Fast and Highly Sensitive Ionic‐Polymer‐Gated WS2–Graphene Photodetectors

The combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer‐scale electronic devices. Presently, long‐lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gate‐voltage pulses, have been employed to achieve bandwidths suitable for applications such as video‐frame‐rate imaging. Here, atomically thin graphene–WS₂ heterostructure photodetectors encapsulated in an ionic polymer are reported, which are uniquely able to operate at bandwidths up to 1.5 kHz whilst maintaining internal gain as large as 10⁶. Highly mobile ions and the nanometer‐scale Debye length of the ionic polymer are used to screen charge traps and tune the Fermi level of the graphene over an unprecedented range at the interface with WS₂. Responsivity R = 10⁶ A W^?1 and detectivity D* = 3.8 × 10¹¹ Jones are observed, approaching that of single‐photon counters. The combination of both high responsivity and fast response times makes these photodetectors suitable for video‐frame‐rate imaging applications.     

Low‐Voltage Photodetectors with High Responsivity Based on Solution‐Processed Micrometer‐Scale All‐Inorganic Perovskite Nanoplatelets

All‐inorganic photodetectors based on scattered CsPbBr₃ nanoplatelets with lateral dimension as large as 10 µm are fabricated, and the CsPbBr₃ nanoplatelets are solution processed governed by a newly developed ion‐exchange soldering mechanism. Under illumination of a 442 nm laser, the photoresponsivity of photodetectors based on these scattered CsPbBr₃ nanoplatelets is as high as 34 A W^?1, which is the largest value reported from all‐inorganic perovskite photodetectors with an external driven voltage as small as 1.5 V. Moreover, the rise and fall times are 0.6 and 0.9 ms, respectively, which are comparable to most of the state‐of‐the‐art all‐inorganic perovskite‐based photodetectors. All the material synthesis and device characterization are conducted at room temperature in ambient air. This work demonstrates that the solution‐processed large CsPbBr₃ nanoplatelets are attractive candidates to be applied in low‐voltage, low‐cost, ultra highly integrated optoelectronic devices.     

Near‐Infrared Photodetectors Based on MoTe2/Graphene Heterostructure with High Responsivity and Flexibility

2D transition metal dichalcogenides (TMDCs) have attracted considerable attention due to their impressively high performance in optoelectronic devices. However, efficient infrared (IR) photodetection has been significantly hampered because the absorption wavelength range of most TMDCs lies in the visible spectrum. In this regard, semiconducting 2D MoTe₂ can be an alternative choice owing to its smaller band gap ≈1 eV from bulk to monolayer and high carrier mobility. Here, a MoTe₂/graphene heterostructure photodetector is demonstrated for efficient near‐infrared (NIR) light detection. The devices achieve a high responsivity of ≈970.82 A W^?1 (at 1064 nm) and broadband photodetection (visible‐1064 nm). Because of the effective photogating effect induced by electrons trapped in the localized states of MoTe₂, the devices demonstrate an extremely high photoconductive gain of 4.69 × 10⁸ and detectivity of 1.55 × 10¹¹ cm Hz^1/2 W^?1. Moreover, flexible devices based on the MoTe₂/graphene heterostructure on flexible substrate also retains a good photodetection ability after thousands of times bending test (1.2% tensile strain), with a high responsivity of ≈60 A W^?1 at 1064 nm at V _DS = 1 V, which provides a promising platform for highly efficient, flexible, and low cost broadband NIR photodetectors.     

