Self-Powered Nanoscale Photodetectors

Improvement of Self-Driven Nanowire-Based Ultraviolet Photodetectors by Metal-Organic Frameworks for Controlling Humanoid Robots

Self-driven photodetectors (PDs) hold significant potential for the development of new information devices, which boast the advantages of ultralow power consumption and straightforward fabrication. In this study, we have proposed and demonstrated a self-driven ultraviolet PD utilizing gallium nitride/metal-organic framework (GaN/MOF) heterojunction nanowires successfully. By introducing Gd-ETTC MOFs on the surface of GaN nanowires, the photocurrent and responsivity of the device can be improved by approximately 75% under 310 nm illumination. Furthermore, they can also be effectively enhanced under visible light illumination. Owing to the appropriate energy level alignment, Gd-ETTC MOFs can serve as both a light harvester and a hole conductor, facilitating the efficient absorption, separation, and transmission of photogenerated carriers. It has been observed that due to reduced interface resistance, MOFs can enhance the charge transport through the acceleration of charge transfer. Furthermore, the PD equipped with MOFs is capable of continuous operation for 30,000 s, a feat attributable to the exceptional stability of both GaN nanowires and Gd-ETTC MOFs. By implementation of the humanoid robot systems, the control commands from the self-driven PD can drive the humanoid robot to execute different actions. The PD-equipped autonomous feedback system of a humanoid robot enables a seamless integration of light perception with intelligent robotic actions. Therefore, the design and demonstration of GaN/MOF nanowires hold significant reference value for further enhancing the performance of PDs and broadening their applications in ultralow-power artificial intelligence systems, humanoid intelligent robots, etc.

Barrier Polarity Reversal Based on Interfacial Modification of Au Nanoparticles for Nonvolatile Multilevel Memory and Optoelectronic Synapses

Optoelectronic synaptic devices, integrating light sensing and information processing capabilities, have emerged as advantageous tools for the implementation of visual neuromorphic computing. However, the transient light-triggered response characteristic typically results in unstable memory retention times and restricted current response ranges, posing significant challenges to the development and practical application of neural network systems. In response to these limitations, this study developed a nonvolatile optoelectronic memory based on the indium tin oxide (ITO)/Au nanoparticles (NPs)/amorphous Ga2O3 (a-Ga2O3)/Pt structure. Unlike conventional optoelectronic memories, this device features a modification with Au NPs that markedly enhances the Schottky barrier height at the interface. Au NPs function as a charge-trapping layer for sensitive and large-scale modulation of the barrier by the light field, thereby enabling the nonvolatile reversal of the device's barrier polarity. This innovative approach enables controllable multilevel data storage with an ultra large on/off ratio (∼104) and excellent retention capability exceeding 12,000 s. Additionally, the device emulates essential synaptic functions and demonstrates potential application values in visual weak signal perception and image memory. This study introduces a mechanism for Schottky barrier polarity control and presents a promising strategy for the development of future high-performance integrated devices and optoelectronic synaptic elements.

Flexo-Phototronic Boosted Self-Powered Ultraviolet Detection in ZnAl:Layered Double Hydroxide Nanosheets/NiO Heterostructure

Developing self-powered and flexible optoelectronic sensors with high responsivity and speed is crucial for modern applications, motivating continuous efforts to enhance their performance. Flexo-phototronics is a less-explored but promising technique to elevate the performance of optoelectronics. Therefore, this work addresses the potential of utilizing the flexo-phototronic effect to enhance the performance of a flexible and self-powered ultraviolet photodetector (UV PD) based on ZnAl:LDH (layered double hydroxides) nanosheets (Ns)/NiO heterostructure. The vertically oriented ZnAl:LDH Ns are synthesized via a simple method involving the immersion of a sputtered 10% Al-doped ZnO thin film in deionized water at room ambient conditions. The fabricated PD exhibits an impressive response to 365 nm UV light, with high sensitivity in the order of 103. The device's photocurrent and responsivity are significantly enhanced by the flexo-phototronic effect, attributed to the flexoelectric properties of ZnAl:LDH Ns. Specifically, applying an inhomogeneous tensile strain of 2% boosted the device responsivity by 57.1% and improved its operational speed. Furthermore, a working model revealing the altered energy-band structure is demonstrated to elucidate the flexo-phototronic-induced boost in the photoresponse. The PD also demonstrated a sustainable performance under severe bending cycles, underlining the good flexibility of the device. The results presented in this study demonstrate a self-powered and flexible UV PD and provide a viable approach to augment the performance of optoelectronics through the flexo-phototronic effect.

Nitrogen-Doped Carbon Quantum Dots with Photoactivation Properties for Ultraviolet Ray Detection

Photoactivation is a phenomenon that could enhance the photoluminescence (PL) and photostability upon UV/vis light exposure, which is usually observed in CdSe/ZnS quantum dots (QDs). However, the photoactivation phenomenon has been scarcely reported in fluorescent carbon quantum dots (CQDs). Herein, the nitrogen-doped carbon quantum dots (N-CQDs) were prepared through a facile solvothermal approach with naphthalenetracarboxylic dianhydride and serine as precursors. Upon simple UV light irradiation for 10 min, the fluorescence quantum yield (QY) of N-CQDs could increase up to 10-fold. Based on this phenomenon, the N-CQDs were explored as an ultraviolet (UV) light sensor to assess the intensity of ultraviolet radiation in sunlight and indirectly evaluate the UV-blocking efficiency of various sunscreen products. Thus, this contribution not only provided an insight into developing a low-cost UV detector but also opened a door for the development of carbon quantum dots with converse-photobleaching properties.

Enhanced Optoelectronic Performance of p-WSe2/Re0.12W0.42Mo0.46S2 Heterojunction

Stacking of van der Waals (vdW) heterostructures and chemical element doping have emerged as crucial methods for enhancing the performance of semiconductors. This study proposes a novel strategy for modifying heterostructures by codoping MoS2 with two elements, Re and W, resulting in the construction of a RexWyMo1-x-yS2/WSe2 heterostructure for the preparation of photodetectors. This approach incorporates multiple strategies to enhance the performance, including hybrid stacking of materials, type-II band alignment, and regulation of element doping. As a result, the RexWyMo1-x-yS2/WSe2 devices demonstrate exceptional performance, including high photoresponsivity (1550.22 A/W), high detectivity (8.17 × 1013 Jones), and fast response speed (rise/fall time, 190 ms/1.42 s). Moreover, the ability to tune the band gap through element doping enables spectral response in the ultraviolet (UV), visible light, and near-infrared (NIR) regions. This heterostructure fabrication scheme highlights the high sensitivity and potential applications of vdW heterostructure (vdWH) in optoelectronic devices.

