Low noise, IR-blind organohalide perovskite photodiodes for visible light detection and imaging

Dark Current in Broadband Perovskite-Organic Heterojunction Photodetectors Controlled by Interfacial Energy Band Offset

Lead halide perovskite and organic semiconductors are promising classes of materials for photodetector (PD) applications. State-of-the-art perovskite PDs have performance metrics exceeding silicon PDs in the visible. While organic semiconductors offer bandgap tunability due to their chemical design with detection extended into the near-infrared (NIR), perovskites are limited to the visible band and the first fraction of the NIR spectrum. In this work, perovskite-organic heterojunction (POH) PDs with absorption up to 950 nm are designed by the dual contribution of perovskite and the donor:acceptor bulk-heterojunction (BHJ), without any intermediate layer. The effect of the energetics of the donor materials is systematically studied on the dark current (Jd) of the device by using the PBDB-T polymer family. Combining the experimental results with drift-diffusion simulations, it is shown that Jd in POH devices is limited by thermal generation via deep trap states in the BHJ. Thus, the best performance is obtained for the PM7-based POH, which delivers an ultra-low noise current of 2 × 10-14 A Hz-1/2 and high specific detectivity of 4.7 × 1012 Jones in the NIR. Last, the application of the PM7-based POH devices as NIR pulse oximeter with high-accuracy heartbeat monitoring at long-distance of 2 meters is demonstrated.

Wide-Range and Multistate Work Functions of Organometallic Halide Perovskite Films Regulated by Ferroelectric Substrates

Work function of organometallic halide perovskite (OHP) films is one of the most crucial photoelectric properties, which dominates the carrier dynamics in OHP-based devices. Despite surface treatments by additives being widely used to promote crystallization and passivate defects in OHP films, these chemical strategies for modulation of work functions face two trade-offs: homogeneity on the surface versus along the thickness; the range versus the accuracy of modulation. Herein, by using ferroelectric substrates of uniform polarization and subnanometer roughness, homogeneous CH3NH3PbI3 films are fabricated with five states of work functions with large spanning (∼0.8 eV) and high precision (sd ∼ 0.01 eV). We reveal that the ferroelectric polarizations and the smooth surfaces regulate CH3NH3+ orientations and suppress distortions of PbI6 octahedrons. The wide-range and multistate work functions originate from the ordered CH3NH3+ orientations and PbI6 octahedrons, which result in intensity enhancements and wavelength shifts in photoluminescence with a 30-fold increase of photoexcited carrier lifetime.

Progress and Application of Halide Perovskite Materials for Solar Cells and Light Emitting Devices

Halide perovskite materials have attracted worldwide attention in the photovoltaic area due to the rapid improvement in efficiency, from less than 4% in 2009 to 26.1% in 2023 with only a nanometer lever photo-active layer. Meanwhile, this nova star found applications in many other areas, such as light emitting, sensor, etc. This review started with the fundamentals of physics and chemistry behind the excellent performance of halide perovskite materials for photovoltaic/light emitting and the methods for preparing them. Then, it described the basic principles for solar cells and light emitting devices. It summarized the strategies including nanotechnology to improve the performance and the application of halide perovskite materials in these two areas: from structure-property relation to how each component in the devices affects the overall performance. Moreover, this review listed the challenges for the future applications of halide perovskite materials.

Highly efficient, self-powered UV photodiodes based on leadfree perovskite nanocrystals through interfacial engineering

Double perovskite crystals are promising alternatives for lead-based perovskites that has potential to address toxicity and instability issues. In this study, Cs2AgBiCl6nanocrystals (NCs) with high absorption coefficients were synthesized by hot-injection method. The bandgap engineering was realized by tuning the halide composition in Cs2AgBiCl6to Cs2AgBiBr6. Both NCs were used as light-absorbing layers in lead-free perovskite photodiodes that exhibit wavelength-selectivity for UV-visible light operatable even at a bias voltage of 0 V. Cs2AgBiBr6-based photodiode exhibits a characteristic detection peak at 340 nm with a responsivity of 3.21 mA W-1, a specific detectivity up to 8.91 × 1010Jones and a fast response speed with a rise/fall time of 30/35 ms. The excellent performance of self-driven photodiodes lights up the prospect of lead-free perovskite NCs in highly efficient optoelectronic devices.

Highly Efficient Ternary Near-Infrared Organic Photodetectors for Biometric Monitoring

Near-infrared (NIR) small-molecule acceptors that absorb at wavelengths of up to 1000 nm are attractive for applications in organic photodetectors (OPDs) and biometrics. In this study, we incorporated IEICO-4F as the third component for PffBT4T-2OD:PC₇₁BM-based OPDs to provide an efficient NIR response while greatly suppressing the leakage current at reverse bias. By varying the blend ratio and thickness (250-600 nm), we obtained an NIR OPD displaying an ultralow dark-current density (J_D = 2.62 nA cm^-2), ultrahigh detectivity [D* = 7.2 × 10¹² Jones (850 nm)], high sensitivity, and photoresponsivity covering the region from the ultraviolet to the NIR. We used tapping-mode atomic force microscopy, optical microscopy, grazing-incidence wide-angle X-ray scattering, and contact angle measurements to investigate the effect of IEICO-4F on the performance of the ternary OPDs. The low compatibility of PffBT4T-2OD and IEICO-4F, originating from weak intermolecular interactions, allowed us to manipulate the degree of phase separation between the donor and acceptor in the ternary blends, leading to an optimized blend morphology featuring efficient charge separation, transport, and collection. To demonstrate its applicability, we integrated our OPD with two light-emitting diodes and used the system for precisely calculated transmissive pulse oximetry.

Vitality surveillance at distance using thin-film tandem-like narrowband near-infrared photodiodes with light-enhanced responsivity

Remote measurement of vital sign parameters like heartbeat and respiration rate represents a compelling challenge in monitoring an individual's health in a noninvasive way. This could be achieved by large field-of-view, easy-to-integrate unobtrusive sensors, such as large-area thin-film photodiodes. At long distances, however, discriminating weak light signals from background disturbance demands superior near-infrared (NIR) sensitivity and optical noise tolerance. Here, we report an inherently narrowband solution-processed, thin-film photodiode with ultrahigh and controllable NIR responsivity based on a tandem-like perovskite-organic architecture. The device has low dark currents (<10^-6 mA cm^-2), linear dynamic range >150 dB, and operational stability over time (>8 hours). With a narrowband quantum efficiency that can exceed 200% at 850 nm and intrinsic filtering of other wavelengths to limit optical noise, the device exhibits higher tolerance to background light than optically filtered silicon-based sensors. We demonstrate its potential in remote monitoring by measuring the heart rate and respiration rate from distances up to 130 cm in reflection.

