Improved Photoresponse Performance of Self-Powered ZnO/Spiro-MeOTAD Heterojunction Ultraviolet Photodetector by Piezo-Phototronic Effect

Optimizing Photoelectrochemical UV Imaging Photodetection: Construction of Anatase/Rutile Heterophase Homojunctions and Oxygen Vacancies Engineering in MOF-Derived TiO2

Self-powered photoelectrochemical (PEC) ultraviolet photodetectors (UVPDs) are promising for next-generation energy-saving and highly integrated optoelectronic systems. Constructing a heterojunction is an effective strategy to increase the photodetection performance of PEC UVPDs because it can promote the separation and transfer of photogenerated carriers. However, both crystal defects and lattice mismatch lead to deteriorated device performance. Here, we introduce a structural regulation strategy to prepare TiO2 anatase-rutile heterophase homojunctions (A-R HHs) with oxygen vacancies (OVs) photoanodes through an in situ topological transformation of titanium metal-organic framework (Ti-MOF) by pyrolysis treatment. The cooperative interaction between A-R HHs and OVs suppresses carrier recombination and accelerates carrier transport, thereby significantly enhancing the photodetection performance of PEC UVPDs. The obtained device realizes a high on/off ratio of 10,752, a remarkable responsivity of 24.15 mA W-1, an impressive detectivity of 3.28 × 1011 Jones, and excellent cycling stability. More importantly, under 365 nm light illumination, a high-resolution image of "HUST" (the abbreviation of Harbin University of Science and Technology) was obtained perfectly, confirming the excellent optical imaging capability of the device. This research not only presents an advanced methodology for constructing TiO2-based PEC UVPDs, but also provides strategic guidance for enhancing their performance and practical applications.

All-Oxide Transparent Photodetector Array for Ultrafast Response through Self-Powered Excitonic Photovoltage Operation

Can photodetectors be transparent and operate in self-powered mode? Is it possible to achieve invisible electronics, independent of the external power supply system, for on-site applications? Here, a ZnO/NiO heterojunction-based high-functional transparent ultraviolet (UV) photodetector operating in the self-powered photovoltaic mode with outstanding responsivity and detectivity values of 6.9 A W-1 and 8.0 × 1012 Jones, respectively, is reported. The highest IUV /Idark value of 8.9 × 104 is attained at a wavelength of 385 nm, together with a very small dark current value of 9.15 × 10-12 A. A large-scale sputtering method is adopted to deposit the heterostructure of n-ZnO and p-NiO sequentially. This deposition instinctively forms an abrupt junction, resulting in a high-quality heterojunction device. Moreover, developing a ZnO/NiO-heterojunction-based 4 × 5 matrix array with an output photovoltage of 4.5 V is preferred for integrating photodetectors into sensing and imaging systems. This transparent UV photodetector exhibits the fastest photo-response time (83 ns) reported for array configurations, which is achieved using an exciton-induced photovoltage based on a neutral donor-bound exciton. Overall, this study provides a simple method for achieving a high-performance large-scale transparent UV photodetector with a self-powered array configuration.

Research advances in ZnO nanomaterials-based UV photode tectors: a review

Ultraviolet photodetectors (UV PDs) have always been the research focus of semiconductor optoelectronic devices due to their wide application fields and diverse compositions. As one of the best-known n-type metal oxides in third-generation semiconductor electronic devices, ZnO nanostructures and their assembly with other materials have received extensive research. In this paper, the research progress of different types of ZnO UV PDs is reviewed, and the effects of different nanostructures on ZnO UV PDs are summarized in detail. In addition, physical effects such as piezoelectric photoelectric effect, pyroelectric effect, and three ways of heterojunction, noble metal local surface plasmon resonance enhancement and formation of ternary metal oxides on the performance of ZnO UV PDs were also investigated. The applications of these PDs in UV sensing, wearable devices, and optical communication are displayed. Finally, the possible opportunities and challenges for the future development of ZnO UV PDs are prospected.

