Technical / research - Page 54

An international team of researchers from EPFL, North Carolina State University, Centre for Hybrid and Organic Solar Energy (CHOSE) at the University of Rome Tor Vergata and Uppsala University has demonstrated a technique for producing perovskite photovoltaic materials on an industrial scale, which could reduce the cost and improve the performance of mass-produced perovskite solar cells. The technique is low-cost, simple and energy-efficient.

'In the lab, researchers produce perovskite photovoltaic materials using a technique called spin coating, which creates a thin film of perovskite on a substrate ' but only on a small scale,' says Aram Amassian, co-corresponding author of a paper on the work and a professor of materials science and engineering at North Carolina State University.

Researchers from Tor Vergata University and University of Zanjan have developed a new method that uses a simple sheet of paper to deposit the perovskite films without any expensive equipment. The way to achieve high performance with this low-cost method is to soak the paper applicator in anti-solvent which almost doubles efficiencies compared to when using it dry, reaching 11% on flexible plastic substrates. Paper, compared to other soft applicators, possesses the right porosity and smoothness for deposition of high quality perovskite films.

Most perovskite films in laboratories around the world are deposited through spin coating which guarantees high control of film thickness as well as morphology. However, most of the ink is expelled during deposition and is wasted. There have been efforts to develop coating techniques for deposition over large areas. The most efficient solar cells fabricated via spin coating involve adding drops of anti-solvent (i.e., a liquid with differing properties to those used in the perovskite precursor inks) during spinning which improves the morphological quality of the perovskite semiconductor films. This method is very difficult to implement when employing large area coating techniques, however, where the careful engineering of the drying processes involve heaters or gas flows to control the morphology of the perovskite film.

A team of researchers from the National University of Singapore (NUS), the University of Hong Kong and Southern University of Science and Technology has reportedly "set a new record in the power conversion efficiency of solar cells made using perovskite and organic materials".

'The main motivation of this study is to improve the power conversion efficiency of perovskite/organic tandem solar cells. In our latest work, we have demonstrated a power conversion efficiency of 23.6% - this is the best performance for this type of solar cells to date,' said Dr. Chen Wei, Research Fellow at the NUS Department of Chemical and Biomolecular Engineering and the first author of this work.

Researchers from Professor Tan Hairen group at Nanjing University in China recently developed all-perovskite tandem solar cells with a conversion efficiency of 26.4%, certified by JET.

The team developed ammonium-cation-passivated Pb-Sn perovskites with long diffusion lengths, enabling subcells with an absorber thickness of ~1.2 μm. Molecular dynamics simulations suggest that widely-used phenethylammonium (PEA) cations are only partially adsorbed on the surface defective sites at perovskite crystallization temperatures. The passivator adsorption is predicted to be enhanced using 4-trifluoromethyl-phenylammonium (CF3-PA), which exhibits a stronger perovskite surface-passivator interaction than does PEA.

Scientists from TU Dresden, collaborating with researchers at Seoul National University (SNU) and Korea University (KU), have demonstrated the role of the re-use of photons ('photon recycling') and light scattering effects in perovskite solar cells, providing a pathway towards high-efficiency solar energy conversion.

The researchers from the Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) at the TU Dresden observed the role of the photon recycling effect. When a photon is radiated inside re-absorbing semiconductors like perovskites, it can be re-absorbed by the emitter itself and generate a new photon via photoluminescence. Such a process of recursively re-absorbing and re-emitting the photons is called photon recycling. While this phenomenon has been previously demonstrated by several research groups, its practical contribution to the efficiency of perovskite solar cells has been under extensive debate. Based on the devices prepared by the groups in SNU and KU, the IAPP researchers discovered that photon recycling and light scattering effects greatly improve the light emission efficiency by a factor of ~5, significantly improving the photovoltage of perovskite solar cells.

Researchers from China's Shaanxi Normal University and Chinese Academy of Sciences (CAS) have designed a perovskite solar cell with a novel defect passivation strategy based on the use of an ionic liquid (IL) perovskite capping layer.

ILs are non-molecular compounds that are composed solely of ions. They are said to possess several advantages over traditional organic solvents, such as negligible vapor pressure at room temperature and high thermal stability.

A team from Israel's Technion Institute of Technology has announced the development of self-healing perovskite nanocrystals.

Having to frequently replace electronics due to malfunctioning of materials is unavoidable today, since every device suffers from degradation as a result of defects that accumulate during use over time. This generates, in addition to customer frustration and costs, a heavy environmental footprint.

Researchers from the Diamond Light Source and the electron Physical Science Imaging Centre (ePSIC), Imperial College London, Yonsei University, Wageningen University and Research, and the University of Leeds have developed a method to stabilize perovskites without compromising their performance.

The researchers used an organic molecule as a 'template' to guide perovskite films into the desired phase as they form.

Researchers from the Hefei Institutes of Physical Science (HFIPS) under the Chinese Academy of Sciences (CAS), University of Science and Technology of China, North Minzu University, Hefei University of Technology, Greece's Institute of Nanoscience and Nanotechnology (INN) and Australia's Greatcell Energy have developed perovskite solar cells with a self-recovery capability and high stability in humid environment by introducing polymer called polyvinylpyrrolidone.

The team has shown that polyvinylpyrrolidone, a long chain insulating polymer, could form hydrogen bonds with ions in the cells and also prevent moisture in the air from invading perovskite materials. The hydrogen-bonding-initiated self-healing repairs the decayed perovskite solar cell back to the original state, continue to work, and alleviate long-term cell instability.

Researchers from Germany's Forschungszentrum Jülich have developed a planar perovskite solar cell that reportedly reached over 1,400'hours of operational stability at elevated temperatures. The 20.9% efficient device was built without the ionic dopants or metal oxide nanoparticles that are commonly used to contact the cell, as these can be subject to secondary reactions at higher temperatures.

The scientists tested many different perovskite mixtures before choosing the perovskite material for the cell, giving great focus to their thermal stability, using a self-constructed, high-throughput screening platform.