Stability

Researchers from Helmholtz-Zentrum Berlin (HZB), Chinese Academy of Sciences (CAS), Swansea University, University of Stuttgart, Henan University, University of Naples Federico II, Queen Mary University of London and Soochow University have investigated a chemical variation that significantly improves the stability of the perovskite thin film in different solar cell architectures, among them the p-i-n architecture.

Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. The international team in this work set out to address this issue and improve the stability of PSCs in the face of these changes. 

A team of researchers, led by Professor Michael Grätzel at EPFL and Xiong Li at the Michael Grätzel Center for Mesoscopic Solar Cells in Wuhan (China), have developed a technique that addresses stability concerns of perovskite solar cells (PSCs) and increases their efficiency.

The researchers introduced a phosphonic acid-functionalized fullerene derivative into the charge-transporting layer of the PSC as a “grain boundary modulator”, which helps strengthen the perovskite crystal structure and increases the PSC’s resistance to environmental stressors like heat and moisture.

Researchers at Switzerland's EPFL and Sungkyunkwan University in Korea have addressed the issue of perovskite solar cells' stability. They focused on the degradation of perovskite thin films, which can be damaged by exposure to moisture, heat, and light. The team looked at two specific crystal facets (the crystal's flat surface), characterized by a particular arrangement of atoms. The arrangement of atoms on these facets can affect the properties and behavior of the crystal, such as its stability and its response to external stimuli like moisture or heat.

The researchers looked at the (100) and (111) facets of perovskite crystals. The (100) facet is a plane that is perpendicular to a crystal's c-axis with its atoms arranged in a repeating pattern in the form of a square grid. In the (111) facet the atoms are arranged in a triangular grid. The study found that the (100) facet, which is most commonly found in perovskite thin films, is particularly prone to degradation as it can quickly transition to an unstable, inactive phase when exposed to moisture. In contrast, the (111) facet was found to much more stable and resistant to degradation.

A team of researchers at EPFL have developed a method that improves both power conversion efficiency and stability of solar cells based on pure iodide as well as mixed-halide perovskites. The new method aslo suppresses halide phase segregation in the perovskite material. The research was carried out by the groups of Professors Michael Grätzel and Ursula Rothlisberger at EPFL and led by Dr Essa A. Alharbi and Dr Lukas Pfeifer.

The method treats perovskite solar cells with two alkylammonium halide modulators that work synergistically to improve solar cell performance. The modulators were used as passivators, compounds used to mitigate defects in perovskites, which are otherwise promoting the aforementioned degradation pathways.

Researchers from Saule Research Institute, Saule Technologies, Centre for Hybrid and Organic Solar Energy (CHOSE), CNR-SCITEC, Istituto Italiano di Tecnologia (IIT), Wroclaw University of Science and Technology, Bydgoszcz University of Science and Technology and Poznan University of Technology have demonstrated an effective strategy to improve the technical aspects of flexible perovskite solar cells,  improving the reliability and efficiency values of these devices.

The team applies large organic ammonium molecules for modifying a buried interface between a hole-transporting layer (HTL) and perovskite-absorbing material. With the 4-fluorophenethylammonium iodide (FPEAI), they achieved 18.66% efficiency for the large-area (1 cm²) flexible solar cell, a significant improvement over the pristine device without modification.

An international research collaboration that was led by UCLA and included teams from Marmara University in Turkey, Sungkyunkwan University in Korea, Dalian University of Technology and Westlake University in China, Washington State University, UC Irvine and Washington University in St. Louis, has developed a way to use perovskites in solar cells while protecting it from the conditions that cause it to deteriorate.

The scientists added small quantities of neodymium ions directly to the perovskite. They found not only that the augmented perovskite was much more durable when exposed to light and heat, but also that it converted light to electricity more efficiently.

Researchers from South-Africa's University of the Western Cape, University of Missouri and Argonne National Laboratory have developed a new way of enhancing the stability and performance of perovskites. 

Missouri University professor Suchismita (Suchi) Guha, the lead author of the study, and her collaborators improved the methods for making lead halide perovskites. Previous techniques for making these thin-film perovskites required liquid processing using solvents, which rendered the films susceptible to degradation when exposed to air. Additionally, with  prior manufacturing processes, one of its molecules undergoes a change to its structure, causing performance limitations in real-world operating conditions. 
With the new technique, the researchers were able to prevent the change, holding the affected molecule in a stable structure throughout a large temperature range. Additionally, the new technique rendered the perovskite air stable, making it appropriate for a potential solar cell. 

Researchers at Oxford University, ARC Centre of Excellence for Exciton Science at Monash University,  National Renewable Energy Laboratory (NREL) and SLAC National Accelerator Laboratory have demonstrated a new way to create stable perovskite solar cells, with fewer defects and the potential to rival silicon's durability.

By removing the solvent dimethyl-sulfoxide and introducing dimethylammonium chloride as a crystallization agent, the researchers were able to better control the intermediate phases of the perovskite crystallization process, leading to thin films of greater quality, with reduced defects and enhanced stability.

Researchers from the Department of Energy’s Ames National Laboratory and The University of Toledo have developed a new characterization tool that allowed them to gain unique insight into a perovskite material. Led by Ames' Jigang Wang, the team developed a microscope that uses terahertz waves to collect data on material samples. The team then used their microscope to explore Methylammonium Lead Iodide (MAPbI₃) perovskite.

Richard Kim, a scientist from Ames Lab, explained the two features that make the new scanning probe microscope unique. First, the microscope uses the terahertz range of electromagnetic frequencies to collect data on materials. This range is far below the visible light spectrum, falling between the infrared and microwave frequencies. Secondly, the terahertz light is shined through a sharp metallic tip that enhances the microscope’s capabilities toward nanometer length scales.

Researchers from China's Huazhong University of Science and Technology and Singapore's National University of Singapore have introduced an eco-friendly and low-cost organic polymer, cellulose acetate butyrate (CAB), to the grain boundaries and surfaces of perovskites, resulting in a high-quality and low-defect perovskite film with a nearly tenfold improvement in carrier lifetime.

The CAB-treated perovskite films have a well-matched energy level with the charge transport layers, thus suppressing carrier nonradiative recombination and carrier accumulation. As a result, the optimized CAB-based device achieved a champion efficiency of 21.5% compared to the control device (18.2%).