Perovskite Solar Cell-Gated Organic Electrochemical Transistors for Flexible Photodetectors with Ultrahigh Sensitivity and Fast Response

Photodetectors (PDs) are the building block of various imaging and sensing applications. However, commercially available PDs based on crystalline inorganic semiconductors cannot meet the requirements of emerging wearable/implantable applications due to their rigidity and fragility, which creates the need for flexible devices. Here, a high-performance flexible PD is presented by gating an organic electrochemical transistor (OECT) with a perovskite solar cell. Due to the ultrahigh transconductance of the OECT, the device demonstrates a high gain of ≈10⁶ , a fast response time of 67 µs and an ultrahigh detectivity of 6.7 × 10¹⁷ Jones to light signals under a low working voltage (≤0.6 V). Thanks to the ultrahigh sensitivity and fast response, the device can track photoplethysmogram signals and peripheral oxygen saturation under ambient light and even provide contactless remote sensing, offering a low-power and convenient way for continuous vital signs monitoring. This work offers a novel strategy for realizing high-performance flexible PDs that are promising for low-power, user-friendly and wearable optoelectronics.

Tunable Multiband Halide Perovskite Tandem Photodetectors with Switchable Response

Photodetectors with multiple spectral response bands have shown promise to improve imaging and communications through the switchable detection of different photon energies. However, demonstrations to date have been limited to only two bands and lack capability for fast switching in situ. Here, we exploit the band gap tunability and capability of all-perovskite tandem solar cells to demonstrate a new device concept realizing four spectral bands of response from a single multijunction device, with fast, optically controlled switching between the bands. The response to monochromatic light is highly selective and narrowband without the need for additional filters and switches to broader response bands on applying bias light. Sensitive photodetection above 6 × 10¹¹ Jones is demonstrated in all modes, with rapid switching response times of <250 ns. We demonstrate proof of principle on how the manipulation of the modular multiband detector response through light conditions enables diverse applications in optical communications with secure encryption.

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.

Multidimensional Perovskites for High Detectivity Photodiodes

Low-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10^-9  mA cm^-2 without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 10¹² Jones at 600 nm. These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.

Narrowband Near-Infrared Photodetectors Based on Perovskite Waveguide Devices

Organic-inorganic perovskites have attracted great interest for developing wavelength-selective photodetectors. Currently, the spectral response range of narrowband photodetectors is mainly concentrated within the visible light region, lacking near-infrared photodetectors. Here, we present perovskite narrowband near-infrared photodetectors achieved by transverse propagation of light in perovskite waveguide devices for the first time. The response spectra of photodetectors are continuously tuned from 750 to 1000 nm by changing the perovskite component and the position of the incident light with the full width at half-maximum of 25-80 nm. The theoretical and experimental results reveal that the typical perovskite photodetectors serve as an optical waveguide to confine and propagate the light, in which the long wavelength light propagates a longer distance; oppositely, the short wavelength light with the higher loss in devices fails to produce a photoresponse, owing to the wavelength dependent absorption of perovskite. This provides a new concept for designing narrowband photodetectors and will simulate new applications.

Perovskite Photo-Sensors with Solution-Processed TiO2 under Low Temperature Process and Ultra-Thin Polyethylenimine Ethoxylated as Electron Injection Layer

A perovskite photo-sensor is promising for a lightweight, thin, flexible, easy-to-coat fabrication process, and a higher incident photon-to-current conversion efficiency. We have investigated perovskite photo-sensors with a solution-processed compact TiO2 under a low-temperature process and an ultra-thin polyethylenimine ethoxylated (PEIE) as an electron injection layer. The TiO2 film is grown from an aqueous solution of titanium tetrachloride (TiCl4) at 70 °C by a chemical bath deposition method. For an alternative process, the ultra-thin PEIE is spin coated on the TiO2 film. Then, the perovskite layer is deposited on the substrate by the one- or two-step methods in the glovebox. Next, a hole transport layer of 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9, 9-spiro-bifluorene (Spiro-OMeTAD) solution is spin coated. The fabricated device structure is a photodiode structure of FTO/TiO2/(without or with) PEIE/(one- or two-step) perovskite layer/Spiro-OMeTAD/Au. For the sensing characteristics, a ratio of photo-to-dark-current density was 2.88 × 104 for the device with PEIE layer. In addition, a power-law relationship is discussed.

Realizing Broadband NIR Photodetection and Ultrahigh Responsivity with Ternary Blend Organic Photodetector

With the advancement of portable optoelectronics, organic semiconductors have been attracting attention for their use in the sensing of white and near-infrared light. Ideally, an organic photodiode (OPD) should simultaneously display high responsivity and a high response frequency. In this study we used a ternary blend strategy to prepare PM6: BTP-eC9: PCBM-based OPDs with a broad bandwidth (350-950 nm), ultrahigh responsivity, and a high response frequency. We monitored the dark currents of the OPDs prepared at various PC71BM blend ratios and evaluated their blend film morphologies using optical microscopy, atomic force microscopy, and grazing-incidence wide-angle X-ray scattering. Optimization of the morphology and energy level alignment of the blend films resulted in the OPD prepared with a PM6:BTP-eC9:PC71BM ternary blend weight ratio of 1:1.2:0.5 displaying an extremely low dark current (3.27 × 10-9 A cm-2) under reverse bias at -1 V, with an ultrahigh cut-off frequency (610 kHz, at 530 nm), high responsivity (0.59 A W-1, at -1.5 V), and high detectivity (1.10 × 1013 Jones, under a reverse bias of -1 V at 860 nm). Furthermore, the rise and fall times of this OPD were rapid (114 and 110 ns), respectively.

