Tunable TiO2 films for high-performing transparent Schottky photodetector

We demonstrate the transparent Schottky photodetector of the configuration Cu/TiO₂/FTO unveiling superior photodetection properties. The improved performance of fabricated photodetector was ascribed to high quality rutile-nanocrystalline TiO₂ films with very high absorption coefficient (~6×10⁵ cm⁻¹) and excitonic localized states. The existence of such localized states in TiO₂ Schottky device offered fastest response time of 1.12 ms suggesting their application in fast switching photodetectors. In addition, the photodetectors showed high responsivity of the value 0.897 A/W and detectivity 4.5×10¹² Jones. This transparent TiO₂ design would provide a functional route for various photoelectric device applications.     

Vertical-type 3D/Quasi-2D n-p Heterojunction Perovskite Photodetector

This research demonstrates a state-of-the-art vertical-transport photodetector with an n-type 3D MAPbI₃/p-type quasi-2D (Q-2D) BA₂MA₂Pb₃I₁₀ perovskite heterojunction. This structure introduces a ≈0.6 V built-in electric field at the n-p junction that greatly improves the characteristics of the perovskite photodetector, and the presence of Q-2D perovskite on the surface improves the life. The electrical polarities of the 3D and the Q-2D perovskite layers are simply controlled by self-constituent doping, making clearly defined n-p characteristics. Doctor-blade coating is used to fabricate the photodetector with a large area. The Q-2D materials with highly oriented (040) Q-2D (n = 2,3) planes are near the surface, and the (111) preferred planes mixed with high index Q-2D materials (n = 4,5) are found near the 3D/Q-2D interface. The stacking and interface are beneficial for carrier extraction and transport, yielding an external quantum efficiency of 77.9%, a carrier lifetime long as 295.7 ns, and a responsibility of 0.41 A W⁻¹. A low dark current density of 6.2 × 10⁻⁷ mA cm⁻² and a high detectivity of 2.82 × 10¹³ Jones are obtained. Rise time and fall time are fast as 1.33 and 10.1 µs, respectively. The results show the application potential of 3D/Q-2D n-p junction perovskite photodetectors.     

All-Dielectric Nanostructure Fabry–Pérot-Enhanced Mie Resonances Coupled with Photogain Modulation toward Ultrasensitive In2S3 Photodetector

As the fresh blood of 2D family, non-layered 2D materials (2DNLMs) have demonstrated great potential in the application of next-generation optoelectronic devices. However, stemming from the weak light absorption brought by atomically thin thickness and the interfacial recombination brought by surface dangling bonds, traditional 2DNLM photodetectors are always accompanied by limited performance. Herein, a structure that integrates Si nanopillar array and non-layered 2D In₂S₃ to construct an ultrasensitive photodetector is designed. In particular, periodically Si nanopillars can act as Fabry–Pérot-enhanced Mie resonators that can effectively control and enhance the light absorption of 2D In₂S₃. On the other hand, a vertical built-in electric field is introduced in the In₂S₃ channel to capture photogenerated holes and leave electrons recycling in In₂S₃, obtaining a high photogain. Benefiting from these two mechanisms, this proposed photodetector presents a high responsivity of 4812 A W⁻¹ and short rise/decay time of 5.2/4.0 ms at the wavelength of 405 nm. Especially, a high light on–off ratio greater than 10⁶ and a record-high detectivity of 5.4 × 10¹⁵ Jones are achieved, representing one of the most sensitive photodetectors based on 2D materials. This deliberate device design concept suggests an effective scheme to construct high-performance 2DNLM optoelectronic devices.     

Organic photodetector with built-in amplification for the detection of visible light with low optical power

We report on an organic-based photodetector that integrates a dual-gate organic thin-film transistor (DG-OTFT) with an organic photodiode (OPD) to produce a device with a high effective responsivity at low optical power and video-rate compatible response. In this device, the OPD operates in photovoltaic mode, instead of the commonly used photoconductive mode, to modulate one of the gate voltages of the DG-OTFT. Effective responsivity values of 10 A W⁻¹ are measured at optical power values lower than 10 nW at 635 nm. Modeling of the operation of this new photodetector suggests that effective responsivity values up to 10⁵ A W⁻¹ can be achieved at optical powers of 1 nW using current printing technology and state-of-the-art organic semiconductors.     

