Dark Current Density Research Articles

Reduction of surface leakage current of InAs/GaSb long-wavelength superlattice detectors using SiO2 and anodic sulfide composite passivation

We investigate two passivation methods for long-wavelength infrared type-II InAs/GaSb superlattice (T2SL) photodiodes with the PπBN structure containing an InAs/AlSb hole barrier layer. In order to eliminate the surface defects of T2SL better to further reduce the surface dark current, anodic vulcanization and SiO2 composite passivation method is adopted to optimize the original SiO2 passivation method. At 77 K, the I–V curve of the devices under the two passivation methods are obtained. Compared with passivation-only SiO2, the dark current density of the anode sulfide and SiO2 composite passivation detector is reduced by one order of magnitude, and the surface resistivity is effectively improved by an order of magnitude. Additionally, the composite passivation method not only improves the uniformity of the device, but also prevents the peeling of the S layer to improve the quality of passivation. This work offers a stable and high-quality passivation method, and it could be popularized passivation in the field of optics, electronics, optoelectronics, and switching devices.

High-mobility organic semiconducting crystal for direct X-ray detection

Tissue-equivalent pure organic semiconducting crystals (OSCs) have unique advantages in direct X-ray detectors (DXDs), especially for biological tissue fluoroscopy, but their low carrier mobility and inherent weak absorption restrict the limit-of-detection (LoD) and sensitivity of DXDs. High-mobility OSCs theoretically facilitate charge collection and performance leaps, however, they are rare and suffer from poor solubility due to high conjugation, leading to nearly impossible crystal growth from solution and subsequent device applications. Here we report an ingenious solution-processed crystal-growth and high-performance DXD using 2,6-diphenylanthracene (2,6-DPA), a high-mobility OSC we developed recently. In contrast to previous OSCs, high-mobility 2,6-DPA exhibits low dark current density and large photoconductive gain, resulting in record-breaking LoD of <85 nGyair s−1 and sensitivity of >103 μC Gyair−1 cm−2. Compared with semiconductors containing high-Z atoms (Z is atomic number), the accuracy of 2,6-DPA based DXDs is not affected by near-edge absorption effects. Moreover, the non-linear relationship between irradiation current and dose rate is confirmed as a high injection effect. High mobility and ingenious crystal growth strategy make 2,6-DPA an ideal active material for DXDs and also provide the possibility for more optoelectronic applications.

Effect of bubbles at the bonded interface on the performance of GeSn/Si PIN photodetector

Due to the large lattice mismatch between GeSn and Si materials, high-density threading dislocation (TD) forms when GeSn films are grown by epitaxial growth. This leads to the increase of the dark current density (DCD) of the device. The wafer-bonded technique is a promising method to prepare high-quality thin films. This has been used to produce the Si-based GeSn materials with low TDD. However, there are a lot of bubbles at the bonded interface, resulting in the deterioration of the performance of the device. The study of bubbles on the performance of the GeSn PIN photodetector (PD) has not been reported. In this paper, the effects of the bonding bubbles on the performance of the device are performed. The photocurrent, dark current, charge concentration, electric field, and 3dB-bandwidth (BW) as a function of the bubble radius and thickness are demonstrated. The effects of the bubble radius and thickness on the 3dB-BW (∼18 GHz) are insignificant when the bubble thickness and radius are set as 1 nm and 1 μm, respectively. The 3dB-BW decreases to ∼17 GHz when the bubbles are close to the sizes of the top mesa. However, the 3dB-BW drops drastically with the increase of the bubble thickness when the bubble radius reaches 7 μm. Most importantly, the 3dB-BW sharply decreases to ∼30 MHz regardless of the thickness of the bubble when the bubble radius of 14 μm is set. This may provide guidance for the application of the wafer-bonded GeSn PIN PD.

Cellulose acetate-derived ternary-doped hierarchically porous carbons blended perovskite active layers for solar cells and X-ray detectors

