2D Photodetectors Research Articles

Enhanced Performance of a Self-Powered Au/WSe2/Ta2NiS5/Au Heterojunction by the Interfacial Pyro-phototronic Effect.

The growing need for wearable electronics and self-powered electronic devices has driven the successful development of self-powered two-dimensional (2D) photodetectors using the photovoltaic effect of Schottky and p-n junctions. However, there is an urgent need to develop multifunctional photodetectors capable of harvesting energy from different sources to overcome their limitations in efficiency and cost. While the pyro-phototronic effect has been shown to effectively influence optoelectronic processes in heterojunctions, the number of reported two-dimensional heterojunctions exhibiting interfacial pyroelectricity is still limited, and the responsivity and detectivity based on such heterojunctions tend to be low. In this study, a photodetector based on an Au/WSe2/Ta2NiS5/Au heterojunction was designed and fabricated. By harnessing the interfacial pyro-phototronic effect arising from the built-in electric fields at the Au/WSe2 Schottky junction and WSe2/Ta2NiS5 heterojunction, the photodetector exhibits a broadband response range of 405-1064 nm, with approximately 12 times enhancement in output current compared to solely relying on the photovoltaic effect. Under 660 nm light irradiation, the self-powered photodetector exhibits a responsivity of 121 mA/W, an external quantum efficiency of 22.64%, and a specific detectivity of 2 × 1012 Jones. Notably, its pyroelectric coefficient exceeds 8 × 103 μC·m-2·K-1. These findings pave the way for effectively detecting weak light and temperature variation while presenting a new strategy for developing high-performance photodetectors utilizing the interfacial pyro-phototronic effect.

2D Gr/WSe2/MoTe2 vertical heterojunction for self-powered photodiode with ultrafast response and high sensitivity

Two-dimensional materials without lattice constraints can be combined into form heterojunctions via van der Waals forces, providing opportunities for the future development of novel high-performance photodetectors. In non-vertical heterojunction devices with long carrier transport channels, SRH recombination due to defect and interface states in the heterojunction and Langevin recombination due to Coulomb interactions induce large amounts of photogenerated carrier recombination, leading to low quantum efficiencies of the heterojunction. At the same time, defect and interface trap states, as well as the long channel of the non-vertical heterojunction device, lead to a slow response speed of the device. In this work, a 2D WSe2/MoTe2 vertical heterojunction photodiode with a transparent graphene top electrode has been designed to simultaneously achieve high sensitivity and fast response speed of photodetectors. Benefiting from the vertical device structure, high-quality interface and low contact resistance, the photogenerated electron-hole pairs can be efficiently separated and transported. The photodiode exhibits remarkable rectification characteristics with a rectification ratio as high as 1.4 × 104, and provides a broadband and self-powered photodetection from the visible to NIR bands (405–1064 nm) with a maximum responsivity of 0.33 A/W at 785 nm. In particular, the photodiode achieves an ultra-fast rise/fall time of 6.49/6.22 μs at 0 V and a further reduction of the response time to 1.68/1.2 μs at a reverse bias of −1 V. This ultra-fast response allows the photodiode to detect switching signals with a cutoff frequency of more than 70 kHz and 200 kHz at 0 V and −1 V, respectively. This work opens up new opportunities for the development of integrated 2D photodetectors with low power consumption, high sensitivity, and high speed.

Plasmonic Photovoltaic Effect of an Original 2D Electron Gas System and Application in Mid‐Infrared Imaging

AbstractOwing to their consistently emerging applications in modern photonics, highly sensitive and rapid mid‐infrared (MIR) photodetectors, operating at high temperatures, are of great significance. Herein, a novel PbTe/Ge heterostructure is introduced. Notably, the discovery of a 2D electron gas (2DEG) system on the surface of the PbTe layer is experimentally identified for the first time. A high‐performance PbTe/Ge heterostructure MIR photodetector utilizing a plasmonic photovoltaic effect is developed by employing asymmetric electrodes. The photodetecting device demonstrates an exceptionally high detectivity of 1.1 × 1011 Jones along with a short response time of 15 ns at room temperature. Additionally, the proposed plasmonic photovoltaic mechanism of the device is investigated and mainly ascribed to the propagating plasmons, generated by the coupling of the 2DEG with incident MIR photons. Moreover, a linear detector array (LDA) of PbTe/Ge is demonstrated for a thermal imaging application, which exhibits promising high‐quality real‐time imaging via the 2D photodetector arrays on Ge‐based integrated circuits. This work opens up a new way for the development of next‐generation, advanced MIR photonic devices and integrated photonic systems.

