September 2017

A collaboration between KAUST and Oxford University researchers has designed a strategy that grows perovskites into centimeter-scale, highly pure crystals thanks to the effect of surface tension. In their natural state, perovskites have difficultly moving solar-generated electricity because they crystallize with randomly oriented grains. The team is working on ways to speed up the flow of these charge carriers using inverse temperature crystallization (ITC) - a technique that uses special organic liquids and thermal energy to force perovskites to solidify into structures resembling single crystals (the optimal arrangements for device purposes).

While ITC produces high-quality perovskites far faster than conventional chemical methods, the intriguing mechanisms that initiate crystallization in hot organic liquids are poorly understood. The team recalls spotting a key piece of evidence during efforts to adapt ITC toward large-scale manufacturing. "At some point, we realized that when crystals appeared, it was usually at the solution's surface," the researchers said. "And this was particularly true when we used concentrated solutions".

Toshiba recently announced the fabrication of a film-based perovskite solar cell mini module with an impressive conversion efficiency of 10.5%. This efficiency rate was achieved in a 5 cm x 5 cm module and is stated by the company to be the highest yet recorded in a multi-cell mini module.

Toshiba achieved this by developing a fabrication process technology for film-based perovskite solar cells. The technology uses a film substrate and scribe process technology based on organic thin film solar cell module fabrication. Since this technology uses a flexible film substrate, it allows roll-to-roll fabrication that reduces costs. Toshiba will continue to refine the technology and expects to see further improvements in efficiency.

Researchers at the Universities of Cambridge and Milan (Politecnico di Milano) investigated the speed at which electrons (created as sunlight hits perovskite solar cell) need to reach the cell's electrode to be converted into flowing electric current before their energy starts to decline. The scientists found that perovskite solar cells will need to take advantage of femtosecond events (about a millionth of a billionth of a second) to stretch the limits of their energy conversion efficiency.

If the cells manage to work that fast, they could achieve an efficiency of 30% or maybe even more, which is currently thought to be the greatest efficiency that solar cells could achieve. Today's best silicon-based solar cells typically operate at efficiencies closer to 20%, but perovskite cells are thinner and regarded as having potential to surpass silicon cells' efficiency.

Researchers from KAUST have found that perovskite thin films for use in solar cells are more effective when glycol ethers are added to the film-forming mix. "It yields more uniform thin films with improved structure and efficiency", explains the team.

"Our aim was to improve the quality of perovskite thin films," say the researchers. The team decided to add glycol ethers to the manufacturing process because they knew these chemicals had previously been used to help create layers of metal oxides. By trying different glycol ether mixtures and conditions the researchers eventually gained better control over the formation of their perovskite thin films, by significantly improving the structure and alignment of the perovskite grains. This increased the reproducibility and efficiency of the perovskites so that they performed more efficiently in solar cell applications. The procedure also operates at lower temperatures than alternatives, which is an important factor in improving cost effectiveness.

Saule Technologies has announced that it will be presenting a prototype and will answer questions regarding its flexible perovskite photovoltaic modules at the 3rd International Conference on Perovskite Solar Cells and Optoelectronics (PSCO-2017) in Oxford, UK.

The company will reportedly be showing an operating module printed on ultra-thin PET foil. Samples available for public viewing will present the stability of the module and underwater operation for the first time. The prototype large-scale production line capable of fabricating solar modules with a nominal power output of 100W/m2 is expected to be operational in fall of 2018.

A team led by scientists from the Department of Chemistry at Imperial recently studied the mechanism that causes perovskite solar cells to degrade quickly, discovering that this breakdown is due to the formation of 'superoxides' that attack the perovskite material. Now, the team went on to determine how the superoxides form and how they attack the perovskite material, and proposed possible solutions to the problem.

Working with researchers at the University of Bath, the team found that superoxide formation is helped by spaces in the structure of the perovskite normally taken up by molecules of iodide. Although iodide is a component of the perovskite material itself, there are defects where iodide is missing. These vacant spots are then used in the formation of superoxides.

Researchers at Shanghai Jiao Tong University in China and the Swiss Federal Institute of Technology have reported the development of a new technique to deposit high-quality large-area perovskite films that does not require solvents or vacuum processing. The method reportedly produces homogeneous films with relatively few defects, which leads to an efficiency of 12.1% for a solar module made from a methylammonium lead halide film that is just over 36 cm2 in size.

The research team has developed a new technique to produce large-area methylammonium lead halide (CH3NH3PbI3) perovskite films that relies on rapidly converting amine complex precursors (CH3NH3I·mCH3NH2 (where m is close to 3) and PbI2·nCH3NH2 (where n is close to 1) to perovskite films and then applying pressure to them.

Fuji Pigment recently reported that it is researching and developing a new type of perovskite quantum dots. Fuji stated that the half width of their emission spectra is substantially narrower than that of InP; this property could very beneficial to the application of the dots in display materials, LED, bio-imaging and more.

emission spectra of perovskite quantum dots under 420 nm of irradiation light

The chemical composition of perovskite quantum dots are either CsPbX3 or CH3NH3PbX3 (X= Cl, Br, I). Their quantum efficiency is 50'80 % and their half width is 15'39 nm. Their base solvent is either hexane or toluene. However, finding alternative solvents is a challenge that is now being addressed.

A team of researchers from Cambridge, MIT, Oxford, Bath and Delft universities is working on perovskite-based "solar tarp" that can be rolled onto a rooftop, instead of using rigid and heavy panels. This could, on top of other advantages, significantly bring down installation costs.

The team explains that the idea of using perovskites isn't new, but the problem had been that tiny imperfections in the mineral's crystal structure would trap electrons before their energy could be tapped. The team successfully tested a treatment that uses the right combination of light and humidity during the manufacturing process to 'fix' the material, getting it ready for potentially years of trouble-free, ultra-efficient use.

Researchers at ETH Zurich have used perovskite materials to create ultra-pure green light for new light-emitting diodes that may pave the way for visibly improved color quality in TVs and smartphones. "To date, no one has succeeded in producing green light as pure as we have," says the ETH Zurich team.

The team explains that it is basically already possible to achieve efficient-enough red and blue light, while green light still needs to improve. This is, the team says, due mainly to human perception, since the eye is able to distinguish between more intermediary green hues than red or blue ones. "This makes the technical production of ultra-pure green very complex, which creates challenges for us when it comes to developing technology and materials," says co-lead author of the report.