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Water molecules’ behavior on perovskite surfaces offers important tools for surface and materials research

Researchers at TU Wien (Vienna) explored the long-standing question of how water molecules behave when they attach to a perovskite surface, by using scanning tunneling microscopes and computer simulations.

Water molecules' behavior on perovskite surfaces offers important tools for surface and materials research

While usually only the outermost atoms at the surface are of importance, in perovskites the deeper layers are important, too. The team studied strontium ruthenate – a typical perovskite material that has a crystalline structure containing oxygen, strontium and ruthenium. When the crystal is broken apart, the outermost layer consists of only strontium and oxygen atoms; the ruthenium is located underneath, surrounded by oxygen atoms. A water molecule that lands on this surface splits into two parts: A hydrogen atom is stripped off the molecule and attaches to an oxygen atom on the crystal’s surface. This process is known as dissociation. However, although they are physically separated, the pieces continue to interact through a weak “hydrogen bond”.

It is this interaction that causes a strange effect: The OH group cannot move freely, and circles the hydrogen atom. Although this is the first observation of such behavior, it was not entirely unexpected as this effect was predicted in the past, based on theoretical calculations, and was finally confirmed with this experiment. When more water is put onto the surface, the spinning stops as the OH group can only move freely in a circle if none of the neighboring spaces are occupied. At first, when two water molecules are in neighboring sites, the spinning OH groups collide and get stuck together, forming pairs. Then, as the amount of water is increased, the pairs stick together and form long chains. Eventually, water molecular cannot find the pair of sites it needs to split up, and attaches instead as a complete molecule.

The new methods that have been developed and applied by the TU Wien research team have made significant advances in surface research. Whereas researchers were previously reliant on indirect measurements, they can now directly map and observe the behavior of individual atoms on the surface. This opens up new possibilities for modern materials research, for example for developing and improving catalysts.


Source: eurekalert

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Correlated Metal Films might someday replace ITO and improve perosvkite solar cells

Researchers at Pennsylvania State University have developed a transparent and electrically conductive material that could make large screen displays, smart windows, touch screens and solar cells more affordable and efficient. The material has the potential to replace indium tin oxide (ITO), the transparent conductor that is currently used for more than 90% of the display market but is expensive, scarce and brittle. 

Correlated Metal Films might someday replace ITO and improve perosvkite solar cells

Along with display technologies, the researchers will investigate the new materials with a type of solar cell that uses organic perovskite materials. The team has reported a design strategy using 10 nm-thick films of an unusual class of materials called correlated metals. In most conventional metals, such as copper, gold, aluminum or silver, electrons flow like a gas. In correlated metals, such as strontium vanadate (a perovskite material) and calcium vanadate, they move more like a liquid. The electron flow produces high optical transparency along with high metal-like conductivity, the researchers said. 

The scientists are trying to make metals transparent by changing the effective mass of their electrons, by choosing materials in which the electrostatic interaction between negatively charged electrons is very large compared to their kinetic energy. As a result of this strong electron correlation effect, electrons ‘sense’ each other and behave like a liquid rather than a gas of noninteracting particles. This electron liquid is still highly conductive, but when one shines a light on it, it becomes less reflective, thus much more transparent. The correlated metals demonstrated excellent performance when benchmarked against ITO, the researchers said. 

The next challenge will be to find a method of implementing these new materials into a large-scale manufacturing process. The researchers claim that they see no reason that strontium vanadate could not replace ITO in the same equipment currently used in industry. 

Source: Photonics


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Flexible perovskite solar cells could benefit from graphene production breakthrough

Researchers involved in the €10.6 million European research project called GRAFOL have reportedly demonstrated a cost-effective roll-to-roll production tool capable of making large sheets of graphene on an industrial scale, which could greatly contribute to flexible thin-film solar cells with transparent electrodes like perovskite PVs.

Flexible perovskite solar cells could benefit from graphene production breakthrough

The project team also believes that this process could be used to establish graphene as a substitute for transparent indium tin oxide (ITO) electrodes used in organic LEDs (OLEDs), enabling flexible designs while helping reduce dependency on ITO.

Major companies were involved in this project, like Aixtron, Intel, Philips, Thales and more, which also aim to take the project results to the next level by introducing new products in the market.

Source: novuslight

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Perovskite crystals to enable creation of tandem solar cells

Researchers at the Swiss materials science and technology research institute, Empa, have discovered a new way to produce thin film tandem solar cells using perovskite crystals. This discovery is a major milestone on the path to produce high-efficiency solar cells with low cost procedures.