Substantially Improving Device Performance of All‐Inorganic Perovskite‐Based Phototransistors via Indium Tin Oxide Nanowire Incorporation

All‐inorganic halide perovskites (IHPs) have attracted enormous attention due to their intrinsically high optical absorption coefficient and superior ambient stabilities. However, the photosensitivity of IHP‐based photodetectors is still restricted by their poor conductivities. Here, a facile design of hybrid phototransistors based on the CsPbBr₃ thin film and indium tin oxide (ITO) nanowires (NWs) integrated into a InGaZnO channel in order to achieve both high photoresponsivity and fast response is reported. The metallic ITO NWs are employed as electron pumps and expressways to efficiently extract photocarriers from CsPbBr₃ and inject electrons into InGaZnO. The obtained device exhibits the outstanding responsivity of 4.9 × 10⁶ A W^?1, which is about 100‐fold better than the previous best results of CsPbBr₃‐based photodetectors, together with the fast response (0.45/0.55 s), long‐term stability (200 h in ambient), and excellent mechanical flexibility. By operating the phototransistor in the depletion regime, an ultrahigh specific detectivity up to 7.6 × 10¹³ Jones is achieved. More importantly, the optimized spin‐coating manufacturing process is highly beneficial for achieving uniform InGaZnO‐ITO/perovskite hybrid films for high‐performance flexible detector arrays. All these results can not only indicate the potential of these hybrid phototransistors but also provide a valuable insight into the design of hybrid material systems for high‐performance photodetection.     

Schottky Barrier‐Controlled Black Phosphorus/Perovskite Phototransistors with Ultrahigh Sensitivity and Fast Response

Phototransistors are recognized as highly sensitive photodetectors owing to their high gain induced by a photogating effect. However, the response speed of a typical phototransistor is rather slow due to the long lifetime of trapped carriers in the channel. Here, a novel Schottky barrier‐controlled phototransistor that shows ultrahigh sensitivity as well as a fast response speed is reported. The device is based on a channel of few‐layer black phosphorous modified with a MAPbI_3?xCl_x perovskite layer, whose channel current is limited by the Schottky barrier at the source electrode. The photoresponse speed of the device can be tuned by changing the drain voltage, which is attributed to a field‐assisted detrapping process of electrons in the perovskite layer close to the Schottky barrier. Under optimal conditions, the device exhibits a high responsivity of 10⁶–10⁸ A W^?1, an ultrahigh specific detectivity up to 9 × 10¹³ Jones, and a response time of ≈10 ms.     

Highly Sensitive and Broadband Organic Photodetectors with Fast Speed Gain and Large Linear Dynamic Range at Low Forward Bias

Photodetectors with high photoelectronic gain generally require a high negative working voltage and a very low environment temperature. They also exhibit low response speed and narrow linear dynamic range (LDR). Here, an organic photodiode is demonstrated, which shows a large amount of photon to electron multiplication at room temperature with highest external quantum efficiency (EQE) from ultraviolet (UV) to near‐infrared region of 5.02 × 10³% (29.55 A W^?1) under a very low positive voltage of 1.0 V, accompanied with a fast response speed and a high LDR from 10^?7 to 10¹ mW cm^?2. At a relatively high positive bias of 10 V, the EQE is up to 1.59 × 10⁵% (936.05 A W^?1). Inversely, no gain is found at negative bias. The gain behavior is exactly similar to a bipolar phototransistor, which is attributed to the photoinduced release of accumulated carriers. The devices at a low voltage exhibit a normalized detectivity (D *) over 10¹⁴ Jones by actual measurements, which is about two or three order of magnitudes higher than that of the highest existing photodetectors. These pave a new way for realization of high sensitive detectors with fast response toward the single photon detection.     

Low‐Noise and Large‐Linear‐Dynamic‐Range Photodetectors Based on Hybrid‐Perovskite Thin‐Single‐Crystals

Organic–inorganic halide perovskites are promising photodetector materials due to their strong absorption, large carrier mobility, and easily tunable bandgap. Up to now, perovskite photodetectors are mainly based on polycrystalline thin films, which have some undesired properties such as large defective grain boundaries hindering the further improvement of the detector performance. Here, perovskite thin‐single‐crystal (TSC) photodetectors are fabricated with a vertical p–i–n structure. Due to the absence of grain‐boundaries, the trap densities of TSCs are 10–100 folds lower than that of polycrystalline thin films. The photodetectors based on CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ TSCs show low noise of 1–2 fA Hz^?1/2, yielding a high specific detectivity of 1.5 × 10¹³ cm Hz^1/2 W^?1. The absence of grain boundaries reduces charge recombination and enables a linear response under strong light, superior to polycrystalline photodetectors. The CH₃NH₃PbBr₃ photodetectors show a linear response to green light from 0.35 pW cm^?2 to 2.1 W cm^?2, corresponding to a linear dynamic range of 256 dB.     

