Infrared Organic Photodetectors Employing Ultralow Bandgap Polymer and Non-Fullerene Acceptors for Biometric Monitoring

trans-Stilbene aggregates and crystallites in polystyrene films: microscopy and spectroscopy studies

Solid and liquid stilbene forms were characterized using a range of techniques, including atomic force microscopy, coherent anti-Stokes Raman scattering microspectroscopy and optical spectroscopy. The obtained experimental results were analyzed by means of quantum chemical calculations and using a non-negative matrix factorization algorithm. It was confirmed that pure cis-stilbene formed a homogeneous fluid film on a glass substrate, whereas pure trans-stilbene formed crystals. Mixtures of trans-stilbene and polystyrene were shown to form stable solid films, which were non-homogeneous on the microscopic scale: stilbene molecules self-organized into microcrystals, which floated on the surface of polystyrene glass.

Enhanced SWIR Light Detection in Organic Semiconductor Photodetectors through Up-Conversion of Mid-Gap Trap States

Shortwave-infrared (SWIR) photodetectors are vital for many scientific and industrial applications including surveillance, quality control and inspection. In recent decades, photodetectors based on organic semiconductors have emerged, demonstrating potential to add real value to broadband and narrowband imaging and sensing scenarios, where factors such as thermal budget sensitivity, large area aperture necessity, cost considerations, and lightweight and conformal flexibility demands are prioritized. It is now recognized that the performance of organic photodetectors (OPDs), notably their specific detectivity, is ultimately limited by trap states, universally present in disordered semiconductors. This work adopts an approach of utilizing these mid-gap states to specifically create a SWIR photo-response. To this end, this work introduces a somewhat counter-intuitive approach of "trap-doping" in bulk heterojunction (BHJs) photodiodes, where small quantities of a guest organic molecule are intentionally incorporated into a semiconducting donor:acceptor host system. Following this approach, this work demonstrates a proof-of-concept for a visible-to-SWIR broadband OPD, approaching (and, to some extent, even exceeding) state-of-the-art performance across critical photodetector metrics. The trap-doping approach is, even though only a proof-of-concept currently, broadly applicable to various spectral windows. It represents a new modality for engineering photodetection using the unconventional strategy of turning a limitation into a feature.

Ultranarrow-bandgap small-molecule acceptor enables sensitive SWIR detection and dynamic upconversion imaging

Short-wavelength infrared (SWIR) light detection plays a key role in modern technologies. Emerging solution-processed organic semiconductors are promising for cost-effective, flexible, and large-area SWIR organic photodiodes (OPDs). However, the spectral responsivity (R) and specific detectivity (D*) of SWIR OPDs are restricted by insufficient exciton dissociation and high noise current. In this work, we synthesized an SWIR small molecule with a spectral coverage of 0.3 to 1.3 micrometers peaking at 1100 nanometers. The photodiode, with optimized exciton dissociation, charge injection, and SWIR transmittance, achieves a record high R of 0.53 ampere per watt and D* of 1.71 × 1013 Jones at 1110 nanometers under zero bias. The D* at 1 to 1.2 micrometers surpasses that of the uncooled commercial InGaAs photodiode. Furthermore, large-area semitransparent all-organic upconversion devices integrating the SWIR photodiode realized static and dynamic SWIR-to-visible imaging, along with excellent upconversion efficiency and spatial resolution. This work provides alternative insights for developing sensitive organic SWIR detection.

Advancing Detectivity and Stability of Near-Infrared Organic Photodetectors via a Facile and Efficient Cathode Interlayer

