Highly Efficient and Ultrasensitive Large-Area Flexible Photodetector Based on Perovskite Nanowires

Exploring Nanoscale Perovskite Materials for Next-Generation Photodetectors: A Comprehensive Review and Future Directions

The rapid advancement of nanotechnology has sparked much interest in applying nanoscale perovskite materials for photodetection applications. These materials are promising candidates for next-generation photodetectors (PDs) due to their unique optoelectronic properties and flexible synthesis routes. This review explores the approaches used in the development and use of optoelectronic devices made of different nanoscale perovskite architectures, including quantum dots, nanosheets, nanorods, nanowires, and nanocrystals. Through a thorough analysis of recent literature, the review also addresses common issues like the mechanisms underlying the degradation of perovskite PDs and offers perspectives on potential solutions to improve stability and scalability that impede widespread implementation. In addition, it highlights that photodetection encompasses the detection of light fields in dimensions other than light intensity and suggests potential avenues for future research to overcome these obstacles and fully realize the potential of nanoscale perovskite materials in state-of-the-art photodetection systems. This review provides a comprehensive overview of nanoscale perovskite PDs and guides future research efforts towards improved performance and wider applicability, making it a valuable resource for researchers.

Highly Efficient Photon Energy Conversion and Ultrasensitive Self-Powered Photodetection via a Monolithic p-3C-SiC Nanothin Film on p-Si/n-Si Double Junction

The pursuit of increased efficiency of photoelectric energy conversion through optimized semiconductor structures remains highly competitive, with current results yet to align with broad expectations. In this study, we discover a significant enhancement in photocurrent performance of a p-3C-SiC nanothin film on p-Si/n-Si double junction (DJ) heterostructure that integrates p-3C-SiC/p-Si heterojunction and p-Si/n-Si homojunction. The vertical photocurrent (VPC) and vertical photoresponsivity exhibit a substantial enhancement in the DJ heterostructure, surpassing by a maximum of 43-fold compared to the p-3C-SiC/n-Si single junction (SJ) counterpart. The p-3C-SiC layer and n-Si substrate of the two heterostructures have similar material and geometrical properties. More importantly, the fabrication costs for the DJ and SJ heterostructure devices are comparable. Our results demonstrate a significant potential for using DJ devices in energy harvesters, micro/nano electromechanical systems, and sensing applications. This research may also lead to the creation of advanced optoelectronic devices using DJ structures, where employing various semiconductor materials to achieve exceptional performance through the application of the concept and theoretical model described in this work.

Anti-Ambipolar Heterojunctions: Materials, Devices, and Circuits

Anti-ambipolar heterojunctions are vital in constructing high-frequency oscillators, fast switches, and multivalued logic (MVL) devices, which hold promising potential for next-generation integrated circuit chips and telecommunication technologies. Thanks to the strategic material design and device integration, anti-ambipolar heterojunctions have demonstrated unparalleled device and circuit performance that surpasses other semiconducting material systems. This review aims to provide a comprehensive summary of the achievements in the field of anti-ambipolar heterojunctions. First, the fundamental operating mechanisms of anti-ambipolar devices are discussed. After that, potential materials used in anti-ambipolar devices are discussed with particular attention to 2D-based, 1D-based, and organic-based heterojunctions. Next, the primary device applications employing anti-ambipolar heterojunctions, including anti-ambipolar transistors (AATs), photodetectors, frequency doublers, and synaptic devices, are summarized. Furthermore, alongside the advancements in individual devices, the practical integration of these devices at the circuit level, including topics such as MVL circuits, complex logic gates, and spiking neuron circuits, is also discussed. Lastly, the present key challenges and future research directions concerning anti-ambipolar heterojunctions and their applications are also emphasized.