Graphene–Ruthenium Complex Hybrid Photodetectors with Ultrahigh Photoresponsivity

The maximum responsivity of a pure monolayer graphene‐based photodetector is currently less than 10 mA W^?1 because of small optical absorption and short recombination lifetime. Here, a graphene hybrid photodetector functionalized with a photoactive ruthenium complex that shows an ultrahigh responsivity of ≈1 × 10⁵ A W^?1 and a photoconductive gain of ≈3 × 10⁶ under incident optical intensity of the order of sub‐milliwatts is reported. This responsivity is two orders of magnitude higher than the precedent best performance of graphene‐based photodetectors under a similar incident light intensity. Upon functionalization with a 4‐nm‐thick ruthenium complex, monolayer graphene‐based photodetectors exhibit pronounced n‐type doping effect due to electron transfer via the metal?ligand charge transfer (MLCT) from the ruthenium complex to graphene. The ultrahigh responsivity is attributed to the long lifetime and high mobility of the photoexcited charge carriers. This approach is highly promising for improving the responsivity of graphene‐based photodetectors.     

In Situ Growth of 120 cm2 CH3NH3PbBr3 Perovskite Crystal Film on FTO Glass for Narrowband‐Photodetectors

Organometal trihalide perovskites have been attracting intense attention due to their enthralling optoelectric characteristics. Thus far, most applications focus on polycrystalline perovskite, which however, is overshadowed by single crystal perovskite with superior properties such as low trap density, high mobility, and long carrier diffusion length. In spite of the inherent advantages and significant optoelectronic applications in solar cells and photodetectors, the fabrication of large‐area laminar perovskite single crystals is challenging. In this report, an ingenious space‐limited inverse temperature crystallization method is first demonstrated to the in situ synthesis of 120 cm² large‐area CH₃NH₃PbBr₃ crystal film on fluorine‐doped tin oxide (FTO) glass. Such CH₃NH₃PbBr₃ perovskite crystal film is successfully applied to narrowband photodetectors, which enables a broad linear response range of 10^?4–10² mW cm^?2, 3 dB cutoff frequency (f _{3 dB}) of ≈110 kHz, and high narrow response under low bias ?1 V.     

Hot‐Pressed CsPbBr3 Quasi‐Monocrystalline Film for Sensitive Direct X‐ray Detection

An X‐ray detector with high sensitivity would be able to increase the generated signal and reduce the dose rate; thus, this type of detector is beneficial for applications such as medical imaging and product inspection. The inorganic lead halide perovskite CsPbBr₃ possesses relatively larger density and a higher atomic number in contrast to its hybrid counterpart. Therefore, it is expected to provide high detection sensitivity for X‐rays; however, it has rarely been studied as a direct X‐ray detector. Here, a hot‐pressing method is employed to fabricate thick quasi‐monocrystalline CsPbBr₃ films, and a record sensitivity of 55 684 µC Gy_air^?1 cm^?2 is achieved, surpassing all other X‐ray detectors (direct and indirect). The hot‐pressing method is simple and produces thick quasi‐monocrystalline CsPbBr₃ films with uniform orientations. The high crystalline quality of the CsPbBr₃ films and the formation of self‐formed shallow bromide vacancy defects during the high‐temperature process result in a large µτ product and, therefore, a high photoconductivity gain factor and high detection sensitivity. The detectors also exhibit relatively fast response speed, negligible baseline drift, and good stability, making a CsPbBr₃ X‐ray detector extremely competitive for high‐contrast X‐ray detections.     

