An ultra-sensitive colloidal quantum dot infrared photodiode exceeding 100 000% external quantum efficiency via photomultiplication

In this study, we present ultrasensitive infrared photodiodes based on PbS colloidal quantum dots (CQDs) using a double photomultiplication strategy that utilizes the accumulation of both electron and hole carriers. While electron accumulation was induced by ZnO trap states that were created by treatment in a humid atmosphere, hole accumulation was achieved using a long-chain ligand that increased the barrier to hole collection. Interestingly, we obtained the highest responsivity in photo-multiplicative devices with the long ligands, which contradicts the conventional belief that shorter ligands are more effective for optoelectronic devices. Using these two charge accumulation effects, we achieved an ultrasensitive detector with a responsivity above 7.84 × 102 A W-1 and an external quantum efficiency above 105% in the infrared region. We believe that the photomultiplication effect has great potential for surveillance systems, bioimaging, remote sensing, and quantum communication.

Zinc-copper dual-ion electrolytes to suppress dendritic growth and increase anode utilization in zinc ion capacitors

The main bottlenecks that hinder the performance of rechargeable zinc electrochemical cells are their limited cycle lifetime and energy density. To overcome these limitations, this work studied the mechanism of a dual-ion Zn-Cu electrolyte to suppress dendritic formation and extend the device cycle life while concurrently enhancing the utilization ratio of zinc and thereby increasing the energy density of zinc ion capacitors (ZICs). The ZICs achieved a best-in-class energy density of 41 watt hour per kilogram with a negative-to-positive (n/p) electrode capacity ratio of 3.10. At the n/p ratio of 5.93, the device showed a remarkable cycle life of 22,000 full charge-discharge cycles, which was equivalent to 557 hours of discharge. The cumulative capacity reached ~581 ampere hour per gram, surpassing the benchmarks of lithium and sodium ion capacitors and highlighting the promise of the dual-ion electrolyte for delivering high-performance, low-maintenance electrochemical energy supplies.

Understanding Colloidal Quantum Dot Device Characteristics with a Physical Model

Colloidal quantum dots (CQDs) are finding increasing applications in optoelectronic devices, such as photodetectors and solar cells, because of their high material quality, unique and attractive properties, and process flexibility without the constraints of lattice match and thermal budget. However, there is no adequate device model for colloidal quantum dot heterojunctions, and the popular Shockley-Quiesser diode model does not capture the underlying physics of CQD junctions. Here, we develop a compact, easy-to-use model for CQD devices rooted in physics. We show how quantum dot properties, QD ligand binding, and the heterointerface between quantum dots and the electron transport layer (ETL) affect device behaviors. We also show that the model can be simplified to a Shockley-like equation with analytical approximate expressions for reverse saturation current, ideality factor, and quantum efficiency. Our model agrees well with the experiment and can be used to describe and optimize CQD device performance.

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.

Synthesis and exceptional operational durability of polyaniline-inspired conductive ladder polymers

Ladder-type structures can impart exceptional stability to polymeric electronic materials. This article introduces a new class of conductive polymers featuring a fully ladder-type backbone. A judicious molecular design strategy enables the synthesis of a low-defect ladder polymer, which can be efficiently oxidized and acid-doped to achieve its conductive state. The structural elucidation of this polymer and the characterization of its open-shell nature are facilitated with the assistance of studies on small molecular models. An autonomous robotic system is used to optimize the conductivity of the polymer thin film, achieving over 7 mS cm-1. Impressively, this polymer demonstrates unparalleled stability in strong acid and under harsh UV-irradiation, significantly surpassing commercial benchmarks like PEDOT:PSS and polyaniline. Moreover, it displays superior durability across numerous redox cycles as the active material in an electrochromic device and as the pseudocapacitive material in a supercapacitor device. This work provides structural design guidance for durable conductive polymers for long-term device operation.