Perovskite crystals to enable creation of tandem solar cells

In tandem solar cells, energy is harvested in two stages, which results in the conversion of sunlight into electricity becoming much more efficient. The top cell is semi-transparent and allows efficient conversion of large energy photons into electricity and the bottom cell converts the remaining transmitted low energy photons in an optimum manner. The tandem solar cells provide 20.5% efficiency when converting light to electricity and the researchers said that this can be increased to 30%. Empa researchers have further emphasized that it has a lot of potential to provide better conversion of solar spectrum into electricity. 

The perovskite film is made with a combination of vapor deposition and spin coating on the layer, followed by annealing at lukewarm temperature. This perovskite crystal absorbs blue and yellow spectrum of visible light and converts them into electricity. Red and infrared radiation simply pass through the crystal, as a result of which, a further solar cell under the semi-transparent perovskite cell can be attached, which converts the remaining light into electricity. The perovskite crystal is processed at 50 degrees Celsius and the process can be potentially applied in low cost roll-to-roll production in the future. The research team also said that the techniques can be applied for large area low cost processing. 

The scientists will have to overcome many obstacles, and to do this they will need lots of interdisciplinary experience and a large number of combinatorial experiments until a semi-transparent high-performance cell is found together with the right base cell, and technologies for electrical interconnections of these solar cells.

Source: worldindustrialreporter


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Perovskites may enable cheaper, more efficient LEDs

Scientists tackle heat loss problem by deploying hot-carrier technology in perovskite solar cells

Researchers at the National Renewable Energy Laboratory (NREL) announced that they have figured out a pathway for dealing with the heat loss problem by deploying hot-carrier technology in perovskite solar cells. Hot carrier solar cells offer simplicity of design, low cost, and high efficiency, but are a long way from being commercialized, as one big challenge is revving up the kinetic energy transfer in order to prevent energy loss. This recent study provides a pathway for pushing perovskite levels upwards, possibly as high as 66%. It determines that charge carriers created by absorbing sunlight by the perovskite cells encounter a bottleneck where phonons (heat carrying particles) that are emitted while the charge carriers cool cannot decay quickly enough. Instead, the phonons re-heat the charge carriers, thereby drastically slowing the cooling…

Florida State researchers have developed a cheaper, more efficient LED, or light-emitting diode, using perovskites.

The researchers spent months using synthetic chemistry to fine-tune the materials in the lab, creating a perovskite material capable of emitting a staggering 10,000 candelas per square meter when powered by 12 volts. The scientists say that such exceptional brightness owes, to a large extent, to the inherent high luminescent efficiency of this surface-treated, highly crystalline nanomaterial.

The perovskite material is easily and quickly made, which the researchers hope will translate to cheap, scalable production. LEDs are more efficient than other lighting sources, but adoption in the home has been slow-going due to their relative expense.

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sounds impressive but doesn’t relate to the normal measure of led efficiency ie lumens per watt ,currently between 50 to 80 . and pretty much all new houses are getting leds now, at $ 20 to $40 per fitting they make sense . cheers MG

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Perovskites enable quantum dots for displays, lasers and solar cells

Scientists at Nanjing University of Science and Technology, China, and colleagues have used quantum dots based on perovskites for QD-based light-emitting devices (QLEDs). These (completely inorganic) materials reportedly solve the stability problem of previously developed hybrid organic鈥搃norganic halide perovskites. Quantum dots (QDs) are nanometer-sized semiconductor materials with highly tunable properties such as bandgap, emission color, and absorption spectrum. These characteristics depend on their size and shape, which can be controlled during the synthesis. The quantum dots’ luminescence wavelength can be tuned by both their size and by the halide ratio. In this research, the team made blue, green, and yellow QLEDs with high quantum yields, using the perovskite quantum dots as the emitting layer. The researchers state that this development could allow the design of new optoelectronic devices, such as…

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Dyesol sells over $7 million in stock

Dyesol sells over $7 million in stockDyesol, the Australia-based Perovskite Solar Cell (PSC) technology developer, aims to raise up to AUD 10 million (USD 7.25 million/EUR 6.8 million) by selling shares to shareholders and investors.

A share purchase plan (SPP) opened on November 19, allowing existing shareholders from Australia or New Zealand to subscribe to new shares priced at AUD 0.26 a piece. The SPP targets AUD 6 million in proceeds, to support Dyesol鈥檚 Technology Development and Business Activity plans and working capital. The SPP is expected to close on December 4.