Near-infrared (NIR) organic photodetectors (OPDs) are pivotal in numerous technological applications due to their excellent responsivity within the NIR region. Polyethylenimine ethoxylated (PEIE) has conventionally been employed as an electron transport layer (hole-blocking layer) to suppress dark current (JD) and enhance charge transport. However, the limitations of PEIE in chemical stability, processing conditions, environmental impact, and absorption range have spurred the development of alternative materials. In this study, we introduced a novel solution: a hybrid of sol-gel zinc oxide (ZnO) and N,N'-bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDINO) as the electron transport layer for NIR-OPDs. Our fabricated OPD exhibited significantly improved responsivity, reduced internal traps, and enhanced charge transfer efficiency. The detectivity, spanning from 400 to 1100 nm, surpassed ∼5 × 1012 Jones, reaching ∼1.1 × 1012 Jones at 1000 nm, accompanied by an increased responsivity of 0.47 A/W. Also, the unpackaged OPD remarkedly demonstrated stable JD and external quantum efficiency (EQE) over 1000 h under dark storage conditions. This innovative approach not only addresses the drawbacks of conventional PEIE-based OPDs but also offers promising avenues for the development of high-performance OPDs in the future.

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Progress in Advanced Infrared Optoelectronic Sensors

Infrared optoelectronic sensors have attracted considerable research interest over the past few decades due to their wide-ranging applications in military, healthcare, environmental monitoring, industrial inspection, and human-computer interaction systems. A comprehensive understanding of infrared optoelectronic sensors is of great importance for achieving their future optimization. This paper comprehensively reviews the recent advancements in infrared optoelectronic sensors. Firstly, their working mechanisms are elucidated. Then, the key metrics for evaluating an infrared optoelectronic sensor are introduced. Subsequently, an overview of promising materials and nanostructures for high-performance infrared optoelectronic sensors, along with the performances of state-of-the-art devices, is presented. Finally, the challenges facing infrared optoelectronic sensors are posed, and some perspectives for the optimization of infrared optoelectronic sensors are discussed, thereby paving the way for the development of future infrared optoelectronic sensors.

Sensitive Organic Photodetectors With Spectral Response up to 1.3 µm Using a Quinoidal Molecular Semiconductor

Detecting short-wavelength infrared (SWIR) light has underpinned several emerging technologies. However, the development of highly sensitive organic photodetectors (OPDs) operating in the SWIR region is hindered by their poor external quantum efficiencies (EQEs) and high dark currents. Herein, the development of high-sensitivity SWIR-OPDs with an efficient photoelectric response extending up to 1.3 µm is reported. These OPDs utilize a new ultralow-bandgap molecular semiconductor featuring a quinoidal tricyclic electron-deficient central unit and multiple non-covalent conformation locks. The SWIR-OPD achieves an unprecedented EQE of 26% under zero bias and an even more impressive EQE of up to 41% under a -4 V bias at 1.10 µm, effectively pushing the detection limit of silicon photodetectors. Additionally, the low energetic disorder and trap density in the active layer lead to significant suppression of thermal-generation carriers and dark current, resulting in excellent detectivity (Dsh *) exceeding 1013 Jones from 0.50 to 1.21 µm and surpassing 1012 Jones even at 1.30 µm under zero bias, marking the highest achievements for OPDs beyond the silicon limit to date. Validation with photoplethysmography measurements, a spectrometer prototype in the 0.35-1.25 µm range, and image capture under 1.20 µm irradiation demonstrate the extensive applications of this SWIR-OPD.

Fast Near-Infrared Photodetectors Based on Nontoxic and Solution-Processable AgBiS2

Solution-processable near-infrared (NIR) photodetectors are urgently needed for a wide range of next-generation electronics, including sensors, optical communications and bioimaging. However, it is rare to find photodetectors with >300 kHz cut-off frequencies, especially in the NIR region, and many of the emerging inorganic materials explored are comprised of toxic elements, such as lead. Herein, solution-processed AgBiS2 photodetectors with high cut-off frequencies under both white light (>1 MHz) and NIR (approaching 500 kHz) illumination are developed. These high cut-off frequencies are due to the short transit distances of charge-carriers in the ultrathin photoactive layer of AgBiS2 photodetectors, which arise from the strong light absorption of this material, such that film thicknesses well below 120 nm are sufficient to absorb >65% of NIR to visible light. It is also revealed that ion migration plays a critical role in the photo-response speed of these devices, and its detrimental effects can be mitigated by finely tuning the thickness of the photoactive layer, which is important for achieving low dark current densities as well. These outstanding characteristics enable the realization of air-stable, real-time heartbeat sensors based on NIR AgBiS2 photodetectors, which strongly motivates their future integration in high-throughput systems.

