidal quantum dots (CQDs), these properties can be tuned by surface chemistry modification, but this has so far been accomplished at the expense of reduced surface passivation and compromised colloidal solubility; this has precluded the realization of advanced architectures such as CQD bulk homojunction solids. Here we introduce a cascade surface modification scheme that overcomes these limitations. This strategy provides control over doping and solubility and enables n -type and p -type CQD inks that are fully miscible in the same solvent with complete surface passivation. This enables the realization of homogeneous CQD bulk homojunction films that exhibit a 1.5 times increase in carrier diffusion length compared with the previous best CQD films. As a result, we demonstrate the highest power conversion efficiency (13.3%) reported among CQD solar cells. It is challenging to realize doping and surface passivation simultaneously in colloidal quantum dot inks. Here Choi et al . employ a cascade surface modification approach to solve the problem and obtain record high efficiency of 13.3% for bulk homojunction solar cells based on these inks.

Avalanche and surge robustness involve fundamental carrier dynamics under high electric field and current density. They are also prerequisites of any power device to survive common overvoltage and overcurrent stresses in power electronics applications such as electric vehicles, electricity grids, and renewable energy processing. Despite tremendous efforts to develop the next-generation power devices using emerging ultra-wide bandgap semiconductors, the lack of effective bipolar doping has been a daunting obstacle for achieving the necessary robustness in these devices. Here we report avalanche and surge robustness in a heterojunction formed between the ultra-wide bandgap n-type gallium oxide and the wide-bandgap p-type nickel oxide. Under 1500 V reverse bias, impact ionization initiates in gallium oxide, and the staggered band alignment favors efficient hole removal, enabling a high avalanche current over 50 A. Under forward bias, bipolar conductivity modulation enables the junction to survive over 50 A surge current. Moreover, the asymmetric carrier lifetime makes the high-level carrier injection dominant in nickel oxide, enabling a fast reverse recovery within 15 ns. This heterojunction breaks the fundamental trade-off between robustness and switching speed in conventional homojunctions and removes a key hurdle to advance ultra-wide bandgap semiconductor devices for power industrial applications. Avalanche and surge robustness are fundamental for power devices to survive overvoltage and overcurrent stresses in typical applications. Here, authors report NiO/Ga 2 O 3 heterojunctions with smaller reverse recovery, higher switching speed, and a robustness competitive to that of conventional homojunctions.

A light field carrying multidimensional optical information, including but not limited to polarization, intensity and wavelength, is essential for numerous applications such as environmental monitoring, thermal imaging, medical diagnosis and free-space communications. Simultaneous acquisition of this multidimensional information could provide comprehensive insights for understanding complex environments but remains a challenge. Here we demonstrate a multidimensional optical information detection device based on zero-bias double twisted black arsenic–phosphorus homojunctions, where the photoresponse is dominated by the photothermoelectric effect. By using a bipolar and phase-offset polarization photoresponse, the device operated in the mid-infrared range can simultaneously detect both the polarization angle and incident intensity information through direct measurement of the photocurrents in the double twisted black arsenic–phosphorus homojunctions. The device’s responsivity makes it possible to retrieve wavelength information, typically perceived as difficult to obtain. Moreover, the device exhibits an electrically tunable polarization photoresponse, enabling precise distinction of polarization angles under low-intensity light exposure. These demonstrations offer a promising approach for simultaneous detection of multidimensional optical information, indicating potential for diverse photonic applications. Multidimensional optical information, including intensity, polarization and wavelength, can be simultaneously detected using double twisted black arsenic–phosphorus homojunctions.

Layered transition metal dichalcogenides have shown tremendous potential for photodetection due to their non-zero direct bandgaps, high light absorption coefficients and carrier mobilities, and ability to form atomically sharp and defect-free heterointerfaces. A critical and fundamental bottleneck in the realization of high performance detectors is their trap-dependent photoresponse that trades off responsivity with speed. This work demonstrates a facile method of attenuating this trade-off by nearly 2x through integration of a lateral, in-plane, electrostatically tunable p-n homojunction with a conventional WSe 2 phototransistor. The tunable p-n junction allows modulation of the photocarrier population and width of the conducting channel independently from the phototransistor. Increased illumination current with the lateral p-n junction helps achieve responsivity enhancement upto 2.4x at nearly the same switching speed (14–16 µs) over a wide range of laser power (300 pW–33 nW). The added benefit of reduced dark current enhances specific detectivity ( D* ) by nearly 25x to yield a maximum measured flicker noise-limited D* of 1.1×10 12 Jones. High responsivity of 170 A/W at 300 pW laser power along with the ability to detect sub-1 pW laser switching are demonstrated. In photodetectors based on 2D materials, a trade-off often exists between responsivity and speed. Here, the authors attenuate this issue via integration of a lateral, in-plane, electrostatically tunable p-n homojunction with a conventional WSe 2 phototransistor.

Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation of gradient tantalum-doped hematite homojunction nanorods by combination of hydrothermal regrowth strategy and hybrid microwave annealing, which enhances the photocurrent density and reduces the turn-on voltage simultaneously. The unusual bi-functional effects originate from the passivation of the surface states and intrinsic built-in electric field by the homojunction formation. The additional driving force provided by the field can effectively suppress charge–carrier recombination both in the bulk and on the surface of hematite, especially at lower potentials. Moreover, the synthesized homojunction shows a remarkable synergy with NiFe(OH) x cocatalyst with significant additional improvements of photocurrent density and cathodic shift of turn-on voltage. The work has nicely demonstrated multiple collaborative strategies of gradient doping, homojunction formation, and cocatalyst modification, and the concept could shed light on designing and constructing the efficient nanostructures of semiconductor photoelectrodes in the field of solar energy conversion. Solar-to-fuel conversion represents a renewable means to harvest sunlight, but the most efficient materials are often expensive or rare. Here, authors demonstrate gradient tantalum-doped hematite homojunctions as a method to improve photoelectrochemical water splitting performances.