Atomic‐Layer Deposition‐Assisted Double‐Side Interfacial Engineering for High‐Performance Flexible and Stable CsPbBr3 Perovskite Photodetectors toward Visible Light Communication Applications

Self‐powered photodetectors (PDs) based on inorganic metal halide perovskites are regarded as promising alternatives for the next generation of photodetectors. However, uncontrollable film growth and sluggish charge extraction at interfaces directly limit the sensitivity and response speed of perovskite‐based photodetectors. Herein, by assistance of an atomic layer deposition (ALD) technique, CsPbBr₃ perovskite thin films with preferred orientation and enlarged grain size are obtained on predeposited interfacial modification layers. Thanks to improved film quality and double side interfacial engineering, the optimized CsPbBr₃ (Al₂O₃/CsPbBr₃/TiO₂, ACT) perovskite PDs exhibit outstanding performance with ultralow dark current of 10^?11 A, high detectivity of 1.88 × 10¹³ Jones and broad linear dynamic range (LDR) of 172.7 dB. Significantly, excellent long‐term environmental stability (ambient conditions >100 d) and flexibility stability (>3000 cycles) are also achieved. The remarkable performance is credited to the synergistic effects of high carrier conductivity and collection efficiency, which is assisted by ALD modification layers. Finally, the ACT PDs are successfully integrated into a visible light communication system as a light receiver on transmitting texts, showing a bit rate as high as 100 kbps. These results open the window of high performance all‐inorganic halide perovskite photodetectors and extends to rational applications for optical communication.     

Gate‐Controlled Graphene–Silicon Schottky Junction Photodetector

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate‐controlled graphene–silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈10⁴), a very high photoresponsivity (≈70 A W⁻¹), and a low dark current in the order of µA cm⁻² in a wide wavelength range (395–850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene‐field‐effect transistor‐based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.     

A Dual‐Gate MoS2 Photodetector Based on Interface Coupling Effect

2D transition metal dichalcogenides (TMDs) based photodetectors have shown great potential for the next generation optoelectronics. However, most of the reported MoS₂ photodetectors function under the photogating effect originated from the charge‐trap mechanism, which is difficult for quantitative control. Such devices generally suffer from a poor compromise between response speed and responsivity (R) and large dark current. Here, a dual‐gated (DG) MoS₂ phototransistor operating based on the interface coupling effect (ICE) is demonstrated. By simultaneously applying a negative top‐gate voltage (V_TG) and positive back‐gate voltage (V_BG) to the MoS₂ channel, the photogenerated holes can be effectively trapped in the depleted region under TG. An ultrahigh R of ≈10⁵ A W^?1 and detectivity (D*) of ≈10¹⁴ Jones are achieved in several devices with different thickness under P_in of 53 µW cm^?2 at V_TG = ?5 V. Moreover, the response time of the DG phototransistor can also be modulated based on the ICE. Based on these systematic measurements of MoS₂ DG phototransistors, the results show that the ICE plays an important role in the modulation of photoelectric performances. The results also pave the way for the future optoelectrical application of 2D TMDs materials and prompt for further investigation in the DG structured phototransistors.     