Metal oxide nanoparticle-modified ITO electrode for high-performance solution-processed perovskite photodetectors

Low dark current density plays a key role in determining the overall performance of perovskite photodetectors (PPDs). To achieve this goal, a hole transport layer (HTL) on the ITO side and a hole blocking layer (HBL) on the metal electrode side are commonly introduced in PPDs. Unlike traditional approaches, we realized a high-performance solution-processed broadband PPD using metal oxide (MO) nanoparticles (NPs) as the HBL on the ITO electrode and PC61BM as another HBL on the metal electrode side to reduce the device dark current. The PPDs based on TiO2 and SnO2 NP-modified layers show similar device performances at -0.5 V: a greater than 105 on/off ratio; over 100 dB linear dynamic range (LDR) under different visible light illumination; around 0.2 A W-1 responsivity (R); greater than 1012 jones detectivity (D*); and ∼20 μs rise time of the device. The MO NP interfacial layer can significantly suppress charge injection in the dark, while the accumulated photogenerated charges at the interface between the MO layer and the perovskite layer introduce band bending, leading to dramatically increased current under illumination. Therefore, the dark current density of the devices is significantly reduced and the optical gain is drastically enhanced. However, after UV illumination, the dark current of the TiO2 device dramatically increases while the dark current of the SnO2 device can stay the same as before since the UV illumination-induced conductivity and barrier height changes in the TiO2 layer cannot recover after removing the UV irradiation. These results indicate that the TiO2 NP layer is suitable for making a vis-NIR photodetector, while the SnO2 NP layer is a good candidate for UV-vis-NIR photodetectors. The facile solution-processed high-performance perovskite photodetector using MO NP-modified ITO is highly compatible with low cost, flexible, and large-area electronics.

Overcoming Nanoscale Inhomogeneities in Thin-Film Perovskites via Exceptional Post-annealing Grain Growth for Enhanced Photodetection

Antisolvent-assisted spin coating has been widely used for fabricating metal halide perovskite films with smooth and compact morphology. However, localized nanoscale inhomogeneities exist in these films owing to rapid crystallization, undermining their overall optoelectronic performance. Here, we show that by relaxing the requirement for film smoothness, outstanding film quality can be obtained simply through a post-annealing grain growth process without passivation agents. The morphological changes, driven by a vaporized methylammonium chloride (MACl)-dimethylformamide (DMF) solution, lead to comprehensive defect elimination. Our nanoscale characterization visualizes the local defective clusters in the as-deposited film and their elimination following treatment, which couples with the observation of emissive grain boundaries and excellent inter- and intragrain optoelectronic uniformity in the polycrystalline film. Overcoming these performance-limiting inhomogeneities results in the enhancement of the photoresponse to low-light (<0.1 mW cm^-2) illumination by up to 40-fold, yielding high-performance photodiodes with superior low-light detection.

In situ construction of a Te/CsPbBr3 heterojunction for self-powered photodetector

In this study, CsPbBr3 particles were prepared by a simple solvent evaporation method in ambient environment; the p-n heterojunction formed by CsPbBr3 particles on the surface of a single long Te wire was used to construct a high-performance Te/CsPbBr3 photodetector. Compared with CsPbBr3 PDs, the Te/CsPbBr3 photodetector showed improved photocurrent, and exhibited characteristics of excellent self-powered performance, broad-spectrum response (UV-visible), and ultra-fast response speed (t rise = 0.09 ms). In addition, under zero bias and upon 540 nm light irradiation, the device had good responsivity (0.35 mA W-1), high photosensitivity (up to 100 on/off ratio), and a detectivity of 1.42 × 1010 Jones. This study provides insight into the possibility of manufacturing high-performance self-powered photodetectors through a simple in situ construction of heterojunctions.

Ultralow dark current in near-infrared perovskite photodiodes by reducing charge injection and interfacial charge generation

Metal halide perovskite photodiodes (PPDs) offer high responsivity and broad spectral sensitivity, making them attractive for low-cost visible and near-infrared sensing. A significant challenge in achieving high detectivity in PPDs is lowering the dark current density (J_D) and noise current (i_n). This is commonly accomplished using charge-blocking layers to reduce charge injection. By analyzing the temperature dependence of J_D for lead-tin based PPDs with different bandgaps and electron-blocking layers (EBL), we demonstrate that while EBLs eliminate electron injection, they facilitate undesired thermal charge generation at the EBL-perovskite interface. The interfacial energy offset between the EBL and the perovskite determines the magnitude and activation energy of J_D. By increasing this offset we realized a PPD with ultralow J_D and i_n of 5 × 10^-8 mA cm^-2 and 2 × 10^-14 A Hz^-1/2, respectively, and wavelength sensitivity up to 1050 nm, establishing a new design principle to maximize detectivity in perovskite photodiodes.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Miniaturized VIS-NIR Spectrometers Based on Narrowband and Tunable Transmission Cavity Organic Photodetectors with Ultrahigh Specific Detectivity above 1014 Jones

Spectroscopic photodetection plays a key role in many emerging applications such as context-aware optical sensing, wearable biometric monitoring, and biomedical imaging. Photodetectors based on organic semiconductors open many new possibilities in this field. However, ease of processing, tailorable optoelectronic properties, and sensitivity for faint light are still significant challenges. Here, the authors report a novel concept for a tunable spectral detector by combining an innovative transmission cavity structure with organic absorbers to yield narrowband organic photodetection in the wavelength range of 400-1100 nm, fabricated in a full-vacuum process. Benefiting from this strategy, one of the best performed narrowband organic photodetectors is achieved with a finely wavelength-selective photoresponse (full-width-at-half-maximum of ≈40 nm), ultrahigh specific detectivity above 10¹⁴ Jones, the maximum response speed of 555 kHz, and a large dynamic range up to 168 dB. Particularly, an array of transmission cavity organic photodetectors is monolithically integrated on a small substrate to showcase a miniaturized spectrometer application, and a true proof-of-concept transmission spectrum measurement is successfully demonstrated. The excellent performance, the simple device fabrication as well as the possibility of high integration of this new concept challenge state-of-the-art low-noise silicon photodetectors and will mature the spectroscopic photodetection into technological realities.

Fast Response Organic Tandem Photodetector for Visible and Near-Infrared Digital Optical Communications

Organic photodetectors (OPDs), which usually work as photodiodes, photoconductors, or phototransistors, have emerged as candidates for next-generation light sensing. However, low response speed caused by low carrier mobility and resistance-capacitance (RC) time constant, severely hinders the commercialization of OPDs. Herein, the authors demonstrate a state-of-the-art OPD with a record response speed of 146.8 ns by employing tandem structure to simultaneously reduce both the carrier transit time and RC time constant of the device, which is faster than that of previously reported OPDs as far as they know. Moreover, benefitting from the multi-level barrier enhancement and voltage division engendered by tandem structure, an ultralow noise current of 7.82 × 10^-14 A Hz^-1/2 is obtained, as well as a wide detection range in 300-1000 nm. In addition, the tandem OPDs are successfully integrated into the optical communication system as signal receivers, demonstrating the precise digital signal communication from visible to near-infrared light. It is believed that tandem OPDs have promising application potential in the wireless transmission system.

