Sensors - Page 7

Researchers at Linköping University, in collaboration with colleagues in China, have developed a tiny unit that is both an optical transmitter and a receiver. "This is highly significant for the miniaturization of optoelectronic systems," says LiU professor Feng Gao.

Chunxiong Bao, postdoc at Linköping University, types in a sentence on a computer screen, and the same sentence immediately appears on the neighboring screen, optically transferred from one diode to another. The diode is made from perovskite.

Researchers at the Chinese Academy of Sciences (CAS) and other collaborators have reported a solution-processed broadband photodetector based on organic-inorganic hybrid perovskite and organic bulk heterojunction, achieving broadband response spectra up to 1000 nm with a high EQE in the NIR region, an ultrafast response speed of 5.6 ns and a wide linear dynamic range of 191 dB.

The team stated that thanks to the high-dynamic-range imaging capacity, high-quality visible-NIR actual imaging is obtained, enabling the accelerated translation of solution-processed photodetector applications from the laboratory to the imaging market.

Researchers from the University of California San Diego, King Abdullah University of Science and Technology and the Air Force Research Laboratory have developed a technique that could enable the fabrication of longer-lasting and more efficient perovskite solar cells, photodetectors, and LEDs.

Strain-engineered, single crystal thin film of perovskite grown on a series of substrates with varying compositions and lattice sizes. Image Credit: David Baillot/UC San Diego Jacobs School of Engineering.

A major obstacle is the tendency of one of the best-performing perovskite crystals, α-formamidinium lead iodide (HC(NH₂)₂PbI₃, known as α-FAPbI₃), to assume a hexagonal structure at room temperature, in which photovoltaic devices are required to operate. This hexagonal structure cannot respond to most of the frequencies of light in solar radiation, and is hence not useful for solar applications as it could be. The team therefore set out to stabilize the structure of α-FAPbI3, using a simple but useful approach known as strain engineering, which has been used to tune the electronic properties of semiconductors.

MIT researchers have designed perovskite photovoltaic-powered sensors that could potentially transmit data for years before they need to be replaced. To this end, the team mounted thin-film perovskite cells as energy-harvesters on inexpensive radio-frequency identification (RFID) tags.

The cells could power the sensors in both bright sunlight and dimmer indoor conditions. Moreover, the team found the solar power actually gives the sensors a major power boost that enables greater data-transmission distances and the ability to integrate multiple sensors onto a single RFID tag.

Researchers from the University of Tennessee and Oak Ridge National Laboratory have found that the environment is a non-trivial component in the operation of organometal halide perovskite (OMHP) devices, playing an important role in the charge transport behavior at the electrode/crystal interface of OMHPs due to coupling between surface mediated redox processes and bulk ionic species.

The team explored environmental and interface effects, namely transport behavior and origins of the gas sensitivity, in MAPbBr₃ single crystal (SC) devices using impedance spectroscopy and G-Mode Kelvin Probe Force Microscopy (G-KPFM). Strong resistive response was found to occur when the crystals were exposed to different environments. It was shown, among other things, that SC response to the environment is extremely different at the surface as compared to the bulk due to the disorder surface chemistry.

Perovskites have shown potential for use as high performance photodetectors, where the responsivity and detectivity of the perovskite photodetector (PePDs) can be improved by engineering its interfacial properties. Researchers from the University of Electronic Science and Technology of China (UESTC) and City University of Hong Kong have reported the applications of bio-inspired materials, deoxyribonucleic acid (DNA) and guanine, as functional interfacial layers for high performance PePDs.

The best bio-material modified PePDs exhibit a ∼2× enhancement of the photo-current than that of the reference PePDs with no modifications. Further optimization of the thickness for the bio-materials based functional layers enables the PePD to achieve a remarkable responsivity of 0.37 A W'1 and detectivity of 1.85'×'1012 Jones at the wavelength of 745 nm.

Researchers from the University of Florida and Pacific Northwest National Laboratory set out to improve global nuclear security by enhancing radiation detectors, and discovered, after evaluating a diverse list of over 60 candidates for alternative semiconductor compounds, that a hybrid organic-inorganic perovskite has the highest potential to succeed.

Better sensors can improve equipment used for detecting and identifying radioactive materials. (Image credit: Pacific Northwest National Laboratory)

The scientists reported that the identification of better sensor materials and the development of smarter algorithms to process detector signals are essential to enhance radiation detectors. Paul Johns, Physicist, University of Florida, said: "The end users of radiation detectors don't necessarily have a background in physics that allows them to make decisions based on the signals that come in. The algorithms used to energy-stabilize and identify radioactive isotopes from a gamma ray spectrum are therefore key to making detectors useful and reliable".

Researchers at the National Tsing Hua University in Taiwan, led by Professor Hao-Wu Lin, have demonstrated that high-performance filter-less artificial human photoreceptors can be realized by integrating a novel optical metal/dielectric/metal microcavity structure with vacuum-deposited perovskite photoresponse devices.

Sensory substitution with flexible electronics is one of the intriguing fields of research. Scientists already fabricate electronic devices that can replicate, to a certain degree degree, some of the human senses ' touch (electronic skin ' e-skin), smell (e-nose), and taste (e-tongue). E-versions of the eye's photoreceptors (e-retinas) could potentially be used in a wide range of applications from robotic humanoid vision to artificial retina implantation for vision restoration or even vision extension into a wider range of wavelength.

Researchers from the Indian Institute of Technology (IIT) Hyderabad, India, have fabricated a perovskite-based low-cost, ultra-sensitive device that is capable of detecting the cardiac biomarker troponin T protein. Troponin T is a cardiac protein that is released into the bloodstream after a heart attack.

Unlike the commercially available test that can detect the protein at nanogram per ml concentration, this device can reportedly detect the protein at an extremely low concentration of femto gram per ml. This could help pave the way for early diagnosis of a heart attack, increasing a patient's survival rate. It even has the potential to be able to predict the onset of a heart attack.

NUS scientists have found that the light emission properties of molecularly thin two-dimensional (2-D) hybrid perovskite can be tuned in a highly reversible way for ultrathin optoelectronic applications. A highly efficient photodetector has been fabricated using hybrid perovskites with the thickness of a single quantum well.

An impression of laser interaction with a molecularly thin 2D perovskites encapsulated by hexagonal boron nitride (blue layer). (Image: NUS)

Each basic unit of a 2D hybrid perovskite is constructed using a semiconducting layer of inorganic material sandwiched between two organic insulating layers. While researchers have studied layered perovskites in their bulk form for many years, the properties of these crystals when their thickness is thinned down to a few and single layers have largely not been explored.