Structural pseudocapacitors with reinforced interfaces to increase multifunctional efficiency

Structural supercapacitors hold promise to expand the energy capacity of a system by integrating load-bearing and energy-storage functions in a multifunctional structure, resulting in weight savings and safety improvements. Here, we develop strategies based on interfacial engineering to advance multifunctional efficiency. The structural electrodes were reinforced by coating carbon-fiber weaves with a uniquely stable conjugated redox polymer and reduced graphene oxide that raised pseudocapacitive capacitance and tensile strength. The solid polymer electrolyte was tuned to a gradient configuration, where it facilitated high ionic conductivity at the electrode-electrolyte interfaces and transitioned to a composition with high mechanical strength in the bulk for load support. The gradient design enabled the multilayer structural supercapacitors to reach state-of-the-art performance matching the level of monofunctional supercapacitors. In situ electrochemical-mechanical measurements established the device durability under mechanical loads. The structural supercapacitor was made into the hull of a model boat to demonstrate its multifunctionality.

Contribution of Sub-Gap States to Broadband Infrared Response in Organic Bulk Heterojunctions

This work studied a series of infrared detectors comprised of organic bulk heterojunctions to explain the origin of their broadband spectral response from the visible to the infrared spanning 1 to 8 μm and the transition from photonic to bolometric operation. Through comparisons of the detector current and the sub-bandgap density of states, the mid- and long-wave infrared response was attributed to charge trap-and-release processes that impact thermal charge generation and the activation energy of charge mobility. We further demonstrate how the sub-bandgap characteristics, mobility activation energy, and effective bandgap are key design parameters for controlling the device temperature coefficient of resistance, which reached up to -7%/K, better than other thin-film materials such as amorphous silicon and vanadium oxide.

Multiplexed printed sensors for in situ monitoring in bivalve aquaculture

Non-intrusive sensors that can be attached to marine species offer opportunities to study the impacts of environmental changes on their behaviors and well-being. This work presents a thin, flexible sensor tag to monitor the effects of dissolved oxygen and salinity on bivalve gape movement. The measurement range studied was 0.5-6 ppm for the dissolved oxygen sensor and 4-40 g kg^-1 for the salinity sensor. The curvature strain sensor based on electrodeposited semiconducting fibers enabled measurements of an oyster's gape down to sub-mm displacement. The multiplexed sensors were fabricated by low-cost techniques, offering an economical and convenient platform for aquaculture studies.

Acid-Base Reaction-Assisted Quantum Dot Patterning via Ligand Engineering and Photolithography

The integration of quantum dots (QDs) into device arrays for high-resolution display and imaging sensor systems remains a significant challenge in research and industry because of issues associated with the QD patterning process. It is difficult for conventional patterning processes such as stamping, inkjet printing, and photolithography to employ QDs and fabricate high-resolution patterns without degrading the properties of QDs. Here, we introduce a novel strategy for the QD patterning process by treating QDs with a bifunctional ligand for acid-base reaction-assisted photolithography. Bifunctional ligands, such as MPA (mercaptopropionic acid) or TGA (thioglycolic acid), have a carboxyl group on one side that allows the QDs to be etched along with the photoresist (PR) by the base developer, while on the opposite side the ligands have a thiol group that passivates the QD surface. Passivating MPA ligands on QDs facilitates patterning of QD films and makes them compatible with harsh photolithography processes. We successfully achieved the patterning of QDs down to 5 μm. We also fabricated high-resolution patterned QD light-emitting diodes (LEDs) and QD photodetector arrays. Our patterning process provides precise control for the fabrication of highly integrated QD-based optoelectronic devices.

Heterojunction bilayers serving as a charge transporting interlayer reduce the dark current and enhance photomultiplication in organic shortwave infrared photodetectors

Previous approaches to induce photomultiplication in organic diodes have increased the photosignal but lacked control over reducing background noise. This work presents a new interlayer design based on a heterojunction bilayer that concurrently enables photomultiplication and suppresses the dark current in organic shortwave infrared detectors to improve the overall detectivity. The heterojunction bilayer consists of a hole-transporting material copper thiocyanate and an electron-transporting material tin oxide, and this combination offers the ability to block charge injection in the dark. Under illumination, the bilayer promotes trap-assisted photomultiplication by lowering the tunneling barrier and amplifying the photocurrent through the injection of multiple carriers per absorbed photon. Upon incorporating the heterojunction interlayer in photodiodes and upconversion imagers, the devices achieve an external quantum efficiency up to 560% and a detectivity of 3.5 × 10⁹ Jones. The upconversion efficiency of the imager doubles with a 1.7 fold improvement in contrast compared to the imager without the heterojunction interlayer. The new interlayer design is generalizable to work with different organic semiconductors, making it attractive and easy to integrate with emerging organic infrared systems.