High Performance and Stable All‐Inorganic Metal Halide Perovskite‐Based Photodetectors for Optical Communication Applications

Photodetectors are critical parts of an optical communication system for achieving efficient photoelectronic conversion of signals, and the response speed directly determines the bandwidth of the whole system. Metal halide perovskites, an emerging class of low‐cost solution‐processed semiconductors, exhibiting strong optical absorption, low trap states, and high carrier mobility, are widely investigated in photodetection applications. Herein, through optimizing the device engineering and film quality, high‐performance photodetectors based on all‐inorganic cesium lead halide perovskite (CsPbI_xBr_3–x), which simultaneously possess high sensitivity and fast response, are demonstrated. The optimized devices processed from CsPbIBr₂ perovskite show a practically measured detectable limit of about 21.5 pW cm^?2 and a fast response time of 20 ns, which are both among the highest reported device performance of perovskite‐based photodetectors. Moreover, the photodetectors exhibit outstanding long‐term environmental stability, with negligible degradation of the photoresponse property after 2000 h under ambient conditions. In addition, the resulting perovskite photodetector is successfully integrated into an optical communication system and its applications as an optical signal receiver on transmitting text and audio signals is demonstrated. The results suggest that all‐inorganic metal halide perovskite‐based photodetectors have great application potential for optical communication.     

A 1300 mm2 Ultrahigh‐Performance Digital Imaging Assembly using High‐Quality Perovskite Single Crystals

By fine‐tuning the crystal nucleation and growth process, a low‐temperature‐gradient crystallization method is developed to fabricate high‐quality perovskite CH₃NH₃PbBr₃ single crystals with high carrier mobility of 81 ± 5 cm² V^?1 s^?1 (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 10⁹ cm^?3 (even four orders of magnitude lower than that of single‐crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 10¹³ Jones, ≈10–100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large‐area (≈1300 mm²) imaging assembly composed of a 729‐pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high‐quality perovskite single‐crystal‐based devices for more advanced imaging sensors.     

Improving All‐Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect

All‐inorganic perovskites have high carrier mobility, long carrier diffusion length, excellent visible light absorption, and well overlapping with localized surface plasmon resonance (LSPR) of noble metal nanocrystals (NCs). The high‐performance photodetectors can be constructed by means of the intrinsic outstanding photoelectric properties, especially plasma coupling. Here, for the first time, inorganic perovskite photodetectors are demonstrated with synergetic effect of preferred‐orientation film and plasmonic with both high performance and solution process virtues, evidenced by 238% plasmonic enhancement factor and 10⁶ on/off ratio. The CsPbBr₃ and Au NC inks are assembled into high‐quality films by centrifugal‐casting and spin‐coating, respectively, which lead to the low cost and solution‐processed photodetectors. The remarkable near‐field enhancement effect induced by the coupling between Au LSPR and CsPbBr₃ photogenerated carriers is revealed by finite‐difference time‐domain simulations. The photodetector exhibits a light on/off ratio of more than 10⁶ under 532 nm laser illumination of 4.65 mW cm^?2. The photocurrent increases from 0.67 to 2.77 μA with centrifugal‐casting. Moreover, the photocurrent rises from 245.6 to 831.1 μA with Au NCs plasma enhancement, leading to an enhancement factor of 238%, which is the most optimal report among the LSPR‐enhanced photodetectors, to the best of our knowledge. The results of this study suggest that all‐inorganic perovskites are promising semiconductors for high‐performance solution‐processed photodetectors, which can be further enhanced by Au plasmonic effect, and hence have huge potentials in optical communication, safety monitoring, and biological sensing.     

Liquid‐Alloy‐Assisted Growth of 2D Ternary Ga2In4S9 toward High‐Performance UV Photodetection

2D ternary systems provide another degree of freedom of tuning physical properties through stoichiometry variation. However, the controllable growth of 2D ternary materials remains a huge challenge that hinders their practical applications. Here, for the first time, by using a gallium/indium liquid alloy as the precursor, the synthesis of high‐quality 2D ternary Ga₂In₄S₉ flakes of only a few atomic layers thick (≈2.4 nm for the thinnest samples) through chemical vapor deposition is realized. Their UV‐light‐sensing applications are explored systematically. Photodetectors based on the Ga₂In₄S₉ flakes display outstanding UV detection ability (R _λ = 111.9 A W^?1, external quantum efficiency = 3.85 × 10⁴%, and D* = 2.25 × 10¹¹ Jones@360 nm) with a fast response speed (τ_ring ≈ 40 ms and τ_decay ≈ 50 ms). In addition, Ga₂In₄S₉‐based phototransistors exhibit a responsivity of ≈10⁴ A W^?1@360 nm above the critical back‐gate bias of ≈0 V. The use of the liquid alloy for synthesizing ultrathin 2D Ga₂In₄S₉ nanostructures may offer great opportunities for designing novel 2D optoelectronic materials to achieve optimal device performance.     