A Case Study of 2D Bi2O2Se Nanoplate Near‐Infrared Photodetectors from the Perspective of Practical Applications

AbstractOver the past several decades infrared (IR) photodetectors have received wide attention due to their important applications. 2D materials, distinguished by their unique electronic structures, ultimate dimensional confinement, and robust light‐matter interactions, provide a promising candidate for fabricating future IR photodetectors. However, there is a lack of reports concerning the practical industrial applications of these 2D photodetectors, despite that some of these 2D photodetectors have demonstrated performance exceeding that of commercial photodetectors. In this work, a case study on 2D Bi2O2Se nanoplate near‐infrared photodetectors from the perspective of practical applications is presented. With the characterization method used for nano detectors, the 2D Bi2O2Se photodetector exhibits a responsivity of 212.5 A W−1, a specific detectivity of 4.99 × 1011 Jones and an external quantum efficiency of 26 887.68% at wavelength of 980 nm, while with the traditional characterization method the photodetector shows a responsivity of 0.13 A W−1 and a specific detectivity of 2.26 × 106 Jones and an external quantum efficiency of 17.87% at wavelength of 900 nm. The Bi2O2Se nanoplate photodetector also presents good passive imaging quality in the near‐infrared wavelength region. These results suggest the great potential of Bi2O2Se nanoplate photodetectors for practical applications.

Ultrahigh Photo-Responsivity and Detectivity in 2D Bismuth Sulfide Photodetector for Vis-NIR Radiation.

Bismuth sulfide (Bi2S3) exhibits a direct energy bandgap and an exceptional optical absorption capability over a broadband radiation, thus presents a novel class of 2D photodetector material. The field effect transistor (FET) photodetector device is fabricated from 2D Bi2S3. An anomalous variation in the transport characteristics of 2D Bi2S3 is observed with the variation in temperature. The electrical resistance reduces by 99.26% at 10 K compared to the response at 300 K. Defects due to the bismuth and sulfur vacancies play a critical role in the dramatic behavior, which is confirmed using photoluminescence, time-resolved photoluminescence, Hall measurements, and energy dispersive X-ray spectroscopy. The density functional theory calculations provide a significant insight into the thermodynamic properties of intrinsic defects in Bi2S3. Moreover, the effect of gate bias on responsivity additionally confirms its invariance at low temperature. The Bi2S3 based FET photodetector achieves ultrahigh responsivity in the order of ≈106 A W-1 and detectivity of ≈1014 Jones. Moreover, the external quantum efficiency of ≈107% is measured in a wide spectrum of optical illumination (532 to 1064nm) with a noise-equivalent power of 3.5 × 10-18W/√Hz at a bias of 0.2V. The extraordinary performance of Bi2S3 photodetector outstands 2D photodetectors.

Interface engineering by constructing vertical junction for reduced noise and improved sensitivity in 2D photodetector

Two-dimensional (2D) materials have been widely demonstrated as promising candidates for next generation photodetectors, while the noticeable channel current is still a limiting factor for photodetection sensitivity. In this work, the interface engineering has been developed by constructing a vertical pn and Schottky junction in the 2D WS2 channel, resulting in a reduced dark current and noise spectral density, significantly improving the sensitivity. Specifically, the WS2 bottom surface is coupled with p-type tellurium (Te) nanoribbon and gold (Au) stripes, thus a vertical pn and Schottky junction can be constructed at WS2/Te and WS2/Au interface, respectively. In both device architectures, the dark current and electric noise are much suppressed due to the formation of depletion region in WS2 channel. Meanwhile, the out-of-plane built-in electric field at junction can facilitate the separation of photo-excited electron–hole pairs, which subsequently yields a faster temporal response. For the WS2/Au device, the incident light can be reflected by the bottom Au and propagate through the WS2 layer again, further boosting the photo-absorption, thus the photodetection sensitivity. The engineered WS2 photodetectors exhibit the noise spectral density as low as 5.36 × 10−14 A Hz−1/2 and high specific detectivity (D*) up to 1.12 × 1011 Jones, which has one–two orders of magnitude improvement compared to the pristine device. This work provides an effective and universal interface engineering strategy to achieve low noise and high sensitivity in 2D photodetectors.