Sensitive, High-Speed, and Broadband Perovskite Photodetectors with Built-In TiO2 Metalenses

Monolithic integration of nanostructured metalenses with broadband light transmission and good charge transport can simultaneously enhance the sensitivity, speed, and efficiency of photodetectors. The realization of built-in broadband metalenses in perovskite photodetectors, however, has been largely challenged by the limited choice of materials and the difficulty in nanofabrication. Here a new type of broadband-transmitting built-in TiO₂ metalens (meta-TiO₂ ) is devised, which is readily fabricated by one-step and lithograph-free glancing angle deposition. The meta-TiO₂ , which comprises of sub-100 nm TiO₂ nanopillars randomly spaced with a wide range of sub-wavelength distances in 5-200 nm, shows high transmittance of light in the wavelength range of 400-800 nm. The meta-TiO₂ also serves as an efficient electron transporting layer to prevent the exciton recombination and facilitate the photoinduced electron extraction and transport. Replacing the conventional mesoporous TiO₂ with the meta-TiO₂ comprehensively leads to enhancing the detection speed by three orders of magnitude to a few hundred nanoseconds, improving the responsivity and detectivity by one order of magnitude to 0.5 A W^-1 and 10¹³ Jones, respectively, and extending the linear dynamic range by 50% to 120 dB.

All-Evaporated, All-Inorganic CsPbI3 Perovskite-Based Devices for Broad-Band Photodetector and Solar Cell Applications

Following the rapid increase of organic metal halide perovskites toward commercial application in thin-film solar cells, inorganic alternatives attracted great interest with their potential of longer device lifetime due to the stability improvement under increased temperatures and moisture ingress. Among them, cesium lead iodide (CsPbI₃) has gained significant attention due to similar electronic and optical properties to methylammonium lead iodide (MAPbI₃), with a band gap of 1.7 eV, high absorption coefficient, and large diffusion length, while also offering the advantage of being completely inorganic, providing a higher thermal stability and preventing material degradation. On a device level, however, it seems also essential to replace organic transport layers by inorganic counterparts to further prevent degradation. In addition, devices are mostly fabricated by spin coating, limiting their reproducibility and scalability; in this case, exploring all-evaporated devices allows us to improve the quality of the layers and to increase their reproducibility. In this work, we focus on the deposition of CsPbI₃ by CsI and PbI₂ co-evaporation. We fabricate devices with an all-inorganic, all-evaporated structure, employing NiO and TiO₂ as transport layers, and evaluate these devices for both photodetector and solar cell applications. As a photodetector, low leakage current, high external quantum efficiency (EQE) and detectivity, and fast rise and decay times were obtained, while as a solar cell, acceptable efficiencies were achieved. These all-inorganic, all-evaporated devices represent one step forward toward higher stability and reproducibility while enabling large area compatibility and easier integration with other circuitry and, in future, the possible commercialization of perovskite-based technology.

High-Performance Photodetectors Based on Nanostructured Perovskites

In recent years, high-performance photodetectors have attracted wide attention because of their important applications including imaging, spectroscopy, fiber-optic communications, remote control, chemical/biological sensing and so on. Nanostructured perovskites are extremely suitable for detective applications with their long carrier lifetime, high carrier mobility, facile synthesis, and beneficial to device miniaturization. Because the structure of the device and the dimension of nanostructured perovskite have a profound impact on the performance of photodetector, we divide nanostructured perovskite into 2D, 1D, and 0D, and review their applications in photodetector (including photoconductor, phototransistor, and photodiode), respectively. The devices exhibit high performance with high photoresponsivity, large external quantum efficiency (EQE), large gain, high detectivity, and fast response time. The intriguing properties suggest that nanostructured perovskites have a great potential in photodetection.

Evaluation of Carbon Based Molecular Junctions as Practical Photosensors

Molecular junctions with partially transparent top contacts permit monitoring photocurrents as probes of transport mechanism and potentially could act as photosensors with characteristics determined by the molecular layer inside the device. Previously reported molecular junctions containing nitroazobenzene (NAB) oligomers and oligomers of two different aromatic molecules in bilayers were evaluated for sensitivity, dark signal, responsivity, and limits of detection, in order to determine the device parameters which have the largest effects on photodetection performance. The long-range transport of photogenerated charge carriers permits the use of molecular layers thick enough to absorb a large fraction of the light incident on the layer. Thick layers also reduce the dark current and its associated noise, thus improving the limit of detection to a few nanowatts on a detector area of 0.00125 cm². Since the photocurrents have much lower activation energy than dark currents do, lowering the detector temperature significantly improves the limit of detection, although the present experiments were limited by environmental and instrumentation noise rather than detector noise. The highest specific detectivity (D*) for the current molecular devices was 3 × 10⁷ cm s^1/2 /W (∼10⁹, if only shot noise is considered) at 407 nm in a carbon/NAB/carbon junction with a molecular layer thickness of 28 nm. Although this is in the low end of the 10⁶-10¹² range for commonly used photodetectors, improvements in device design based on the current results should increase D* by 3-4 orders of magnitude, while preserving the wavelength selectivity and tunability associated with molecular absorbers. In addition, operation outside the 300-1000 nm range of silicon detectors and very low dark currents may be possible with molecular junctions.

Atomic and electronic structure of cesium lead triiodide surfaces

The (001) surface of the emerging photovoltaic material cesium lead triiodide (CsPbI₃) is studied. Using first-principles methods, we investigate the atomic and electronic structure of cubic (α) and orthorhombic (γ) CsPbI₃. For both phases, we find that CsI-termination is more stable than PbI₂-termination. For the CsI-terminated surface, we then compute and analyze the surface phase diagram. We observe that surfaces with added or removed units of nonpolar CsI and PbI₂ are most stable. The corresponding band structures reveal that the α phase exhibits surface states that derive from the conduction band. The surface reconstructions do not introduce new states in the bandgap of CsPbI₃, but for the α phase, we find additional surface states at the conduction band edge.

Block copolymer micelles enable facile synthesis of organic-inorganic perovskite nanostructures with tailored architecture

We report a distinct method for the production of organic-inorganic hybrid perovskite (OIHP) nanostructures using block copolymer micelles as scaffolds. We reveal that various nanostructures can be obtained by controlling the parameters related to micelle disassembly. The strategy reported herein can be generalized for the fabrication of diverse nanostructures toward target-oriented potential applications.

