Researchers make theoretical prediction of 2-D semiconductor tin dioxide

Recently, Prof. Zheng Xiaohong's research group from the Institute of Solid State Physics (ISSP) of the Hefei Institute of Physical Science (HFIPS) predicted a new two-dimensional (2-D) tin dioxide (SnO2) monolayer phase (P-4 m2) via first-principles calculations.

Bulk SnO2 is an important n-type wide-bandgap (~3.6 eV) semiconductor and is widely used as electrode materials, chemical sensor components, etc. but systematic study of possible tin oxide phases in 2-D is still missing. In particular, given the claims of magnetism in SnO2 thin films, it is worth investigating whether a stable SnO2 2-D phase can be synthesized or magnetism can be induced.

In this research, the researchers provided direct evidence of a stable and new 2-D phase of SnO2 (δ- SnO2) with auxetic properties based on density functional theory method, which was impressive for its negative in-plane Poisson's ratio and high electron mobility.

In addition, they found double Mexican-hat-like band edges near the Fermi level presented by the valence band structure of SnO2 and therefore a ferromagnetic phase transition and half-metallic ground state could be induced by hole doping within a very wide concentration range.

A clear semiconductor based on tin could improve solar power generation

Mobility is a key parameter for semiconductor performance and relates to how quickly and easily electrons can move inside a substance. Researchers have now achieved the highest mobility among thin films of tin dioxide ever reported. This high mobility could allow engineers to create thin and even transparent tin dioxide semiconductors for use in next-generation LED lights, photovoltaic solar panels or touch-sensitive display technologies.

Tin and oxygen can be combined in a certain way to become tin dioxide, a material that can be made into a semiconductor. Semiconductors are the basis of computer chips, solar panels and more. Since the 1960s, tin dioxide has found use in industrial applications including gas sensors and transparent electrodes for solar devices. The material is suitable for these things because of its high mobility. For most applications, higher is better. However, the high mobility of tin oxide was only possible in large bulk crystals, until now.

"We demonstrated the highest mobility in a thin film of tin oxide ever achieved. Improved mobility not only enhances the conductivity but also the transparency of the material," said Shoichiro Nakao, a researcher from the Department of Chemistry at the University of Tokyo. "Generally, transparency and conductivity cannot coexist in a material. Typical transparent materials such as glass or plastic are insulating, whereas conducting materials like metals are opaque. Few materials exhibit transparent conductivity—it's very interesting!"

Scientists boost stability of low-cost, large-area solar modules

Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) have resolved a fundamental weakness in a promising solar technology known as Perovskite Solar Cells, or PSCs. Their innovations appear to improve both the devices' stability and scalability in one fell swoop and could be key to moving PSCs to market.

Third-generation solar cells efficiently convert sunlight into usable electricity and cost less energy to manufacture than old-school silicon cells. PSCs, in particular, have garnered the attention of science and industry thanks to their low cost and high efficiency. Though their performance is promising in lab tests, the devices still suffer from low stability and cannot be produced commercially until they're built to last.

"We need solar modules that can last for at least 5 to 10 years. For now, the lifetime of PSCs is much shorter," said Dr. Longbin Qiu, first author of the paper and a postdoctoral scholar in the OIST Energy Materials and Surface Sciences Unit, led by Prof. Yabing Qi.

Discovery points the way to better and cheaper transparent conductors

Researchers at the University of Liverpool have made a discovery that could improve the conductivity of a type of glass coating which is used on items such as touch screens, solar cells and energy efficient windows.

Coatings are applied to the glass of these items to make them electrically conductive whilst also allowing light through. Fluorine doped tin dioxide is one of the materials used in commercial low cost glass coatings as it is able to  simultaneously allow light through and conduct electrical charge but it turns out that tin dioxide has as yet untapped potential for improved performance.

In a paper published in the journal Advanced Functional Materials, physicists identify the factor that has been limiting the conductivity of fluorine doped tin dioxide, which should be highly conductive because fluorine atoms substituted on oxygen lattice sites are each expected to give an additional free electron for conduction.

The scientists report, using a combination of experimental and theoretical data, that for every two fluorine atoms that give an additional free electron, another one occupies a normally unoccupied lattice position in the tin dioxide crystal structure.