Recent advance of high-quality perovskite nanostructure and its application in flexible photodetectors

Flexible photodetectors (PDs) have garnered increasing attention for their potential applications in diverse fields, including weather monitoring, smart robotics, smart textiles, electronic eyes, wearable biomedical monitoring devices, and so on. Notably, perovskite nanostructures have emerged as a promising material for flexible PDs due to their distinctive features, such as a large optical absorption coefficient, tunable band gap, extended photoluminescence decay time, high carrier mobility, low defect density, long exciton diffusion lengths, strong self-trapped effect, good mechanical flexibility, and facile synthesis methods. In this review, we first introduce various synthesis methods for perovskite nanostructures and elucidate their corresponding optical and electrical properties, encompassing quantum dots, nanocrystals, nanowires, nanobelts, nanosheets, single-crystal thin films, polycrystalline thin films, and nanostructured arrays. Furthermore, the working mechanism and key performance parameters of optoelectronic devices are summarized. The review also systematically compiles recent advancements in flexible PDs based on various nanostructured perovskites. Finally, we present the current challenges and prospects for the development of perovskite nanostructures-based flexible PDs.

Deep-Ultraviolet Transparent Electrode Design for High-Performance and Self-Powered Perovskite Photodetector

In this study, a highly crystalline and transparent indium-tin-oxide (ITO) thin film was prepared on a quartz substrate via RF sputtering to fabricate an efficient bottom-to-top illuminated electrode for an ultraviolet C (UVC) photodetector. Accordingly, the 26.6 nm thick ITO thin film, which was deposited using the sputtering method followed by post-annealing treatment, exhibited good transparency to deep-UV spectra (67% at a wavelength of 254 nm), along with high electrical conductivity (11.3 S/cm). Under 254 nm UVC illumination, the lead-halide-perovskite-based photodetector developed on the prepared ITO electrode in a vertical structure exhibited an excellent on/off ratio of 1.05 × 104, a superb responsivity of 250.98 mA/W, and a high specific detectivity of 4.71 × 1012 Jones without external energy consumption. This study indicates that post-annealed ITO ultrathin films can be used as electrodes that satisfy both the electrical conductivity and deep-UV transparency requirements for high-performance bottom-illuminated optoelectronic devices, particularly for use in UVC photodetectors.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi₂O₂Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi₂O₂Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi₂O₂Se/MoSe₂ photodiode designed with type-II band alignment demonstrates a high rectification ratio of 10³. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 μs (zero bias) and 17.17 A/W and 100/110 μs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi₂O₂Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi₂O₂Se nanowires. Furthermore, 1D Bi₂O₂Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

Single-Crystal Nanowire Cesium Tin Triiodide Perovskite Solar Cell

This work reports for the first time a highly efficient single-crystal cesium tin triiodide (CsSnI₃ ) perovskite nanowire solar cell. With a perfect lattice structure, low carrier trap density (≈5 × 10¹⁰ cm^-3 ), long carrier lifetime (46.7 ns), and excellent carrier mobility (>600 cm² V^-1 s^-1 ), single-crystal CsSnI₃ perovskite nanowires enable a very attractive feature for flexible perovskite photovoltaics to power active micro-scale electronic devices. Using CsSnI₃ single-crystal nanowire in conjunction with highly conductive wide bandgap semiconductors as front-surface-field layers, an unprecedented efficiency of 11.7% under AM 1.5G illumination is achieved. This work demonstrates the feasibility of all-inorganic tin-based perovskite solar cells via crystallinity and device-structure improvement for the high-performance, and thus paves the way for the energy supply to flexible wearable devices in the future.

Fabrication of High-Performance Visible-Blind Ultraviolet Photodetectors Using Electro-ionic Conducting Supramolecular Nanofibers