Enhanced Performance of Perovskite Single-Crystal Photodiodes by Epitaxial Hole Blocking Layer

Introducing hole/electron transporting and blocking layers is considered to enhance the performance of electronic devices based on organic-inorganic hybrid halide perovskite single crystals (PSCs). In many photodiodes, the hole/electron transporting or blocking materials are spin-coated or thermal-evaporated on PSC to fabricate heterojunctions. However, the heterojunction interfaces due to lattice mismatch between hole/electron, transporting or blocking materials and perovskites easily form traps and cracks, which cause noise and leakage current. Besides, these low-mobility transporting layers increase the difficulty of transporting carriers generated by photons to the electrode; hence, they also increase the response time for photo detection. In the present study, MAPbCl₃-MAPbBr_2.5Cl_0.5 heterojunction interfaces were realized by liquid-phase epitaxy, in which MAPbBr_2.5Cl_0.5 PSC acts as an active layer and MAPbCl₃ PSC acts as a hole blocking layer (HBL). Our PIN photodiodes with epitaxial MAPbCl₃ PSC as HBL show better performance in dark current, light responsivity, stability, and response time than the photodiodes with spin-coated organic PCBM as HBL. These results suggest that the heterojunction interface formed between two bulk PSCs with different halide compositions by epitaxy growth is very useful for effectively blocking the injected charges under high external electric field, which could improve the collection of photo-generated carriers and hereby enhance the detection performance of the photodiode. Furthermore, the PIN photodiodes made of PSC with epitaxial HBL show the sensitivities of 7.08 mC Gy_air ^-1 cm^-2, 4.04 mC Gy_air ^-1 cm^-2, and 2.38 mC Gy_air ^-1 cm^-2 for 40-keV, 60-keV, and 80-keV X-ray, respectively.

Perovskite Photodetectors Based on p-i-n Junction With Epitaxial Electron-Blocking Layers

Organic-inorganic hybrid perovskite single crystals (PSCs) have been emerged as remarkable materials for some optoelectronic applications such as solid-state photodetectors, solar cells and light emitting diodes due to their excellent optoelectronic properties. To decrease the dark current, function layers based on spin-coating method are frequently requested for intrinsic PSCs to block the injected current by forming energy barrier. However, the amorphous function layers suffer from small carrier mobility and high traps density, which limit the speed of the photoelectric response of perovskite devices. This work supposes to grow thick MAPbBr₃ and MAPbI₃ mono-crystalline thin films on the surface of intrinsic MAPbBr_2.5Cl_0.5 PSCs substrate by a heteroepitaxial growth technique to act as electron-blocking layers. Meanwhile, C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) layers are deposited on the opposite surface of substrate PSCs by spin-coating method to block injected holes. This Au-MAPbI₃-MAPbBr₃-MAPbBr_2.5Cl_0.5PSCs-C60-PCBM-Ag heterostructure can be used as excellent X-ray photodetector (XPD) due to its low dark current density of 6.97 × 10^-11 A cm^-2 at -0.5 V bias, high responsivity of 870 mA/W at -100 V bias and X-ray sensitivity as high as 59.7 μC mGy^-1 cm^-2 at -50 V bias.

Interface engineering for gain perovskite photodetectors with extremely high external quantum efficiency

Efficient CH3NH3PbI3 photodetectors (PDs) with an extremely high gain of the maximum external quantum efficiency (EQE) of 140 000% within the ultraviolet region to the near infrared region (NIR) and an extremely high responsivity (R) under a low bias of -5 V were successfully fabricated. The fabricated devices manifested outstanding environmental stability with only 10% degradation of EQE after being exposed to air for 24 h. These obtained results indicate the promising potential of perovskite PDs for visible light communication applications.

Growth of centimeter-scale perovskite single-crystalline thin film via surface engineering

Modern electronic and photonic devices rely on single-crystalline thin film semiconductors for high performance and reproducibility. The emerging halide perovskites have extraordinary electronic and photonic properties and can be synthesized via low cost solution-based methods. They have been used in a variety of devices with performance approaching or over the devices based on conventional materials. However, their solution based growth method is intrinsically challenge to grow large scale single-crystalline thin film due to the random nucleation and isotropous growth of the crystal. Here, we report the growth of centimeter-scale perovskite single-crystalline thin films by controlling the nucleation density and growth rate of the crystal under a spatially confined growth condition. The hydrophobic treatment on substrates inhibits nucleation and accelerates the growth of single-crystalline thin film, providing enough space for initial nucleus growing up quickly without touching each other. Single-crystalline perovskite thin-film with an aspect ratio of 1000 (1 cm in side length, 10 μm in thickness) has been successfully grown. The low trap density and the high mobility of the as-grown thin film show a high crystallinity. The photodetector based on the perovskite thin film has achieved a gain ~ 104, benefitting from the short transit time of the carries due to the high mobility and thin thickness of the active layer. Our work opens up a new route to grow large scale perovskite single-crystalline thin films, providing a platform to develop high- performance devices.

All-solution-processed UV-IR broadband trilayer photodetectors with CsPbBr3 colloidal nanocrystals as carriers-extracting layer

Colloidal quantum dots (CQDs) are very promising nanomaterials for optoelectronics due to their tunable bandgap and quantum confinement effect. All-inorganic CsPbX₃ (X = Br, Cl and I) perovskite nanocrystals (NCs) have attracted enormous interests owing to their promising and exciting applications in photovoltaic devices. In this paper, all-solution-processed UV-IR broadband trilayer photodetectors ITO/ZnO/PbS/CsPbBr₃/Au and ITO/ZnO/CsPbBr₃/PbS/Au with high performance were presented. The role of CsPbBr₃ QDs layer as the carriers-extracting layer in the trilayer devices was discussed. As compared with bilayer device ITO/ZnO/PbS/Au, both the dark currents and photocurrents under illumination from trilayer photodetectors are enhanced, but the trilayer photodetector ITO/ZnO(80 nm)/PbS(150 nm)/CsPbBr₃(50 nm)/Au showed a maximum specific detectivity (D*) of 8.3 × 10¹² Jones with a responsivity (R) of 35 A W^-1 under 1.6 mW cm^-2 980 nm illumination. However, another trilayer photodetector ITO/ZnO(80 nm)/CsPbBr₃(50 nm)/PbS(150 nm)/Au showed a maximum D* of 1.73 × 10¹² Jones with a R of 5.31 A W^-1 under 6.8 mW cm^-2 405 nm illumination. Further, the underlying mechanism for the enhanced performance of trilayer photodetectors was discussed. Thus, this strategy of all-solution-processed heterojunction configuration paves a facile way for broadband photodetectors with high performance.