High-Sensitivity Photoelectrochemical Ultraviolet Photodetector with Stable pH-Universal Adaptability Based on Whole Single-Crystal Integrated Self-Supporting 4H-SiC Nanoarrays

Emerging photoelectrochemical (PEC) photodetectors (PDs) have notable advantages over conventional PDs and have attracted extensive attention. However, harsh liquid environments, such as those with high corrosivity and attenuation, substantially restrict their widespread application. Moreover, most PEC PDs are constructed by assembling numerous nanostructures on current collector substrates, which inevitably contain abundant interfaces and defects, thus greatly weakening the properties of PDs. To address these challenges, a high-performance pH-universal PEC ultraviolet (UV) PD based on a whole single-crystal integrated self-supporting 4H-SiC nanopore array photoelectrode is constructed, which is fabricated using a two-step anodic oxidation approach. The PD exhibits excellent photodetection behavior, with high responsivity (218.77 mA W-1), detectivity (6.64 × 1013 Jones), external quantum efficiency (72.47%), and rapid rise/decay times (17/48 ms) under 375 nm light illumination with a low intensity of 0.15 mW cm-2 and a bias voltage of 0.6 V, which is fall in the state-of-the-art of the wide-bandgap semiconductor-based PDs reported thus far. Furthermore, the SiC PEC PD exhibits excellent photoresponse and long-term operational stability in pH-universal liquid environments. The improved photodetection performance of the SiC PEC PD is primarily attributed to the synergistic effect of the nanopore array structure, integrated self-supporting configuration, and single-crystal structure of the whole photoelectrode.

Bulk Photovoltaic Effect in Polar 3D Perovskitoid Enables Self-Powered Polarization-Sensitive Photodetection

The family of polar hybrid perovskites, in which bulk photovoltaic effects (BPVEs) drive steady photocurrent without bias voltage, have shown promising potentials in self-powered polarization-sensitive photodetection. However, reports of BPVEs in 3D perovskites remain scare, being mainly hindered by the limited dipole moment or lack of symmetry breaking. Herein, a polar 3D perovskitoid, (BDA)Pb2Br6 (BDA = NH3C4H8NH3), where the spontaneous polarization (Ps)-induced BPVE drives self-powered photodetection of polarized-light is reported. Emphatically, the edge-sharing Pb2Br10 dimer building unit allows the optical anisotropy and polarity in 3D (BDA)Pb2Br6, which triggers distinct optical absorption dichroism ratio of ≈2.80 and BPVE dictated photocurrent of 3.5 µA cm-2. Strikingly, these merits contribute to a polarization-sensitive photodetection with a high polarization ratio (≈4) under self-powered mode, beyond those of 2D hybrid perovskites and inorganic materials. This study highlights the potential of polar 3D perovskitoids toward intelligent optoelectronic applications.

A 1T'-MoTe2/GaN van der Waals Schottky junction for self-powered UV imaging and optical communication

Schottky-type self-powered UV photodetectors are promising for next-generation imaging systems. Nevertheless, conventional device fabrication using high-energy metal deposition brings unintentional interface defects, leading to deteriorated device performance and inhomogeneities. Emerging two-dimensional (2D) metallic materials offer an alternative pathway to overcoming such limitations because of their naturally passivated surfaces and the ease of combining with mature bulk semiconductors via van der Waals (vdW) integration. Here, we report the controllable preparation of MoTe2 in the pure 1T' phase and the fabrication of a high-performance 1T'-MoTe2/GaN vdW Schottky photodiode. With the reduced interface states and suppressed dark current as low as 20 pA at zero bias, the photodiode exhibits a remarkable UV-to-visible (R350/R400) rejection ratio of 1.6 × 104, a stable photoresponsivity of ∼50 mA W-1 and a detectivity of 3.5 × 1012 Jones under 360 nm illumination. The photocurrent ON/OFF ratio reaches ∼4.9 × 106 under 10.5 mW irradiation (360 nm). In particular, the 1T'-MoTe2/GaN Schottky diode shows excellent weak-light detection capability, which could detect a 3 nW 360 nm laser and the light emission from a lighter with a pronounced Ilight/Idark ratio of ∼2. Finally, the applications of the device in self-powered UV imaging and optical communication are demonstrated. These results reveal the great prospects of 2D/3D integration in multifunctional optoelectronics, which may inspire novel 2D-related devices and expand their applications in widespread fields.

Realizing Ultrafast Response Speed for Self-Powered Photodetectors with a Molecular-Doped Lateral InSe Homojunction

The implementation of energy-saving policies has stimulated intensive interest in exploring self-powered optoelectronic devices. The 2D p-n homojunction exhibits effective generation and separation of carriers excited by light, realizing lower power consumption and higher performance photodetectors. Here, a self-powered photodetector with high performance is fabricated based on an F4-TCNQ localized molecular-doped lateral InSe homojunction. Compared with the intrinsic InSe photodetector, the switching light ratio (Ilight/Idark) of the p-n homojunction device can be enhanced by 2.2 × 104, and the temporal response is also dramatically improved to 24/30 μs. Benefiting from the built-in electric field, due to the formation of an InSe p-n homojunction after partial doping of F4-TCNQ on InSe, the device possesses a high responsivity (R) of 93.21 mA/W, with a specific detectivity (D*) of 1.14 × 1011 Jones. These results suggest a promising approach to get a lateral InSe p-n homojunction and reveal the potential application of the device for next generation low-consumption photodetectors.

Wide Bandgap Semiconductors for Ultraviolet Photodetectors: Approaches, Applications, and Prospects

Ultraviolet (UV) light, invisible to the human eye, possesses both benefits and risks. To harness its potential, UV photodetectors (PDs) have been engineered. These devices can convert UV photons into detectable signals, such as electrical impulses or visible light, enabling their application in diverse fields like environmental monitoring, healthcare, and aerospace. Wide bandgap semiconductors, with their high-efficiency UV light absorption and stable opto-electronic properties, stand out as ideal materials for UV PDs. This review comprehensively summarizes recent advancements in both traditional and emerging wide bandgap-based UV PDs, highlighting their roles in UV imaging, communication, and alarming. Moreover, it examines methods employed to enhance UV PD performance, delving into the advantages, challenges, and future research prospects in this area. By doing so, this review aims to spark innovation and guide the future development and application of UV PDs.

Self-powered photodetectors: a device engineering perspective

Nanoscale self-powered photodetectors that can work without any external source of energy are required for future applications. There is potential demand for these devices in areas like wireless surveillance, weather forecasting, remote monitoring, and places where the availability of power is scarce. This study provides an overview of state of the art research trends and improvements in self-powered photodetectors. A device engineering perspective for improvement in the figures of merit has been presented along with a description of additional effects like pyro-phototronic, piezo-phototronic, and surface plasmonics.

Nanovaccines: An effective therapeutic approach for cancer therapy

Cancer vaccines hold considerable promise for the immunotherapy of solid tumors. Nanomedicine offers several strategies for enhancing vaccine effectiveness. In particular, molecular or (sub) cellular vaccines can be delivered to the target lymphoid tissues and cells by nanocarriers and nanoplatforms to increase the potency and durability of antitumor immunity and minimize negative side effects. Nanovaccines use nanoparticles (NPs) as carriers and/or adjuvants, offering the advantages of optimal nanoscale size, high stability, ample antigen loading, high immunogenicity, tunable antigen presentation, increased retention in lymph nodes, and immunity promotion. To induce antitumor immunity, cancer vaccines rely on tumor antigens, which are administered in the form of entire cells, peptides, nucleic acids, extracellular vesicles (EVs), or cell membrane-encapsulated NPs. Ideal cancer vaccines stimulate both humoral and cellular immunity while overcoming tumor-induced immune suppression. Herein, we review the key properties of nanovaccines for cancer immunotherapy and highlight the recent advances in their development based on the structure and composition of various (including synthetic and semi (biogenic) nanocarriers. Moreover, we discuss tumor cell-derived vaccines (including those based on whole-tumor-cell components, EVs, cell membrane-encapsulated NPs, and hybrid membrane-coated NPs), nanovaccine action mechanisms, and the challenges of immunocancer therapy and their translation to clinical applications.