At the same time, the company is planning to attract selected financial institutions to subscribe for up to AUD 4 million in stock on similar terms. The price per share of AUD 0.26 represents a 19% discount to the volume weighted average price (VWAP) of Dyesol鈥檚 shares on the Australian Securities Exchange for the 5 trading days immediately prior to November 19.

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Perovskite/silicon tandem solar cell achieves record efficiency

Researchers from Helmholtz-Zentrum Berlin (HZB) and the university 脡cole Polytechnique F茅d茅rale de Lausanne (EPFL) in Switzerland have combined a silicon heterojunction solar cell with a perovskite solar cell monolithically into a tandem device and reached a record efficiency of 18%, stating it has the potential to reach 30% after additional modifications.

Perovskite/silicon tandem solar cell achieves record efficiency

Designing such silicon-perovskite tandem cells can be challenging, as perovskite cells tend to require coating onto titanium dioxide layers, which must first be sintered at around 500 掳C. The amorphous silicon layers that cover the crystalline silicon wafer in silicon heterojunction degrade at this temperature. Now the team from EPFL and HZB has managed to overcome hurdles and manufacture this kind of monolithic tandem cell, by depositing a layer of tin dioxide at low temperatures instead of using titanium dioxide. A thin layer of perovskite could then be spin-coated onto this intermediate layer and covered with hole-conductor material. The team also used a transparent protective layer to avoid the metal oxides sputtering and consequently destroying the perovskite layer and hole-conductor material.

The teams claim there is even potential to reach efficiency levels as high as 30%. They are happy with the 18% efficiency, but say that light is still being lost at the surface in the present architecture and that could potentially be dealt with. A textured foil on the front side might be able to catch this light and couple it into the cell, which would further increase the cell鈥檚 efficiency. The heterojunction silicon solar cell that simultaneously functions as the bottom cell and the substrate for the perovskite top cell also has potential for improvement. Also, this perovskite-silicon tandem cell is presently still being fabricated on a polished silicon wafer. By texturing this wafer with light-trapping features, such as random pyramids, the efficiency might be increased further to 25% or even 30%.

Source: Helmholtz-Berlin via rsc


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EPFL researchers working towards a perovskite material that turns light and X-rays into electricity

Scientists tackle heat loss problem by deploying hot-carrier technology in perovskite solar cells

Researchers at the National Renewable Energy Laboratory (NREL) announced that they have figured out a pathway for dealing with the heat loss problem by deploying hot-carrier technology in perovskite solar cells. Hot carrier solar cells offer simplicity of design, low cost, and high efficiency, but are a long way from being commercialized, as one big challenge is revving up the kinetic energy transfer in order to prevent energy loss. This recent study provides a pathway for pushing perovskite levels upwards, possibly as high as 66%. It determines that charge carriers created by absorbing sunlight by the perovskite cells encounter a bottleneck where phonons (heat carrying particles) that are emitted while the charge carriers cool cannot decay quickly enough. Instead, the phonons re-heat the charge carriers, thereby drastically slowing the cooling…

Researchers at the Swiss EPFL are working on developing a perovskite-based material that can convert light and X-rays into electricity and holds great potential for use in photovoltaics as well as space exploration.

The scientists have chosen to use methylammonium lead iodide (CH3NH3PbI3), a material already used in conventional perovskite solar cells, where it harvests visible-light photons that are then converted into electricity. They fabricated single crystals of methylammonium lead iodide and tested them on photocurrent generation while irradiating them with X-rays, where they found 75% charge-collection efficiency in millimeter-sized crystals. This high-efficiency current conversion for X-ray radiation also matched the material鈥檚 high X-ray absorption coefficient.

In terms of degradation, the material鈥檚 performance decreased less than 20% when hit with X-ray doses similar to those in space, which may represent very promising stability for high-radiation doses. According to the researchers, the combination of these features can lead to fabricating photovoltaic cells that can harvest visible, X-ray, and even gamma-ray photons. Such technology can have far-reaching advantages for space exploration, as well as converting waste radiation in nuclear powerplants.