Herein, we have synthesized hetero-atoms (nitrogen (N), sulfur (S), phosphorus (P))-doped porous carbons (PCs) which upon dispersion in perovskite precursor solution with different (2–8 wt.%) modify its morphology and improve optoelectronic characteristics of the perovskite active layer (AL) results into enhancing efficiency and stability of perovskite solar cells (PSCs). The results indicate that PCs (6 wt.%) modifies perovskite AL-constructed PSCs and X-ray photodetectors outperform other investigated devices. The excellent PSCs (AL@NSPCPC) demonstrate power conversion efficiency (PCE) of 13.81%, fill factor (FF) 64.77%, current density Jsc (23.518 mA/cm2), and open circuit voltage Voc (0.906 V), which is significantly higher than pristine AL 10.42%, 57.01%, 20.423 mA/cm2, and 0.895 V, respectively. Furthermore, the sample (AL@NSP-CPC) when constructs in the geometry of an X-ray photodetector, shows 15.56 μA/cm2, 4.66 mA/Gy·cm2, 5.26×10−4 cm2/V·s, and 3.58 × 1015 cm−3 of collected charge density (CCD), dark current density (DCD), sensitivity, mobility, and trap density, respectively. Thus, heteroatom-doped PCs modified perovskite layers demonstrate promise for constructing PSCs and X-ray photodetectors opening future research in exploiting these abundant, and inexpensive carbons materials having large mobility and tunable morphology along with surface passivation at perovskite/hole transport layer (HTL) interface to further enhance their photovoltaic parameters.

Photon-trapping-enhanced avalanche photodiodes for mid-infrared applications

The fast development of mid-wave infrared photonics has increased the demand for high-performance photodetectors that operate in this spectral range. However, the signal-to-noise ratio, regarded as a primary figure of merit for mid-wave infrared detection, is strongly limited by the high dark current in narrow-bandgap materials. Therefore, conventional mid-wave infrared photodetectors such as HgCdTe require cryogenic temperatures to avoid excessively high dark current. To address this challenge, we report an avalanche photodiode design using photon-trapping structures to enhance the quantum efficiency and minimize the absorber thickness to suppress the dark current. The device exhibits high quantum efficiency and dark current density that is nearly three orders of magnitude lower than that of the state-of-the-art HgCdTe avalanche photodiodes and nearly two orders lower than that of previously reported AlInAsSb avalanche photodiodes that operate at 2 µm. Additionally, the bandwidth of these avalanche photodiodes reaches ~7 GHz, and the gain–bandwidth product is over 200 GHz; both are more than four times those of previously reported 2 µm avalanche photodiodes.

Recent Progress in III–V Photodetectors Grown on Silicon

An efficient photodetector (PD) is a key component in silicon-based photonic integrated circuits (PICs). III–V PDs with low dark current density, large bandwidth, and wide operation wavelength range have become increasingly important for Si photonics in various applications. Monolithic integration of III–V PDs on Si by direct heteroepitaxy exhibits the lowest cost, the largest integration density, and the highest throughput. As the research of integrating III–V lasers on Si flourishes in the last decade, various types of III–V PDs on Si with different device structures and absorption materials have also been developed. While the integration of III–V lasers on Si using various technologies has been systematically reviewed, there are few reviews of integrating III–V PDs on Si. In this article, we review the most recent advances in III–V PDs directly grown on Si using two different epitaxial techniques: blanket heteroepitaxy and selective heteroepitaxy.

Comprehensive experimental study of NBνN barrier structures based on n-HgCdTe MBE for detection in MWIR and LWIR spectra

This work is devoted to a comprehensive experimental study of the electrical and photoelectric characteristics of barrier photosensitive structures in the NBνN configuration based on n-HgCdTe (MCT). Seven different types of photosensitive structures for middle wavelength (MWIR) and long wavelength (LWIR) infrared (IR) radiation ranges grown by molecular beam epitaxy (MBE) have been studied by complex conductivity spectroscopy method. The current-voltage characteristics (CVC) were measured both in the dark and in the presence of illumination. Based on the measured dependences of the dark current density on temperature and the ratio of the perimeter to the area of the structure, the dominant contribution of the bulk current component compared to the surface component for the MWIR structure (x ∼ 0.30) was established. This fact was confirmed by the value of the activation energy (from the Arrhenius plots) corresponding to the band gap. The results of frequency measurements of the differential conductivity of MIS structures based on NBνN also give a close activation energy, which corresponds to the diffusion limitation. LWIR structures (x ∼ 0.20) are characterized by an increase in the contribution of the surface leakage current in the total dark current. In this case, the activation energy determined from MIS measurements exceeds the band gap of the ν-layer, which is associated with the presence of an energy barrier for holes in the valence band. It is shown that if the problem of passivation of mesa structures is solved, it is possible to fabricate efficient MWIR and LWIR nBn, NBνN detectors based on MBE HgCdTe with high threshold parameters.