2D CuInP2Se6 in High‐Sensitivity UV‐vis And X‐Ray Detection

AbstractMetal thio(seleno)phosphates are renowned for their multifaceted physical characteristics and versatile applications, particularly in optoelectronics. In detection applications, a low and stable dark current is crucial, enhancing the sensitivity and signal‐to‐noise ratio of detectors. Herein, a van der Waals layered material has synthesized, CuInP2Se6. Despite its nanometric scale, 2D CuInP2Se6 detector transcends the conventional absorption inefficiencies tied to ultrathin materials. It delivers exceptional ultraviolet–visible detection, characterized by an ultralow, stable dark current of 150 fA, and a noise power density of 27.7 fA Hz−1/2 at room temperature. The in‐depth investigation reveals a responsivity of 4.47 A W−1, an external quantum efficiency of 1369%, a special detectivity of 1.44 × 1013 Jones, and a rapid response speed of 280 µs, positioning it at the pinnacle of 2D photodetector performance. The CuInP2Se6’s ultralow, stable dark current paves the way for X‐ray detection, achieving an unprecedented sensitivity of 1.32 × 105 µC Gyair−1 cm−2 and a low detection limit of 0.15 µGyair s−1. Furthermore, 2D CuInP2Se6 detector exhibits a remarkable image‐sensing capability, adeptly capturing intricate patterns with high resolution. This discovery indicates its promise in revolutionizing integrated micro/nano optoelectronic devices, opening avenues for advancements in light and X‐ray detection and imaging technologies.

Prediction and simulation of a potential barrier block in Van der Waals heterojunction photodetectors.

The pBp structure can effectively suppress the dark current of a photodetector by blocking the majority of carriers. However, it is a big challenge to carry out large-scale simulation optimization for two-dimensional (2D) pBp heterojunction photodetectors due to a lack of the device models. Here, a numerical simulation model of the 2D pBp heterojunction was established based on the finite element method to solve this problem. Using this model, the spatial distribution of the energy band is clarified for each layer. The concentration of nonuniformly distributed electrons, induced by the incident light and bias voltage, is obtained by solving the diffusion and drift equations. The characteristics of the photocurrent and the dark current could be presented and the quantum efficiency could be calculated by counting the ratio of the number of carriers collected at the terminals and the carriers photogenerated. The material parameters could be modified for the optimization of the simulation and prediction. In using our model, a B P/M o S 2/graphene photodetector was constructed, and the simulation results show that it works effectively under a reverse bias ranging from -0.3 to 0V. The external quantum efficiency is 18%, while the internal efficiency approaches 85%. The doping in the barrier region definitely does not affect the dark current and the photocurrent. These results are similar to experimental results published earlier. In addition, with the BP bandgap width of 0.8eV and incident wavelength of 1.7µm, the dark current density predicted by the model could reach 3.3×10-8 A/c m 2, which is two orders lower than the reported 2D photodetectors at room temperature. This proposed model provides a way to design 2D pBp heterojunction photodetectors.

SnS2/MoS2 van der Waals Heterostructure Photodetector with Ultrahigh Responsivity Realized by a Photogating Effect.