Programmatic introduction of parenchymal cell types into blood vessel organoids

Pluripotent stem cell-derived organoids have transformed our ability to recreate complex three-dimensional models of human tissue. However, the directed differentiation methods used to create them do not afford the ability to introduce cross-germ-layer cell types. Here, we present a bottom-up engineering approach to building vascularized human tissue by combining genetic reprogramming with chemically directed organoid differentiation. As a proof of concept, we created neuro-vascular and myo-vascular organoids via transcription factor overexpression in vascular organoids. We comprehensively characterized neuro-vascular organoids in terms of marker gene expression and composition, and demonstrated that the organoids maintain neural and vascular function for at least 45 days in culture. Finally, we demonstrated chronic electrical stimulation of myo-vascular organoid aggregates as a potential path toward engineering mature and large-scale vascularized skeletal muscle tissue from organoids. Our approach offers a roadmap to build diverse vascularized tissues of any type derived entirely from pluripotent stem cells.

Broadband infrared photodetection using a narrow bandgap conjugated polymer

Photodetection spanning the short-, mid-, and long-wave infrared (SWIR-LWIR) underpins modern science and technology. Devices using state-of-the-art narrow bandgap semiconductors require complex manufacturing, high costs, and cooling requirements that remain prohibitive for many applications. We report high-performance infrared photodetection from a donor-acceptor conjugated polymer with broadband SWIR-LWIR operation. Electronic correlations within the π-conjugated backbone promote a high-spin ground state, narrow bandgap, long-wavelength absorption, and intrinsic electrical conductivity. These previously unobserved attributes enabled the fabrication of a thin-film photoconductive detector from solution, which demonstrates specific detectivities greater than 2.10 × 10⁹ Jones. These room temperature detectivities closely approach those of cooled epitaxial devices. This work provides a fundamentally new platform for broadly applicable, low-cost, ambient temperature infrared optoelectronics.

Printing Multi-Material Organic Haptic Actuators

Haptic actuators generate touch sensations and provide realism and depth in human-machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. One promising approach is to combine the advantages of organic actuator materials and additive printing technologies. This powerful combination can lead to devices that are ergonomic, readily customizable, and economical for researchers to explore potential benefits and create new haptic applications. Here, an overview of emerging organic actuator materials and digital printing technologies for fabricating haptic actuators is provided. In particular, the focus is on the challenges and potential solutions associated with integration of multi-material actuators, with an eye toward improving the fidelity and robustness of the printing process. Then the progress in achieving compact, lightweight haptic actuators by using an open-source extrusion printer to integrate different polymers and composites in freeform designs is reported. Two haptic interfaces-a tactile surface and a kinesthetic glove-are demonstrated to show that printing with organic materials is a versatile approach for rapid prototyping of various types of haptic devices.

High-Efficiency Electrospray Deposition Method for Nonconductive Substrates: Applications of Superhydrophobic Coatings

When highly insulating materials are used as substrates for electronic devices, manufacturing yields become worse, and electronic components are often damaged due to undissipated electrostatic charges on such substrates. In the case of electrospray deposition, the problem of undissipated charges is particularly vexing. If charges accumulated on the substrate are not properly compensated, a repulsive force is generated against the incoming charged droplets, which negatively affects the uniformity and deposition rate of the coating layer. In order to overcome this limitation, we demonstrated a new electrospray method, which can significantly increase the deposition efficiency even in the presence of accumulated charges on nonconductive substrates. A highly reliable superhydrophobic layer was uniformly deposited on highly insulating substrates, including printed circuit board (PCB), polyester (PET), and polyimide (PI) substrates.