Direct Z-Scheme Heterostructure of Vertically Oriented SnS2 Nanosheet on BiVO4 Nanoflower for Self-Powered Photodetectors and Water Splitting

The construction of nanostructured Z-scheme heterostructure is a powerful strategy for realizing high-performance photoelectrochemical (PEC) devices such as self-powered photodetectors and water splitting. Considering the band structure and internal electric field direction, BiVO4 is a promising candidate to construct SnS2 -based heterostructure. Herein, the direct Z-scheme heterostructure of vertically oriented SnS2 nanosheet on BiVO4 nanoflower is rationally fabricated for efficient self-powered PEC photodetectors. The Z-scheme heterostructure is identified by ultraviolet photoelectron spectroscopy, photoluminescence spectroscopy, PEC measurement, and water splitting. The SnS2 /BiVO4 heterostructure shows a superior photodetection performance such as excellent photoresponsivity (10.43 mA W-1 ), fast response time (6 ms), and long-term stability. Additionally, by virtue of efficient Z-scheme charge transfer and unique light-trapping nanostructure, the SnS2 /BiVO4 heterostructure also displays a remarkable photocatalytic hydrogen production rate of 54.3 µmol cm-2 h-1 in Na2 SO3 electrolyte. Furthermore, the synergistic effect between photo-activation and bias voltage further improves the PEC hydrogen production rate of 360 µmol cm-2 h-1 at 0.8 V, which is an order of magnitude above the BiVO4 . The results provide useful inspiration for designing direct Z-scheme heterostructures with special nanostructured morphology to signally promote the performance of PEC devices.

Self-Driven Gr/WSe2/Gr Photodetector with High Performance Based on Asymmetric Schottky van der Waals Contacts

Two-dimensional (2D) self-driven photodetectors have a wide range of applications in wearable, imaging, and flexible electronics. However, the preparation of most self-powered photodetectors is still complex and time-consuming. Simultaneously, the constant work function of a metal, numerous defects, and a large Schottky barrier at the 2D/metal interface hinder the transmission and collection of optical carriers, which will suppress the optical responsivity of the device. This paper proposed a self-driven graphene/WSe2/graphene (Gr/WSe2/Gr) photodetector with asymmetric Schottky van der Waals (vdWs) contacts. The vdWs contacts are formed by transferring Gr as electrodes using the dry-transfer method, obviating the limitations of defects and Fermi-level pinning at the interface of electrodes made by conventional metal deposition methods to a great extent and resulting in superior dynamic response, which leads to a more efficient and faster collection of photogenerated carriers. This work also demonstrates that the significant surface potential difference of Gr electrodes is a crucial factor to ensure their superior performance. The self-driven Gr/WSe2/Gr photodetector exhibits an ultrahigh Ilight/Idark ratio of 106 with a responsivity value of 20.31 mA/W and an open-circuit voltage of 0.37 V at zero bias. The photodetector also has ultrafast response speeds of 42.9 and 56.0 μs. This paper provides a feasible way to develop self-driven optoelectronic devices with a simple structure and excellent performance.

High performance self-powered photodetector based on van der Waals heterojunction

Self-powered photodetectors that do not require external power support are expected to play a key role in future photodetectors due to their low power characteristics, but achieving high responsivity remains a challenge. 2D van der Waals heterojunctions are a promising technology for high-performance self-powered photodetectors due to their excellent optical and electrical properties. Here, we fabricate a self-powered photodetector based on In2Se3/WSe2/ReS2van der Waals heterojunction self-powered photodetector. Due to the presence of ReS2layer, photocurrent is enhanced as a result of the increase in light absorption efficiency and the effective region for generating photogenerated carriers. The built-in electric field is enhanced by a negative 'back-gate voltage' along the p-n junction vertical direction generated by the electrons in the photo-generated electrons accumulation layer. Accordingly, the optical responsivity and the photoresponse speed of this heterojunction self-powered photodetector are greatly boosted. The proposed self-powered photodetector based on the In2Se3/WSe2/ReS2heterojunction exhibits a high responsivity of 438 mA W-1, which is 17 times higher compared to the In2Se3/WSe2photodetector, a self-powered current (1.1 nA) that is an order of magnitude higher than that of the In2Se3/WSe2photodetector, and a fast response time that is 250% faster. Thus the self-powered photodetector with a stronger built-in electric field and a wider depletion zone can provide a new technological support for the fabrication of high responsivity, low power consumption and high speed self-powered photodetectors based on van der Waals heterojunctions.

Negative Photoconductivity in 2D α-MoO3/Ir Self-Powered Photodetector: Impact of Post-Annealing

Surface plasmon technology is regarded as having significant potential for the enhancement of the performance of 2D oxide semiconductors, especially in terms of improving the light absorption of 2D MoO3 photodetectors. An ultrathin MoO3/Ir/SiO2/Si heterojunction Schottky self-powered photodetector is introduced here to showcase positive photoconductivity. In wafer-scale production, the initial un-annealed Mo/2 nm Ir/SiO2/Si sample displays a sheet carrier concentration of 5.76 × 1011/cm², which subsequently increases to 6.74 × 1012/cm² after annealing treatment, showing a negative photoconductivity behavior at a 0 V bias voltage. This suggests that annealing enhances the diffusion of Ir into the MoO3 layer, resulting in an increased phonon scattering probability and, consequently, an extension of the negative photoconductivity behavior. This underscores the significance of negative photoconductive devices in the realm of optoelectronic applications.

Self-Powered Wavelength-Dependent Dual-Polarity Response Photodetector Based on CdS@PEDOT:PSS@Au Sandwich-Structured Core-Shell Nanorod Arrays

Self-powered operation and multifunctionality have significantly oriented the development of photodetectors (PDs), which could be realized through nanoarchitecture construction and energy band structure design. Herein, a self-powered wavelength-dependent dual-polarity response PD based on (CdS@PEDOT:PSS@Au) sandwich-structured core-shell nanorod arrays (NRAs) is proposed. The synthesis approach of this three-layer heterostructure consists of a hydrothermal reaction, spin coating, and thermal evaporation. The n-CdS/p-PEDOT:PSS junction and the PEDOT:PSS/Au Schottky junction at the interfaces provide two photocurrent driving forces in opposite directions, and their contribution to the net photocurrent is controlled by the incident light wavelength due to the different light absorption ranges of the CdS core and the PEDOT:PSS shell. As a result, the polarity of the photocurrent switches from negative to positive as the wavelength increases. In addition, the response speed of negative photocurrents (∼10 ms) is faster than that of positive photocurrents (∼100 ms), which is consistent with the underlying mechanism of the dual-polarity response. Furthermore, color discrimination and imaging capabilities are demonstrated by deploying the PDs as sensing pixels and recognizing green and red patterns. The sandwich-structured core-shell NRA heterojunction system introduces a novel idea for dual-polarity response PDs.