High-Performance van der Waals Metal-Insulator-Semiconductor Photodetector Optimized with Valence Band Matching

The vertical metal-insulator-semiconductor (MIS) photodetectors based on van der Waals heterostructures (vdWHs), fabricated by rationally stacking different layers without the limit of lattice-match, have attracted broad interest due to their wide wavelength monitoring range, high responsivity, high detectivity, and fast response. Here, for the first time, the control of barrier height in vdWHs MIS photodetectors is systematically investigated. Optimizing semiconducting and insulating layers enables lowering the hole barrier height to achieve a high performance of the device. Graphene/hexagonal boron nitride (h-BN)/SnS₂ device shows the best photodetection performance compared to the other common 2D semiconductors. The lowest barrier height ensures that the photo-induced holes transfer efficiently to the graphene electrode and the dark current is highly suppressed by the h-BN layers. Consequently, the graphene/h-BN/SnS₂ MIS photodetectors have a high photoresponsivity of 2 A W⁻¹, a high detectivity of 10¹³ Jones, and a photocurrent/dark current ratio of 5.2 × 10⁵ at a low applied bias of −0.6 V. The highest detectivity reaches 9.6 × 10¹³ Jones which is 100–1000 times greater than previously reported vdWHs MIS photodetectors.     

Ultrahigh Speed and Broadband Few‐Layer MoTe2/Si 2D–3D Heterojunction‐Based Photodiodes Fabricated by Pulsed Laser Deposition

2D transition metal dichalcogenides are promising candidates for high‐performance photodetectors. However, the relatively low response speed as well as the complex transfer process hinders their wide applications. Herein, for the first time, the fabrication of a few‐layer MoTe₂/Si 2D–3D vertical heterojunction for high‐speed and broadband photodiodes by a pulsed laser deposition technique is reported. Owing to the high junction quality, ultrathin MoTe₂ film thickness, and unique vertical n–n heterojunction structure, the photodiode exhibits excellent device performance in terms of a high responsivity of 0.19 A W^?1 and a large detectivity of 6.8 × 10¹³ Jones. The device is also capable of detecting a broadband light with wavelength spanning from 300 to 1800 nm. More importantly, the device possesses an ultrahigh response speed up to 150 ns with a 3‐dB electrical bandwidth approaching 0.12 GHz. This work paves the way toward the fabrication of novel 2D–3D heterojunctions for high‐performance, ultrafast photodetectors.     

All-Inorganic CsPbBr3 Perovskite Nanocrystals/2D Non-Layered Cadmium Sulfide Selenide for High-Performance Photodetectors by Energy Band Alignment Engineering

Perovskites have attracted intensive attention as promising materials for the application in various optoelectronic devices due to their large light absorption coefficient, high carrier mobility, and long charge carrier diffusion length. However, the performance of the pure perovskite nanocrystals-based device is extremely restricted by the limited charge transport capability due to the existence of a large number of the grain boundary between perovskite nanocrystals. To address these issues, a high-performance photodetector based on all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure has been demonstrated through energy band engineering with designed typed-II heterostructure. The photodetector exhibits an ultra-high light-to-dark current ratio of 1.36 × 10⁵, a high responsivity of 2.89 × 10² A W⁻¹, a large detectivity of 1.28 × 10¹⁴ Jones, and the response/recovery time of 0.53s/0.62 s. The enhancement of the optoelectronic performance of the heterostructure photodetector is mainly attributed to the efficient charge carrier transfer ability between the all-inorganic CsPbBr₃ perovskites and 2D cadmium sulfide selenide resulting from energy band alignment engineering. The charge carriers’ transfer dynamics and the mechanism of the CsPbBr₃ perovskites/2D non-layered nanosheets interfaces have also been studied by state-state PL spectra, fluorescence lifetime imaging microscopy, time-resolved photoluminescence spectroscopy, and Kelvin probe force microscopy measurements.     