Fundamentals and Applications of ZnO-Nanowire-Based Piezotronics and Piezo-Phototronics

The piezotronic effect is a coupling effect of semiconductor and piezoelectric properties. The piezoelectric potential is used to adjust the p-n junction barrier width and Schottky barrier height to control carrier transportation. At present, it has been applied in the fields of sensors, human-machine interaction, and active flexible electronic devices. The piezo-phototronic effect is a three-field coupling effect of semiconductor, photoexcitation, and piezoelectric properties. The piezoelectric potential generated by the applied strain in the piezoelectric semiconductor controls the generation, transport, separation, and recombination of carriers at the metal-semiconductor contact or p-n junction interface, thereby improving optoelectronic devices performance, such as photodetectors, solar cells, and light-emitting diodes (LED). Since then, the piezotronics and piezo-phototronic effects have attracted vast research interest due to their ability to remarkably enhance the performance of electronic and optoelectronic devices. Meanwhile, ZnO has become an ideal material for studying the piezotronic and piezo-phototronic effects due to its simple preparation process and better biocompatibility. In this review, first, the preparation methods and structural characteristics of ZnO nanowires (NWs) with different doping types were summarized. Then, the theoretical basis of the piezotronic effect and its application in the fields of sensors, biochemistry, energy harvesting, and logic operations (based on piezoelectric transistors) were reviewed. Next, the piezo-phototronic effect in the performance of photodetectors, solar cells, and LEDs was also summarized and analyzed. In addition, modulation of the piezotronic and piezo-phototronic effects was compared and summarized for different materials, structural designs, performance characteristics, and working mechanisms' analysis. This comprehensive review provides fundamental theoretical and applied guidance for future research directions in piezotronics and piezo-phototronics for optoelectronic devices and energy harvesting.

Piezo-phototronic effect on photocatalysis, solar cells, photodetectors and light-emitting diodes

The piezo-phototronic effect (a coupling effect of piezoelectric, photoexcitation and semiconducting properties, coined in 2010) has been demonstrated to be an ingenious and robust strategy to manipulate optoelectronic processes by tuning the energy band structure and photoinduced carrier behavior. The piezo-phototronic effect exhibits great potential in improving the quantum yield efficiencies of optoelectronic materials and devices and thus could help increase the energy conversion efficiency, thus alleviating the energy shortage crisis. In this review, the fundamental principles and challenges of representative optoelectronic materials and devices are presented, including photocatalysts (converting solar energy into chemical energy), solar cells (generating electricity directly under light illumination), photodetectors (converting light into electrical signals) and light-emitting diodes (LEDs, converting electric current into emitted light signals). Importantly, the mechanisms of how the piezo-phototronic effect controls the optoelectronic processes and the recent progress and applications in the above-mentioned materials and devices are highlighted and summarized. Only photocatalysts, solar cells, photodetectors, and LEDs that display piezo-phototronic behavior are reviewed. Material and structural design, property characterization, theoretical simulation calculations, and mechanism analysis are then examined as strategies to further enhance the quantum yield efficiency of optoelectronic devices via the piezo-phototronic effect. This comprehensive overview will guide future fundamental and applied studies that capitalize on the piezo-phototronic effect for energy conversion and storage.

Novel Self-Powered Photodetector with Binary Photoswitching Based on SnSx/TiO2 Heterojunctions

Binary photoresponse characteristics can help realize optical signal processing and logic operations. UV photodetectors (PDs) with SnS_x nanoflakes and TiO₂ nanorod arrays (NRs) show a novel binary photoswitching behavior (change in current from positive to negative) by manipulating the light wavelength without an external power source, utilizing the interfacial recombination of the photogenerated carriers in the type-I SnS_x/TiO₂ heterojunctions. The enhanced responsivity (R*), detectivity (D^*), and fast photoresponse time for self-powered SnS_x/TiO₂PDs can be achieved by adjusting the phase ratio of SnS and SnS₂ nanoflakes. The binary photoswitching in the self-powered UV PDs can be applied in the encrypted optical signal processing and imaging in some special conditions without external bias.