Enhancing UV photodetection performance of an individual ZnO microwire p-n homojunction via interfacial engineering

As a typical broad bandgap semiconductor, ZnO has received considerable attention for developing optoelectronic devices in ultraviolet wavelengths, but suffers from a lack of high-quality single-crystalline p-type ZnO. Herein, we report the realization of a homojunction ultraviolet photodetector, which involves a p-type Sb-doped ZnO microwire (ZnO:Sb MW) and n-type ZnO layer. The p-type conductivity of the as-synthesized ZnO:Sb MWs was evidenced using an individual wire field-effect transistor. Due to its good rectifying ability and excellent photovoltaic effect, the constructed p-ZnO:Sb MW/n-ZnO homojunction is able to work as an ultraviolet photodetector in self-biased and reversely biased manners. By appropriately engineering the band alignment of the p-ZnO:Sb/n-ZnO homojunction via a MgO interface modification layer, the optimized photodetector exhibits performance-enhanced ultraviolet detection capabilities, such as the light on/off ratio reaching up to 1.6 × 10⁸, responsivity of over 267 mA W^-1 and specific detectivity of approximately 1.2 × 10¹⁴ Jones upon 365 nm light illumination at 0 V. The detector also produces faster response with rise/recovery times of 102 μs/3.6 ms. This study not only employed a novel method to synthesize genuine p-type ZnO with excellent stability and reproducibility, but also opened up substantial opportunities for developing high-performance ZnO homojunction optoelectronic devices.

Light-Induced Electric Field Enhanced Self-Powered Photodetector Based on Van der Waals Heterojunctions

Self-powered photodetectors have attracted widespread attention due to their low power consumption which can be driven by the built-in electric field instead of external power, but it is very difficult to achieve high responsivity and fast response speed concurrently. Here, a self-powered photodetector with light-induced electric field enhancement based on a 2D InSe/WSe₂ /SnS₂ van der Waals heterojunction is designed. The light-induced electric field derived from the photo-generated electrons of SnS₂ accumulated at the SnS₂ /WSe₂ interface produces an additional negative gate voltage applied to the WSe₂ layer, which enhances the built-in electric field in the InSe/WSe₂ /SnS₂ heterojunction. Accordingly, the photocurrent and photoresponse speed of the heterostructure device are largely improved. The self-powered photodetector based on the InSe/WSe₂ /SnS₂ heterostructure exhibits a high responsivity of 550 mA W^-1 , which is a 50 times increase compared to the InSe/WSe₂ photodetector, and the response speed (110/120 µs) is one order of magnitude faster than that of the InSe/WSe₂ photodetector. The high responsivity and fast speed are caused by the stronger built-in electric field modulated by a light-induced electric field, which can separate carriers effectively and reduce drift times. This device architecture can provide a new avenue to fabricate high-responsivity, fast self-power photodetectors by utilizing the van der Waals heterojunction.

A Review of Perovskite-Based Photodetectors and Their Applications

Perovskite photodetectors have attracted much research and attention because of their outstanding photoelectric characteristics, such as good light harvesting capability, excellent carrier migration behavior, tunable band gap, and so on. Recently, the reported studies mainly focus on materials synthesis, device structure design, interface engineering and physical mechanism analysis to improve the device characteristics, including stability, sensitivity, response speed, device noise, etc. This paper systematically summarizes the application fields and device structures of several perovskite photodetectors, including perovskite photoconductors, perovskite photodiodes, and perovskite phototransistors. Moreover, based on their molecular structure, 3D, 2D, 1D, and 0D perovskite photodetectors are introduced in detail. The research achievements and applications of perovskite photodetectors are summarized. Eventually, the future research directions and main challenges of perovskite photodetectors are prospected, and some possible solutions are proposed. The aim of the work is to provide a new thinking direction for further improving the performance of perovskite photodetectors.

Enhanced self-powered ion-modulated photodetector based on an asymmetric composite structure of superionic conductor RbAg4I5 and graphene

Traditional strategies for self-powered devices face limitations in performance improvement due to the trade-off relationship between different parameters. Here, a new kind of ion-modulation self-powered photodetector is first proposed and fabricated by depositing superionic conductor RbAg₄I₅ on one side of monolayer graphene. The graphene homojunction is successfully formed at the boundary of the asymmetric structure due to the formation of bound states of ions and electrons at the contact interface. This kind of homojunction avoids the trade off between response parameters of traditional self-powered devices because the dissociation of bound states under light irradiation dominates the generation of a photocurrent. The experimental results indicate that the prepared photodetector can achieve great photo response with responsivity of 20 mA/W and a response speed of 700 µs for ultraviolet and visible light when no bias is applied, which is better than most existing graphene-based self-powered devices in single or overall parameters. Further, a semi-quantitative model is systematically established according to the internal mechanism and realizes a good consistency with experimental results. The work provides a new idea and offers the foundation to develop excellent self-powered devices based on superionic materials with good properties in controllability and modulation.

Highly Sensitive Photoelectric Detection and Imaging Enhanced by the Pyro-Phototronic Effect Based on a Photoinduced Dynamic Schottky Effect in 4H-SiC

Silicon carbide (SiC), one of the third-generation semiconductor materials with excellent electrical and optoelectronic properties, is ideal for high light-sensing performance. Here, a self-powered SiC ultraviolet (UV) photodetector (PD) is constructed with wider applicability and higher commercialization potential. The great performance of the PD is realized by a remarkable photoinduced dynamic Schottky effect derived from the symbiotic modulation of Schottky and Ohmic contact. Using the pyro-phototronic effect that exists in the N-doped 4H-SiC single crystal PDs, a fast pyroelectric response time of 0.27 s is achieved, which is almost ten times shorter than that obtained from the steady-state signal under UV illumination. The maximal transient photoresponsivity reaches 9.12 nA mW^-1 , which is ≈20% higher than the conventional photoelectric signal. Moreover, different regions of the 4H-SiC centimeter-scale chip output distinct signals under UV illumination, demonstrating efficient optical imaging and information transmission capabilities of this device. This work not only reveals the fundamental optoelectronic physics lying in this vital third-generation semiconductor, but also sheds light on its potential photosensing applications for large-scale commercialization.

Significant performance enhancement of UV-Vis self-powered CsPbBr3 quantum dot-based photodetectors induced by ligand modification and P3HT embedding

In this work, we report a novel, to the best of our knowledge, strategy to improve the performance of UV-Vis self-powered CsPbBr₃ quantum dot (QD) based photodetectors (PDs) by ligand modification and poly(3-hexylthiophene) (P3HT) embedding. Compared with those based on pure QDs, modified PDs show a shortened response time by nearly ten times, and increases of maximum responsivity and specific detectivity by nearly 45 and 97 times, respectively. Such PDs also show a high stability with 90% of the initial photocurrent being maintained even after storage in ambient air without any encapsulation for 30 days.