Organic Thin-Film Red-Light Photodiodes with Tunable Spectral Response Via Selective Exciton Activation

Red and near-infrared light detection is vital for numerous applications, including full-color imaging, optical communication, and machine vision. However, this development is hindered by a limited choice of small band gap and narrow-bandwidth materials. Here, we report a device principle with a simple organic planar heterojunction architecture that enables a selective activation of excitons for tuning the photoresponse spectra to fabricate thin-film, filterless, red-light organic photodiodes. A sequential solution-processed active layer is formed by depositing the top layer of PC₇₁BM onto the predeposited bottom layer of doped P3HT. By adjusting the ratio of PTB7 in P3HT, an improved responsivity and a red-shift of the photoresponse peak from 645 to 745 nm are demonstrated simultaneously. Furthermore, the responsivity of 745 nm is enhanced over 5 times with a narrow full width at half-maximum of ∼50 nm at optimized doping ratio compared to the pristine PTB7 device. As a result, a high specific detectivity in excess of 10¹² Jones and broad linear dynamic range of 103 dB are achieved. This design concept shows the possibility of realizing tunable red-light selectivity even at relatively thin-film thickness, which is intriguing for the implementation of high-resolution image sensors in the near future.

Enhanced Flexibility and Stability in Perovskite Photodiode-Solar Cell Nanosystem Using MoS2 Electron-Transport Layer

Hybrid organic-inorganic perovskites and MoS₂ are highly attractive as emerging materials for various kinds of optoelectronic devices. Here, we first report perovskite photodiode-solar cell nanosystems (PPSNs) by employing bilayer (BL) MoS₂ and triethylenetetramine-doped graphene (TETA-GR) as the electron-transport layer (ETL) and transparent conductive electrode (TCE), respectively. The rigid/flexible PPSNs exhibit 0.42/0.40 AW^-1 responsivity (R), 37.2/80.1 pW Hz^-1/2 noise equivalent power, 1.1 × 10¹⁰/5.0 × 10⁹ cm Hz^1/2 W^-1 specific detectivity at a zero-bias photodiode mode (i.e., self-power operation), similar to or even greater than those of previous reports, and 14.27/12.12% power conversion efficiency at a photovoltaic mode. The PPSNs show high long-term stabilities by maintaining more than 78% of the initial R for 30 days. The flexible PPSNs maintain about 80% of the original R during 1000 bending tests at 4 mm radius of curvature, indicating excellent mechanical properties. These high performances result from the enhanced TCE properties, well-matched band offsets at the cathode/ETL/active layer interfaces, and the reduced carrier recombination/charge-transfer resistance by the use of TETA-GR TCE and BL-MoS₂ ETL.

Photomultiplication Type Broad Response Organic Photodetectors with One Absorber Layer and One Multiplication Layer

Broad response organic photodetectors (OPDs) with a photomultiplication (PM) effect are achieved with one absorber layer and one multiplication layer. The response range of the PM-OPDs is primarily determined by materials in the absorber layer, and the external quantum efficiency (EQE) of the PM-OPDs is mainly controlled by the multiplication layer. Here, double-layered PM-OPDs were designed with an ITO/ZnO/PM6:Y6/PC₇₁BM:P3HT (100:5, w/w)/Au structure, where PM6:Y6 is employed as an absorber layer and PC₇₁BM:P3HT is used as a multiplication layer. The optimal PM-OPDs exhibit a broad response covering 350-950 nm. Meanwhile, the optimal PM-OPDs exhibit the largest EQE value of ∼1200% and a maximum specific detectivity (D*) of ∼6.8 × 10^-12 cm Hz^1/2 W^-1 under a 10 V bias. This double-layered approach may be a smart strategy for realizing PM-OPDs with an easily adjustable response range.

Polyvinylpyrrolidone as additive for perovskite solar cells with water and isopropanol as solvents

The recent years have witnessed a fast-paced development of perovskite solar cells (PSCs). Unfortunately, the vast majority of PSCs relies on the use of highly polar aprotic solvents during the preparation process, such as dimethylformamide (DMF), which is toxic and detrimental to both humans and the environment. Here, we describe the preparation of PSCs under ambient conditions from an aqueous solution of lead nitrate, to which polyvinylpyrrolidone (PVP) was added in order to enhance the photoelectric performance of the PSCs. By a combination of SEM, EIS, PL and UV spectroscopy and other characterization approaches, we show that the PVP additive is effective in inhibiting carrier recombination, enhancing composite resistance and reducing film defects. Ultimately, we achieved an outstanding photoelectric performance of the PVP-doped PSCs shown by a power conversion efficiency (PCE) of 15.19% and an average steady-state PCE of 14.55% under AM 1.5G simulated solar irradiation with a shadow mask of 0.1 cm². The PCE continued to be over 80% of the initial PCE after 60 days of storage. FInally, the introduced PVP-doped PSCs present a low-cost and low-toxicity way to commercialize perovskite solar cells.

P3HT-based visible-light organic photodetectors using PEI/PAA multilayers as a p-type buffer layer

A low leakage current is critical for achieving organic photodetectors (OPDs) with high detectivity. The insertion of buffer layers is an effective approach for reducing the reverse-biased leakage current. In this study, polyelectrolyte multilayers comprising polyethyleneimine (PEI) and polyacrylic acid (PAA) were introduced by a spin-assisted layer-by-layer technique into an OPD as a p-type buffer layer. Although PEI/PAA multilayers are insulators, when used as a buffer layer in our device, they suppressed the leakage current and also provided a high photocurrent due to the light-assisted tunneling effect. The prepared device configuration was ITO/(PEI/PAA)2/P3HT:PC60BM/Yb/Al. The performances of the OPDs were investigated by measuring the current-voltage characteristics, external quantum efficiency, and transient photocurrent. In addition, the operating mechanism of the OPDs was confirmed by impedance analysis. The device comprising (PEI/PAA)2 showed a specific detectivity of 3.11 × 1012 Jones and a bandwidth of 103.2 kHz at -1 V and 525 nm. This performance is a numerical value that can be used in devices such as a line scan camera. In addition, because this device is fabricated by a low-temperature solution process, flexible and large-area substrates can be used.