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Perovskites enable quantum dots for displays, lasers and solar cells

Scientists at Nanjing University of Science and Technology, China, and colleagues have used quantum dots based on perovskites for QD-based light-emitting devices (QLEDs). These (completely inorganic) materials reportedly solve the stability problem of previously developed hybrid organic鈥搃norganic halide perovskites. Quantum dots (QDs) are nanometer-sized semiconductor materials with highly tunable properties such as bandgap, emission color, and absorption spectrum. These characteristics depend on their size and shape, which can be controlled during the synthesis. The quantum dots’ luminescence wavelength can be tuned by both their size and by the halide ratio. In this research, the team made blue, green, and yellow QLEDs with high quantum yields, using the perovskite quantum dots as the emitting layer. The researchers state that this development could allow the design of new optoelectronic devices, such as…

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Scientists design a method to develop high-quality perovskite materials capable of utilizing longer-wavelength light

A research team from Japan’s National Institute for Materials Science (NIMS) has developed a new method of fabricating high-quality perovskite materials, capable of utilizing longer-wavelength sunlight of 800 nm or longer. The method may mark a new approach to enhance the efficiency of perovskite solar cells.

Scientists design a method to develop high-quality perovskite materials capable of utilizing longer-wavelength light

Perovskite solar cells currently possess optical absorption spectra that lean toward shorter wavelengths. To improve the energy conversion efficiency of these cells, it is crucial to develop perovskite materials with optical absorption spectra expanded to include longer wavelengths. This is why several research institutes are developing perovskite materials that include two types of cations, MA and FA, capable of absorbing light in the longer wavelength region. However, these cations are not without issues – mainly that their mixing ratio and crystallization temperature are difficult to control. Moreover, due to their tendency to form a mixed crystal phase, there had been no effective method established to fabricate high-purity, single-crystalline perovskite materials.

Now, the researchers designed a method that enables the creation of perovskite materials with a 40 nm wider optical absorption spectrum, a high short-circuit current and high open-circuit voltage. The method was used to fabricate a new type of mixed cation-based perovskite material. A pure, single-crystalline precursor material, (FAI)1-xPbI2, was fabricated under altering temperatures. A reaction was performed between the precursor and MAI (methylammonium iodide). The resulting perovskite material, (MA)xFA1-xPbI3, was a single crystalline phase and had a long fluorescence lifetime. The observations indicated that electrons in the material rarely recombine and they have long lifetimes. The optical absorption spectrum of the solar cells employing this material covered up to 840 nm, which was 40 nm wider than the spectrum of conventional perovskite material (MA3PbI3). As a result, the solar cells that were developed obtained 1.4 mA/cm2 higher short-circuit current than the MAPbI3 solar cells that were manufactured under the same conditions.

The researchers intend to continue their studies in order to develop high-quality perovskite solar cells capable of utilizing a broader spectrum of sunlight by adjusting the ratio of the two cations.

Source: edn-europe


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Scientists use inorganic replacements to achieve improved efficiency and durability in perovskite solar cells

Scientists at the National Institute for Materials Science (NIMS) announced the improvement of power conversion efficiency (PCE) of perovskite solar cells to over 16% while employing cells that were greater than 1 cm2. The high efficiency cells also passed the durability test (exposure to AM 1.5G 100 mW/cm2 sunlight for 1,000 hours), which is considered to be a basic criterion for practical use. These achievements were made by replacing the conventional organic materials with inorganic materials as the electron and hole extraction layers of the solar cells. 

Scientists use inorganic replacements to achieve improved efficiency and durability in perovskite solar cells

The researchers replaced the conventional organic materials with robust inorganic materials for use in electron and hole extraction layers. Since these layers have high electrical resistance, it was necessary to reduce the thickness of the layers to several nanometers. However, as the area of these thin layers increases, the occurrence of defects called pinholes also increases, leading to decreased PCEs. To deal with this problem, the researchers increased the electrical conductivity of these layers by more than 10 times through heavily doping both electron and hole extraction layers. In this way, they fabricated layers that have fewer pinholes over wide areas and are applicable at thicknesses of up to 10 to 20 nm. Using these layers, a PCE of 16% was repeatedly attained while employing cells that were greater than 1 cm2. The use of inorganic materials also contributed to PCE reduction within 10% even after undergoing 1,000 hours of continuous exposure to sunlight at an intensity of 1 sun, demonstrating outstanding reliability. 

Following these encouraging results, the researchers aim to develop more efficient light absorbing material capable of utilizing a greater amount of sunlight and precisely controlling the interfaces in the devices, for achieving higher PCEs and stability. 

Source: Nanowerk via Science








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