Photoresponsivity is a fundamental parameter used to quantify the ability of photoelectric conversion of a photodetector device. High-responsivity photodetectors are essential for numerous optoelectronic applications. Due to the strong light-matter interactions and the high carrier mobility, two-dimensional (2D) materials are promising candidates for the next-generation photodetectors. However, poor light absorption, lack of photoconductive gain, and the interfacial recombination lead to the relatively low responsivity of 2D photodetectors. The photogating effect, which extends the lifetime of photoexcited carriers, provides a simple approach to enhance responsivity in photodetector devices. Here, the O2 plasma treatment introduced surface traps on the SnS2 surface, leading to a gate-tunable photogating effect in SnS2/MoS2 heterojunctions. The heterojunction device exhibits an ultrahigh responsibility of up to 28 A/W. Moreover, the photodetector possesses a wide spectral photoresponse spanning from 300 to 1100 nm and a high specific detectivity (D*) of 4 × 1011 Jones under a 532 nm laser at VDS = 1 V. These results demonstrate that O2 plasma treatment is an efficient and simple avenue to achieve photogating effects, which can be employed to enhance the performance of van der Waals heterostructure photodetector devices and make them suitable for future integration into advanced electronic and optoelectronic systems.

Asymmetric Schottky contacts induced via localized ultrafast laser irradiation for ultrasensitive, self-powered, 2D photodetectors

Self-powered photodetectors hold great promise for addressing power-related challenges in the “Internet of Things (IoT)” era. However, the self-powered performances of a metal-semiconductor-metal (MSM) structure photodetector are inherently limited due to the presence of the symmetric Schottky contacts, leading to canceling photocurrents in opposite directions, while constructing an asymmetric MSM structure demands complicated design or sustained external fields. Herein, we propose a novel contact engineering strategy based on localized femtosecond (fs) laser irradiation, achieving an asymmetric band structure in an MSM-structure photodetector with pristine symmetric Schottky contacts. As a result, a MoS2 photodetector that exhibits exceptional photoresponse and self-powered performances is successfully fabricated. The device type transitions from a photoconductor to a photodiode, exhibiting a significant improvement in the rectification ratio from 1 to > 104. A comprehensive study on fs laser-based contact engineering is conducted by investigating atom diffusion, element variation, and Schottky barrier height variation. Notably, the photodetector demonstrates an exceptional zero-bias responsivity of 1.72 A/W, with a short circuit current of 37.2 nA and maximum output electric power of 1.67 nW. Our work provides a new strategy for modifying the energy band structure and facilitates the fabrication of high-performance self-powered photodetectors.

Nitrogen Pretreatment of Growth Substrates for Vacancy-Saturated MoS2.

Two-dimensional transition-metal dichalcogenides (2D TMDCs) are considered promising materials for optoelectronics due to their unique optical and electric properties. However, their potential has been limited by the occurrence of atomic vacancies during synthesis. While post-treatment processes have demonstrated the passivation of such vacancies, they increase process complexity and affect the TMDC's quality. We here introduce the concept of pretreatment as a facile and powerful route to solve the problem of vacancies in MoS2. Low-temperature nitridation of the sapphire substrate prior to growth provides a nondestructive method to MoS2 modification without introducing new processing steps or increasing the thermal budget. Spectroscopic characterization and atomic-resolution microscopy reveal the incorporation of nitrogen from the sapphire surface layer into chalcogen vacancies. The resulting MoS2 with nitrogen-saturated defects shows a decrease in midgap states and more intrinsic doping as confirmed by ab initio calculations and optoelectronic measurements. The demonstrated pretreatment method opens up new routes toward future, high-performance 2D electronics, as evidenced by a 3-fold reduction in contact resistance and a 10-fold improved performance of 2D photodetectors.

High-performance 2D WS2 photodetector enhanced by charge-transfer doping through NH3 annealing

Transition metal dichalcogenides (TMDs) are potential candidates towards the next-generation photodetector, owing to their tunable energy bandgap and strong light–matter interaction. However, the low charge-carrier mobility and insufficient quantum efficiency of TMDs-based devices restrain their optoelectronic performances. Therefore, an effective and facile doping method needs to be developed for overcoming their poor optoelectronics properties. Here, we demonstrate a controllable nondegenerate n-doping technique for 2D TMDs materials by annealing under NH3 flow. The on/off current ratio and field-effect mobility of the device after annealing treatment increases about 2 orders of magnitude and 23 times, respectively. We attribute this remarkable doping effect to the physical adsorption and chemical adsorption of NH3 as well as the associated formation of isolated sulfur vacancies, which is dynamically activated during the annealing treatment, and further verified by the atomic-scale characterization and density functional theory calculations. The annealing temperature and time present a controllable modulation on the electron doping levels of the WS2 channel. The fabricated WS2 photodetector can operate in a broad range of visible light at room temperature. At 532 nm wavelength, the responsivity of 2.97 A/W, external quantum efficiency of 699% and specific detectivity of over 1010 Jones indicate its great potential in sensitive and power-efficient photodetectors. Our results provide an effective method to realize controllable n-doping of 2D materials, aiming for fabricating high-performance 2D photodetectors.