Self-Powered, Self-Healed, and Shape-Adaptive Ultraviolet Photodetectors

The emergence of self-healing devices in recent years has drawn a great amount of attention in both academics and industry. Self-healed devices can autonomically restore a rupture as unexpected destruction occurs, which can efficiently prolong the life span of the devices; hence, they have an enhanced durability and decreased replacement cost. As a result, integration of wearable devices with self-healed electronics has become an indispensable issue in smart wearable devices. In this study, we present the first self-powered, self-healed, and wearable ultraviolet (UV) photodetector based on the integration of agarose/poly(vinyl alcohol) (PVA) double network (DN) hydrogels, which have the advantages of good mechanical strength, self-healing ability, and tolerability of multiple types of damage. With the integration of a DN hydrogel substrate, the photodetector enables 90% of the initial efficiency to be restored after five healing cycles, and each rapid healing time is suppressed to only 10 s. The proposed device has several merits, including having an all spray coating, self-sustainability, biocompatibility, good sensitivity, mechanical flexibility, and an outstanding healing ability, which are all essential to build smart electronic systems. The unprecedented self-healed photodetector expands the future scope of electronic skin design, and it also offers a new platform for the development of next-generation wearable electronics.

Surface/Interface Engineering for Constructing Advanced Nanostructured Photodetectors with Improved Performance: A Brief Review

Semiconductor-based photodetectors (PDs) convert light signals into electrical signals via a photon–matter interaction process, which involves surface/interface carrier generation, separation, and transportation of the photo-induced charge media in the active media, as well as the extraction of these charge carriers to external circuits of the constructed nanostructured photodetector devices. Because of the specific electronic and optoelectronic properties in the low-dimensional devices built with nanomaterial, surface/interface engineering is broadly studied with widespread research on constructing advanced devices with excellent performance. However, there still exist some challenges for the researchers to explore corresponding mechanisms in depth, and the detection sensitivity, response speed, spectral selectivity, signal-to-noise ratio, and stability are much more important factors to judge the performance of PDs. Hence, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge-carrier behaviors and improve the photoelectric performance of related PDs. Here, in this brief review, we would like to introduce and summarize the latest research on enhancing the photoelectric performance of PDs based on the designed structures by considering their surface/interface engineering and how to obtain advanced nanostructured photo-detectors with improved performance, which could be applied to design and fabricate novel low-dimensional PDs with ideal properties in the near future.

Zinc oxide ultraviolet photodetectors: rapid progress from conventional to self-powered photodetectors

Currently, the development of ultraviolet (UV) photodetectors (PDs) has attracted the attention of the research community because of the vast range of applications of photodetectors in modern society. A variety of wide-band gap nanomaterials have been utilized for UV detection to achieve higher photosensitivity. Specifically, zinc oxide (ZnO) nanomaterials have attracted significant attention primarily due to their additional properties such as piezo-phototronic and pyro-phototronic effects, which allow the fabrication of high-performance and low power consumption-based UV PDs. This article primarily focuses on the recent development of ZnO nanostructure-based UV PDs ranging from nanomaterials to architectural device design. A brief overview of the photoresponse characteristics of UV PDs and potential ZnO nanostructures is presented. Moreover, the recent development in self-powered PDs and implementation of the piezo-phototronic effect, plasmonic effect and pyro-phototronic effect for performance enhancement is highlighted. Finally, the research perspectives and future research direction related to ZnO nanostructures for next-generation UV PDs are summarized.

Bias-Controlled Tunable Electronic Transport with Memory Characteristics in an Individual ZnO Nanowire for Realization of a Self-Driven UV Photodetector with Two Symmetrical Electrodes

ZnO nanostructures are exceedingly important building blocks for nanodevices due to their wide band gap and large exciton binding energy. However, their electronic transport characteristics are unstable and unrepeatable with external environment variation. Here, we demonstrate that electron transport of an individual ZnO nanowire-based device with the two same electrodes can be controllably modulated by applying a relatively large uni-/bidirectional bias. After being modulated, moreover, their electrical properties can well be maintained at relatively low operation bias and room temperature, demonstrating a memory behavior. The presence of surface states related to lattice periodicity breaking and traps associated with oxygen vacancy (V_o) and zinc interstitial (Zn_i) deep-level defects plays a crucial role in tunable electron transport with a memory feature. For the single nanowire-based two-terminal device, two back-to-back connected surface barrier diodes with series resistance are formed. The filling and emptying of traps near two end electrodes can remarkably adjust the width and height of the surface barrier. At a relatively low bias, the unmodulated conductance is governed by the electron hopping of bulk traps since the height of emptied traps is higher than that of the surface barrier, whereas at a relatively large bias, it is dominated by thermion emission due to a dramatic decrease of the surface barrier width resulting from the electron injection into traps from a negative electrode. Moreover, it will be beneficial for a thin surface barrier to penetrate UV light and separate photoexcited electron-hole pairs. After being asymmetrically modulated by a unidirectional injection, it can be successfully applied to realize a self-driven UV photodetector based on a photovoltaic effect in the symmetrical two-electrode structure. Our work provides a new route to tune electrical properties of nanostructures, which may inspire the development of novel electronic and optoelectronic devices.