The Influence of Dimensionality on the Charge‐Density‐Wave Transition and its Application on Mid‐Infrared Photodetection

Abstract2D charge density wave (CDW) materials receive much attention for high responsivity and broadband photodetection in recent years due to their collective electron transport and narrow bandgap. However, the high dark current density problem hinders their real application. Here, a sharp CDW transition in quasi‐1D (TaSe4)2I is reported and applied for broadband photodetection. Especially at mid‐infrared region, the device shows both high photo responsivity of 1.18 ×103 A W−1 and large light on/off ratio of 80, which is superior to 2D CDW TaS2 and most reported low‐dimensional materials. Such high performance relies on two aspects. One is the much lower dark current density resulting from the pseudo gap associated with 1D Luttinger liquid state, which is supported by finite size scaling of nonlinear I–V at variable temperatures and occurrence of 1D structural phase transition consolidated by in situ Raman spectroscopy. The other is the high photocurrent associated with the “Fröhlich superconductivity” state, manifested by an ultrasensitive switching, which can be only accessible in 1D CDW materials, in agreement with the authors’ density functional theory calculation. This work thus reveals the pivotal role of dimensionality in CDW phase transition and paves a way for implementing highly sensitive broadband photodetector.

Probing into Reverse Bias Dark Current in Perovskite Photodiodes: Critical Role of Surface Defects

AbstractMinimizing reverse bias dark current density (Jdark) while retaining high external quantum efficiency is crucial for promising applications of perovskite photodiodes, and it remains challenging to elucidate the ultimate origin of Jdark. It is demonstrated in this study that the surface defects induced by iodine vacancies are the main cause of Jdark in perovskite photodiodes. In a targeted way, the surface defects are thoroughly passivated through a simple treatment with butylamine hydroiodide to form ultrathin 2D perovskite on its 3D bulk. In the passivated perovskite photodiodes, Jdark as low as 3.78 × 10‐10 A cm‐2 at ‐0.1 V is achieved, and the photoresponse is also enhanced, especially at low light intensities. A combination of the two improvements realizes high specific detectivity up to 1.46 × 1012 Jones in the devices. It is clarified that the trap states induced by the surface defects can not only raise the generation‐recombination current density associated with the Shockley–Read–Hall mechanisms in the dark (increasing Jdark), but also provide additional carrier recombination paths under light illumination (decreasing photocurrent). The critical role of surface defects on Jdark of perovskite photodiodes suggests that making trap‐free perovskite thin films, for example, by fine preparation and/or surface engineering, is a top priority for high‐performance perovskite photodiodes.

Tex Se1- x Photodiode Shortwave Infrared Detection and Imaging.

Short-wave infrared detectors are playing an increasingly important role in the fields of autonomous driving, food safety, disease diagnosis and scientific research. However, the mature short-wave infrared camera such as InGaAs has the disadvantage of complexly heterogeneous integration with complementary metal-oxide-semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, we report a low-cost, high-performance, and high-stability Tex Se1- x short-wave infrared photodiode detector. The Tex Se1- x thin film is fabricated through CMOS-compatible low-temperature evaporation and post-annealing process, showcasing the potential of direct integration on the readout circuit. The device demonstrates a broad-spectrum response of 300-1600nm, a room-temperature specific detectivity of 1.0 × 1010 Jones, a -3dB bandwidth up to 116kHz, and a linear dynamic range of over 55dB, achieving the fastest response among Te-based photodiode devices and a dark current density 7 orders of magnitude smaller than Te-based photoconductive and field-effect transistor devices. With a simple Si3 N4 packaging, the detector shows high electric stability and thermal stability, meeting the requirements for vehicular applications. Based on the optimized Tex Se1- x photodiode detector, we demonstrate the applications in material identification and masking imaging. Our work paves a new way for CMOS-compatible infrared imaging chips. This article is protected by copyright. All rights reserved.

Efficient, Ambient‐Stable, All‐Polymer Organic Photodetector for Machine Learning‐Promoted Intelligent Monitoring of Indoor Plant Growth

AbstractThe blend ratio and thickness of the PM6:PY‐IT active layer are optimized to realize highly efficient all‐polymer organic photodetectors (OPDs). Ultralow dark current densities of less than 5.92 × 10−10A cm−2(at −1 V) appear when the PM6:PY‐IT active layers have thicknesses in the range of 250–400 nm and blend ratios between 1:1 and 1:1.4, suggesting a wide fabrication window. Fast rise/fall times of 560/250 ns are measured with a cut‐off frequency of 530 kHz for the OPD incorporating a 250‐nm‐thick 1:1 blend. This OPD provides superior performance, with a high detectivity of 2.98 × 1013Jones and a wide linear dynamic range of 138 dB (at 530 nm (−1 V)). In addition, the ultralow dark current of the OPD retains excellent long‐term stability over 500 h of aging testing (thermal stress, ambient conditions, and continuous illumination). With the integration of specific light filters, a system is realized for the efficient detection of indoor plant‐growth lighting, allowing the rapid and accurate detection (&gt;97%) of photosynthetic photon flux at various wavelengths of light that directly determine the photosynthesis and photomorphogenesis of indoor plants, supervised by machine learning. The artificial intelligence‐trained OPD effectively improves detection accuracy.

