May 2017

Researchers from the University of Utah discovered that organic-inorganic hybrid perovskites feature two contradictory properties - easily controlled electron spin and long spin lifetime (up to a nanosecond). This is a unique combination of two highly sought after properties for spintronics devices.

The specific material used in this research is the hybrid perovskite methyl-ammonium lead iodine (CH3NH3PbI3). In their study, a thin film of this material was placed in front of an ultrafast laser that was used to set the electron's spin orientation and also observe the spin precession.

EPFL researchers have designed a new type of inorganic nanocomposite that makes perovskite quantum dots (nanometer-sized semiconducting materials with unique optical properties) exceptionally stable against exposure to air, sunlight, heat, and water.

Quantum dots made from perovskites have already been shown to hold potential for solar panels, LEDs and laser technologies. However, perovskite quantum dots have major issues with stability when exposed to air, heat, light, and water. The EPFL team has now succeeded in building perovskite quantum dot films with a technique that helps them overcome these weaknesses.

Researchers from the Korea Advanced Institute of Science and Technology (KAIST) and Sungkyunkwan University have developed a perovskite-based semi-transparent solar cell that is reportedly highly efficient and functions very effectively as a thermal mirror.

A major key to achieving semitransparent solar cells is to develop a transparent electrode for the cell's uppermost layer that is compatible with the photoactive material. The Korean team developed a 'top transparent electrode' (TTE) that works well with perovskite solar cells. The TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive index layer and an interfacial buffer layer. This TTE, placed as a solar cell's top-most layer, can be prepared without damaging ingredients used in the development of perovskite solar cells. Unlike conventional transparent electrodes that only transmit visible light, the team's TTE both allows visible light to pass through and reflects infrared rays.

Researchers at the National Institute of Standards and Technology (NIST) and the University of Nebraska have found evidence for a property of perovskites that may affect their long-term stability as solar cells.

The unexpected feature that the team found is known as ferroelasticity, a spontaneous rearrangement of the internal structure of perovskites in which each crystal subdivides into a series of tiny regions, or domains, that have the same atomic arrangement but which are oriented in different directions. This rearrangement creates a spontaneous strain in each domain that exists even in the absence of any external stress (force).

Researchers from Lund University in Sweden and Fudan University in China have designed a new structural organization using perovskites that could greatly benefit perovskite-based solar cells. Perovskites, in their regular form, are sensitive to moisture and dissolve in contact with water, and even normal humidity deteriorates the material. Now, the researchers claim to have overcome this problem.

"We have succeeded in producing thin sheets with a water-repelling surface, making the whole construction much more stable. In addition, we have succeeded in orienting the sheets so as to obtain acceptable solar cells, with an efficiency of ten percent," says professor of chemical physics at Lund University.

Researchers at Lomonosov Moscow state University have designed a new method that allows to obtain highly crystalline organic-inorganic perovskite films for solar cells.

Currently, two main approaches are used for obtaining such materials. The first one involves coating with chemical agents from a vaporous state and the second one is solution crystallization. "As part of the study we've found out several new compounds - polyiodides, which are liquid at room temperature, possessing unique properties. They look like viscous liquids of dark brown color with metal gleam, obtained from two solid powders, which simply melt while blending. Liquid state of such compounds allows not to use hazard solvents and, moreover, their chemical composition contributes to formation of a necessary perovskite upon contact with a metallic lead film or other lead compounds. As a result of the chemical interaction between a lead film and polyiodide melts, a perovskite film, comprised of large interpenetrating crystals, is formed", a team member explains.

Leading simulation and measurement tool provider Fluxim and Perovskite-Info have teamed up to offer a 20% discount on Fluxim's large-area PV simulation software LAOSS.

LAOSS is a software tool that simulates large area semiconductor devices (PV and OLED), taking into account the voltage drop in the electrodes due to important resistive effects when the size of the device increases. LAOSS facilitates electrode layout optimization and material choice, which can save substantial time and resources. Any material class of PV devices can be modeled in a few clicks, from emerging technologies like perovskite and OPV to established Si or thin film technology.

Scientists at the Australian National University (ANU), which only last month reported a new world record in the development of perovskite-based solar cells (26% efficiency in converting sunlight into energy), have now announced a new achievement in making perovskite solar cells. Interestingly, this was done by learning from the blue Morpho Didius butterfly how to direct different colors of light.

The ANU team developed structures similar to the butterfly's tiny cone-shaped nanostructures that scatter light. These allow them to finely control the direction of light in experiments, which the scientists say can be very useful in next-generation solar cells, such as tandem solar cells with a perovskite and a silicon layer. In such tandem cells, the perovskite layers are meant to absorb the blue, green and ultraviolet colors of sunlight and leave the red, orange and yellow light to the silicon layer.

Researchers at Imperial College London have studied the mechanism that causes perovskite solar cells to degrade so quickly. Their findings could pave the way for a more efficient, longer-lasting solar cell. Previous research by ICL scientists showed "superoxides" work to break down the perovskite material. Now, the ICL team discovered how superoxides form and cause damage.

When light hits perovskite, electrons are released and react with oxygen to form superoxides. The formation of superoxides is aided by gaps in the perovskite nanostructure, normally occupied by iodide. Superoxides take advantage of these iodide-less defects.

Researchers at the Karlsruhe Institute of Technology (KIT) in Germany have detected strips of nanostructures with alternating directions of polarization in the perovskite layers, that might serve as transport paths for charge carriers.

The perovskites used by the KIT team were defined as metal organic compounds with a special crystal structure and excellent photovoltaic properties. An interdisciplinary team of researchers analyzed perovskite solar cells by means of piezoresponse force microscopy and found ferroelectric nanostructures in the light-absorbing layers. Ferroelectric crystals form domains of identical electrical polarization direction. The KIT scientists observed that, during thin-layer development, lead iodide perovskites form about 100 nm wide stripes of ferroelectric domains with alternating electric fields. This alternating electric polarization in the material might play an important role in the transport of photogenerated charges out of the solar cell and, hence, explain the special photovoltaic properties of perovskites.