High‐Performance Near‐IR Photodetector Using Low‐Bandgap MA0.5FA0.5Pb0.5Sn0.5I3 Perovskite

Photodetectors with ultrafast response are explored using inorganic/organic hybrid perovskites. High responsivity and fast optoelectronic response are achieved due to the exceptional semiconducting properties of perovskite materials. However, most of the perovskite‐based photodetectors exploited to date are centered on Pb‐based perovskites, which only afford spectral response across the visible spectrum. This study demonstrates a high‐performance near‐IR (NIR) photodetector using a stable low‐bandgap Sn‐containing perovskite, (CH₃NH₃)_0.5(NH₂CHNH₂)_0.5Pb_0.5Sn_0.5I₃ (MA_0.5FA_0.5Pb_0.5Sn_0.5I₃), which is processed with an antioxidant additive, ascorbic acid (AA). The addition of AA effectively strengthens the stability of Sn‐containing perovskite against oxygen, thereby significantly inhibiting the leakage current. Consequently, the derived photodetector shows high responsivity with a detectivity of over 10¹² Jones ranging from 800 to 970 nm. Such low‐cost, solution processable NIR photodetectors with high performance show promising potential for future optoelectronic applications.     

All‐Layered 2D Optoelectronics: A High‐Performance UV–vis–NIR Broadband SnSe Photodetector with Bi2Te3 Topological Insulator Electrodes

Nanoelectronics is in urgent demand of exceptional device architecture with ultrathin thickness below 10 nm and dangling‐bond‐free surface to break through current physical bottleneck and achieve new record of integration level. The advance in 2D van der Waals materials endows scientists with new accessibility. This study reports an all‐layered 2D Bi₂Te₃‐SnSe‐Bi₂Te₃ photodetector, and the broadband photoresponse of the device from ultraviolet (370 nm) to near‐infrared (808 nm) is demonstrated. In addition, the optimized responsivity reaches 5.5 A W^?1, with the corresponding eternal quantum efficiency of 1833% and detectivity of 6 × 10¹⁰ cm Hz^1/2 W^?1. These figures‐of‐merits are among the best values of the reported all‐layered 2D photodetectors, which are several orders of magnitude higher than those of the previous SnSe photodetectors. The superior device performance is attributed to the synergy of highly conductive surface state of Bi₂Te₃ topological insulator, perfect band alignment between Bi₂Te₃ and SnSe as well as small interface potential fluctuation. Meanwhile, the all‐layered 2D device is further constructed onto flexible mica substrate and its photoresponse is maintained roughly unchanged upon 60 bending cycles. The findings represent a fundamental scenario for advancement of the next generation high performance and high integration level flexible optoelectronics.     

High-performing MoS2-embedded Si photodetector

Transition metal dichalcogenides (TMDs) are a new class of materials that replace advanced functional materials like graphene, CNT etc., in photovoltaics and sensors. In the present work, the 2-dimensional tri-layer MoS₂ is applied for high-performing photodetector. Here, the conventional n-doped p-type Si (n-Si/p-Si) was coated with tri-layer MoS₂ film using CVD method. HRTEM reveals the presence of tri-layer with highly ordered lattice planes. Characteristic peaks of Mo and S are obtained in XPS profile. Due to spin-orbit coupling, the 3d band of Mo and 2p band of S are split into two states. Raman spectrum of MoS₂ film shows two peaks, corresponding to its in-plane and out-of-plane vibrational modes. The wave number difference between these modes is measured as 22.97 cm⁻¹, which ensures that there are three layers in MoS₂ film. The splitting of valence band generates multiple excitons which are marked as A and B in the absorption profile. The excitonic transition corresponds to the direct band gap of MoS₂ (ie., 1.9 eV). The prepared MoS₂/n-Si/p-Si photodetector includes two rectifying junctions with considerable built-in potentials. A high rectification ratio was measured as 51.37 to ensure the quality junction formation. The photoresponse ratio of the MoS₂/n-Si/p-Si photodetector was obtained as 58.74 to confirm the quality junction formation between MoS₂ and Si with high detectivity of 5.42 × 10¹⁴ Jones. Moreover, the extremely fast rise and fall times of 33 µs and 30 µs were achieved without any external bias application. The functional use of MoS₂ window design would provide the high potential for the enhanced photoelectric devices, such as photodetectors and solar cells.     