High Detectivity Graphene‐Silicon Heterojunction Photodetector

A graphene/n‐type silicon (n‐Si) heterojunction has been demonstrated to exhibit strong rectifying behavior and high photoresponsivity, which can be utilized for the development of high‐performance photodetectors. However, graphene/n‐Si heterojunction photodetectors reported previously suffer from relatively low specific detectivity due to large dark current. Here, by introducing a thin interfacial oxide layer, the dark current of graphene/n‐Si heterojunction has been reduced by two orders of magnitude at zero bias. At room temperature, the graphene/n‐Si photodetector with interfacial oxide exhibits a specific detectivity up to 5.77 × 10¹³ cm Hz^1/2 W^‐1 at the peak wavelength of 890 nm in vacuum, which is highest reported detectivity at room temperature for planar graphene/Si heterojunction photodetectors. In addition, the improved graphene/n‐Si heterojunction photodetectors possess high responsivity of 0.73 A W^?1 and high photo‐to‐dark current ratio of ≈10⁷. The current noise spectral density of the graphene/n‐Si photodetector has been characterized under ambient and vacuum conditions, which shows that the dark current can be further suppressed in vacuum. These results demonstrate that graphene/Si heterojunction with interfacial oxide is promising for the development of high detectivity photodetectors.     

Lateral Graphene‐Contacted Vertically Stacked WS2/MoS2 Hybrid Photodetectors with Large Gain

A demonstration is presented of how significant improvements in all‐2D photodetectors can be achieved by exploiting the type‐II band alignment of vertically stacked WS₂/MoS₂ semiconducting heterobilayers and finite density of states of graphene electrodes. The photoresponsivity of WS₂/MoS₂ heterobilayer devices is increased by more than an order of magnitude compared to homobilayer devices and two orders of magnitude compared to monolayer devices of WS₂ and MoS₂, reaching 10³ A W^?1 under an illumination power density of 1.7 × 10² mW cm^?2. The massive improvement in performance is due to the strong Coulomb interaction between WS₂ and MoS₂ layers. The efficient charge transfer at the WS₂/MoS₂ heterointerface and long trapping time of photogenerated charges contribute to the observed large photoconductive gain of ≈3 × 10⁴. Laterally spaced graphene electrodes with vertically stacked 2D van der Waals heterostructures are employed for making high‐performing ultrathin photodetectors.     

MoS2–HgTe Quantum Dot Hybrid Photodetectors beyond 2 µm

Mercury telluride (HgTe) colloidal quantum dots (CQDs) have been developed as promising materials for the short and mid‐wave infrared photodetection applications because of their low cost, solution processing, and size tunable absorption in the short wave and mid‐infrared spectrum. However, the low mobility and poor photogain have limited the responsivity of HgTe CQD‐based photodetectors to only tens of mA W^?1. Here, HgTe CQDs are integrated on a TiO₂ encapsulated MoS₂ transistor channel to form hybrid phototransistors with high responsivity of ≈10⁶ A W^?1, the highest reported to date for HgTe QDs. By operating the phototransistor in the depletion regime enabled by the gate modulated current of MoS₂, the noise current is significantly suppressed, leading to an experimentally measured specific detectivity D* of ≈10¹² Jones at a wavelength of 2 µm. This work demonstrates for the first time the potential of the hybrid 2D/QD detector technology in reaching out to wavelengths beyond 2 µm with compelling sensitivity.