Perovskite sensors - Page 8

A research team at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has fabricated a sensitive photodetector based on lead-free perovskite single crystals.

"We have developed a high performance photodetector based on MA3Sb2I9 microsingle crystals (MSCs)," said Prof. HAN. Scientists found that MA3Sb2I9 single crystals exhibited a low trap-state density of ~1010 cm-3, high carrier mobility of 12.8 cm2 V-1 s-1 and long carrier diffusion length reaching 3.0 μm.

Researchers from Northwestern University and Argonne National Laboratory research team have developed a perovskite-based next-generation device for nuclear radiation detection that could provide a significantly less expensive alternative to the detectors now in commercial use.

The high-performance material is used in a device that can detect gamma rays, weak signals given off by nuclear materials, and can efficiently identify individual radioactive isotopes. The new material also has the advantage of inexpensive production. Potential uses for the new device include more widespread detectors for nuclear weapons and materials as well as applications in biomedical imaging, astronomy and spectroscopy.

A research team composed of scientists from Michigan State University and University of Michigan has deployed a new approach to growing all inorganic lead-free halide perovskites.

"Epitaxial growth has long since revolutionized the study of many electronic materials including silicon, oxide perovskites, and III-V semiconductors," said Richard Lunt, an Associate Professor at Department of Chemical Engineering and Materials Science, Michigan State University who has supervised the project. "There is very little known about the epitaxial growth of halide perovskites, but these exciting materials hold enormous potential. This has motivated us to explore this entirely new research area."

Researchers from the Russian ITMO University have developed effective nanoscale light sources based on a halide perovskite. These nanosources are subwavelength nanoparticles which serve both as emitters and nanoantennas and allow enhancing light emission inherently without additional devices. Moreover, the perovskite enables tuning the emission spectra throughout a visible range by varying the composition of the material. The new nanoparticles are a promising platform for creating compact optoelectronic devices such as optical chips, light-emitting diodes, or sensors.

The nanoscale light sources and nanoantennas have already found a wide range of applications in several areas, such as ultra compact pixels, optical detection, or telecommunications. However, the fabrication of nanostructure-based devices is rather complicated due to the limited luminescence efficiency of the materials used typically as well as non-directional and relatively weak light emission of single quantum dots or molecules. An even more challenging task is placing a nanoscale light source precisely near a nanoantenna.

Researchers at Duke University have developed a method to create otherwise unattainable (or extremely hard to create) hybrid thin-film materials. The new technique could open the door to new generations of solar cells, light-emitting diodes and photodetectors.

The most common perovskite used in solar energy today, methylammonium lead iodide (MAPbI3), can convert light to energy as well as today's best commercially available solar panels. This can even be done using a fraction of the material - a piece 100 times thinner than a typical silicon-based solar cell. Methylammonium lead iodide is one of the few perovskites that can be created using standard industry production techniques, though it still has issues with scalability and durability. To truly unlock the potential of perovskites, however, new manufacturing methods are needed because the mixture of organic and inorganic molecules in a complex crystalline structure can be difficult to make. Organic elements are particularly delicate, but are critical to the hybrid material's ability to absorb and emit light effectively.

Researchers from Empa and ETH Zurich have developed a perovskite-based sensor prototype that absorbs light almost optimally and is also cheap to produce.

The team explains that the working mechanism of the human eye, not very different than various image sensors, is based on three different types of sensory cells for the perception of color: cells that are respectively sensitive to red, green and blue alternate in the eye and combine their information to create an overall colored image. However, this mechanism has inherent limitations: as each individual pixel can only absorb a small part of the light spectrum that hits it, a large part of the light is lost. In addition, the sensors used in various applications have basically reached the limits of miniaturization, and unwanted image disturbances can occur; these are known as color moiré effects and have to be removed from the finished image.

Researchers at the University of Groningen provided new insight into hybrid perovskite traps - the loss of electric charges that happens in both silicon and perovskite, and reduces the efficiency of photovoltaic cells.

The new insight happened by chance. The researchers placed a perovskite crystal in a vacuum chamber in an attempt to cool it down and while pumping out the air, a laser was left on, that excited the crystal. This laser light produced electronic charges in the crystal, which emitted light when they recombined. In this instance the crystal should have emitted green light, but surprisingly, when the air was removed from around it, the green light disappeared too. However, when the air was let back in again, the light emission was restored. So apparently, without air, most charges disappear into the traps.