Laser ablation fabrication of ap-NiO/n-Si heterojunction for broadband and self-powered UV-Visible-NIR photodetection

We report on the optoelectronic characteristics ofp-NiO/n-Si heterojunction photodiode for broadband photodetection, fabricated by depositing ap-type NiO thin film onto a commercialn-type silicon substrate using pulsed laser deposition (PLD) technique. The structural properties of the PLD-grownp-NiO material were analysed by means of x-ray diffraction and x-ray photoelectron spectroscopy, confirming its crystalline nature and revealing the presence of Ni vacancies, respectively. Hall measurements confirmed thep-type semiconducting nature of the NiO thin film having a carrier concentration of 8.4 × 10¹⁶cm^-3. The current-voltage (I-V) characteristics of thep-NiO/n-Si heterojunction photodevice were investigated under different wavelengths ranging from UV to NIR. The self-bias properties under different illuminations of light were also explored systematically. Under self-bias condition, the photodiode exhibits excellent responsivities of 12.5 mA W^-1, 24.6 mA W^-1and 30.8 mA W^-1with illumination under 365 nm, 485 nm, and 850 nm light, respectively. In addition, the time dependency of the photoresponse of the fabricated photodevice has also been investigated and discussed thoroughly.

Self-Powered Sb2S3 Thin-Film Photodetectors with High Detectivity for Weak Light Signal Detection

Photodetectors (PDs) for weak light signal detection have wide applications for optical communication and imaging. Antimony sulfide (Sb₂S₃) as a nontoxic and stable light-sensitive material becomes a promising candidate for weak light PDs, which are developing in the direction of high response, high speed, and low cost. Herein, a self-powered Sb₂S₃ PD with the structure of FTO/TiO₂/Sb₂S₃/Au is developed to achieve weak light detection for 300-750 nm visible light. We control the Sb₂S₃ thickness with about 460 nm to match depletion region width (438 nm) and obtain an excellent photoresponsivity and 3 dB bandwidth. Furtherly, we prepare pyramid structure polydimethylsiloxane (PDMS) on the illuminating surface to enhance the performance of weak light detection by light-trapping effects. The photocurrent of Sb₂S₃ PD with 20 μm-sized PDMS texture achieves 13.6% improvement compared with the control one. Under weak 530 nm light illumination of 1 μW cm^-2, the self-powered Sb₂S₃ PD with PDMS achieves high responsivity (3.41 A W^-1), large detectivity (2.84 × 10¹³ Jones), and ultrafast speed (15 μs). The present Sb₂S₃ PD and light-trapping strategy are expected to provide an alternative to future commercial weak light detection applications.

Advances in Self-Powered Ultraviolet Photodetectors Based on P-N Heterojunction Low-Dimensional Nanostructures

Self-powered ultraviolet (UV) photodetectors have attracted considerable attention in recent years because of their vast applications in the military and civil fields. Among them, self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures are a very attractive research field due to combining the advantages of low-dimensional semiconductor nanostructures (such as large specific surface area, excellent carrier transmission channel, and larger photoconductive gain) with the feature of working independently without an external power source. In this review, a selection of recent developments focused on improving the performance of self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures from different aspects are summarized. It is expected that more novel, dexterous, and intelligent photodetectors will be developed as soon as possible on the basis of these works.

High-performance unbiased Ge metal-semiconductor-metal photodetector covered with asymmetric HfSe2 contact geometries

A Ge metal-semiconductor-metal photodetector covered with asymmetric HfSe₂ contact geometries has been proposed to realize high-performance unbiased photodetection at 1550 nm. At -1 V bias, the responsivity of this device shows a 71% improvement compared to the device without HfSe₂. Moreover, the responsivity and detectivity of this device at zero bias can reach to 71.2 mA/W and 3.27×10¹⁰ Jones, respectively. Furthermore, the fall time of this device is 2.2 µs and 53% shorter than the device without HfSe₂. This work provides a feasible way to develop unbiased Ge-based photodetectors in the near-IR communications band.

Bioinspired Self-Powered Piezoresistive Sensors for Simultaneous Monitoring of Human Health and Outdoor UV Light Intensity

The exact fabrication of precise three-dimensional structures for piezoresistive sensors necessitates superior manufacturing methods or tooling, which are accompanied by time-consuming processes and the potential for environmental harm. Herein, we demonstrated a method for in situ synthesis of zinc oxide nanorod (ZnO NR) arrays on graphene-treated cotton and paper substrates and constructed highly sensitive, flexible, wearable, and chemically stable strain sensors. Based on the structure of pine trees and needles in nature, the hybrid sensing layer consisted of graphene-attached cotton or paper fibers and ZnO NRs, and the results showed a high sensitivity of 0.389, 0.095, and 0.029 kPa^-1 and an ultra-wide linear range of 0-100 kPa of this sensor under optimal conditions. Our study found that water absorption and swelling of graphene fibers and the associated reduction of pore size and growth of zinc oxide were detrimental to pressure sensor performance. A random line model was developed to examine the effects of different hydrothermal times on sensor performance. Meanwhile, pulse detection, respiration detection, speech recognition, and motion detection, including finger movements, walking, and throat movements, were used to show their practical application in human health activity monitoring. In addition, monolithically grown ZnO NRs on graphene cotton sheets had been integrated into a flexible sensing platform for outdoor UV photo-indication, which is, to our knowledge, the first successful case of an integrated UV photo-detector and motion sensor. Due to its excellent strain detection and UV detection abilities, these strategies are a step forward in developing wearable sensors that are cost-controllable and high-performance.

Design and Optimize the Performance of Self-Powered Photodetector Based on PbS/TiS3 Heterostructure by SCAPS-1D

Titanium trisulphide (TiS₃) has been widely used in the field of optoelectronics owing to its superb optical and electronic characteristics. In this work, a self-powered photodetector using bulk PbS/TiS₃ p-n heterojunction is numerically investigated and analyzed by a Solar Cell Capacitance Simulator in one-Dimension (SCAPS-1D) software. The energy bands, electron-holes generation or recombination rate, current density-voltage (J-V), and spectral response properties have been investigated by SCAPS-1D. To improve the performance of photodetectors, the influence of thickness, shallow acceptor or donor density, and defect density are investigated. By optimization, the optimal thickness of the TiS₃ layer and PbS layer are determined to be 2.5 μm and 700 nm, respectively. The density of the superior shallow acceptor (donor) is 10¹⁵ (10²²) cm⁻³. High quality TiS₃ film is required with the defect density of about 10¹⁴ cm⁻³. For the PbS layer, the maximum defect density is 10¹⁷ cm⁻³. As a result, the photodetector based on the heterojunction with optimal parameters exhibits a good photoresponse from 300 nm to 1300 nm. Under the air mass 1.5 global tilt (AM 1.5G) illuminations, the optimal short-circuit current reaches 35.57 mA/cm² and the open circuit voltage is about 870 mV. The responsivity (R) and a detectivity (D*) of the simulated photodetector are 0.36 A W⁻¹ and 3.9 × 10¹³ Jones, respectively. The simulation result provides a promising research direction to further broaden the TiS₃-based optoelectronic device.

