Stability - Page 18

Researchers from King Abdullah University of Science and Technology (KAUST) and National Yang Ming Chiao Tung University have reported what they say is the first-ever successful photovoltaic (PV) damp-heat test of perovskite solar cells.

The damp-heat test is an accelerated and rigorous environmental aging test aimed at determining the ability of solar panels to withstand prolonged exposure to high humidity penetration and elevated temperatures. The test is run for 1,000 hours under a controlled environment of 85% humidity and 85 degrees Celsius. It is meant to replicate multiple years of outdoor exposure and evaluate factors such as corrosion and delamination.

Researchers from Korea and the USA have used an imaging technique to observe structural changes at the atomic level suggesting strategies to reduce perovskite solar cell degradation.

Perovskite solar cells (PSCs) tend to degrade quickly. When they are exposed to sunlight, freely moving ion vacancies form in the structure and migrate towards the electrodes. In dark conditions, the effect is reversed, and the ions are once again redistributed in the perovskite structure. Repeated cycles of this ion transport during the operation of the solar cell permanently degrade the cell and result in short lifetimes. However, degradation at the atomic level due to ion migration has not been directly observed.

Los Alamos National Laboratory researchers and their collaborators have examined the performance properties of two-dimensional perovskites in conditions representative of a device structure, finding those structures can be as efficient as their three-dimensional counterparts.

'We discovered that intrinsic to this material, there are some shallow defects or 'trap states' that can help the charge transport over a long distance,' said Wanyi Nie, researcher with the Center for Integrated Nanotechnologies group at Los Alamos National Laboratory. 'The travel distance is slightly lower than three-dimensional perovskites, but is much greater than what people believed in a typical 2D quantum-confined system. So this is a critical finding that two-dimensional perovskites can be efficient as three-dimensional perovskites.'

Scientists from the Xi'an Jiaotong University, Chinese Academy of Science and City University of Hong Kong have reported the fabrication of a highly stable perovskite solar cell by capping the photoactive layer with low-dimensional (LD) perovskitoids.

Atomic structure of (A) (p-PBA)Pb2I6 (1D) and (B) (m-PBA)2PbI6 (0D). Image from study

'Perovskitoids have the potential to effectively modify 3D perovskite due to its diverse PbI₆ connection styles and high stability,' the researchers stated, referring to the properties of the 1D and 0D capping layer materials used for 3D perovskite (m-PBA)₂PbI₆. 'Both 1D and 0D perovskitoids have intrinsically low defect densities and can withstand relatively high lattice strains; thus, they can serve as blocking channels for undesired Shockley-Read-Hall recombination and material degradation.'

Researchers from KAUST and the University of Bologna have examined the root causes of harmful top-contact delamination in p-i-n perovskite/silicon tandem solar cells. Their findings aim to improve the stability of tandem modules, and prompt a search for new interfacial linking strategies to enable mechanically strong perovskite-based solar cells, as required for commercialization.

In their work, by combining macroscopic and microscopic analyses, the team identified the interface between the fullerene electron transport layer and the tin oxide buffer layer at the origin of such delamination. Specifically, they found that the perovskite morphology and its roughness play a significant role in the microscopic adhesion of the top layers, as well as the film processing conditions, particularly the deposition temperature and the sputtering power.

A research group at FAU and the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) have worked on a design aimed at significantly increasing the operational stability and life span of perovskite solar cells. Their design is based on a bilayer of polymers that protects the perovskites from corrosion at the same time as allowing uninterrupted charge transfer.

Until now, despite perovskite solar cells' potential, two major disadvantages have become apparent. Firstly, they do not have a particularly long life span, as perovskites tend to corrode on their interfaces and their performance capacity sinks rapidly, sometimes within days. Secondly, perovskite modules are not particularly robust in elevated temperatures, which severely limits their stability in practical use scenarios. This is mainly down to the layers doped with ions that are required for transporting the charge carriers but that can also lead to undesired secondary reactions.

Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have developed blue LEDs based on metal halide perovskites, that, for the first time, uses asymmetrical bridges to hold the layers of perovskite together, creating a more stable structure.

'Perovskites have the potential to be a real game-changer in the lighting industry,' said first author Dr. Yuqiang Liu, a former post-doctoral researcher in the OIST Energy Materials and Surface Sciences Unit and currently a professor at Qingdao University, China. 'In only a few short years, the efficiency of perovskite LEDs ' how well they can transfer electrical energy into light energy ' has shot up to a level that rivals traditional LEDs, and soon will surpass them.'

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.

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.