Solution-Processed Phototransistors Combining Organic Absorber and Charge Transporting Oxide for Visible to Infrared Light Detection

This report demonstrates high-performance infrared phototransistors that use a broad-band absorbing organic bulk heterojunction (BHJ) layer responsive from the visible to the shortwave infrared, from 500 to 1400 nm. The device structure is based on a bilayer transistor channel that decouples charge photogeneration and transport, enabling independent optimization of each process. The organic BHJ layer is improved by incorporating camphor, a highly polarizable additive that increases carrier lifetime. An indium zinc oxide transport layer with high electron mobility is employed for rapid charge transport. As a result, the phototransistors achieve a dynamic range of 127 dB and reach a specific detectivity of 5 × 10¹² Jones under a low power illumination of 20 nW/cm², outperforming commercial germanium photodiodes in the spectral range below 1300 nm. The photodetector metrics are measured with respect to the applied voltage, incident light power, and temporal bandwidth, demonstrating operation at a video-frame rate of 50 Hz. In particular, the frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions.

Emerging Design and Characterization Guidelines for Polymer-Based Infrared Photodetectors

Infrared photodetectors are essential to many applications, including surveillance, communications, process monitoring, and biological imaging. The short-wave infrared (SWIR) spectral region (λ = 1-3 μm) is particularly powerful for health monitoring and medical diagnostics because biological tissues show low absorbance and minimal SWIR autofluorescence, enabling greater penetration depth and improved resolution in comparison with visible light. However, current SWIR photodetection technologies are largely based on epitaxially grown inorganic semiconductors, which are costly, require complex processing, and impose cooling requirements incompatible with wearable electronics. Solution-processable semiconductors are being developed for infrared detectors to enable low-cost direct deposition and facilitate monolithic integration and resolution not achievable using current technologies. In particular, organic semiconductors offer numerous advantages, including large-area and conformal coverage, temperature insensitivity, and biocompatibility, for enabling ubiquitous SWIR optoelectronics. This Account introduces recent efforts to advance the spectral response of organic photodetectors into the SWIR. High-performance visible to near-infrared (NIR) organic photodetectors have been demonstrated by leveraging the wealth of knowledge from organic solar cell research in the past decade. On the other hand, organic semiconductors that absorb in the SWIR are just emerging, and only a few organic materials have been reported that exhibit photocurrent past 1 μm. In this Account, we survey novel SWIR molecules and polymers and discuss the main bottlenecks associated with charge recombination and trapping, which are more challenging to address in narrow-band-gap photodetectors in comparison with devices operating in the visible to NIR. As we call attention to discrepancies in the literature regarding performance metrics, we share our perspective on potential pitfalls that may lead to overestimated values, with particular attention to the detectivity (signal-to-noise ratio) and temporal characteristics, in order to ensure a fair comparison of device performance. As progress is made toward overcoming challenges associated with losses due to recombination and increasing noise at progressively narrower band gaps, the performance of organic SWIR photodetectors is steadily rising, with detectivity exceeding 10¹¹ Jones, comparable to that of commercial germanium photodiodes. Organic SWIR photodetectors can be incorporated into wearable physiological monitors and SWIR spectroscopic imagers that enable compositional analysis. A wide range of potential applications include food and water quality monitoring, medical and biological studies, industrial process inspection, and environmental surveillance. There are exciting opportunities for low-cost organic SWIR technologies to be as widely deployable and affordable as today's ubiquitous cell phone cameras operating in the visible, which will serve as an empowering tool for users to discover information in the SWIR and inspire new use cases and applications.

Stretchable Dry Electrodes with Concentric Ring Geometry for Enhancing Spatial Resolution in Electrophysiology

The multichannel concentric-ring electrodes are stencil printed on stretchable elastomers modified to improve adhesion to skin and minimize motion artifacts for electrophysiological recordings of electroencephalography, electromyography, and electrocardiography. These dry electrodes with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate interface layer are optimized to show lower noise level than that of commercial gel disc electrodes. The concentric ring geometry enables Laplacian filtering to pinpoint the bioelectric potential source with spatial resolution determined by the ring distance. This work shows a new fabrication approach to integrate and create designs that enhance spatial resolution for high-quality electrophysiology monitoring devices.

