Phosphorus, a crucial nutrient for organism development in the ecosystem, poses a significant environmental challenge due to the excessive discharge of phosphates into water, leading to widespread algae proliferation and degradation of water quality. Therefore, it is essential to develop a real-time monitoring method for determining phosphorus concentration in water. In this study, we functionalized the electrode with lanthanide-based receptors and utilized a portable potentiostat with amperometric measurement to investigate phosphate sensing within a real-time monitoring platform. This study provides a basis for portable electronics in phosphate monitoring in environmental sensing.
Low-energy, infrared (IR) photodetection forms the foundation for industrial, scientific, energy, medical, and defense applications. State-of-the-art technologies suffer from limited modularity, intrinsic fragility, high-power consumption, require cooling, and are largely incompatible with integrated circuit technologies. Conjugated polymers offer low-cost and scalable fabrication, solution processability, room temperature operation, and other attributes that are not available using current technologies. Here, we demonstrate new materials and device paradigms that enable an understanding of emergent light-matter interactions and optical to electrical transduction of IR light. Photodiodes show a response to 2.0 μm, while photoconductors respond across the near- to long-wave infrared (1–14 µm). Fundamental investigations of polymer and device physics have resulted in improving performance to levels now matching commercial inorganic detectors. This is the longest wavelength light detected for organic materials and the performance exceeds graphene at longer wavelengths. Photoconductors outperform their inorganic counterparts and operate at room temperature with higher response speeds.
With our marine ecosystems under threat from climate change, there is an urgent need to continuously monitor marine conditions. One key indicator is the dissolved oxygen level, but existing sensors are limited by size and costs that preclude widespread non-intrusive monitoring. This work reports a new dual-gate design based on organic electrochemical transistors (OECTs) to track dissolved oxygen concentration in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents. We present the novel operating principle, by deriving the channel conductance with respect to potentials on the two gates. The sensor achieved a detection limit of 0.5 ppm dissolved oxygen concentration in seawater. The device demonstrated reliable operation over five days and was capable of monitoring oxygenation changes arising from the photosynthesis cycles of saltwater macro-algae.
Low-cost, compact sensor systems for in-situ monitoring of marine conditions will provide critical information to understand how pollution and oxygen levels correlate to fish kills and aquaculture issues. The compatibility of organic electrochemical transistors (OECTs) with aqueous environments makes them promising sensor components in an ocean-sensing platform. This presentation will discuss the development of dissolved oxygen (DO) sensors, which has a detection limit to 3 ppm as required in marine studies. The challenges in balancing the oxygen reduction reaction with the doping/dedeoping process in OECTs will be shown and mitigated by using multiple voltage rails. The DO sensor will be used in conjunction with pH ion-selective transistors, to provide multi-modal measurements that assess how these parameters correlate to water quality. We will show the device sensitivity and stability under simulated marine environment.
Shortwave Infrared (SWIR) light imaging is critical in a variety of applications ranging from medical diagnosis, industrial inspection and safety monitoring, etc. due to their information-rich merits. This report presents an organic up-conversion imager for SWIR light imaging. The imager integrates an organic SWIR photodiode (OPD) and an organic light emitting diode (OLED) to convert invisible SWIR image directly into visible image without sophisticated data acquisition and processing electronics. Our imager is capable of imaging light signal with wavelength up to 1400 nm, due to the sensitivity of the novel OPD. The design guidelines for attaining highly sensitive and low voltage up-conversion imagers are revealed by studying the photo responsivity and current-voltage characteristics of the SWIR PD and OLED. The results show that the elimination of deep trap states in the SWIR PD favors the photo sensitivity and reduces the operating voltage of the up-conversion imager.
Short wavelength infrared (SWIR) sensors are important to applications in environmental monitoring, medical diagnosis and optical communications, but there are only a few organic semiconductors that show optoelectronic response in the SWIR region. Recently we demonstrated a family of novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the bulk heterojunction photodiodes based on these polymers show detectivity up to 1E11 Jones at a wavelength of 1.37 micron, with absorption edge extending out to 1.7 micron. A SWIR photodiode was incorporated into the etalon-array reconstructive spectroscopy system to demonstrate its imaging capabilities.
As the initial performance is very promising, we proceed to investigate the stability of the encapsulated devices and to infer the degradation mechanisms. The performance of photodiodes were monitored by IV measurement, external quantum efficiency (EQE) and electrochemical impedance spectroscopy. The IV measurement and electrochemical impedance spectroscopy were conducted both in the dark and under illumination, to track over several weeks the change in charge generation and recombination processes under the short circuit and open circuit conditions. The characteristics from band-to-band absorption and from absorption in charge-transfer states were compared to quantify the lifetime and recombination losses of photogenerated carriers in these devices.
KEYWORDS: Short wave infrared radiation, Infrared radiation, Infrared photography, Chemical analysis, Polymers, Transistors, Electronics, Infrared detectors, Signal to noise ratio, Analytical research
Low-cost infrared photo-transistors with improved detectivity (i.e. higher signal-to-noise ratio) could find further use in spectral analysis, which is important for chemical identifications, as well as other applications from environmental monitoring to optical communications. Accordingly, the main goal of this research is to advance printed, flexible photo-transistors by using a family of novel donor-acceptor polymers with narrow bandgap that are responsive in the short wavelength infrared (SWIR) region. In particular, the transistors show optical response extending out to a wavelength of 1.8 micrometer. The external quantum efficiency and the rectification ratio are used to characterize the performance of devices with different polymer layer thickness, in order to optimize detectivity. The individual transistors could further be exploited for the fabrication of integrated arrays for bio-medical and/ or robotic applications. It paves the way to large-area, conformal designs that are currently not achievable with conventional inorganic SWIR materials.
Photosensors responsive to the short wavelength infrared (SWIR) spectra are used in a variety of applications including environmental monitoring, medical diagnosis and optical communications. However, most organic semiconductors do not absorb in the SWIR region. Here we show novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the polymers are processed into photodiodes with structure of ITO/PEDOT:PSS/Bulk Heterojunction (BHJ)/Al. The performance of devices with different polymer structures are compared through metrics including detectivity, quantum efficiency, response time and rectification ratio, to determine the mechanisms of charge recombination loss in charge transfer states and charge transport process. We also use different solution-processed interfacial functional layers (e.g. ZnO, MoO3, TiO2) as electrode interface structures. The results provide guideline for selecting suitable polymers and design of device structures, to enable high performance SWIR photosensor via scalable solution-processed fabrication.
Conjugated organic molecules effectively produce and harvest visible light and find utility in a variety of emergent optoelectronic technologies. There is currently interest in expanding the scope of these materials to extend functionality into the infrared (IR) spectral regions and endow functionality relevant in emergent technologies. Developing an understanding of the interplay between chemical and electronic structure in these systems will require control of the frontier orbital energetics (separation, position, and alignment), ground state electronic configurations, interchain arrangements, solid-state properties, and many other molecular features with synthetic precision that has yet to be demonstrated. Bridgehead imine substituted 4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) structural units, in combination with strong acceptors with progressively delocalized π-systems, afford modular donor-acceptor copolymers with broad and long wavelength absorption that spans technologically relevant wavelength (λ) ranges from 0.7 < λ < 3.2 μm.1 Here we demonstrate that electronic and structural manipulation play a major role in influencing the energetics of these systems and ultimately controlling the band gap of the materials. These results bear implication in the development of very narrow band gap systems where precise control will be necessary for achieving desired properties such as interactions with longer wavelength light.
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