Flexible Broadband Organic Photodetectors with Ternary Planar-Mixed Heterojunction Semiconductors and Solution-Processed Polymeric Electrode

Flexible organic photodetectors (OPDs) hold immense promise in health monitoring sensors, flexible imaging sensors, and portable optical communication. Nevertheless, the actualization of high-performance flexible electronics has been hindered by rigid electrodes such as metals or metal oxides. In this work, we constructed a flexible broadband organic photodetector using a solution-processed polymeric electrode, which exhibits flexibility surpassing that of conventional indium tin oxide (ITO) electrodes. Additionally, we employed a planar-mixed heterojunction (PMHJ) through a sequential deposition method and introduced PC71BM as the third constituent into the PM6/Y6 binary active layer, resulting in enhanced photodetection performance and a broadend spectral range. The optimized OPDs demonstrated remarkable detectivity (D*) exceeding 1012 Jones in brodband from 300 to 900 nm, with a champion D* of 6.31 × 1012 Jones at 790 nm. Furthermore, after undergoing 500 cycles of bending, the D* retained approximately 78% of its original performance, highlighting the outstanding mechanical stability. This work presents a promising pathway toward the development of flexible broadband OPDs using a straightforward method, offering enhanced compatibility in diverse application scenarios and propelling the frontier of flexible optoelectronic research.

Shortwave Infrared Organic Photodiodes Realized by Polaron Engineering

A novel approach for developing shortwave IR (SWIR) organic photodiodes (OPDs) using doped polymers is presented. SWIR OPDs are challenging to produce because of the limitations in extending the absorption of conjugated molecules and the high dark currents of SWIR-absorbing materials. Herein, it is shown that the conversion of bound polarons to free polarons by light energy can be utilized as an SWIR photodetection mechanism. To maximize the bound-polaron density and bound-to-free polaron ratio of the doped polymer film, the doping process is engineered and dopant molecules are diffused into the crystalline domain of the polymer matrix and a direct correlation between the bound-to-free polaron ratio and device performance is confirmed. The optimized double-doped SWIR OPD exhibits a high external quantum efficiency of 77 100% and specific detectivity of 1.11 × 1011 Jones against SWIR. These findings demonstrate the application potential of polarons as alternatives for Frenkel excitons in SWIR OPDs.

Exploration of charge transfer analysis and photovoltaics properties of A-D-A type non-fullerene phenazine based molecules to enhance the organic solar cell properties

To intensify the photovoltaic properties of organic solar cells, density functional theory (DFT) based computational techniques were implemented on six non-fullerene A-D-A type small molecules (N1-N6) modified from reference molecule (R) which consists of phenazine fused with 1,4- Dimethyl-4H-3,7-dithia-4-aza- cyclopenta [α] pentalene on both sides with one of its phenyl rings acting as the central donor unit, further attached with 2-(5,6-Difluoro-2-methylene-3-oxo-indan-1-ylidene)-malononitrile acceptor groups at terminal sites. All proposed compounds have a phenazine base modified with a variety of substituents at the terminals. Transition density matrix, density of states, frontier molecular orbitals, intramolecular charge transfer abilities and optoelectronic properties of these compounds were investigated using B3LYP/6-31G (d, p) and B3LYP/6-31G++ (d,p) level of theory. All six designed compounds exhibited a bathochromic sift in their λmax as compared to the R molecule. All designed molecules also have reduced band gap and smaller excitation energy than R. Among all, N6 exhibited highest λmax and lowest bandgap as compared to reference molecule indicating its promising photovoltaic properties. Decreased hole and electron reorganization energy in several of the suggested compounds is indicative of greater charge mobility in them. PTB7-Th donor was employed to calculate open circuit voltage of all investigated molecules. N1-N5 molecules had improved optoelectronic properties, significant probable power conversion efficiency as evident from their absorption aspects, high values of Voc, and fill factor, compared to R molecule. Designed A-D-A type NF based molecules make OSCs ideal for use in wearable devices, building-integrated photovoltaics and smart fabrics.