The detection of ultraviolet (UV) light is vital for various applications, such as chemical-biological analysis, communications, astronomical studies, and also for its adverse effects on human health. Organic UV photodetectors are gaining much attention in this scenario because they possess properties such as high spectral selectivity and mechanical flexibility. However, the achieved performance parameters are much more inferior than the inorganic counterparts because of the lower mobility of charge carriers in organic systems. Here, we report the fabrication of a high-performance visible-blind UV photodetector, using 1D supramolecular nanofibers. The nanofibers are visibly inactive and exhibit highly responsive behavior mainly for UV wavelengths (275-375 nm), the highest response being at ∼275 nm. The fabricated photodetectors demonstrate desired features, such as high responsivity and detectivity, high selectivity, low power consumption, and good mechanical flexibility, because of their unique electro-ionic behavior and 1D structure. The device performance is shown to be improved by several orders through the tweaking of both electronic and ionic conduction pathways while optimizing the electrode material, external humidity, applied voltage bias, and by introducing additional ions. We have achieved optimum responsivity and detectivity values of around 6265 A W^-1 and 1.54 × 10¹⁴ Jones, respectively, which stand out compared with the previous organic UV photodetector reports. The present nanofiber system has great potential for integration in future generations of electronic gadgets.

Solution Processed Photodetectors with PVK-WS2 Nanotube/Nanofullerene Organic-Inorganic Hybrid Films

Organic-inorganic hybrid photodetectors have attracted increased interest due to their exceptional properties, such as flexibility, transparency, and low cost for many promising applications. Low-dimensional tungsten disulfide (WS₂) nanostructures have outstanding electrical and optical properties, making them ideal candidates for ultrasensitive photodetector devices. In this paper, photodetectors were fabricated with hybrid thin films containing two different WS₂ nanomaterials, one-dimensional (1D) WS₂ nanotubes (WS₂-NTs) and a zero-dimensional (0D) WS₂ nanofullerene (WS₂-FLs) hybrid with poly(N-vinyl carbazole) (PVK). The electrical responses of the devices under visible-light illuminations were studied. The photodetector devices with 0D WS₂-FLs/PVK hybrid thin films have relatively higher sensitivity and stable voltage responses to visible light. Besides, the hybrid film shows a strong surface-enhanced Raman effect (SERS). These materials and new strategies enable the creation of a new class of processed photodetectors for practical applications.

Metal Electrode-Free Halide Perovskite-Based Flexible Ultraviolet-C Photodetector with Large Area

Ultraviolet-C (UVC) photodetector has appealed to a numerous number of research owing to its manifold applications in wireless communication, flame monitoring, and medicine. However, in addition to superior performance and high stability of recent studies, scalability and production cost are important factors for commercialization and practical implementation. In this study, a halide perovskite-based UVC photodetector was fabricated using spin-coating process and low-temperature annealing. Corning® Willow® Glass was selected as the substrate for the bottom-illuminated device due to its flexibility and exceptional optical transmission (approximately 60%) in the deep-UV region. The device had a vertical structure with a large active area (1 cm²) owing to the judicious utilization of electrodes. Under bent state with a curvature radius of 25 mm, the as-fabricated device exhibited high response and repeatability with an on/off ratio of 9.57 × 10³, a fast response speed of 45/46 ms (rise/fall times) at zero bias under the illumination of a 254-nm UV lamp. The results are based on a flexible and lightweight photodetector without the utilization of notable metal electrodes.

Quasi-Epitaxial Growth of β-Ga2O3-Coated Wide Band Gap Semiconductor Tape for Flexible UV Photodetectors

The epitaxial growth of technically important β-Ga₂O₃ semiconductor thin films has not been realized on flexible substrates due to the limitations of high-temperature crystallization conditions and lattice-matching requirements. We demonstrate the epitaxial growth of β-Ga₂O₃(-201) thin films on flexible CeO₂(001)-buffered Hastelloy tape. The results indicate that CeO₂(001) has a small bi-axial lattice mismatch with β-Ga₂O₃(-201), inducing simultaneous double-domain epitaxial growth. Flexible photodetectors are fabricated on the epitaxial β-Ga₂O₃-coated tape. Measurements reveal that the photodetectors have a responsivity of 4 × 10⁴ mA/W, with an on/off ratio reaching 1000 under 254 nm incident light and 5 V bias voltage. Such a photoelectrical performance is within the mainstream level of β-Ga₂O₃-based photodetectors using conventional rigid single-crystal substrates. More importantly, it remained robust against more than 20,000 bending test cycles. Moreover, the technique paves the way for the direct in situ epitaxial growth of other flexible oxide semiconductor devices in the future.