Enhanced Spectral Response of ZnO-Nanorod-Array-Based Ultraviolet Photodetectors by Alloying Non-Isovalent Cu-O with CuAlO2 P-Type Layer.

CuAlO2 was synthesized by a hydrothermal method, in which the Cu-O dimers were incorporated by simply altering the ratio of the reactants and the temperature. The incorporation process increases the grain size in CuAlO2, and modulates the work function and binding energies for CuAlO2 due to the partial substitution of Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying non-isovalent Cu-O with a CuAlO2 host. Based on the ZnO nanorod arrays (NRs) ultraviolet photodetector, CuAlO2/Cu-O fabricated by the low-cost drop-coating method was used as the p-type hole transport layer. The incorporation of the Cu-O clusters into CuAlO2 lattice to enhance the conductivity of CuAlO2 is an effective way for improving ZnO NRs/CuAlO2 device performance. The photodetectors exhibit significant diode behavior, with a rectification ratio approaching 30 at ±1 V, and a dark saturation current density 0.81 mA cm-2. The responsivity of the ZnO-NRs-based UV photodetector increases from 13.2 to 91.3 mA/W at 0 V bias, with an increase in the detectivity from 2.35 × 1010 to 1.71 × 1011 Jones. Furthermore, the ZnO NRs/[CuAlO2/Cu-O] photodetector exhibits a maximum responsivity of 5002 mA/W at 1.5 V bias under 375 nm UV illumination.

Effects of doping and minority carrier lifetime on mid-wave infrared InGaAs/InAsSb superlattice nBn detector performance

The effect of majority carrier concentration and minority carrier lifetime on the performance of mid-wave infrared ( λ cutoff = 5.5 μ m ) nBn detectors with variably doped InGaAs/InAsSb type-II superlattice absorbers is investigated. The detector layer structures are grown by molecular beam epitaxy such that their absorbing layers are either undoped, uniformly doped with a target density of 4 × 1015 cm−3, or doped with a graded profile, and variable-area mesa detector arrays are fabricated. Each material's temperature-dependent minority carrier lifetime is determined by time-resolved photoluminescence, and majority carrier concentration is extracted from capacitance–voltage measurements. Detector performance is evaluated with dark current and photocurrent measurements, from which quantum efficiency and shot-noise-limited noise-equivalent irradiance are calculated. The two doped detectors have lower dark current densities compared to their undoped counterpart due to the reduction in diffusion current as well as suppression of depletion current. Although both intentionally doped devices exhibit lower minority carrier lifetimes relative to the undoped device, the device with graded doping maintains a comparable quantum efficiency to the undoped device. Ultimately, the graded doping structure exhibits the highest sensitivity with a shot noise-limited noise-equivalent irradiance of 6.3 × 1010 photons/cm2 s in low-background light conditions, within a factor of 4× of an infrared detector pixel with Rule 07 dark current density and unity quantum efficiency. A detailed analysis of the dark current, quantum efficiency, and minority carrier lifetime provides insight into the material and device design factors that must be considered to realize a device with optimal sensitivity.

Long-wave bilayer graphene/HgCdTe based GBp type-II superlattice unipolar barrier infrared detector

Type-II superlattice (T2SL) material is used to design highly efficient next-generation infrared (IR) detectors. The flexibility of the material allows the integration of unipolar barrier IR detector architecture to suppress generation-recombination currents by blocking the majority charge carriers and improve device performance. This paper presents a self-powered T2SL unipolar barrier detector that operates in the long-wave IR regime. It comprises a contact layer made of p+-bilayer graphene (G) and a barrier layer made of p–-Hg1–xCdx=0.41Te (B) placed over a p+-Hg1–xCdx=0.2217Te absorber layer (p) and is known as the GBp detector. The optoelectronic characterization of the unipolar GBp detector is carried out using the Silvaco Atlas TCAD software. Under self-powered mode operation, the proposed GBp detector exhibits an improvement in photocurrent density of about 108 times. The dark current density of 0.4nA/cm2, the photocurrent responsivity of 7.82 A/W, the quantum efficiency of 91.44%, and the detectivity of 4.48 × 1014 cmHZ1/2/W are found at the liquid nitrogen temperature with a bias of –0.5 V. A dichroic ratio of 249 and a response time of less than 1 ps are likewise exhibited by the GBp detector. The substantial electric field at the contact/barrier heterointerface and the high barrier height in the conduction band, which result in an increased photodetection response, are attributed to this improved performance.