Retinomorphic Motion Detector Fabricated with Organic Infrared Semiconductors

Organic retinomorphic sensors offer the advantage of in-sensor processing to filter out redundant static backgrounds and are well suited for motion detection. To improve this promising structure, here, the key role of interfacial energetics in promoting charge accumulation to raise the inherent photoresponse of the light-sensitive capacitor is studied. Specifically, incorporating appropriate interfacial layers around the photoactive layer is crucial to extend the carrier lifetime, as confirmed by intensity-modulated photovoltage spectroscopy. Compared to its photodiode counterpart, the retinomorphic sensor shows better detectivity and response speed due to the additional insulating layer, which reduces the dark current and the RC time constant. Lastly, three retinomorphic sensors are integrated into a line array to demonstrate the detection of movement speed and direction, showing the potential of retinomorphic designs for efficient motion tracking.

NIR-II Absorbing Monodispersed Oligomers Based on N-B←N Unit

Organic molecules with near-infrared II (NIR II) light absorption are essential for many biological and opto-electronic applications. Herein, we report monodispersed oligomers as NIR II light absorber using a new molecular design strategy of resonant N-B←N unit, i.e. balanced resonant boron-nitrogen covalent bond (B-N) and boron-nitrogen coordination bond (B←N). We synthesize a series of monodispersed oligomers with thiophene-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (TB), which contains resonant N-B←N unit, as the repeating unit. The TB pentamer exhibits the maximum absorption wavelength of 1169 nm, which is the longest for oligomers reported so far. Organic photodetectors (OPDs) with the TB tetramer as the electron acceptor shows the specific detectivity of 2.98×1011 Jones at 1180 nm under zero bias. This performance is among the best for NIR II OPDs. These results indicate a new kind of NIR II absorbing molecules as excellent opto-electronic materials.

High Detectivity Near Infrared Organic Photodetectors Using an Asymmetric Non-Fullerene Acceptor for Optimal Nanomorphology and Suppressed Dark Current

Recently, the development of non-fullerene acceptors (NFAs) for near-infrared (NIR) organic photodetectors (OPDs) has attracted great interest due to their excellent NIR light absorption properties. Herein, we developed NFAs by substituting an electron-donating moiety (branched alkoxy thiophene (BAT)) asymmetrically (YOR1) and symmetrically (YOR2) for the Y6 framework. YOR1 exhibited nanoscale phase separation in a film blended with PTB7-Th. Moreover, substituting the BAT unit effectively extended the absorption wavelengths of YOR1 over 1000 nm by efficient intramolecular charge transfer and extension of the conjugation length. Consequently, YOR1-OPD exhibited significantly reduced dark current and improved responsivity by simultaneously satisfying optimal nanomorphology and significant suppression of charge recombination, resulting in 1.98 × 1013 and 3.38 × 1012 Jones specific detectivity at 950 and 1000 nm, respectively. Moreover, we successfully demonstrated the application of YOR1-OPD in highly sensitive photoplethysmography sensors using NIR light. This study suggests a strategic approach for boosting the overall performance of NIR OPDs targeting a 1000 nm light signal using an all-in-one (optimal morphology, suppressed dark current, and extended NIR absorption wavelength) NFA.

Boosting the Performance of Organic Photodetectors with a Solution-Processed Integration Circuit toward Ubiquitous Health Monitoring

Organic photodetectors, as an emerging wearable photoplethysmographic (PPG) technology, offer exciting opportunities for next-generation photonic healthcare electronics. However, the mutual restraints among photoresponse, structure complexity, and fabrication cost have intrinsically limited the development of organic photodetectors for ubiquitous health monitoring in daily activities. Here, an effective route to dramatically boost the performance of organic photodetectors with a solution-processed integration circuit for health monitoring application is reported. Through creating an ideal metal-semiconductor junction interface that minimizes the trap states within the device, solution-printed organic field-effect transistors (OFETs) are achieved with an ultrahigh signal amplification efficiency of 37.1 S A-1 , approaching the theoretical thermionic limit. Consequently, monolithic integration of the OFET with an organic photoconductor enables the remarkable amplification of photoresponse signal-to-noise ratio by more than four orders of magnitude from 5.5 to 4.6 × 105 , which is able to meet the demand for accurately extracting physiological information from the PPG waveforms. This work offers an effective and versatile approach to greatly enhance the photodetector performance, promising to revolutionize health monitoring technologies.

