Efficiency - Page 33

Researchers from the University of Amsterdam and NWO-Institute AMOLF have examined the efficiency gain offered by perovskite/silicon tandem solar cells containing several semiconductors with diverse energy gaps, with a spectrum splitter added between the top and bottom terminals.

This design allows the tandem solar cells to be responsive to a wider region of the sunlight's spectrum. However, such cells usually deal with ineffective light trapping and management due to parasitic light absorption in inactive layers and reflection between layers. Various studies have looked into these issues, yet the idea of spreading sunlight in the tandem subcells with controlled spectral splitting was not adequately investigated.

Researchers from the Australian National University (ANU), China's Sun Yat-sen University and Chinese Academy of Sciences (CAS) have reportedly set a new record conversion efficiency for perovskite-based solar cells, improving on a record they already held.

The recent research details how a solar conversion efficiency of 22.6% for a one square centimeter cell was achieved through improvements on previous perovskite solar cells.

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 at EPFL, Zurich University of Applied Sciences, Ulsan National Institute of Science and Technology, University of Ulsan and Uppsala University have designed an innovative way to increase the performance of perovskite solar cells and maintain it at a high level even at large scales. The new approach replaces the electron-transport layer with a thin layer of quantum dots.

With this new approach, the team, led by Professor Michael Grätzel at EPFL and Dr Dong Suk Kim at the Korea Institute of Energy Research, addressed one of the major obstacles facing the commercialization of perovskite solar cells - the fact that their power-conversion efficiency and operational stability drop as they scale up, making it a challenge to maintain high performance in a complete solar cell.

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.

The Army Research Office and the Office of Naval Research have provided financial support for a new perovskite research, along with the National Science Foundation and the Energy Department's Office of Science. The researchers are a team of engineers working out of the lab of Aditya Mohite at Rice University.

The project was a collaborative one that also involved Purdue and Northwestern universities. The Energy Department was also involved via its Los Alamos, Argonne and Brookhaven laboratories. So were the Institute of Electronics and Digital Technologies in France, with additional support from the Academic Institute of France.

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.