Design and modeling of high-performance mid-wave infrared InAsSb-based nBn photodetector using barrier band engineering approaches

We report a new nBn photodetector (nBn-PD) design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for mid-wavelength infrared (MWIR) applications. In this structure, delta-doped compositionally graded barrier (δ-DCGB) layers are suggested, the advantage of which is creation of a near zero valence band offset in nBn photodetectors. The design of the δ-DCGB nBn-PD device includes a 3 µm absorber layer (n-InAs0.81Sb0.19), a unipolar barrier layer (AlSb), and 0.2 μm contact layer (n-InAs0.81Sb0.19) as well as a 0.116 µm linear grading region (InAlSb) from the contact to the barrier layer and also from the barrier to the absorber layer. The analysis includes various dark current contributions, such as the Shockley–Read–Hall (SRH), trap-assisted tunneling (TAT), Auger, and Radiative recombination mechanisms, to acquire more precise results. Consequently, we show that the method used in the nBn device design leads to diffusion-limited dark current so that the dark current density is 2.596 × 10−8 A/cm2 at 150 K and a bias voltage of − 0.2 V. The proposed nBn detector exhibits a 50% cutoff wavelength of more than 5 µm, the peak current responsivity is 1.6 A/W at a wavelength of 4.5 µm and a − 0.2 V bias with 0.05 W/cm2 backside illumination without anti-reflective coating. The maximum quantum efficiency at 4.5 µm is about 48.6%, and peak specific detectivity (D*) is of 3.37 × 1010 cm⋅Hz1/2/W. Next, to solve the reflection concern in this nBn devices, we use a BaF2 anti-reflection coating layer due to its high transmittance in the MWIR window. It leads to an increase of almost 100% in the optical response metrics, such as the current responsivity, quantum efficiency, and detectivity, compared to the optical response without an anti-reflection coating layer.Graphical

Cationic Molecular Metal Chalcogenide Ligand‐Passivated Colloidal Quantum Dots and Their Application to Suppressed Dark‐Current Near‐Infrared Photodetectors

AbstractThe surface of colloidal‐type quantum dots (QDs) is protected with surfactants to maintain their nanoscale size and dispersion in various solvents. Such protection is advantageous to the processability of the dots, but the surfactants also act as insulators, thereby adversely affecting the electrical properties of the resulting devices. Anion‐type molecular metal chalcogenide complexes (MCCs) have been developed as an alternative to these surfactants. However, anionic ligands limit the charges of the resulting QDs to negative values; thus, additional processes are required to compensate for these charges. Herein, this work prepares cationic‐type dimetal diselenium perchlorate MCCs (M2Se2(ClO4)2, M = Mn, Zn, and Sn) and applies them to stabilize colloidal QDs. The resulting M2Se2‐PbS QDs are then used to fabricate near‐infrared photodetectors (NIR‐PDs). The devices exhibit remarkably suppressed dark current densities (JD) of as low as 4.92 × 10−10 A cm−2 when compared with PDs based on 1,2 ethandithiol‐PbS (EDT‐PbS) (JD = 1.41 × 10−8 A cm−2). In addition, the devices exhibit a high responsivity of 0.07 A W−1 in response to 950 nm NIR light signals, as well as an excellent specific detectivity of 5.66 × 1012 Jones at 950 nm. Finally, this work fabricates hybrid‐type QD films using cationic and anionic MCC‐PbS QDs and obtains a high external quantum efficiency (EQE) of 13.1%.

Bandwidth Characteristics of Mid-Wavelength Infrared PIN HgCdTe Avalanche Photodiodes

HgCdTe avalanche photodiodes (APDs) are used in mid-wavelength infrared (MWIR) photoelectric detectors in free-space optical communication, three-dimensional light detection, and ranging. Although HgCdTe has a small electronic effective mass and high mobility, there is a gap between the actual bandwidth of the device and the theoretical limit, and it is important to analyze the carrier transport mechanism in these devices. A two-dimensional finite element model is used to analyze the carrier transport mechanism for different device structures and bias voltages. The structural parameters of the device are optimized on the basis of a comprehensive determination of its bandwidth characteristics. Experimental data and calculation results are found to be consistent. This structural optimization increases the device bandwidth from 27.1 MHz to 553 MHz, with a gain-normalized dark current density (GNDCD) of less than 10−6 A/cm2. The results obtained here can provide guidance for the design of high-speed HgCdTe devices.