CdS@CdSe Core/Shell Quantum Dots for Highly Improved Self-Powered Photodetection Performance

Uniform, well-defined cadmium sulfide@cadmium selenide core/shell quantum dots (CdS@CdSe QDs) were, for the first time, successfully synthesized by a solvothermal method and chemical bath growth for photoelectrochemical activities. The as-synthesized CdS@CdSe QDs not only exhibit superior self-powered photoresponse behavior and excellent stability under ambient conditions but also display significantly improved current densities and photoresponsivity compared to those of individual CdS QDs or CdSe QDs, mainly due to the built-in electric field, and thus have great potential in the fields of renewable energy and renewable energy consumption for carbon neutrality target achievement.

A transparent, self-powered photodetector based on p-CuI/n-TiO2heterojunction film with high on-off ratio

Ultraviolet(UV) photodetectors(PDs) can monitor UV radiation, enabling it to be effective for many applications, such as communication, imaging and sensing. The rapid progress on portable and wearable optoelectronic devices places a great demand on self-powered PDs. However, high-performance self-powered PDs are still limited. Herein we display a transparent and self-powered PD based on a p-CuI/n-TiO₂heterojunction, which exhibits a high on-off ratio (∼10⁴at 310 nm) and a fast response speed (rise time/decay time = 0.11 ms/0.72 ms) without bias. Moreover, the device shows an excellent UV-selective sensitivity as a solar-blind UV PD with a high UV/visible rejection ratio (R_{300 nm}/R_{400 nm}= 5.3 × 10²), which can be ascribed to the wide bandgaps of CuI and TiO₂. This work provides a feasible route for the construction of transparent, self-powered PDs based on p-n heterojunctions.

Self-Powered InP Nanowire Photodetector for Single-Photon Level Detection at Room Temperature

Highly sensitive photodetectors with single-photon level detection are one of the key components to a range of emerging technologies, in particular the ever-growing field of optical communication, remote sensing, and quantum computing. Currently, most of the single-photon detection technologies require external biasing at high voltages and/or cooling to low temperatures, posing great limitations for wider applications. Here, InP nanowire array photodetectors that can achieve single-photon level light detection at room temperature without an external bias are demonstrated. Top-down etched, heavily doped p-type InP nanowires and n-type aluminium-doped zinc oxide (AZO)/zinc oxide (ZnO) carrier-selective contact are used to form a radial p-n junction with a built-in electric field exceeding 3 × 10⁵  V cm^-1  at 0 V. The device exhibits broadband light sensitivity and can distinguish a single photon per pulse from the dark noise at 0 V, enabled by its design to realize near-ideal broadband absorption, extremely low dark current, and highly efficient charge carrier separation. Meanwhile, the bandwidth of the device reaches above 600 MHz with a timing jitter of 538 ps. The proposed device design provides a new pathway toward low-cost, high-sensitivity, self-powered photodetectors for numerous future applications.

Sensing of ultraviolet light: a transition from conventional to self-powered photodetector

Clouds in the sky pass almost 80% of ultraviolet (UV) radiation to the earth's surface, which has a significant impact on humankind. Conventional UV photodetectors (PDs) require an external battery, which not only increases the device size but also has a limited life span and maintenance costs can be prohibitively expensive. An alternative and more technically-sound solution would be the use of self-powered UV PDs that can operate independently, eliminating the need for an external source. Although many exciting studies have been done and state-of-the-art research is underway to successfully fabricate self-powered UV PDs, periodic reviews on this topic are deemed essential so that the technology's readiness can be properly evaluated and critical challenges can be addressed in a timely manner. In this article, the key issues and most exciting developments made in recent years on built-in electric field assisted self-powered UV PDs based on p-n homojunctions, p-n heterojunctions, and Schottky junctions followed by energy harvester integrated UV PDs are extensively reviewed. Finally, a summary and comparison of different types of self-powered UV PDs as well as future challenges that need to be addressed are discussed. This review sets a foundation providing essential insights into the present status of self-powered UV PDs with which researchers can engage and deal with the major challenges.

Quantum Tunneling Induced Optical Rectification and Plasmon-Enhanced Photocurrent in Nanocavity Molecular Junctions

Molecular junctions offer the opportunity for downscaling optoelectronic devices. Separating two electrodes with a single layer of molecules accesses the quantum-tunneling regime at low voltages (<1 V), where tunneling currents become highly sensitive to local nanometer-scale geometric features of the electrodes. These features generate asymmetries in the electrical response of the junction which combine with the incident oscillating optical fields to produce optical rectification and photocurrents. Maximizing photocurrents requires accurate control of the overall junction geometry and a large confined optical field in the optimal location. Plasmonic nanostructures such as metallic nanoparticles are prime candidates for this application, because their size and shape dictate a consistent junction geometry while strongly enhancing the optical field from incident light. Here we demonstrate a robust lithography-free molecular optoelectronic device geometry, where a metallic nanoparticle on a self-assembled molecular monolayer is sandwiched between planar bottom and semitransparent top electrodes, to create molecular junctions with reproducible morphology and electrical response. The well-defined geometry enables predictable and intense plasmonic localization, which we show creates optical-frequency voltages ∼ 30 mV in the molecular junction from 100 μW incident light, generating photocurrent by optical rectification (>10 μA/W) from only a few hundred molecules. Quantitative agreement is thus obtained between DC- and optical-frequency quantum-tunneling currents, predicted by a simple analytic equation. By measuring the degree of junction asymmetry for different molecular monolayers, we find that molecules with a large DC rectification ratio also boost zero-bias electrical asymmetry, making them good candidates for sensing and energy harvesting applications in combination with plasmonic nanomaterials.

High-Performance Multifunctional Photodetector and THz Modulator Based on Graphene/TiO2/p-Si Heterojunction

In this paper, we have reported a multifunctional device from graphene/TiO₂/p-Si heterojunction, followed by its systematical analysis of optical response in a device under ultraviolet-visible-infrared band and transmission changes of terahertz waves in the 0.3-1.0 THz band under different bias voltages. It is found that photodetector in the "back-to-back" p-n-p energy band structure has a seriously unbalanced distribution of photogenerated carriers in the vertical direction when light is irradiated from the graphene side. So this ensures a higher optical gain of the device in the form of up to 3.6 A/W responsivities and 4 × 10¹³ Jones detectability under 750 nm laser irradiation. Besides, the addition of TiO₂ layer in this terahertz modulator continuously widens the carrier depletion region under negative bias, thereby realizing modulation of the terahertz wave, making the modulation depth up to 23% under - 15 V bias. However, almost no change is observed in the transmission of terahertz wave when a positive bias is applied. A similar of an electronic semiconductor diode is observed that only allows the passage of terahertz wave for negative bias and blocks the positive ones.

