Sensors - Page 6

Northwestern University researchers have developed new perovskite-based devices to assist in the detection and identification of radioactive isotopes. This method could allow the identification of legal versus illegal gamma rays - such detectors are critical for national security, where they're used to detect illegal nuclear materials smuggled across borders and aid in nuclear forensics, as well as in medical diagnostics imaging.

Using cesium lead bromide in the form of perovskite crystals, the research team found they were able to create highly efficient detectors in both small, portable devices for field researchers and very large detectors.

Under the Japan Science and Technology Agency (JST) Strategic Basic Research Programs, researcher Ayumi Ishii (Toin University of Yokohama, specially appointed lecturer) has developed a photodiode using a crystalline film composed of lead perovskite compounds with organic chiral molecules to detect circularly polarized light without a filter.

A technology to detect "polarization," or oscillation direction of light, can visualize object surfaces with damages, foreign objects, and distortions. Furthermore, detection of "circularly polarized light," or rotating electric field of light makes it possible for us to identify stress intensity and distribution of objects. Conventional photodiodes for camera or sensor applications cannot detect polarization of light directly, and therefore, various types of filters must be attached on top of the device to separate the information of polarization spatially. These structures cause substantial losses of sensitivity and resolution in the light detection, especially detection of circularly polarized light is heretofore considered difficult. Thus, it has been much sought-after to develop a new sensor for detection of circularly polarized light without any filters.

A team of scientists, led by Professors Hyunsik Im, Hyungsang Kim and Jungwon Kwak from Dongguk University and Asan Medical Center in Korea,have developed perovskite metal halide nanocrystals based hybrid materials with high quantum yields for efficient X-ray detection and high-resolution X-ray imaging.

Using the hybrid nanomaterial scintillators, they designed a scalable and cost-effective X-ray detector panel in liquid form. The hybrid nanomaterial scintillator works under X-ray irradiation typically employed in both diagnosis and treatment. More interestingly, the hybrid scintillator has a faster scintillation decay process over the conventional scintillators, which is beneficial for digital motion X-ray. The reported method and scintillation mechanism will be extended to enhance the quantum yield of various types of scintillators, enabling low-dose radiation detection in various fields including fundamental science and imaging.

Scientists at UC San Diego have developed a new method to fabricate perovskites as single-crystal thin films, which are more efficient for use in solar cells and optical devices than the current state-of-the-art polycrystalline forms of the material.

Their fabrication method - which uses standard semiconductor fabrication processes - results in flexible single-crystal perovskite films with controlled area, thickness, and composition. These single-crystal films showed fewer defects, greater efficiency, and enhanced stability than their polycrystalline counterparts, which could lead to the use of perovskites in solar cells, LEDs, and photodetectors.

The performance of photodetectors based on perovskite polycrystalline thin films is still considered to be at a distance from expected values. One reason is that the carrier transport at the interface is easily affected by grain boundaries and grain defects. Many research groups have tried to combine perovskite polycrystalline thin films with high-mobility, two-dimensional materials to improve device performance, and have achieved promising results, but the negative effects of perovskite polycrystalline grain boundaries still remain.

To solve this problem, a team led by Assoc. Prof. Yu Weili from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, and Prof. GUO Chunlei from the University of Rochester synthesized a low-surface-defect-density CH₃NH₃PbBr₃ microplate through the inverse temperature crystallization strategy. They prepared an effective vertical structure photodetector combining a high-quality perovskite single crystal with monolayer graphene with high carrier mobility.

An international research team, led by Stefan Weber from the Max Planck Institute for Polymer Research in Mainz, has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell.

Clever alignment of these electron highways could make perovskite solar cells more efficient. When solar cells convert sunlight into electricity, the electrons of the material inside the cell absorb the energy of the light. The electrons excited by the sunlight are collected by special contacts on the top and bottom of the cell. However, if the electrons remain in the material for too long, they can lose their energy again. To minimize losses, they should therefore reach the contacts as quickly as possible. Microscopically small structures in the perovskites - so-called ferroelastic twin domains - could be helpful in this respect: They can influence how fast the electrons move.

A UNIST research team has developed an electrode that can significantly improve the stability of perovskite solar cells. UNIST announced that its research team developed 'flexible and transparent metal electrode-based perovskite solar cells with a graphene interlayer'.

The team suppressed interdiffusion and degradation using a graphene material with high impermeability, the team said. Team leader professor Hyesung Park commented that the research will greatly help not only solar cells but other perovskite-based flexible photoelectric devices such as LEDs and smart sensors.

A research group led by Prof. Luo Junhua from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported the first halide double perovskite ferroelectric, (n-propylammonium)₂CsAgBiBr₇, which exhibits distinct ferroelectricity with a notable saturation polarization of about 1.5 μCcm^-2.

Halide double perovskites have been found to be a promising environmentally friendly optoelectronic and photovoltaic material, exhibiting inherent thermodynamic stability, high defect tolerance and appropriate band gaps. However, no ferroelectric material based on halide double perovskites has been discovered until now.

A research team led by Juan Casanova and Eduard Llobet from the Departamento de Ingeniería Electrónica, Eléctrica y Automática at the Universitat Politècnica de València (URV), used graphene and perovskites to create a nanosensor that detects nitrogen dioxide with 300% improved sensitivity.

The team used graphene that is hydrophobic (water and moisture-resistant) and sensitive in gas detection, but with some limitations: it is not very selective and its sensitivity declines over time. In addition, the researchers used perovskites, a crystalline-structure material commonly used in the field of solar cells. However, they quickly deteriorate when they are exposed to the atmosphere. That's the reason why the team decided to combine perovskites with a hydrophobic material able to repel water molecules - in order to prove they can prevent or slow down their deterioration.

Researchers at Los Alamos National Laboratory and Argonne National Laboratory have designed a new perovskite-based X-ray detector prototype that might revolutionize medical imaging, with dramatic reduction in radiation exposure and the associated health risks, while also boosting resolution in security scanners and research applications.

'The perovskite material at the heart of our detector prototype can be produced with low-cost fabrication techniques,' said Hsinhan (Dave) Tsai, an Oppenheimer Postdoctoral fellow at Los Alamos National Laboratory. 'The result is a cost-effective, highly sensitive, and self-powered detector that could radically improve existing X-ray detectors, and potentially lead to a host of unforeseen applications.'