Few‐Layered PtS2 Phototransistor on h‐BN with High Gain

The very recently rediscovered group‐10 transition metal dichalcogenides (TMDs) such as PtS₂ and PtSe₂, have joined the 2D material family as potentially promising candidates for electronic and optoeletronic applications due to their theoretically high carrier mobility, widely tunable bandgap, and ultrastability. Here, the first exploration of optoelectronic application based on few‐layered PtS₂ using h‐BN as substrate is presented. The phototransistor exhibits high responsivity up to 1.56 × 10³ A W^?1 and detectivity of 2.9 × 10¹¹ Jones. Additionally, an ultrahigh photogain ≈2 × 10⁶ is obtained at a gate voltage V _g = 30 V, one of the highest gain among 2D photodetectors, which is attributed to the existence of trap states. More interestingly, the few‐layered PtS₂ phototransistor shows a back gate modulated photocurrent generation mechanism, that is, from the photoconductive effect dominant to photogating effect dominant via tuning the gate voltage from the OFF state to the ON state. Such good properties combined with gate‐controlled photoresponse of PtS₂ make it a competitive candidate for future 2D optoelectronic applications.     

High-Performing Quasi-2D Perovskite Photodetectors with Efficient Charge Transport Network Built from Vertically Orientated and Evenly Distributed 3D-Like Phases

Quasi-two-dimensional (Q-2D) perovskites are emerging as one of the most promising materials for photodetectors. However, a significant challenge to Q-2D perovskites for photodetection is their insufficient charge transport ability, which is mainly attributed to their hybrid low-dimensional n-phase structure. This study demonstrates that evenly-distributed 3D-like phases with vertical orientation throughout the film can greatly facilitate charge transport and suppress charge recombination, outperforming the prevalent phase structure with a vertical dimension gradient. Based on such a phase structure, a Q-2D Ruddlesden−Popper perovskite self-powered photodetector achieving a combination of exceptional figures-of-merit is realized, including a responsivity of 0.45 AW⁻¹, a peak specific detectivity of 2.3 × 10¹³ Jones, a 156 dB linear dynamic range, and a rise/fall time of 2.89 µs/1.93 µs. The desired phase structure is obtained by utilizing a double-hole transport layer (HTL), combining hydrophobic PTAA and hydrophilic PEDOT: PSS. Besides, the dependence of the hybrid low-dimensional phase structure is also identified on the surface energy of the buried HTL substrate. This study gives insight into the correlation between Q-2D perovskites’ phase structure and performance, providing a valuable design guide for Q-2D perovskite-based photodetectors.     

High Gain Solution-Processed Carbon-Free BiSI Chalcohalide Thin Film Photodetectors

Chalcohalide semiconductors are an emergent class of materials for optoelectronics. Here, the first work on BiSI chalcohalide thin film photodetectors (PDs) is presented. An entirely new method for the fabrication of bismuth chalcohalide thin films (BiOI and BiSI) is developed. This method circumvents the use of any ligands or counter ions during fabrication and provides highly pure thin films free of carbon residues and other contaminants. When integrated into lithographically patterned lateral PDs these BiSI thin films show outstanding performances and high stability. The direct ≈1.55 eV bandgap of BiSI perfectly accommodates optical sensing over the full visible spectrum. The responsivity (R) of the BiSI PDs reaches 62.1 A W⁻¹, which is the best value reported to date across chalcohalide materials of any type. The BiSI PDs display remarkable sensitivity to low light levels, supporting a broad operational detectivity ≈10¹² Jones over four decades in light intensity, with a peak specific detectivity (D*) of 2.01 × 10¹³ Jones. The dynamics of photocurrent generation are demonstrated to be dominated by photoconductive gain. These results cement BiSI as an exciting candidate for high performance photodetector applications and encourage ongoing work in BiSX (X = Cl, Br, I) materials for optoelectronics.     

High-performance omnidirectional self-powered photodetector constructed by CsSnBr3/ITO heterostructure film

Omnidirectional photodetectors attract enormous attention due to their prominent roles in optical tracking systems and omnidirectional cameras. However, it is still a challenge for the construction of high-performance omnidirectional photodetectors where the incident light can be effectively absorbed in multiple directions and the photo-generated carriers can be effectively collected. Here, a high-performance omnidirectional self-powered photodetector based on the CsSnBr₃/indium tin oxide (ITO) heterostructure film was designed and demonstrated. The as-fabricated photodetector exhibited excellent self-powered photodetection performance, showing responsivity and detectivity up to 35.1 ​mA/W and 1.82 ​× ​10¹⁰ Jones, respectively, along with the smart rise/decay response time of 4 ​ms/9 ​ms. Benefitting from the excellent photoelectric properties of the CsSnBr₃ film as well as the ability of the CsSnBr₃/ITO heterostructure to efficiently separate and collect photo-generated carriers, the as-fabricated photodetector also exhibited excellent omnidirectional self-powered photodetection performance. All the results have certified that this work finds an efficient way to realize high-performance omnidirectional self-powered photodetectors.     