Toward facile broadband photodetectors based on self-assembled ZnO nanobridge/rubrene heterointerface

ZnO nanowire photodetectors have attracted much attention due to their excellent optoelectronic performance. However, operating speed remains a challenge, and scalability is also impeded by uncontrolled transfer methods and sophisticated fabrication process. In this paper, we have fabricated an excellent ZnO nanobridge ultraviolet photodetector array by using a simple one-step method. The faster photoresponse speed and a broader response wavelength (from UV to visible range) have been achieved by constructing a type-II ZnO/rubrene heterointerface. Performance enhancement is believed to arise from the well-matching band alignment and highly efficient separation of photogenerated electron-hole pairs at the heterointerface. Our strategy provides a simple and promising route to develop cost-effective and highly sensitive UV-vis photodetectors.

Piezophototronic Effect Modulated Multilevel Current Amplification from Highly Transparent and Flexible Device Based on Zinc Oxide Thin Film

In this work, a strain modulated highly transparent and flexible ZnO/Ag-nanowires/polyethylene terephthalate optoelectronic device is developed. By utilizing the applied external strain-induced piezophototronic effects of a ZnO thin film, a UV-generated photocurrent is tuned in a wide range starting from 0.01 to 85.07 µA and it is presented in a comprehensive map. Particularly, the performance of the device is effectively enhanced 7733 times by compressive strain, as compared to its dark current in a strain-free state. The observed results are explained quantitatively based on the modulation of oxygen desorption/absorption on the ZnO surface under the influence of applied strains. The presented simple optoelectronic device can be easily integrated into existing planar structures, with potential applications in highly transparent smart windows, wearable electronics, smartphones, security communication, and so on.

Piezo-phototronic mediated enhanced photodetection characteristics of plasmonic Au-g-C3N4/CdS/ZnO based hybrid heterojunctions on a flexible platform

We have studied the piezo-phototronic induced enhancement in the photo-response of CdS/ZnO heterojunctions attached with plasmonic Au nanoparticle loaded 2D-graphitic carbon nitride (g-C3N4). The hybrid g-C3N4/CdS/ZnO heterojunction favours the charge carrier separation through the formation of a step-like band alignment. Furthermore, the integration of plasmonic Au loaded g-C3N4 nanosheets on the conventional CdS/ZnO heterojunction facilitates improved visible light absorption properties. The heterojunction device on a flexible platform under the application of a strain (∼0.017%) exhibits ∼102 times higher photoresponse over the control sample at a constant bias of ∼2 V. The variation in the photo-response under different bending conditions has been explained in terms of the improved charge transport through the modified energy bands at the interface of ZnO. The improved piezo-phototronic properties originated from the plasmonic properties of Au loaded g-C3N4 and the piezoelectric characteristics of c-axis oriented ZnO films may be used for future flexible photonic devices.

Enhanced photoresponse of a high-performance self-powered UV photodetector based on ZnO nanorods and a novel electrolyte by the piezo-phototronic effect

A flexible self-powered ultraviolet (UV) photodetector based on ZnO nanorods (NRs) and a novel iodine-free quasi solid-state electrolyte was fabricated. The obtained device has a fast and high response to UV light illumination at zero bias and also shows long-term stability. The responsivity is 50.5 mA W⁻¹ and the response time is less than 0.2 s. Strain-induced piezo-phototronic potential within wurtzite-structured ZnO can optimize the performance of corresponding optoelectronic devices since it could effectively tune the charge carriers' separation and transport. The photoresponse performances of the photodetector under different upward angles (tensile strain) and downward angles (compressive strain) at 0 V bias were studied in detail. A 163% change of responsivity was obtained when the downward angle reached 60°. The enhancement could be interpreted by the piezo-phototronic effect. The piezoelectric potential (piezopotential) at the ZnO NRs/electrolyte interface can expand the built-in field, and as a result, it is easier for charge carriers to separate and transport.