Green-Solvent-Processed High-Performance Broadband Organic Photodetectors

Solution-processed organic photodetectors with broadband activity have been demonstrated with an environmentally benign solvent, ortho-xylene (o-xylene), as the processing solvent. The organic photodetectors employ a wide band gap polymer donor PBDB-T and a narrow band gap small-molecule non-fullerene acceptor CO1-4F, both dissolvable in o-xylene at a controlled temperature. The o-xylene-processed devices have shown external quantum efficiency of up to 70%, surpassing the counterpart processed with chlorobenzene. With a well-suppressed dark current, the device can also present a high specific detectivity of over 1012 Jones at -2 V within practical operation frequencies and is applicable for photoplethysmography with its fast response. These results further highlight the potential of green-solvent-processed organic photodetectors as a high-performing alternative to their counterparts processed in toxic chlorinated solvents without compromising the excellent photosensing performance.

High-Speed Printing of Narrow-Band-Gap Sn-Pb Perovskite Layers toward Cost-Effective Manufacturing of Optoelectronic Devices

Narrow-band-gap Sn-Pb perovskites have emerged as one of the most promising solution-processed near-infrared (NIR) light-detection technologies, with the key figure-of-merit parameters already rivaling those of commercial inorganic devices, but maximizing the cost advantage of solution-processed optoelectronic devices depends on the ability to fast-speed production. However, weak surface wettability to perovskite inks and evaporation-induced dewetting dynamics have limited the solution printing of uniform and compact perovskite films at a high speed. Here, we report a universal and effective methodology for fast printing of high-quality Sn-Pb mixed perovskite films at an unprecedented speed of 90 m h^-1 by altering the wetting and dewetting dynamics of perovskite inks with the underlying substrate. A line-structured SU-8 pattern surface to trigger spontaneous ink spreading and fight ink shrinkage is designed to achieve complete wetting with a near-zero contact angle and a uniform dragged-out liquid film. The high-speed printed Sn-Pb perovskite films have both large perovskite grains (>100 μm) and excellent optoelectronic properties, yielding highly efficient self-driven NIR photodetectors with a large voltage responsivity over 4 orders of magnitude. Finally, the potential application of the self-driven NIR photodetector in health monitoring is demonstrated. The fast printing methodology provides a new possibility to extend the manufacturing of perovskite optoelectronic devices to industrial production lines.

Enhanced sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure

One of the key challenges facing organic photodiodes (OPDs) is increasing the detection into the infrared region. Organic semiconductor polymers provide a platform for tuning the bandgap and optoelectronic response to go beyond the traditional 1000-nanometer benchmark. In this work, we present a near-infrared (NIR) polymer with absorption up to 1500 nanometers. The polymer-based OPD delivers a high specific detectivity D^* of 1.03 × 10¹⁰ Jones (-2 volts) at 1200 nanometers and a dark current J_d of just 2.3 × 10^-6 ampere per square centimeter at -2 volts. We demonstrate a strong improvement of all OPD metrics in the NIR region compared to previously reported NIR OPD due to the enhanced crystallinity and optimized energy alignment, which leads to reduced charge recombination. The high D^* value in the 1100-to-1300-nanometer region is particularly promising for biosensing applications. We demonstrate the OPD as a pulse oximeter under NIR illumination, delivering heart rate and blood oxygen saturation readings in real time without signal amplification.

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 (J_D) 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 J_D (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.