Van der Waals heterojunction ReSe2/WSe2polarization-resolved photodetector

Polarization-resolved photodetectors,a significant branch of photodetection,can more effectively distinguish the target from the background by exploiting polarization-sensitive characteristics.However,due to the absence of intrinsic polarized absorption properties of many materials,there is still a great challenge to develop the high-performance polarization-resolved photodetectors.Here,we report a van der Waals heterojunction(vdWH)ReSe₂/WSe₂photodetector,which performs a high responsivity of~0.28 A/W and a high detectivity of 1.1×10¹²Jones under the illumination of 520 nm laser at room temperature.Remarkably,scanning photocurrent mapping(SPCM)measurements demonstrate the photoresponse of devices closely depend on the polarized angle of the incident light,indicating the effective polarized light detection.This work paves the way to develop high-performance polarization-resolved photodetectors based on two-dimensional(2D)materials.     

High-Performance Ultraviolet Photodetectors Enabled by van der Waals Schottky Junction Based on TiO2 Nanorod Arrays/Au-Modulated Ti3C2Tx MXene

Two-dimensional transition metal carbides and nitrides (MXenes) show tremendous potential for optoelectronic devices due to their excellent electronic properties. Here, a high-performance ultraviolet photodetector based on TiO₂ nanorod arrays/Ti₃C₂T_x MXene van der Waals (vdW) Schottky junction by all-solution process technique is reported. The Ti₃C₂T_x MXene modulated by the Au electrode increases its work function from 4.41 to 5.14 eV to form a hole transport layer. Complemented by the dangling bond-free surface of Ti₃C₂T_x, the Fermi-level pinning effect is suppressed and the electric-field strength of the Schottky junction is enhanced, which promotes charge separation and transport. After applying a bias of −1.5 V, the photovoltaic effect is favorably reinforced, while the hole-trapping mechanism (between TiO₂ and oxygen) and reverse pyroelectric effect are largely eliminated. As a result, the responsivity and specific detectivity of the device with FTO/TiO₂ nanorod arrays/Ti₃C₂T_x/Au structure reach 1.95 × 10⁵ mA W⁻¹ and 4.3 × 10¹³ cm Hz^1/2 W⁻¹ (370 nm, 65 mW cm⁻²), respectively. This work provides an effective approach to enhance the performance of photodetectors by forming the vdW Schottky junction and choosing metal electrodes to modulate MXene as a suitable charge transport layer.     

H-BN-Encapsulated Uncooled Infrared Photodetectors Based on Tantalum Nickel Selenide

Uncooled broadband spectrum detection, spanning from visible to mid-wave-infrared regions, offers immense potential for applications in environmental monitoring, optical telecommunications, and radar systems. While leveraging proven technologies, conventional mid-wave-infrared photodetectors are encumbered by high dark currents and the necessity for cryogenic cooling. Correspondingly, innovative low-dimensional materials like black phosphorus manifest weak photoresponse and instability. Here, tantalum nickel selenide (Ta₂NiSe₅) infrared photodetectors with an operational wavelength range from 520 nm to 4.6 µm, utilizing a hexagonal boron nitride (h-BN) encapsulation technique are introduced. The h-BN encapsulated metal-Ta₂NiSe₅-metal photodetector demonstrates a responsivity of 0.86 A W⁻¹, a noise equivalent power of 1.8 × 10⁻¹¹ W Hz^−1/2, and a peak detectivity of 8.75 × 10⁸ cm Hz^1/2 W⁻¹ at 4.6 µm under ambient conditions. Multifaceted mechanisms of photocurrent generation in the novel device prototype subject are scrutinized to varying wavelengths of radiation, by characterizing the temporal-, bias-, power-, and temperature-dependent photoresponse. Moreover, the photopolarization dependence is delved and concealed-target imaging is demonstrated, which exhibits polarization angle sensitivity and high-fidelity imaging across the visible, short-wave, and mid-wave-infrared bands. The observations, which reveal versatile detection modalities, propose Ta₂NiSe₅ as a promising low-dimensional material for advanced applications in nano-optoelectronic device.     