Fabrication and characterization of a porous ZnO flexible UV photodetector on fiberglass and the electrode dimensions effect

In this study, three flexible metal-semiconductor-metal ultraviolet photodetectors are fabricated on the FR4 fiberglass substrate based on the porous zinc oxide by radiofrequency sputtering. Their copper electrodes were created by printed circuit board, a simple and cheap method. Here, the effect of porosity on the photodetector parameters is discussed. The results show that the difference in the finger size in the photodetectors leads to differences in the parameters. In these photodetectors, as the fingers increase in length, dark current increases from 0.25 to 67.3 µA, photocurrent from 1.98 to 208 µA, and response time from 430 to 570 ms. Also, with expanding finger width, these parameters changed 18.48 µA, 26.8 µA, and 440 ms, respectively.

Surface ligand engineering of CsPbBr3 perovskite nanowires for high-performance photodetectors

Surface ligand engineering is of great importance for the preparation of one-dimensional (1D) CsPbBr₃ nanowires for high-performance photodetectors. The traditional long-chain terminated ligands such as oleylamine/oleic acid (C18) used in the preparation of CsPbBr₃ nanowires will form an electrically insulating layer on the surface of the nanowires, which hinders the effective transport of charge carriers in optoelectronic devices. In this paper, short-chain ligands, including dodecylamine/dodecanoic acid (C12), octylamine/octanoic acid (C8) and hexylamine/hexanoic acid (C6), are introduced to partially replace long-chain ligands (C18) to successfully prepare various CsPbBr₃ nanowires via a solvothermal method. Microstructure characterization indicates that the four kinds of nanowires before/after surface ligand engineering, which are named as C18-CsPbBr₃, C12/18-CsPbBr₃, C8/18-CsPbBr₃ and C6/18-CsPbBr₃, all have high aspect ratio and purity. As compared with CsPbBr₃ with long-chain terminated ligands, the C8/18-CsPbBr₃ and C6/18-CsPbBr₃ nanowires with shorter chain ligands exhibit superior photoluminescence (PL) performance and stability under adverse conditions such as ultraviolet irradiation and high temperature. The constructed photodetectors based on C8/18-CsPbBr₃ and C6/18-CsPbBr₃ nanowires have shown improved performances. This work provides a new idea for the preparation of CsPbBr₃ nanowires with high optical properties, stability and charge transport, and the prepared CsPbBr₃ nanowires have potential application prospects in optoelectronic devices.

Effect of vacancy concentration on the lattice thermal conductivity of CH3NH3PbI3: a molecular dynamics study

Hybrid halide perovskites are drawing great interest for photovoltaic and thermoelectric applications, but the relationship of thermal conductivities with vacancy defects remains unresolved. Here, we present a systematic investigation of the thermal conductivity of perfect and defective CH3NH3PbI3, performed using classical molecular dynamics with an ab initio-derived force field. We calculate the lattice thermal conductivity of perfect CH3NH3PbI3 as the temperature increases from 300 K to 420 K, confirming a good agreement with the previous theoretical and experimental data. Our calculations reveal that the thermal conductivities of defective systems at 330 K, containing vacancy defects such as VMA, VPb and VI, decrease overall with some slight rises, as the vacancy concentration increases from 0 to 1%. We show that such vacancies act as phonon scattering centers, thereby reducing the thermal conductivity. Moreover, we determine the elastic moduli and sound velocities of the defective systems, revealing that their slower sound speed is responsible for the lower thermal conductivity. These results could be useful for developing hybrid halide perovskite-based solar cells and thermoelectric devices with high performance.