A flexible UV detector exhibits high performance. The photoresponse of the device under different upward angles (tensile strain) and downward angles (compressive strain) were studied. A 163% change in responsivity was obtained when the downward angle reached 60°.

High-Performance Graphene/β-Ga2O3 Heterojunction Deep-Ultraviolet Photodetector with Hot-Electron Excited Carrier Multiplication

Solar-blind ultraviolet (SBUV) detection has important applications in wireless secure communication, early warning, and so forth. However, the desired key device for SBUV detection and high-sensitivity and low-noise "sandwich" photodetector with large detective area is difficult to be fabricated because it is usually hard for traditional wide band gap semiconductors to boast both high conductivity and high SBUV transparency. Here, we proposed to use graphene as the transparent conductive layer to form graphene/β-Ga₂O₃ heterojunction. With the help of large-area graphene and hot carrier multiplication, a SBUV photodetector with large detective area, low dark current, and high sensitivity was successfully assembled. Its photoresponsivity is 1-3 orders of magnitude higher than that of the conventional SBUV photodetectors, and its response speed can rival the best device ever reported.

Self-Powered Photodetector Based on Electric-Field-Induced Effects in MAPbI3 Perovskite with Improved Stability

A monolith photodetector is presented that utilizes the material properties of MAPbI₃ perovskite for self-powered operation and achieves improved stability by composting with polystyrene. The self-powered operation makes this device suitable for remote applications and in smart systems. Improved stability of more than 20 days, with performance maintained by over 80% under ambient conditions, is achieved by incorporating polystyrene without additional fabrication steps. A plain MAPbI₃ device in comparison shows a performance degradation of 70-85% within 4 days of operation. The incorporation of polystyrene also improves the current detectivity of the device by over 70 times compared to plain perovskite.

Ultrahigh-Performance Self-Powered Flexible Double-Twisted Fibrous Broadband Perovskite Photodetector

Self-powered flexible photodetectors without an external power source can meet the demands of next-generation portable and wearable nanodevices; however, the performance is far from satisfactory becuase of the limited match of flexible substrates and light-sensitive materials with proper energy levels. Herein, a novel self-powered flexible fiber-shaped photodetector based on double-twisted perovskite-TiO₂ -carbon fiber and CuO-Cu₂ O-Cu wire is designed and fabricated. The device shows an ultrahigh detectivity of 2.15 × 10¹³ Jones under the illumination of 800 nm light at zero bias. CuO-Cu₂ O electron block bilayer extends response range of perovskite from 850 to 1050 nm and suppresses dark current down to 10^-11 A. The fast response speed of less than 200 ms is nearly invariable after dozens of cycles of bending at the extremely 90 bending angle, demonstrating excellent flexibility and bending stability. These parameters are comparable and even better than reported flexible and even rigid photodetectors. The present results suggest a promising strategy to design photodetectors with integrated function of self-power, flexibility, and broadband response.

Self-Powered Nanoscale Photodetectors

Novel self-powered nanoscale photodetectors that can work without an external power source, which have great application potential in next-generation nanodevices that operate wirelessly and independently, are being widely studied. This review aims to give a comprehensive summary of the state-of-the-art research results on self-powered nanoscale photodetectors. An introduction of recent progress on Schottky junction photodetectors is provided. Two types of Schottky junctions are discussed in detail: metal-semiconductor and semiconductor-graphene junctions. Next, recent developments of p-n junction photodetectors are highlighted, including homojunction and heterojunction photodetectors. Then, piezo-phototronic effect enhanced photodetection performances of Schottky junctions and p-n junctions are discussed. Then, significant results on the photoelectrochemical-cell-based photodetector and integrated self-powered nanosystem are presented, followed by a systematic comparison of different types of photodetectors. Finally, a summary of the previous results is given, and the major challenges that need to be addressed in the future are outlined. The hope is that this review can provide valuable insights into the current status of self-powered photodetectors and spur new structure and device designs to further enhance photodetection performance.