Nanoscale characterization of an all-oxide core-shell nanorod heterojunction using intermodulation atomic force microscopy (AFM) methods

The electrical properties of an all-oxide core-shell ZnO-Co₃O₄ nanorod heterojunction were studied in the dark and under UV-vis illumination. The contact potential difference and current distribution maps were obtained utilizing new methods in dynamic multifrequency atomic force microscopy (AFM) such as electrostatic and conductive intermodulation AFM. Light irradiation modified the electrical properties of the nanorod heterojunction. The new techniques are able to follow the instantaneous local variation of the photocurrent, giving a two-dimensional (2D) map of the current-voltage curves and correlating the electrical and morphological features of the heterostructured core-shell nanorods.

Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors

Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of ∼2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects. Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices. Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes. Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors. In fact, the 2D morphology of the GaS flakes intrinsically minimizes the distance between the photogenerated charges and the surface area at which the redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious for standard solid-state configurations. Consequently, PEC-type 2D GaS photodetectors display a relevant UV-selective photoresponse. In particular, they attain responsivities of 1.8 mA W^-1 in 1 M H₂SO₄ [at 0.8 V vs reversible hydrogen electrode (RHE)], 4.6 mA W^-1 in 1 M Na₂SO₄ (at 0.9 V vs RHE), and 6.8 mA W^-1 in 1 M KOH (at 1.1. V vs RHE) under 275 nm illumination wavelength with an intensity of 1.3 mW cm^-2. Beyond the photodetector application, 2D GaS-based PEC-type devices may find application in tandem solar PEC cells in combination with other visible-sensitive low-band-gap materials, including transition-metal monochalcogenides recently established for PEC solar energy conversion applications.

MoS2/h-BN/Graphene Heterostructure and Plasmonic Effect for Self-Powering Photodetector: A Review

A photodetector converts optical signals to detectable electrical signals. Lately, self-powered photodetectors have been widely studied because of their advantages in device miniaturization and low power consumption, which make them preferable in various applications, especially those related to green technology and flexible electronics. Since self-powered photodetectors do not have an external power supply at zero bias, it is important to ensure that the built-in potential in the device produces a sufficiently thick depletion region that efficiently sweeps the carriers across the junction, resulting in detectable electrical signals even at very low-optical power signals. Therefore, two-dimensional (2D) materials are explored as an alternative to silicon-based active regions in the photodetector. In addition, plasmonic effects coupled with self-powered photodetectors will further enhance light absorption and scattering, which contribute to the improvement of the device's photocurrent generation. Hence, this review focuses on the employment of 2D materials such as graphene and molybdenum disulfide (MoS2) with the insertion of hexagonal boron nitride (h-BN) and plasmonic nanoparticles. All these approaches have shown performance improvement of photodetectors for self-powering applications. A comprehensive analysis encompassing 2D material characterization, theoretical and numerical modelling, device physics, fabrication and characterization of photodetectors with graphene/MoS2 and graphene/h-BN/MoS2 heterostructures with plasmonic effect is presented with potential leads to new research opportunities.

Self-powered broadband photodetector based on a solution-processed p-NiO/n-CdS:Al heterojunction

Solution-processed photodetectors have emerged as the next generation of sensing technology owing to their ease of integration with electron devices and of tuning photodetector performance. Currently, novel self-powered photodetectors without an external power source, for use in sensing, imaging and communication, are in high demand. Herein, we successfully developed a self-powered photodetector based on a novel solution-processed p-NiO/n-CdS:Al heterojunction, which shows an excellent current rectification characteristic ratio of up to three orders in the dark and distinctive photovoltaic behavior under light illumination. The complete solution synthesis route followed the development of CdS:Al thin films on ITO substrates by chemical bath deposition and NiO thin films by the sol-gel route. Optical absorption data revealed that NiO is more active in the UV region and CdS:Al has a majority of absorption in the visible region; so, upon light illumination, the effective separation of photogenerated carriers produces fast photodetection in the UV-visible region. The photoresponsivity values of the fabricated device were calculated to be 55 mA W^-1 and 30 mA W^-1 for UV and visible illumination, respectively. Also, the device has a fast rise and decay photoresponse speed at zero bias voltage, due to the self-driven photovoltaic effect which makes this heterojunction a self-powered device. This complete solution and new method of fabrication make it possible to combine different materials and flexible substrates, enhancing its potential applications in photodetectors, optoelectronic devices and sensors.

Pt/AlGaN Nanoarchitecture: Toward High Responsivity, Self-Powered Ultraviolet-Sensitive Photodetection

Energy-saving photodetectors are the key components in future photonic systems. Particularly, self-powered photoelectrochemical-type photodetectors (PEC-PDs), which depart completely from the classical solid-state junction device, have lately intrigued intensive interest to meet next-generation power-independent and environment-sensitive photodetection. Herein, we construct, for the first time, solar-blind PEC PDs based on self-assembled AlGaN nanostructures on silicon. Importantly, with the proper surface platinum (Pt) decoration, a significant boost of photon responsivity by more than an order of magnitude was achieved in the newly built Pt/AlGaN nanoarchitectures, demonstrating strikingly high responsivity of 45 mA/W and record fast response/recovery time of 47/20 ms without external power source. Such high solar-blind photodetection originates from the unparalleled material quality, fast interfacial kinetics, as well as high carrier separation efficiency which suggests that embracement of defect-free wide-bandgap semiconductor nanostructures with appropriate surface decoration offers an unprecedented opportunity for designing future energy-efficient and large-scale optoelectronic systems on a silicon platform.

Liquid-Phase Exfoliated GeSe Nanoflakes for Photoelectrochemical-Type Photodetectors and Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) systems represent powerful tools to convert electromagnetic radiation into chemical fuels and electricity. In this context, two-dimensional (2D) materials are attracting enormous interest as potential advanced photo(electro)catalysts and, recently, 2D group-IVA metal monochalcogenides have been theoretically predicted to be water splitting photocatalysts. In this work, we use density functional theory calculations to theoretically investigate the photocatalytic activity of single-/few-layer GeSe nanoflakes for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in pH conditions ranging from 0 to 14. Our simulations show that GeSe nanoflakes with different thickness can be mixed in the form of nanoporous films to act as nanoscale tandem systems, in which the flakes, depending on their thickness, can operate as HER- and/or OER photocatalysts. On the basis of theoretical predictions, we report the first experimental characterization of the photo(electro)catalytic activity of single-/few-layer GeSe flakes in different aqueous media, ranging from acidic to alkaline solutions: 0.5 M H2SO4 (pH 0.3), 1 M KCl (pH 6.5), and 1 M KOH (pH 14). The films of the GeSe nanoflakes are fabricated by spray coating GeSe nanoflakes dispersion in 2-propanol obtained through liquid-phase exfoliation of synthesized orthorhombic (Pnma) GeSe bulk crystals. The PEC properties of the GeSe nanoflakes are used to design PEC-type photodetectors, reaching a responsivity of up to 0.32 AW-1 (external quantum efficiency of 86.3%) under 455 nm excitation wavelength in acidic electrolyte. The obtained performances are superior to those of several self-powered and low-voltage solution-processed photodetectors, approaching that of self-powered commercial UV-Vis photodetectors. The obtained results inspire the use of 2D GeSe in proof-of-concept water photoelectrolysis cells.

