#cesium

One-dimensional nanomaterials with highly anisotropicoptoelectronic properties can be used within energy harvesting applications, flexible electronics and biomedical imaging devices. In materials science and nanotechnology, 3-D patterning methods can be used to precisely assemble nanowires with locally controlled composition and orientation to allow new optoelectronic device designs. In a recent report, Nanjia Zhou and an interdisciplinary research team at the Harvard University, Wyss Institute of Biologically Inspired Engineering, Lawrence Berkeley National Laboratory and the Kavli Energy Nanoscience Institute developed and 3-D printed nanocomposite inks composed of brightly emitting colloidal cesium lead halide perovskite (CsPbX₃, where X= Cl, Br, or I) nanowires.

They suspended the bright nanowires in a polystyrene-polyisoprene-polystyrene block copolymer matrix and defined the nanowire alignment using a programmed print path. The scientist produced optical nanocomposites that exhibited highly polarized absorption and emission properties. To highlight the versatility of the technique they produced several devices, including optical storage, encryption, sensing and full color displays. The work is now published on Science Advances.

A team of researchers working at Oxford University has found a way to add cesium to perovskite solar cells to boost the performance of silicon, while maintaining the efficiency benefits it offers. In their paper published in the journal Science, the team describes their process which included finding a way to overcome the problem of efficiency loss in such materials that normally come about due to a limited range of solar spectrum use.

As researchers around the world continue to look for the next-generation material to use for solar power collection to increase efficiency, others continue to seek ways to improve the standard now in use: silicon. In this new effort the research team noted the work done by others looking into the possibility of using perovskites (minerals made mostly of calcium titanate) as possible replacements for silicon, and found a way to add cesium to the mineral to make it work in tandem with silicon to create a solar collector that is up to 25 percent more efficient than those now in use. Such an improvement in performance could signal a transformation in real world use—solar power has thus far not proven to be efficient enough for the average consumer to cut the cord from the utility company—doubling efficiency might just make doing so a smart investment.

Up until now, efforts to get perovskites to work in tandem with silicon have been held back by inefficiencies in the cells due to the range of solar spectrum they were able to use—attempts to tweak the mix have led to instability in the materials. To overcome this problem, the team at Oxford came up with a process based on substituting certain ions in the material with cesium ions—it solved the spectrum problem, they report, while maintaining the stability of the overall structure.

Researchers at the U.S. Naval Research Laboratory (NRL) Center for Computational Materials Science, working with an international team of physicists, have revealed that nanocrystals made of cesium lead halide perovskites (CsPbX3), is the first discovered material which the ground exciton state is “bright,” making it an attractive candidate for more efficient solid-state lasers and light emitting diodes (LEDs).

“The discovery of such material, and understanding of the nature of the existence of the ground bright exciton, open the way for the discovery of other semiconductor structures with bright ground excitons,” said Dr. Alexander Efros, research physicist, NRL. “An optically active bright exciton in this material emits light much faster than in conventional light emitting materials and enables larger power, lower energy use, and faster switching for communication and sensors.”

The work, which was partially sponsored by the Office of Naval Research through a program managed by Dr. Chagaan Baatar, studied lead halide perovskites with three different compositions, including chlorine, bromine, and iodine. Nanocrystals made of these compounds and their alloys can be tuned to emit light at wavelengths that span the entire visible range, while retaining the fast light emission that gives them their superior performance.