Flexible Photodetectors Based on Novel Functional Materials

Flexible photodetectors have attracted a great deal of research interest in recent years due to their great possibilities for application in a variety of emerging areas such as flexible, stretchable, implantable, portable, wearable and printed electronics and optoelectronics. Novel functional materials, including materials with zero-dimensional (0D) and one-dimensional (1D) inorganic nanostructures, two-dimensional (2D) layered materials, organic semiconductors and perovskite materials, exhibit appealing electrical and optoelectrical properties, as well as outstanding mechanical flexibility, and have been widely studied as building blocks in cost-effective flexible photodetection. Here, we comprehensively review the outstanding performance of flexible photodetectors made from these novel functional materials reported in recent years. The photoresponse characteristics and flexibility of the devices will be discussed systematically. Summaries and challenges are provided to guide future directions of this vital research field.

Visible-Blind UV Photodetector Based on Single-Walled Carbon Nanotube Thin Film/ZnO Vertical Heterostructures

Ultraviolet (UV) photodetectors based on heterojunctions of conventional (Ge, Si, and GaAs) and wide bandgap semiconductors have been recently demonstrated, but achieving high UV sensitivity and visible-blind photodetection still remains a challenge. Here, we utilized a semitransparent film of p-type semiconducting single-walled carbon nanotubes (SC-SWNTs) with an energy gap of 0.68 ± 0.07 eV in combination with a molecular beam epitaxy grown n-ZnO layer to build a vertical p-SC-SWNT/n-ZnO heterojunction-based UV photodetector. The resulting device shows a current rectification ratio of 10³, a current photoresponsivity up to 400 A/W in the UV spectral range from 370 to 230 nm, and a low dark current. The detector is practically visible-blind with the UV-to-visible photoresponsivity ratio of 10⁵ due to extremely short photocarrier lifetimes in the one-dimensional SWNTs because of strong electron-phonon interactions leading to exciton formation. In this vertical configuration, UV radiation penetrates the top semitransparent SC-SWNT layer with low losses (10-20%) and excites photocarriers within the n-ZnO layer in close proximity to the p-SC-SWNT/n-ZnO interface, where electron-hole pairs are efficiently separated by a high built-in electric field associated with the heterojunction.

Surface photo-charge effect in doped-ZnO nanorods for high-performance self-powered ultraviolet photodetectors

The unique photo-charge characteristics of chlorine-doped zinc oxide nanorods (Cl-ZnO NRs) are explored for the first time in ultraviolet (UV) photodetector (PD) that offers an outstanding self-powered photoresponse towards low UV illumination signals. A self-powered Cl-ZnO NRs PD exhibits superior photon detection speed of the order of a few ms with high sensitivity and photoelasticity. Therefore, the presented PD opens up a novel route to fabricate highly efficient self-powered PDs on a large scale without employing complex multilayer systems.

Three-dimensional nano-heterojunction networks: a highly performing structure for fast visible-blind UV photodetectors

Visible-blind ultraviolet photodetectors are a promising emerging technology for the development of wide bandgap optoelectronic devices with greatly reduced power consumption and size requirements. A standing challenge is to improve the slow response time of these nanostructured devices. Here, we present a three-dimensional nanoscale heterojunction architecture for fast-responsive visible-blind UV photodetectors. The device layout consists of p-type NiO clusters densely packed on the surface of an ultraporous network of electron-depleted n-type ZnO nanoparticles. This 3D structure can detect very low UV light densities while operating with a near-zero power consumption of ca. 4 × 10^-11 watts and a low bias of 0.2 mV. Most notably, heterojunction formation decreases the device rise and decay times by 26 and 20 times, respectively. These drastic enhancements in photoresponse dynamics are attributed to the stronger surface band bending and improved electron-hole separation of the nanoscale NiO/ZnO interface. These findings demonstrate a superior structural design and a simple, low-cost CMOS-compatible process for the engineering of high-performance wearable photodetectors.