High-Rubidium-Formamidinium-Ratio Perovskites for High-Performance Photodetection with Enhanced Stability

Formamidinium lead trihalide perovskites have emerged as promising photovoltaic materials owing to their superior absorption coefficient properties. However, one big challenge is the material phase stability and thermal stability at high temperature. In this work, a large quantity of rubidium (Rb) ions is incorporated into formamidinium (FA) perovskite thin films to improve the material phase stability and thermal stability. Photodiodes based on optimized FA_0.7Rb_0.3PbI₃ perovskites deliver a high responsivity of 0.43 A W^-1, a detectivity of >10¹² Jones, a relatively large linear dynamic range of 125 dB, and an ultrafast response speed of approximately 300 ns. Moreover, these photodiodes present lower dark current and higher photocurrent after baking at high temperature. These results are very promising for photodetection at high operational temperature. In addition, the high-ratio rubidium-incorporated perovskite films may have great potential in fabricating other high-performance optoelectronic devices, i.e., light-emitting diodes and solar cells with excellent phase stability and high temperature thermostability.

Achieving High-Quality Sn-Pb Perovskite Films on Complementary Metal-Oxide-Semiconductor-Compatible Metal/Silicon Substrates for Efficient Imaging Array

Although Sn-Pb perovskites sensing near-ultraviolet-visible-near-infrared light could be an attractive alternative to silicon in photodiodes and imaging, there have been no clear studies on such devices constructed on metal/silicon substrates, hindering their direct integration with complementary metal-oxide semiconductor (CMOS) and silicon electronics. Typically, high surface roughness and severe pinholes of Sn-rich binary perovskites make it difficult for them to fulfill the requirements of efficient photodiodes and imaging. These issues cause inherently high dark current and poor (dark and photo-) current uniformity. Herein, we propose and demonstrate the room-temperature crystallization in the Sn-rich binary perovskite system to effectively control film crystallization kinetics. With experimental and theoretical studies of the crystallization mechanism, we successfully tune the density and location of nanocrystals in precursor films to achieve compact nanocrystals, which coalesce into high-quality (smooth, dense, and pinhole-free) perovskites with intensified preferred orientation and decreased trap density. The high-quality perovskites reduce dark current and improve (dark and photo-) current uniformity of perovskite photodiodes on CMOS-compatible metal/silicon substrates. Meanwhile, self-powered devices achieve a high responsivity of 0.2 A/W at 940 nm, a large dynamic range of 100 dB, and a fast fall time of 2.27 μs, exceeding those of most silicon-based imaging sensors. Finally, a 6 × 6 pixel integrated photodiode array is successfully demonstrated to realize the imaging application. The work contributes to understanding the fundamentals of the crystallization of Sn-rich binary perovskites and advancing perovskite integration with Si-based electronics.

Acceptor-free photomultiplication-type organic photodetectors

A series of organic photodetectors (OPDs) is prepared with two donor materials as active layers, with the only difference being the weight ratio of the two donors (one polymer and one small molecule). The OPDs work according to a photodiode model with an external quantum efficiency (EQE) of less than 10% at -10 V when the weight ratio of the two materials is 1 : 1 (wt/wt). The EQE of an OPD with P3HT:DRCN5T (100 : 2, wt/wt) as the active layer reaches 1400% at -10 V, exhibiting the photomultiplication (PM) phenomenon. The EQE values of PM-type OPDs can be markedly improved along with a bias increase, and the champion EQE reaches 10 600% at -20 V. The small number of small molecules can be used as electron traps due to the different lowest unoccupied molecular orbital (LUMO) levels of the two donors, and photogenerated electrons can be trapped in the small molecules surrounded by P3HT. The trapped electrons near the Al electrode can induce interfacial band bending for efficient hole tunneling injection from an external circuit. This work provides a new strategy for realizing acceptor-free PM-type OPDs, which may inspire us to further develop organic electronic devices with single type organic semiconducting materials.

High-Performance Near-Infrared-Selective Thin Film Organic Photodiode Based on a Molecular Approach Targeted to Ideal Semiconductor Junctions

A molecular approach to achieve wide linear dynamic range (LDR) and near-infrared (NIR)-selective thin film organic photodiodes (OPDs) with high detectivity is reported. Comparative studies based on two NIR-selective polymers are systematically investigated: the commercially available poly[(4,4'-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b']dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTBT) and the synthesized poly[(4,4'-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b']-dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT). The introduction of sp²-hybridized side chains in the PCPDTSBT structure can improve chain planarity and thus intermolecular interactions, as confirmed by Raman spectroscopy and grazing incidence X-ray diffraction studies. The favorable crystalline orientation of PCPDTSBT leads to enhanced photocurrent and suppressed noise current, compared to that of PCPDTBT, followed by a sharp increase in the specific detectivity of PCPDTSBT-based NIR OPDs by 1.54 × 10¹² Jones. The physics behind PCPDTSBT is analyzed employing optical simulation, temperature-dependent junction analyses, and Mott-Schottky analysis. Furthermore, it is found that PCPDTSBT possesses an exceptional nonsaturation photocurrent, which leads to a wide LDR of 128 dB. This study shows the possibility of realizing thin film NIR-selective OPDs using synthetic approaches.

High-Performance Photomultiplication Photodiode with a 70 nm-Thick Active Layer Assisted by IDIC as an Efficient Molecular Sensitizer

Here, a smart strategy for decreasing the active layer thickness of the organic photodiode down to 70 nm is demonstrated by utilizing a trap-assisted photomultiplication mechanism with the optimized chemical composition. Despite the presence of a high dark current, dramatically enhanced external quantum efficiency (EQE) via photomultiplication can allow significantly reduced active layer thickness, yielding high detectivity comparable to that of conventional Si. To achieve this, a spatially confined and electrically isolated optical sensitizer, 2,2'-((2 Z,2' Z)-((4,4,9,9-tetrahexyl-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1 H-indene-2,1-diylidene))dimalononitrile (IDIC) was introduced strategically between a hole transport active layer and a cathode. A nonfullerene acceptor, IDIC, turned out to be a much more efficient sensitizer than the conventional fullerene-based acceptors, as confirmed by the effective lowering of the Schottky barrier under illumination, as well as the highest EQE exceeding 130 000%. Due to its favorable electronic structure as well as two-dimensional molecular structure, a high detectivity over 10¹² Jones was successfully demonstrated while maintaining the active layer thickness as 70 nm.

High-Performance Copper Oxide Visible-Light Photodetector via Grain-Structure Model

Recently, copper oxide (CuO)-based visible-light photodetectors have attracted great interest due to their narrow bandgap (1.2 eV), low cost, and ease of fabrication. However, there has been insufficient theoretical analysis and study of CuO-based photodetectors, resulting in inferior performance in terms of responsivity, detectivity, and response speed. This work develops a method to enhance the performance of CuO photodetectors by engineering a grain structure based on a newly-developed theoretical model. In the developed theoretical grain-structure model, the grain size and the connections between grains are considered because they can strongly affect the optoelectronic characteristics of CuO photodetectors. Based upon the proposed model, the engineered CuO device achieves enhanced optoelectronic performance. The engineered device shows high responsivity of 15.3 A/W and detectivity of 1.08 × 10¹¹ Jones, which are 18 and 50 times better than those of the unoptimized device, and also shows fast rising and decaying response speeds of 0.682 s and 1.77 s, respectively. In addition, the proposed method is suitable for the mass-production of performance-enhanced, reliable photodetectors. By using a conventional semiconductor fabrication process, a photodetector-array is demonstrated on a 4-inch wafer. The fabricated devices show uniform, high, and stable optoelectronic performance for a month.