Giant Superlinear Power Dependence of Photocurrent Based on Layered Ta2 NiS5 Photodetector.

Photodetector based on two-dimensional (2D) materials is an ongoing quest in optoelectronics. 2D photodetectors are generally efficient at low illuminating power but suffer severe recombination processes at high power, which results in the sublinear power-dependent photoresponse and lower optoelectronic efficiency. The desirable superlinear photocurrent is mostly achieved by sophisticated 2D heterostructures or device arrays, while 2D materials rarely show intrinsic superlinear photoresponse. This workreports the giant superlinear power dependence of photocurrent based on multilayer Ta2 NiS5 . While the fabricated photodetector exhibits good sensitivity (3.1 mS W-1 per □) and fast photoresponse (31 µs), the bias-, polarization-, and spatial-resolved measurements point to an intrinsic photoconductive mechanism. By increasing the incident power density from 1.5 to 200 µW µm-2 , the photocurrent power dependence varies from sublinear to superlinear. At higher illuminating conditions, prominent superlinearity is observed with a giant power exponent of γ = 1.5. The unusual photoresponse can be explained by a two-recombination-center model where density of states of the recombination centers (RC) effectively closes all recombination channels. The photodetector is integrated into camera for taking photos with enhanced contrast due to superlinearity. This work provides an effective route to enable higher optoelectronic efficiency at extreme conditions.

Air-Stable Violet Phosphorus/MoS2 van der Waals Heterostructure for High-Responsivity and Gate-Tunable Photodetection.

Violet phosphorus (VP), a newly emerging elemental 2D semiconductor, with attractive properties such as tunable bandgap, high carrier mobility, and unusual structural anisotropy, offers significant opportunities for designing high-performance electronic and optoelectronic devices. However, the study on fundamental property and device application of 2D VP is seriously hindered by its inherent instability in ambient air. Here, a VP/MoS2 van der Waals heterostructure is constructed by vertically staking few-layer VP and MoS2 , aiming to utilize the synergistic effect of the two materials to achieve a high-performance 2D photodetector. The strong optical absorption of VP combining with the type-II band alignment of VP/MoS2 heterostructure make VP play a prominent photogating effect. As a result, the VP/MoS2 heterostructure photodetector achieves an excellent photoresponse performances with ultrahigh responsivity of 3.82 × 105 AW-1 , high specific detectivity of 9.17 × 1013 Jones, large external quantum efficiency of 8.91 × 107 %, and gate tunability, which are much superior to that of individual MoS2 device or VP device. Moreover, the VP/MoS2 heterostructure photodetector indicates superior air stability due to the effective protection of VP by MoS2 encapsulation. This work sheds light on the future study of the fundamental property and optoelectronic device application of VP.

2D SiP2/h-BN for a Gate-Controlled Phototransistor with Ultrahigh Sensitivity.

Two-dimensional (2D) materials are extremely attractive for the construction of highly sensitive photodetectors due to their unique electronic and optical properties. However, developing 2D photodetectors with ultrahigh sensitivity for extremely low-light-level detection is still a challenge owing to the limitation of high dark current and low detectivity. Herein, a gate-controlled phototransistor based on 2D SiP2/hexagonal boron nitride (h-BN) was rationally designed and demonstrated ultrahigh sensitivity for the first time. With a back-gate device geometry, the SiP2/h-BN phototransistor exhibits an ultrahigh detectivity of 3.4 × 1013 Jones, which is one of the highest values among 2D material-based photodetectors. In addition, the phototransistor also shows a gate tunable responsivity of ≤43.5 A/W at a gate voltage of 30 V due to the photogating effect. The ultrahigh sensitivity of the SiP2-based phototransistor is attributed to the extremely low dark current suppressed by the phototransistor configuration and the improved photocurrent by using h-BN as a substrate to reduce charge scattering. This work provides a facile strategy for improving the detectivity of photodetectors and validates the great potential of 2D SiP2 phototransistors for ultrasensitive optoelectronic applications.