Temperature-Dependent Detectivity of Near-Infrared Organic Bulk Heterojunction Photodiodes

Bulk heterojunction photodiodes are fabricated using a new donor-acceptor polymer with a near-infrared absorption edge at 1.2 μm, achieving a detectivity up to 10¹² Jones at a wavelength of 1 μm and an excellent linear dynamic range of 86 dB. The photodiode detectivity is maximized by operating at zero bias to suppress dark current, while a thin 175 nm active layer is used to facilitate charge collection without reverse bias. Analysis of the temperature dependence of the dark current and spectral response demonstrates a 2.8-fold increase in detectivity as the temperature was lowered from 44 to -12 °C, a relatively small change when compared to that of inorganic-based devices. The near-infrared photodiode shows a switching speed reaching up to 120 μs without an external bias. An application using our NIR photodiode to detect arterial pulses of a fingertip is demonstrated.

Donor–acceptor polymers with tunable infrared photoresponse

NIR-SWIR photoresponsive donor–acceptor polymers enable the detection of infrared light when incorporated into bulk heterojunction photodiodes.

Printed dose-recording tag based on organic complementary circuits and ferroelectric nonvolatile memories

We have demonstrated a printed electronic tag that monitors time-integrated sensor signals and writes to nonvolatile memories for later readout. The tag is additively fabricated on flexible plastic foil and comprises a thermistor divider, complementary organic circuits, and two nonvolatile memory cells. With a supply voltage below 30 V, the threshold temperatures can be tuned between 0 °C and 80 °C. The time-temperature dose measurement is calibrated for minute-scale integration. The two memory bits are sequentially written in a thermometer code to provide an accumulated dose record.

Electronic readout enzyme-linked immunosorbent assay with organic field-effect transistors as a preeclampsia prognostic

Organic field-effect transistor (OFET) sensors can meet the need for portable and real-time diagnostics. An electronicreadout enzyme-linked immunosorbent assay using OFETs for the detection of a panel of three biomarkers in complex media to create a pre-eclampsia prognostic is demonstrated, along with biodetection utilizing a fully inkjet-printed and flexible OFET to underscore our ability to produce disposable devices.

Sol-gel solution-deposited InGaZnO thin film transistors

Thin film transistors (TFTs) fabricated by solution processing of sol-gel oxide semiconductor precursors in the group In-Ga-Zn are described. The TFT mobility varies over a wide range depending on the precursor materials, the composition, and the processing variables, with the highest mobility being about 30 cm(2)/(V s) for IZO and 20 cm(2)/(V s) for IGZO. The positive dark bias stress effect decreases markedly as the mobility increases and the high mobility devices are quite stable. The negative bias illumination stress effect is also weaker in the higher mobility TFTs, and some different characteristic properties are observed. The TFT mobility, threshold voltage, and bias stress properties are discussed in terms of the formation of self-compensated donor and acceptor states, based on the chemistry and thermodynamics of the sol-gel process.

Dependence of charge injection on temperature, electric field, and energetic disorder in an organic semiconductor

In order to determine energetic disorder's role in facilitating charge injection from gold into a molecularly doped polymer, we have examined the dependence of current on the local electric field, measured using electric force microscopy, at temperatures ranging from 250 to 330 K. From these data we infer, in a single experiment, the temperature dependence of the main factors governing the injection current: the electric-field induced lowering of the image-potential barrier, the interfacial charge density, and the mobility. In this system, the Schottky effect is anomolously large, and the interfacial charge density is larger than expected and strikingly non-Arhennius. Our analysis indicates that these effects are all a consequence of the Gaussian density of states in the organic.

Materials with opiate receptor binding activity in bovine testis and ovine pancreas

Two groups of opiate-like materials, one with a molecular weight equal to or greater than 5000 daltons and another with a molecular weight smaller than 5000 daltons as judged by gel filtration on Sephadex G-25, were detected in bovine testes. The existence of opiate-like materials with a molecular weight smaller than 5000 daltons was demonstrated in ovine pancreas. The pancreatic fraction most strongly adsorbed on CM-cellulose possessed the highest opiate receptor binding activity. Bovine testis contained corticotropin-like material(s) which stimulated corticosterone production by isolated rat adrenal cells.