Patterning Multicolor Hybrid Perovskite Films via Top-Down Lithography

Lead-halide perovskites have attracted great attention due to their excellent optoelectronic properties, with rapid progress being made in their performance as light-emitting diodes (LEDs), photodiodes, and solar cells. Demonstrating large scale, high-resolution patterning of perovskites is a key enabling step to unlock their full potential for a range of optoelectronic applications. However, the development of a successful top-down lithography fabrication procedure has so far been hampered by the incompatibility of perovskite films with the solvents used during lithographic processes. Here, we perform a study on the effect of different lithographic solvents on perovskite films and use this insight to develop photolithography and electron-beam lithography procedures for patterning perovskite films. This procedure uses standard resists at low temperatures and achieves micron-scale features with flat tops. Furthermore, we expand this platform to produce arrays of multicolor pixels for potential commercial perovskite LED display applications.

Bifunctional Etalon-Electrode To Realize High-Performance Color Filter Free Image Sensor

Organic photodiodes (OPDs), based on organic semiconductors with high absorption coefficients for visible light, are emerging as potential candidates for replacing silicon photodiodes in image sensors, particularly due to the possibility of realizing a thin thickness and exclusion of color filters, both of which can contribute to a dramatically enhanced degree of integration for image sensors. Despite years of research, techniques have not yet been developed that allow the OPD itself to have color selectivity while maintaining a thin (<1 μm) OPD thickness, in combination with a sufficiently high detectivity (>10¹² cm·Hz^0.5/W). To solve this issue, we introduce a concept of "etalon-electrode", which can perform the function of electrode and simultaneously the function of selective wavelength transparency. A strategically designed OPD architecture consisting of an etalon-electrode, a panchromatic organic active layer, and a counter electrode displays well-defined narrowband R-/G-/B-selective detectivity spectra depending on precision-adjusted thickness composition of the etalon-electrode. While a thin thickness of OPD is preserved at less than 800 nm including electrodes, active layer, and other buffer layers for all R-/G-/B-selective OPDs, high average detectivity values over 10¹² cm·Hz^0.5/W are demonstrated. Furthermore, the characteristic of imparting color selectivity by the etalon-electrode enables a more facile full color patterning, such that a prototype of a 10 × 10 image sensor with a pixel pitch of 500 μm is realized, resulting in accurate picturing of a well-defined full color image.

Solution Processed Trilayer Structure for High-Performance Perovskite Photodetector

Due to their outstanding performance, low cost, ease of fabrication, diverse photonic, and optoelectronic applications, metal halides perovskite have attracted extensive interest in photodetector applications. Currently, devices made by metal oxides, metal sulfides, and 2D materials had achieved good responsivity, but suffered from high dark current, slow response speed, small on-off ratio, and poor stability. Whole performances of these photodetectors are not satisfactory. Here, a lateral perovskite (CH₃NH₃PbBr₃)/Ethanolamine/TiO₂ (in ethanol) trilayer photodetector is designed for achieving high performance. EA treatment enhances electron extraction and reduces undesired recombination. This trilayer device shows good performances with low dark current of 1.5 × 10^-11 A, high on-off ratio of 2700, high photodetectivity of 1.51 × 10¹² Jones, high responsivity of 0.13 A W^-1, and high stability, comparative to conventional single layer devices. This work provides the way to improve the performance of metal halide perovskite photodetectors.

Self-assembled KCu7S4 nanowire monolayers for self-powered near-infrared photodetectors

Near infrared light (NIR) photodetectors based on one-dimensional semiconductor nanowires have generated considerable interest due to their practical application in versatile fields. We present a facile yet efficient approach to rationally integrating KCu₇S₄ semiconductor nanowires by the Langmuir-Blodgett (LB) technique. A self-powered near infrared (NIR) light photodetector is fabricated by transferring a close-packed KCu₇S₄ nanowire monolayer to the surface of a silicon wafer. The as-fabricated Si/KCu₇S₄ heterojunction with a close-packed and well-aligned nanowire array exhibits splendid photovoltaic performance when illuminated by NIR light, allowing the detection of NIR light without an exterior power supply. The photodetector exhibits a high sensitivity to NIR light (980 nm, 295.3 μW cm^-2) with responsivity (R) 15 mA W^-1 and detectivity (D*) 2.15 × 10¹² cm Hz^1/2 W^-1. Significantly, the device shows the capability to work under high pulsed light irradiation up to 50 kHz with a high-speed response (response time τ_r 7.4 μs and recovery time τ_f 8.6 μs). This facilitates the fabrication of low-cost and high-speed photodetectors and integrated optoelectronic sensor circuitry.

Perovskite/Organic Bulk-Heterojunction Integrated Ultrasensitive Broadband Photodetectors with High Near-Infrared External Quantum Efficiency over 70

Ultraviolet-visible-near infrared (UV-Vis-NIR) broadband detection is important for image sensing, communication, and environmental monitoring, yet remains as a challenge in achieving high external quantum efficiency (EQE) in the broad spectrum range. Herein, sensitive broadband integrated photodetectors (PDs) with high EQE levels are reported. The organic bulk-heterojunction (OBHJ) layer, based on a NIR sensitive organic acceptor, is employed to extend the response spectrum of the perovskite PDs. A key strategy of introducing dual electron transport materials respectively for Vis and NIR regions into the active layer of integrated PDs is applied. Further combined with the proper energy level alignment and reasonable distribution of PC₆₁ BM in the active layer, the extraction and transport of photo induced charges in between perovskite and OBHJ is promoted efficiently. The integrated PD with the optimized structure exhibits an EQE mostly beyond 70% in the Vis-NIR region, which is the highest value among the ever reported solution-processable broadband PDs. The highest responsivity is 0.444 and 0.518 A W^-1 in the Vis and NIR region, respectively. The specific detectivity is beyond 10¹⁰ Jones in the range from 340 to 940 nm, enabling the device to detect weak signals in the UV to NIR broad region.