Efficiency - Page 34

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.

Researchers from the Imperial College of London and University College London have demonstrated the photovoltaic-boosting effect that phosphorene nanoribbons (PNRs) can bring to perovskite solar cells. When applied in tandem with a perovskite solar cell, PNR-boosted cells achieved an efficiency above 21%, which the researchers defined as "on par with traditional silicon cell output levels".

PNRs, first produced in 2019, have many theoretical use cases, including enhancing batteries, biomedical sensors, and quantum computing. The PNRs directly aided the perovskite cells' hole mobility, improving overall efficiency.

Researchers from the Femtosecond Spectroscopy Unit, led by Professor Keshav Dani, at the Okinawa Institute of Science and Technology Graduate University (OIST) and Optoelectronics Materials and Device Spectroscopy Group, led by Dr. Sam Stranks at the University of Cambridge, have identified three different kinds of defect clusters in perovskite thin films, which likely occur during fabrication and may impede efficiency of perovskite solar cells.

The perovskite material lies at the heart of the solar cell, which consists of many different layers. When the sun hits the solar cell, its energy is absorbed by the perovskite, causing electrons to jump into a higher energy level and leaving holes behind. All the electrons then move in one direction through the layers of the solar cell to the electrical contact and the holes, in the other direction, thus generating a current.

In a joint collaborative effort between the University of Pavia in Italy and the Technische Universität Dresden in Germany, researchers have developed a novel method to significantly improve the efficiency of inverted architecture perovskite solar cells.

The method is based on a modification of the interfaces of the perovskite active layer by introducing small amounts of organic halide salts at both the bottom and the top of the perovskite layer. Such organic halide salts, typically used for the formation of two-dimensional perovskites, led to the suppression of microstructural flaws and passivation of the defects of the perovskite layer. Using this approach, the team has achieved a power conversion efficiency of 23.7%, which they say is the highest reported to date for an inverted architecture perovskite solar cell.

Researchers at Nankai University in China have developed a Dion-Jacobson (DJ) two-dimensional perovskite solar cell. They claim it exhibits a power conversion efficiency of 18.82%, as well as remarkable light, thermal, environmental, and operational stability.

Two-dimensional (2D) Dion-Jacobson (DJ) phase perovskites have sparked interest in the scientific community due to their stability against harsh environmental conditions and their competitive performance in optoelectronic applications. Solar cells based on DJ perovskites, however, tend to show comparatively poor performance compared to their 3D counterparts.

Researchers at the National Renewable Energy Laboratory (NREL), along with collaborators from the SLAC National Accelerator Laboratory, University of Toledo, Princeton University, University of Arizona, University of Kentucky, and University of Colorado, have found away to improve the efficiency of perovskite solar cells by as much as 16%.

The effort involved combining a two-dimensional (2D) perovskite layer with a three-dimensional (3D) perovskite layer, which yielded a solar cell with improvements in both efficiency and stability.

Recent research has shown that the incorporation of graphene-related materials improves the performance and stability of perovskite solar cells. Graphene is hydrophobic, which can enhance several properties of perovskite solar cells. Firstly, it can enhance stability and the passivation of electron traps at the perovskite's crystalline domain interfaces. Graphene can also provide better energy level alignment, leading to more efficient devices.

In a recent study, Spain-based scientists used pristine graphene to improve the properties of MAPbI₃, a popular perovskite material. Pristine graphene was combined with the metal halide perovskite to form the active layer of the solar cells. By analyzing the resulting graphene/perovskite material, it was observed that an average efficiency value of 15% under high-stress conditions was achieved when the optimal amount of graphene was used.

Researchers from Rice University and collaborators from Purdue and Northwestern universities, U.S. Department of Energy national laboratories Los Alamos, Argonne and Brookhaven and the Institute of Electronics and Digital Technologies (INSA) in Rennes, France, have reached a new benchmark in the design of atomically thin solar cells made of semiconducting perovskites, boosting their efficiency while also focusing on their stability.

The lab of Aditya Mohite of Rice's George R. Brown School of Engineering discovered that sunlight itself contracts the space between atomic layers in 2D perovskites enough to improve the material's photovoltaic efficiency by up to 18%.

Researchers from the University of Cambridge, in collaboration with Cambridge's Cavendish Laboratory, the Diamond Light Source synchrotron facility in Didcot and the Okinawa Institute of Science and Technology in Japan, have used a suite of correlative, multimodal microscopy methods to visualize, for the first time, why perovskite materials are seemingly so tolerant of defects in their structure.

The impressive performance of perovskites is surprising, as the typical model for an excellent semiconductor is a very ordered structure, but the array of different chemical elements combined in perovskites creates a much 'messier' landscape. This heterogeneity causes defects in the material that lead to nanoscale 'traps', which reduce the photovoltaic performance of the devices. But despite the presence of these defects, perovskite materials still show efficiency levels comparable to their silicon alternatives. In fact, earlier research by the same group has shown the disordered structure can actually increase the performance of perovskite optoelectronics, and their latest work seeks to explain why.

Three HZB teams, led by Prof. Christiane Becker, Prof. Bernd Stannowski and Prof. Steve Albrecht, have jointly managed to bring the efficiency of perovskite silicon tandem solar cells to a new record value of 29.80%. This result has been officially certified by Fraunhofer ISE CalLab and is documented in the NREL-charts.

The perovskite silicon tandem cell is based on two innovations: A nanotextured front side ( left) and a back side with dielectric reflector (right). © Alexandros Cruz /HZB

Several HZB groups have been working intensively since 2015 on both the perovskite semiconductors and silicon technologies and the combination of both into innovative tandem solar cells. In January 2020, HZB had achieved a record 29.15 % for a perovskite silicon tandem solar cell. Then, also in 2020, the company Oxford PV was able to announce a certified efficiency of 29.52%. Since then, the race for new records has been on. "An efficiency of 30% is like a psychological threshold for this fascinating new technology which could revolutionize the photovoltaic industry in the near future," explains Steve Albrecht, who is working on perovskite thin films at the HySPRINT lab at HZB. Bernd Stannowski, group leader for silicon technology, adds: "I would particularly emphasize the good cooperation between the different groups and institutes at HZB. This is how we managed to develop these new tandem solar cells entirely at HZB and once again get the world record."