High-Performance Near-Infrared Photodetectors Based on Surface-Doped InSe

2D InSe is one of the semimetal chalcogenides that has been recently given attention thanks to its excellent electrical properties, such as high mobility near 1000 cm² V⁻¹ s⁻¹ and moderate band gap of ≈1.26 eV suitable for IR detection. Here, high-performance visible to near-infrared (470–980 nm wavelength (λ)) photodetectors using surface-doped InSe as a channel and few-layer graphenes (FLG) as electrodes are reported, where the InSe top region is relatively p-doped using AuCl₃. The surface-doped InSe photodetectors show outstanding performance, achieving a photoresponsivity (R) of ≈19 300 A W⁻¹ and a detectivity (D*) of ≈3 × 10¹³ Jones at λ = 470 nm, and R of ≈7870 A W⁻¹ and D* of ≈1.5 × 10¹³ Jones at λ = 980 nm, superior to previously reported 2D material-based IR photodetectors operating without an applied gate bias. Surface doping using AuCl₃ renders a band bending at the junction between the InSe surface and the top FLG contact, which facilitates electron-hole pair separation and immediate photodetection. Multiple doped or undoped InSe photodetectors with different device structures are investigated, providing insight into the photodetection mechanism and optimizing performance. Encapsulation with hexagonal boron nitride dielectric also allows for 3-month stability.     

Ultra-Stable and Sensitive Ultraviolet Photodetectors Based on Monocrystalline Perovskite Thin Films

The detection of ultraviolet (UV) radiation with effective performance and robust stability is essential to practical applications. Metal halide single-crystal perovskites (ABX₃) are promising next-generation materials for UV detection. The device performance of all-inorganic CsPbCl₃ photodetectors (PDs) is still limited by inner imperfection of crystals grown in solution. Here wafer-scale single-crystal CsPbCl₃ thin films are successfully grown by vapor-phase epitaxy method, and the as-constructed PDs under UV light illumination exhibit an ultralow dark current of 7.18 pA, ultrahigh ON/OFF ratio of ≈5.22 × 10⁵, competitive responsivity of 32.8 A W⁻¹, external quantum efficiency of 10867% and specific detectivity of 4.22 × 10¹² Jones. More importantly, they feature superb long-term stability toward moisture and oxygen within twenty-one months, good temperature tolerances at low and high temperatures. The ability of the photodetector arrays for excellent UV light imaging is further demonstrated.     

Spraying Perovskite Intermediate Enabling Inch-Scale Microwire Film Fabrication for Integration Compatible Efficient-Photodetectors Array

Metal halide perovskite microwires (MWs) have emerged as promising photoactive materials for highly efficient photodetectors (PDs). However, large-scale MWs film fabrication is still a formidable challenge for achieving integration compatible perovskite PDs arrays, owing to precipitation and structure crushing of MWs during deposition and annealing. Herein, a strategy of fabrication of inch-scale perovskite MWs films is presented by depositing perovskite intermediate suspension through spray-coating, which addresses the trade-off present between the high flatness of MWs film and its large-scale fabrication. The single crystalline perovskite MWs weave a film with high enough flatness rendering narrow performance distribution of high efficiency on the 7 × 7 PDs arrays. The formamidinium lead iodide (FAPbI₃) PDs arrays show average responsivity and detectivity of (1.60 ± 0.46) A W⁻¹ and (1.49 ± 0.50) × 10¹² Jones. The methanaminium lead iodide (MAPbI₃) PDs arrays show average responsivity and detectivity of (0.065 ± 0.046) A W⁻¹ and (2.54 ± 0.77) × 10¹¹ Jones. The champion PDs based on FAPbI₃ MWs film and MAPbI₃ MWs film show detectivity of 1.26 × 10¹³ and 9.67 × 10¹¹ Jones, which are much higher than that of corresponding polycrystalline films and located on the top ranking of similar devices.