Direct Fabrication of Micron-Thickness PVA-CNT Patterned Films by Integrating Micro-Pen Writing of PVA Films and Drop-on-Demand Printing of CNT Micropatterns

The direct fabrication of micron-thickness patterned electronics consisting of patterned PVA films and CNT micropatterns still faces considerable challenges. Here, we demonstrated the integrated fabrication of PVA films of micron-thickness and CNT-based patterns by utilising micro-pen writing and drop-on-demand printing in sequence. Patterned PVA films of 1-5 μm in thickness were written first using proper micro-pen writing parameters, including the writing gap, the substrate moving velocity, and the working pressure. Then, CNT droplets were printed on PVA films that were cured at 55-65 °C for 3-15 min, resulting in neat CNT patterns. In addition, an inertia-pseudopartial wetting spreading model was established to release the dynamics of the droplet spreading process over thin viscoelastic films. Uniform and dense CNT lines with a porosity of 2.2% were printed on PVA substrates that were preprocessed at 55 °C for 9 min using a staggered overwriting method with the proper number of layers. Finally, we demonstrated the feasibility of this hybrid printing method by printing a patterned PVA-CNT film and a micro-ribbon. This study provides a valid method for directly fabricating micron-thickness PVA-CNT electronics. The proposed method can also provide guidance on the direct writing of other high-molecular polymer materials and printing inks of other nanosuspensions.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Low-Dimensional Metal Halide Perovskite Photodetectors

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record-breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high-performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low-dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low-dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low-dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low-dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low-dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low-dimensional MHP-based PDs in the future.

Flexible Ultrathin Single-Crystalline Perovskite Photodetector

Flexible optoelectronic devices attract considerable attention due to their prominent role in creating novel wearable apparatus for bionics, robotics, health care, and so forth. Although bulk single-crystalline perovskite-based materials are well-recognized for the high photoelectric conversion efficiency than the polycrystalline ones, their stiff and brittle nature unfortunately prohibits their application for flexible devices. Here, we introduce ultrathin single-crystalline perovskite film as the active layer and demonstrate a high-performance flexible photodetector with prevailing bending reliability. With a much-reduced thickness of 20 nm, the photodetector made of this ultrathin film can achieve a significantly increased responsivity as 5600A/W, 2 orders of magnitude higher than that of recently reported flexible perovskite photodetectors. The demonstrated 0.2 MHz 3 dB bandwidth further paves the way for high-speed photodetection. Notably, all its optoelectronic characteristics resume after being bent over thousands of times. These results manifest the great potential of single-crystalline perovskite ultrathin films for developing wearable and flexible optoelectronic devices.

Long and Ultrastable All-Inorganic Single-Crystal CsPbBr3Microwires: One-Step Solution In-Plane Self-Assembly at Low Temperature and Application for High-Performance Photodetectors

As ideal building blocks for optoelectronic devices, one-dimensional (1D) single-crystal perovskite microwires (MWs) have received widespread attention due to their unique physical and chemical properties. Herein, a one-step solution in-plane self-assembly method is proposed to directly grow millimeter-long CsPbBr₃ MWs with superior crystal quality at atmospheric environment. This method effectively avoids the use of toxic antisolvents. Furthermore, a MW-based photodetector is successfully fabricated, showing high photoresponsivity (20 A/W) and fast response (less than 0.3 ms). The stability of the photodetector is also confirmed by aging MW in air for 60 days, which shows a negligible change of photocurrent from 1.29 to 1.25 nA (-3 V) under the same experimental conditions. This work provides a low-cost and fast synthesis method for the preparation of single-crystal perovskite MWs and demonstrates their potential application for high-performance and stable photoelectronic device.