Free-Standing Multilayer MoS2-BP Heterostructures for High Performance Self-Powered Photodetector

Phototransistors based on two-dimensional materials such as graphene, transition metal sulfides, and black phosphorus are widely used in in recent years. However, these materials have weak optical absorption, low carrier mobility or poor air stability, which restrict their application in the field of high-sensitivity detection. The inter-stacking of two-dimensional semiconductors can achieve excellent performance, and has promising applications in the field of optoelectronics. The stacking of two-dimensional semiconductors can form van der Waals heterostructures with low defect states and spatial homogeneity, which is an effective way to improve the performance of 2D photodetectors. Based on this, this paper constructs a free-standing multilayer MoS2-BP heterostructure by mechanical exfoliation for high performance self-powered photodetector. The strong space charge region can effectively separate the photogenerated carriers, so it has a good photodetection capability in the self-driven state. Moreover, we analyse and summarize the working mechanism of photodetectors based on 2D materials, and review high sensitivity detectors of recent years based on 2D material heterojunction. Finally, the challenges to further improve the detection sensitivity are pointed out. Thus, our free-standing multilayer MoS2-BP heterostructure propose a useful experience and reference for the future development of self-power photodetectors.

A facile covalent strategy for ultrafast negative photoconductance hybrid graphene/porphyrin-based photodetector

As a powerful complement to positive photoconductance (PPC), negative photoconductance (NPC) holds great potential for photodetector. However, the slow response of NPC relative to PPC devices limits their integration. Here, we propose a facile covalent strategy for an ultrafast NPC hybrid 2D photodetector. Our transistor-based graphene/porphyrin model device with a rise time of 0.2 ms and decay time of 0.3 ms has the fastest response time in the so far reported NPC hybrid photodetectors, which is attributed to efficient photogenerated charge transport and transfer. Both the photosensitive porphyrin with an electron-rich and large rigid structure and the built-in graphene frame with high carrier mobility are prone to the photogenerated charge transport. Especially, the intramolecular donor-acceptor system formed by graphene and porphyrin through covalent bonding promotes photoinduced charge transfer. This covalent strategy can be applied to other nanosystems for high-performance NPC hybrid photodetector.

A Review of Perovskite-Based Photodetectors and Their Applications.

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

Synthesis of Ultrathin Topological Insulator β-Ag2 Te and Ag2 Te/WSe2 -Based High-Performance Photodetector.

β-Ag2 Te has attracted considerable attention in the application of electronics and optoelectronics due to its narrow bandgap, high mobility, and topological insulator properties. However, it remains a significant challenge to synthesize 2D Ag2 Te because of the non-layered structure of Ag2 Te. Herein, the synthesis of large-size, ultrathin single crystal topological insulator 2D Ag2 Te via the van der Waals epitaxial method for the first time is reported. The 2D Ag2 Te crystal exhibits p-type conduction behavior with high carrier mobility of 3336 cm2 V-1 s-1 at room temperature. Taking advantage of the high mobility and perfect electron structure of Ag2 Te, the Ag2 Te/WSe2 heterojunctions are fabricated via mechanical stacking and show an ultrahigh rectification ratio of 2×105 . Ag2 Te/WSe2 photodetector also exhibits self-driven properties with a fast response speed (40 µs/60 µs) in the near-infrared region. High responsivity (219mA W-1 ) and light ON/OFF ratio of 6×105 are obtained under the photovoltaic mode. The overall performance of the Ag2 Te/WSe2 photodetector is significantly competitive among all reported 2D photodetectors. These results indicate that 2D Ag2 Te is a promising candidate for future electronic and optoelectronic applications.

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction.

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS3 with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS2, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS3/MoS2 heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS3 photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS3/MoS2 heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS3/MoS2 heterojunction system may accelerate the design and fabrication of other 2D functional devices.