January 2016

Researchers at EPFL in Switzerland have designed a standardized way to make nanowires out of perovskite, by guiding the growth of perovskite nanowires with nanofluidic channels. The researchers used a single-step, 'slip-coating' method to produce the first ever nanowires from methylammonium lead iodide, a material that has attracted attention for its ability to absorb light and produce electrical current in response.

Researchers at MIT developed a thin-film material whose phase and electrical properties can be switched between metallic and semiconducting, simply by applying a small voltage. The material then stays in its new configuration until switched back by another voltage. The discovery could pave the way for a new kind of nonvolatile computer memory chips that retain information when the power is switched off, and for energy conversion and catalytic applications.

The researchers demonstrated that electrical bias can induce a phase transition in the material, which was achieved by changing the oxygen content in material. This work involves the thin-film material strontium cobaltite (SrCoOx), which has two different structures depending on how many oxygen atoms per unit cell it contains. When more oxygen is present, SrCoOx forms the tightly-enclosed, cage-like crystal structure of perovskite, whereas a lower concentration of oxygen produces the more open structure of brownmillerite.

Chinese and Australian researchers have designed a water-resistant perovskite solar cell that can operate in a humid environment and maintain its efficiency over three weeks.

Such cells typically have a methylammonium lead iodide (CH3NH3PbI3) structure, which previous groups have attempted to modify or change completely in order to improve its stability. The researchers in this study, however, have adopted a different approach. Recognizing that water molecules are absorbed by lead in the perovskite's surface layer, the team decided to replace a portion of the surface cations with hydrophobic tetra-alkyl ammonium ions. They invented a dipping technique capable of functionalizing perovskite films in a simple and effective manner.

A team of researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) has engineered a hole-transporting material for perovskite solar cells that costs only a fifth of other existing material options, and offers an improved efficiency of 20.2%.

A 3D illustration of fluorine-dithiophene molecules on a surface of perovskite crystals.

EPFL developed a modified hole-transporting material - a simple dissymmetric fluorine-dithiophene (FDT). The researchers explain that FDT can be easily modified, meaning it could act as a blueprint for the next generation of low-cost hole-transporting materials.

Scientists at the Polish Academy of Sciences (IPC PAS) Warsaw University of Technology have designed a rapid and environmentally safe method of production of perovskite substances, by solid-state mechanochemical processes like grinding powders, rather than in solutions at a high temperature. The described process is said to be surprisingly simple and effective.

In the process, two powders are poured into the ball mill: a white one, methylammonium iodide CH3NH3I, and a yellow one, lead iodide PbI2. After several minutes of milling, no trace is left of the substrates. Inside the mill, there is only a homogeneous black powder: the perovskite CH3NH3PbI3, all done by reactions occurring only in solids at room temperature.

Researchers at the University of Nebraska-Lincoln presented an innovation that could improve perovskite solar cells' efficiency, pushing it forward on the way to rivaling silicon-based cells. The developed process increased the perovskite solar cells' efficiency by more than 2 percentage points, to 19.4%, and the researchers also stress their hopes of achieving 25% efficiency in 3-5 years.

The process involves applying heat and a solvent to a chemical layer that transports energy absorbed by the perovskite to an electrode. Though the effects are not visible to the naked eye, this "solvent annealing" process is said to be similar to polishing a floor so that objects will move more easily across it. This process has been acknowledged by other researchers as "an important direction for further improving the efficiency of perovskite solar cells".

Researchers from an Oxford-Berlin (Helmholtz-Zentrum) collaboration reported that an ultimate efficiency of 30% should be attainable with perovskite-silicon tandem solar cells. They discovered a structurally stable perovskite composition with its band gap tuned to an optimum value of 1.75 eV.

Tandem solar cells work by absorbing the high energy photons (visible light) in a top cell which generates a high voltage, and the lower energy photons (Infra red) in a rear cell, which generates a lower voltage. This increases the theoretical maximum efficiency by about 50% in comparison to a standalone silicon cell. To maximize efficiency, the amount of light absorbed in the top cell has to precisely match the light absorbed in the rear cell. However, the band gap of ~1.6eV of the standard perovskite material is too small to fully exploit the efficiency potential of this technology.

A team of scientists from the School of Science and Engineering in Shanghai have developed a multi-functional inverse opal-like TiO2 electron transport layer (IOT-ETL) for a cost-efficient perovskite solar cell with high power conversion Efficiency.

The researchers introduced an IOT-ETL, produced by a simple polystyrene-assistant method. It was created to replace the traditional compact layer and mesoporous scaffold layer in perovskite solar cells. The new devise improved the light harvesting efficiency by enhancing the light scatting property in the devices.