Flexible, ultra-stable and color tunable fluorescent films based on all inorganic perovskite quantum dots embedded in polymer

Colloidal perovskite CsPbX₃ (X = Cl, Br, I) nanocrystals (CPNCs)/polymers composites have attracted extensive attention due to their potential to be developed as flexible phosphor films for lighting applications. However, to maintain high quantum efficiency and photo stability of CPNCs in such composites remains a daunting challenge. Here, we have demonstrated a layered composite structure consisting of CPNCs and polydimethylsiloxane (PDMS) with multi-color emission and long-term stability. By tuning the molar ratio between CsPbCl_1.58Br_1.42 and CsPbBr_1.35I_1.65, flexible fluorescent films as down-converter layers with a high luminescent efficiency and a controllable color temperature spanning from 3194 K to 5901 K have been demonstrated. Furthermore, due to embedding inside such composites, the quantum efficiency of CPNCs exhibited negligible changes during seven months in ambient conditions. The carrier dynamics based on time-resolved photoluminescence (PL) and transient absorption spectroscopy reveal that the hot electron tunneling and trapping process are significant in the composite film. This work provides a good understanding of CPNC materials in complex composite for the development of flexible, robust, color controllable fluorescent films for lighting applications.

Transparent, flexible MAPbI3 perovskite microwire arrays passivated with ultra-hydrophobic supramolecular self-assembly for stable and high-performance photodetectors

The emergence of organic-inorganic hybrid perovskites (OHPs) has revolutionised the potential performance of optoelectronic devices; most perovskites are opaque and hence incompatible with transparent optoelectronics and sensitive to environmental degradation. Here, we have reported a single-step fabrication of ultra-long MAPbI₃ perovskite microwire arrays over a large area using stencil lithography based on sequential vacuum sublimation. The environmental stability of MAPbI₃ is empowered with a newly designed and synthesized transparent supramolecular self-assembly based on a mixture of two tripodal l-Phe-C₁₁H₂₃/C₇F₁₅ molecules, which showed a contact angle of 105° and served as ultra-hydrophobic passivation layers for more than 45 days in an ambient atmosphere. The MAPbI₃ microwire arrays passivated with the supramolecular self-assembly demonstrated for the first time both excellent transparency of ∼89% at 550 nm and a remarkable photoresponse with a photo-switching ratio of ∼10⁴, responsivity of 789 A W^-1, detectivity of 10¹⁴ Jones, linear dynamic range of ∼122 dB, and rise time of 432 μs. Furthermore, the photodetector fabricated on a flexible PET substrate demonstrated robust mechanical flexibility even beyond 1200 bending cycles. Therefore, the scalable stencil lithography and supramolecular passivation approaches have the potential to deliver next-generation transparent, flexible, and stable optoelectronic devices.

Back-Reflected Performance-Enhanced Flexible Perovskite Photodetectors through Substrate Texturing with Femtosecond Laser

Recently, enhancing the performance of flexible perovskite photodetectors through facile and effective means has gained greater attention. In contrast to typical approaches through modifying light-active materials, we present here a simple but effective design by improving light-matter interactions through near-field optical interference on a back-reflected substrate, whose architecture includes a morphologically flat top surface and a backscattering surface textured with micro/nanostructures by the femtosecond laser direct writing. A CH₃NH₃PbI₃ perovskite film and poly(ethylene terephthalate) are selected as the light-active and base materials, respectively. Under a 1 V bias voltage actuation and 532 nm laser irradiation at an intensity of 10 mW cm^-2, the flexible device exhibits excellent performance in photoresponsivity (47.1 mA W^-1), detectivity (3.7 × 10¹¹ Jones), and on/off ratio (4600). Due to the near-field optical enhancement of the substrate and the strong light-matter interaction, the above performance parameters are enhanced by at least 5 times over a wide spectral range of 220-780 nm. Such enhancement behaviors are independent of active material properties and therefore can be compatible with other operations such as crystalline transformation, doping, and interface modification. Moreover, the alteration of stress distribution on the structured substrate facilitates the bending robustness and stability. These features highlight the potential of back-reflected design in the development of flexible perovskite photoelectric devices, which are especially suitable for large-scale industrial production.