Low-Voltage High-Performance UV Photodetectors: An Interplay between Grain Boundaries and Debye Length

Accurate detection of UV light by wearable low-power devices has many important applications including environmental monitoring, space to space communication, and defense. Here, we report the structural engineering of ultraporous ZnO nanoparticle networks for fabrication of very low-voltage high-performance UV photodetectors. A record high photo- to dark-current ratio of 3.3 × 10⁵ and detectivity of 3.2 × 10¹² Jones at an ultralow operation bias of 2 mV and low UV-light intensity of 86 μW·cm^-2 are achieved by controlling the interplay between grain boundaries and surface depletion depth of ZnO nanoscale semiconductors. An optimal window of structural properties is determined by varying the particle size of ultraporous nanoparticle networks from 10 to 42 nm. We find that small electron-depleted nanoparticles (≤40 nm) are necessary to minimize the dark-current; however, the rise in photocurrent is tampered with decreasing particle size due to the increasing density of grain boundaries. These findings reveal that nanoparticles with a size close to twice their Debye length are required for high photo- to dark-current ratio and detectivity, while further decreasing their size decreases the photodetector performance.

High-performance of self-powered UV photodetector with long-term stability based on ZnO nanorods and an iodine-free quasi solid-state electrolyte

Self-powered UV photodetector based on ZnO nanorods and an iodine-free quasi solid-state electrolyte exhibits high photoresponse and great stability.

Phenomenal Ultraviolet Photoresponsivity and Detectivity of Graphene Dots Immobilized on Zinc Oxide Nanorods

A combination of dimensionally reduced graphene quantum dots (GQDs) having edge effects and the vertically aligned ZnO nanorods shows highly selective visible-blind ultraviolet (UV) sensing. The GQD immobilized ZnO nanorod heterostructure shows remarkable responsivity of ∼6.62 × 10⁴ A/W and detectivity of ∼1.78 × 10¹⁵ Jones under 365 nm (10 μW) incident light and 2 V bias potential with high stability of at least 5 cycles, fast response time of 2.14 s, and recovery time of 0.91 s. The grain boundary assisted electron transport across GQDs was calculated from the normalized absorption below bandgap. The highest UV responsivity and detectivity were found to be proportional to the lowest trap state density at the grain boundaries (Q_t) and minimum grain boundary potential (E_b). For the best GQD, Q_t and E_b were found to be ∼4 × 10¹³ cm^-2 and 0.4 meV, respectively. The phenomenal performance of ZnO-GQD heterostructure is attributed to the efficient immobilization of GQDs on ZnO nanorods and the idea of employing GQDs as photosensitizers than solely as electron transporting medium. The efficiency of GQDs is superior to carbon quantum dots (CQDs) containing minimal graphitic domains, and graphene oxide (GO) or reduced graphene oxide (rGO) having larger dimensions preventing their immobilization on ZnO nanorods.

Interface Engineering To Boost Photoresponse Performance of Self-Powered, Broad-Bandwidth PEDOT:PSS/Si Heterojunction Photodetector

Organic-inorganic hybrid heterojunctions are poised to push toward novel optoelectronics applications, such as photodetectors, but significant challenges complicating practical use remain. Although all organic based photodetectors have been reported with great success, their potential in high-speed, broadband, self-powered photodetectors have not been fully explored. Herein, a self-powered, broad bandwidth of photodetector based on

PEDOT

PSS/Si heterojunction is built by a facial low temperature spin-coating method. By interface engineering of heterojunction with optimal band alignment and heteromicrostructures, enhanced photoresponse performances are obtained. The bandwidth of the hybrid photodetector could be broadened by 10 kHz after interfacial passivation by a methyl group. Further manipulating the geometrical structure of the hybrid heterojunction with silicon nanowire, a broad spectrum response from 300 to 1100 nm, with bandwidth as high as 40.6 kHz, fast response speed of 2.03 μs and high detection of 4.1 × 10(11) Jones under zero bias was achieved. Meanwhile, the close dependence between the photoresponse performance of heterojunctions and Si nanowire length is observed in the top-coverage configuration. Finally, a coverage effects model is proposed based on the competition of Si bulk and surface recombination, which is also confirmed by the designed bottom-coverage experiment. The mechanisms behind the enhanced photoresponse of the hybrid photodetector is attributed to the optimum band alignment, as well as the optimum balance of carrier dissociation and recombination of heterojunction. The scalable and low temperature method would be of great convenience for large-scale fabrication of the

PEDOT

PSS/Si hybrid photodetector.