Architecturally simple organic photodiodes with highly competitive figures of merit via a facile self-assembly strategy

Photodetectors (PDs) based on organic materials exhibit potential advantages such as low-temperature processing, and superior mechanical properties and form factors. They have seen rapid strides toward achieving performance metrics comparable to inorganic counterparts. Here, a simplified device architecture is employed to realize stable and high-performance organic PDs (OPDs) while further easing the device fabrication process. In contrast to the sequential deposition of the hole blocking layer (HBL) and active layer (conventional 'two-step' processing), the proposed strategy forms a self-assembled HBL and active layer in a 'single-step' process. A high-performance UV-Vis-NIR OPD based on the PM6:BTP-eC9 system is demonstrated using this cost-effective processing strategy. The green solvent processed proof-of-concept device exhibits remarkable responsivity of ∼0.5 A W^-1, lower noise current than conventional two-step OPD, ultrafast rise/fall times of 1.4/1.6 μs (comparable to commercial silicon diode), and a broad linear dynamic range of 140 dB. Importantly, highly stable (light and heat) devices compared to those processed by the conventional method are realized. The broad application potential of this elegant strategy is proven by demonstrating the concept in three representative systems with broadband sensing competence.

Organic photodiodes: device engineering and applications

Organic photodiodes (OPDs) have shown great promise for potential applications in optical imaging, sensing, and communication due to their wide-range tunable photoelectrical properties, low-temperature facile processes, and excellent mechanical flexibility. Extensive research work has been carried out on exploring materials, device structures, physical mechanisms, and processing approaches to improve the performance of OPDs to the level of their inorganic counterparts. In addition, various system prototypes have been built based on the exhibited and attractive features of OPDs. It is vital to link the device optimal design and engineering to the system requirements and examine the existing deficiencies of OPDs towards practical applications, so this review starts from discussions on the required key performance metrics for different envisioned applications. Then the fundamentals of the OPD device structures and operation mechanisms are briefly introduced, and the latest development of OPDs for improving the key performance merits is reviewed. Finally, the trials of OPDs for various applications including wearable medical diagnostics, optical imagers, spectrometers, and light communications are reviewed, and both the promises and challenges are revealed.

Electron-donating amine-interlayer induced n-type doping of polymer:nonfullerene blends for efficient narrowband near-infrared photo-detection

Inherently narrowband near-infrared organic photodetectors are highly desired for many applications, including biological imaging and surveillance. However, they suffer from a low photon-to-charge conversion efficiencies and utilize spectral narrowing techniques which strongly rely on the used material or on a nano-photonic device architecture. Here, we demonstrate a general and facile approach towards wavelength-selective near-infrared phtotodetection through intentionally n-doping 500-600 nm-thick nonfullerene blends. We show that an electron-donating amine-interlayer can induce n-doping, resulting in a localized electric field near the anode and selective collection of photo-generated carriers in this region. As only weakly absorbed photons reach this region, the devices have a narrowband response at wavelengths close to the absorption onset of the blends with a high spectral rejection ratio. These spectrally selective photodetectors exhibit zero-bias external quantum efficiencies of ~20-30% at wavelengths of 900-1100 nm, with a full-width-at-half-maximum of ≤50 nm, as well as detectivities of >10¹² Jones.

Dual-acceptor alloy model delivers high detection performance of organic NIR detectors for real-time arterial pulse monitoring

Near-infrared organic photodetectors (NIR-OPDs) have significant potential in the fields of human sign monitoring, industrial defect detection, and military. We propose a method to construct high-performance NIR-OPDs by introducing narrow-band acceptor materials with very similar structures in bulk heterojunctions (BHJs) so that they form an alloy model during the film formation process, which in turn promotes the generation and dissociation of photogenerated excitons to achieve high-performance NIR detectors. Here, we choose the narrow-band materials IEICO-4F and IEICO-4Cl as dual-acceptors and PTB7-Th as the donor to construct NIR-OPDs. Benefiting from the alloy model formation, the dark current of the device is significantly suppressed compared with the binary control, while the photocurrent of the device is enhanced. The optimized NIR-OPD achieved a detectivity of more than 2.6×1012 Jones at -0.1V bias. With the optimized device performance, we can clearly monitor the human arterial pulse information, and the phases of the cardiac cycle of the heart can be accurately identified. This work demonstrates a new method for constructing highperformance NIR-OPDs and shows great potential for contactless human arterial pulse monitoring.