Edge-Epitaxial Growth of InSe Nanowires toward High-Performance Photodetectors

Semiconducting nanowires offer many opportunities for electronic and optoelectronic device applications due to their unique geometries and physical properties. However, it is challenging to synthesize semiconducting nanowires directly on a SiO₂ /Si substrate due to lattice mismatch. Here, a catalysis-free approach is developed to achieve direct synthesis of long and straight InSe nanowires on SiO₂ /Si substrates through edge-homoepitaxial growth. Parallel InSe nanowires are achieved further on SiO₂ /Si substrates through controlling growth conditions. The underlying growth mechanism is attributed to a selenium self-driven vapor-liquid-solid process, which is distinct from the conventional metal-catalytic vapor-liquid-solid method widely used for growing Si and III-V nanowires. Furthermore, it is demonstrated that the as-grown InSe nanowire-based visible light photodetector simultaneously possesses an extraordinary photoresponsivity of 271 A W^-1 , ultrahigh detectivity of 1.57 × 10¹⁴ Jones, and a fast response speed of microsecond scale. The excellent performance of the photodetector indicates that as-grown InSe nanowires are promising in future optoelectronic applications. More importantly, the proposed edge-homoepitaxial approach may open up a novel avenue for direct synthesis of semiconducting nanowire arrays on SiO₂ /Si substrates.

Low-cost photodetector architectures fabricated at room-temperature using nano-engineered silicon wafer and sol-gel TiO2 - based heterostructures

In the last decades, significant research has been done on the nanocrystalline forms of titanium dioxide (TiO2). Amorphous TiO2 has not been studied intensively despite being significantly less expensive compared to crystalline TiO2. This study reveals significant improvement in UV-VIS photodetection properties from heterostructures fabricated in ambient environment using n-type silicon nanowire arrays and amorphous TiO2 sol-gel. Our ultra-low-cost UV-VIS photodetectors can cover a wide range of applications. We report fast rise/decay time constants of 0.23 ms/0.17 ms and high responsivity up-to 6.0 A/W in the UV and 25.0 A/W in the visible range under low (1 V) external bias. The large surface area due to the nanowire array architecture leads to 2 orders of magnitude enhancement in photo-response. Besides the final electrode deposition, the entire device fabrication is performed using low-cost, all solution-based methods in ambient conditions. These low-cost UV-Visible broadband photodetectors can potentially serve a wide range of applications.

Enhanced Photoresponsivity of a GaAs Nanowire Metal-Semiconductor-Metal Photodetector by Adjusting the Fermi Level

Metal-semiconductor-metal (MSM)-structured GaAs-based nanowire photodetectors have been widely reported because they are promising as an alternative for high-performance devices. Owing to the Schottky built-in electric fields in the MSM structure photodetectors, enhancements in photoresponsivity can be realized. Thus, strengthening the built-in electric field is an efficacious way to make the detection capability better. In this study, we fabricate a single GaAs nanowire MSM photodetector with superior performance by doping-adjusting the Fermi level to strengthen the built-in electric field. An outstanding responsivity of 1175 A/W is obtained. This is two orders of magnitude better than the responsivity of the undoped sample. Scanning photocurrent mappings and simulations are performed to confirm that the enhancement in responsivity is because of the increase in the hole Schottky built-in electric field, which can separate and collect the photogenerated carriers more effectively. The eloquent evidence clearly proves that doping-adjusting the Fermi level has great potential applications in high-performance GaAs nanowire photodetectors and other functional photodetectors.

Halide Perovskite Nanocrystals for Next-Generation Optoelectronics

Colloidal perovskite nanocrystals (PNCs) combine the outstanding optoelectronic properties of bulk perovskites with strong quantum confinement effects at the nanoscale. Their facile and low-cost synthesis, together with superior photoluminescence quantum yields and exceptional optical versatility, make PNCs promising candidates for next-generation optoelectronics. However, this field is still in its early infancy and not yet ready for commercialization due to several open challenges to be addressed, such as toxicity and stability. Here, the key synthesis strategies and the tunable optical properties of PNCs are discussed. The photophysical underpinnings of PNCs, in correlation with recent developments of PNC-based optoelectronic devices, are especially highlighted. The final goal is to outline a theoretical scaffold for the design of high-performance devices that can at the same time address the commercialization challenges of PNC-based technology.