An n-Type All-Fused-Ring Molecule with Photoresponse to 1000nm for Highly Sensitive Near-Infrared Photodetector.

Most of all-fused-ring π-conjugated molecules have wide or medium bandgap and show photo response in the visible range. In this work, an all-fused-ring n-type molecule, which exhibits an ultrasmall optical bandgap of 1.22eV and strong near-infrared (NIR) absorption with an onset absorption wavelength of 1013nm is reported. The molecule consists of 14 aromatic rings and has electron donor-acceptor characteristics. It exhibits excellent n-type properties with low-lying HOMO/LUMO energy levels of -5.48eV/-3.95 eV and high electron mobility of 7.0×10-4 cm2 V-1 s-1 . Most importantly, its thin film exhibits a low trap density of 5.55×1016 cm-3 because of the fixed molecular conformation and consequently low conformation disorder. As a result, organic photodetector (OPD) based on the compound exhibits a remarkably low dark current density (Jd ) of 2.01×10-10 Acm-2 at 0V. The device shows a shot-noise-limited specific detectivity (Dsh *) of exceeding 1013 Jones at 400-1000nm wavelength region with a peak specific detectivity of 4.65×1013 Jones at 880nm. This performance is among the best reported for self-powered NIR OPDs.

High Responsivity of Narrowband Photomultiplication Organic Photodetector via Interfacial Modification

AbstractNarrowband‐response organic photodetectors with high responsivity are widely demanded in areas of substance detection, industry automation, smart wearable devices, etc. Photomultiplication‐type organic photodetectors (PM‐OPDs) with high responsivity usually have a broadband photoresponse due to the broadband absorption nature of the photoactive materials. In this work, effort is made to develop a high‐performance filterless narrowband PM‐OPD using the charge injection narrowing (CIN) effect. A 0.8 nm thick Al2O3 interlayer is used to mitigate the dark current density (JD) in the narrowband PM‐OPD, prepared using a 2.8 µm thick blend layer of P3HT:[6,6]‐phenyl‐C70‐butyric acid methyl ester (PC70BM), achieving a peak responsivity of 1334 A W−1 at 650 nm, with a full‐width at half‐maximum of 40 nm. The narrowband PM‐OPD also possesses an impressive high specific detectivity of 9.73 × 1013 Jones. It is shown that the use of a 0.8 nm thick Al2O3 interlayer significantly suppresses the JD, creating a high energy barrier at the anode/photoactive interface and achieving a narrowband photoresponse behavior due to the CIN effect. The results of this work provide an exciting option for a variety of applications for OPDs with low cost, flexibility, and high sensitivity.

Efficient Near-Infrared Organic Photodetectors with Spectral Response up to 1600 nm for Accurate Alcohol Concentration Detection

The development of near-infrared organic photodetectors (NIR-OPDs) in 1000-1700 nm is essential for medical monitoring, food quality inspection, machine vision, and biomedical imaging. However, when solving the high dark current density (JD) in bulk-heterojunction (BHJ) NIR-OPDs based on narrow-bandgap systems, it is often accompanied by photocurrent loss, which is a great challenge in achieving high-performance NIR-OPDs. Here, an ideal hybrid pseudo-PHJ (planar-heterojunction)/BHJ structure is proposed to overcome this challenge, which is introducing the N2200 layer between the cathode and BHJ. The introduction of the N2200 raises the external charge injection barrier and reduces the trap density, thus achieving significant suppression of JD (6.22 × 10-7 A cm-2 at -0.2 V bias, about 2 orders of magnitude lower compared to the BHJ NIR-OPDs). Meanwhile, the hybrid structure combines the advantages of PHJ and BHJ, thus maintaining a high photocurrent, resulting in responsivity and detectivity of 18.71 mA W-1 and 4.19 × 1010 Jones, respectively, at 1400 nm at -0.2 V bias, which is superior to the performance of BHJ NIR-OPDs. And the hybrid structured NIR-OPDs are proven to rapidly quantify the alcohol content of mixtures to within 2% accuracy, which exhibits great potential for application in the food and pharmaceutical industries.