Photovoltaic and flexible deep ultraviolet wavelength detector based on novel β-Ga2O3/muscovite heteroepitaxy

Flexible and self-powered deep ultraviolet (UV) photodetectors are pivotal for next-generation electronic skins to enrich human life quality. The fabrication of epitaxial β-Ga₂O₃ thin films is challenging on flexible substrates due to high-temperature growth requirements. Herein, β-Ga₂O₃ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\stackrel{-}{2}$$\end{document}2- 0 1) films are hetero-epitaxially grown on ultra-thin and environment-friendly muscovite mica which is the first time β-Ga₂O₃ epitaxy growth on any flexible substrate. Integration of Gallium oxide with muscovite enables high-temperature processing as well as excellent flexibility compared to polymer substrates. Additionally, the metal–semiconductor-metal (MSM) photodetector on β-Ga₂O₃ layer shows an ultra-low dark current of 800 fA at zero bias. The photovoltaic peak responsivity of 11.6 µA/W is obtained corresponding to very weak illumination of 75 μW/cm² of 265 nm wavelength. Thermally stimulated current (TSC) measurements are employed to investigate the optically active trap states. Among these traps, trap with an activation energy of 166 meV dominates the persistence photocurrent in the devices. Finally, photovoltaic detectors have shown excellent photocurrent stability under bending induced stress up to 0.32%. Hence, this novel heteroepitaxy opens the new way for flexible deep UV photodetectors.

Self-powered broadband photo-detection and persistent energy generation with junction-free strained Bi2Te3 thin films

We experimentally demonstrate efficient broadband self-powered photo-detection and power generation in thin films of polycrystalline bismuth telluride (Bi₂Te₃) semiconductors under inhomogeneous strain. The developed simple, junction-free, lightweight, and flexible photo-detectors are composed of a thin active layer and Ohmic contacts on a flexible plastic substrate, and can operate at room temperature and without application of an external bias voltage. We attribute the observed phenomena to the generation of an electric field due to a spontaneous polarization produced by strain gradient, which can separate both photo-generated and thermally-generated charge carriers in bulk of the semiconductor material, without a semiconductor junction. We show that the developed photo-detectors can generate electric power during both the daytime and the nighttime, by either harnessing solar and thermal radiation or by emitting thermal radiation into the cold sky. To the best of our knowledge, this is the first demonstration of the power generation in a simple junction-free device under negative illumination, which exhibits higher voltage than the previously used expensive commercial HgCdTe photo-diode. Significant improvements in the photo-detector performance are expected if the low-charge-mobility polycrystalline active layer is replaced with high-quality single-crystal material. The technology is not limited to Bi₂Te₃ as the active material, and offers many potential applications in night vision, wearable sensors, long-range LIDAR, and daytime/nighttime energy generation technologies.

Role of nanowire length on the performance of a self-driven NIR photodetector based on mono/bi-layer graphene (camphor)/Si-nanowire Schottky junction

In this article, we have demonstrated a solid carbon source such as camphor as a natural precursor to synthesize a large area mono/bi-layer graphene (MLG) sheet to fabricate a nanowire junction-based near infrared photodetectors (NIRPDs). In order to increase the surface-to-volume ratio, we have developed Si-nanowire arrays (SiNWAs) of varying lengths by etching planar Si. Then, the camphor-based MLG/Si and MLG/SiNWAs Schottky junction photodetectors have been fabricated to achieve an efficient response with self-driven properties in the near infrared (NIR) regime. Due to a balance between light absorption capability and surface recombination centers, devices having SiNWAs obtained by etching for 30 min shows a better photoresponse, sensitivity and detectivity. Fabricated NIRPDs can also be functioned as self-driven devices which are highly responsive and very stable at low optical power signals up to 2 V with a fast rise and decay time of 34/13 ms. A tremendous enhancement has been witnessed from 36 μA W^-1 to 22 mA W^-1 in the responsivity at 0 V for MLG/30 min SiNWAs than planar MLG/Si PDs indicating an important development of self-driven NIRPDs based on camphor-based MLG for future optoelectronic devices.

In Situ Conformal Coating of Polyaniline on GaN Microwires for Ultrafast, Self-Driven Heterojunction Ultraviolet Photodetectors

Independent and zero-maintenance systems would be in urgent need in the near future internet of things. Here, we present high-performance, self-driven organic/inorganic heterojunction ultraviolet (UV) photodetectors (PDs) by in situ polymerization of polyaniline (PANI) on Gallium nitride microwires. The GaN microwires with a high crystalline quality are grown on patterned Si substrates by metal organic chemical vapor deposition. Using a facile in situ chemical polymerization method, PANI is conformally coated on the surface of GaN microwires. The constructed GaN/PANI hybrid microwire PD exhibits a high responsivity of 178 mA/W, a remarkable detectivity of 4.67 × 10¹⁴ jones, and an ultrafast UV photoresponse speed (rise time of 0.2 ms and fall time of 0.3 ms) under zero bias. The intimate heterojunction in the form of N-Ga-N bonds between GaN and PANI may account for the observed high performances. The presented self-driven microwire UV PDs featuring ultrahigh-speed (sub-millisecond) response to UV light may find applications in future nano/micro-photosensor networks.

2D material broadband photodetectors

Our review provides a comprehensive overview of the latest evolution of broadband photodetectors (BBPDs) based on 2D materials (2DMs). We begin with BBPDs built on various 2DM channels, including narrow-bandgap 2DMs, 2D topological semimetals, 2D charge density wave compounds, and 2D heterojunctions. Then, we introduce defect-engineered 2DM BBPDs, including vacancy engineering, heteroatom incorporation, and interfacial engineering. Subsequently, we summarize 2DM based mixed-dimensional (0D-2D, 1D-2D, 2D-3D, and 0D-2D-3D) BBPDs. Finally, we provide several viewpoints for the future development of this burgeoning field.

Effect of Ag/rGO on the Optical Properties of Plasmon-Modified SnO2 Composite and Its Application in Self-Powered UV Photodetector

A facile hydrothermal method was employed to synthesize silver–reduced graphene oxide (Ag/rGO) plasmon-modified SnO2 composite, by incorporating Ag–reduced graphene oxide (Ag/rGO) into SnO2 nanorods as a photoanode for assembling a self-powered ultraviolet photodetector (UVPD). The as-synthesized samples were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and UV visible spectrophotometer. The as-prepared Ag/rGO films show enhanced light absorption attributed to the localized surface plasmon resonance (LSPR). The optimized 1.0 wt.% Ag/rGO incorporated into SnO2-based UVPD exhibits a significant photocurrent response due to the enhanced absorption light and effective suppression of charge recombination. This UVPD demonstrates a high performance, with photocurrent density reaching 0.29 mAcm−2 compared to the SnO2-based device with 0.16 mAcm−2. This device also exhibits a high on:off ratio of 195 and fast response time, which are superior to that of the free-modified one. In addition, the UVPD based on plasmon-modified SnO2 photoanode treated with TiCl4-aqueous solution has attained a higher photocurrent with a maximum value reaching 5.4 mAcm−2, making this device favorable in ultraviolet detection.