Stability

Researchers from City University of Hong Kong have introduced a novel and durable 2D thermochromic perovskite, Tha₂MAPbI₄ (TMPI, Tha = thiourea, MA = methylamine), wherein Tha acts as a Lewis acid-base adduct. TMPI demonstrates a reversible transition, achieving 83.7% luminous transmittance in the cold state and 35.2% in the hot state, thereby showcasing a substantial solar modulation ability of 24.7%. 

The background for this development is that despite growing interest in thermochromic metal halide perovskite (MHPs) for smart window applications, existing MHP smart windows predominantly feature 3D perovskite, which exhibits a deficiency in environmental stability, presenting persistent challenges for practical applications. 

In November 29, Hangzhou Xianna Optoelectronic Technology Co., Ltd. delivered its perovskite α-tandem modules for the China Three Gorges New Energy 50 MW PV demonstration project, in what is said to mark the first commercial application of four-terminal perovskite-silicon tandem modules in China. 

Once the PV power plant utilizing these tandem modules is completed and connected to the local grid, it will significantly alleviate the local grid's supply-demand imbalance, reduce environmental pollution, and improve air quality. The design work for a 500 kW demonstration plant has already been completed, with plans to collaborate with engineering institutes for on-site module layout design. The demonstration plant is expected to be connected to the grid and operational by the end of 2024.

Researchers from China's Tianjin University of Technology, Zhejiang Sci-Tech University, University of Electronic Science and Technology of China, North China Electric Power University and South China University of Technology have shown that the introduction of azetidinium iodide (AZI) into the precursor solution of a 1.77 eV bandgap FA_0.8Cs_0.2Pb(I_0.6Br_0.4)₃ perovskite significantly improves the efficiency and stability of the perovskite cells. 

Devices fabricated with 2 mol% AZI (relative to FAI, noted as AZ2) in perovskite layer exhibited a high PCE of 19.16 % and a high open-circuit voltage of 1.31 V. When stored under nitrogen atmosphere and illuminated under 1 sun conditions for 300 h, AZ2 device retained 80 % of the initial values. 

Researchers from Huaqiao University, Gold Stone (Fujian) Energy Company, Beijing Huairou Laboratory and Kunshan Shengcheng Photoelectric Technology have reported a four-terminal (4T) perovskite-silicon solar cell with a perovskite-based top cell, with an energy bandgap of 1.67 and lower surface defects. 

Structure of the 4T perovskite/silicon tandem solar cells. Image from Nature Communications

The team integrated a wide-bandgap perovskite solar cell with a hybrid back contact device in a four-terminal tandem cell that achieves high efficiency and stability. The group used a new surface passivation strategy that reportedly helped gain the cell's strong performance.

Researchers at the Canadian University of Saskatchewan recently gained insight as to why solar cells made with lead halide perovskite degrade prematurely. These discoveries could advance the reliability these solar cells.

In experiments conducted at the Canadian Light Source (CLS) synchrotron, Dr. Tim Kelly, a professor of chemistry at USask, sought to determine why perovskite-based solar cells fail under certain conditions. The researchers initially suspected that the issue lay in the perovskite formulation. By employing X-ray diffraction to analyze the material’s atomic structure in real-time, the team observed that humidity played a critical role in cell degradation. Moisture caused ions within the perovskite to mobilize, migrate to the electrode, and corrode it, rendering the device inoperative.

Over the past five years, six Fraunhofer Institutes combined their expertise in the Fraunhofer lighthouse project "MaNiTU" to identify the most sustainable paths to market of perovskite-silicon tandem solar cells made of stable materials and manufactured using scalable production processes. They were able to show that high cell efficiencies can be achieved using industry-oriented processes, however, they found that such high efficiencies were only currently achievable with lead perovskite materials. Based on these findings, the researchers developed suitable recycling concepts to ensure sustainability.

In the "MaNiTU" project, the Fraunhofer researchers produced new materials with perovskite crystal structures and compared them with existing materials at the cell level. The comparisons showed that high efficiencies can only be achieved with lead perovskites. They then successfully fabricated highly efficient demonstrators, for example, a perovskite silicon tandem solar cell of more than 100 square centimeters with screen-printed metallization and produced mini modules for single and interconnected tandem solar cells. Subsequent life cycle analyses showed that by using suitable production and recycling processes and degradation rates comparable to today's silicon technology, it is feasible to make a sustainable product.

As it currently remains challenging to obtain precise control over the formation of the thin 2D layer used in 2D/3D heterojunction perovskite solar cells, researchers from China's Jinan University set out to design a method for the precise preparation of 2D/3D perovskite heterojunctions.

Using their new method, the team constructed two different 2D/3D heterojunctions using a vapor-solution mixed deposition method and compared them with heterojunctions formed via conventional solution methods, achieving a PCE of the device from 20.67 % to 22.68%. The new strategy could be a useful way to optimize perovskite films and advance the fabrication of high-efficiency perovskite solar cells.

The ICN2 Nanostructured Materials for Photovoltaic Energy (NMPE) Group, led by CSIC Research Prof. Mónica Lira-Cantú, has reported an achievement in advancing solar energy technologies. In collaboration with the National University of Engineering (UNI) in Peru and NASA's High Altitude Student Platform (HASP), the researchers launched perovskite solar cells (PSCs) into the stratosphere to evaluate their stability and performance under extreme conditions.

The project was an collaboration. Kenedy Tabah Tanko, PhD student at ICN2, was responsible for fabricating and encapsulating the PSCs, under the supervision of Prof. Monica Lira-Cantu. Meanwhile, the payload, designed to measure the cells' performance in flight, was crafted by UNI students, under the supervision of Dr. Mónica Marcela Gómez. Finally, the NASA Balloon Program Office (BPO) and the Louisiana Space Consortium (LaSPACE) provided the platform for the experiment, allowing the PSCs to be launched 36 km into the stratosphere from New Mexico, USA.

Passivation of 3D perovskite light-harvesting layers with 2D perovskites is an effective strategy to boost the stability, PCEs and reliability of perovskite solar cells. These 2D layers can protect the light-harvesting layers, reducing their reactivity to environmental factors and thus preventing them from degrading quickly over time. 

Researchers from China's Wuhan University of Technology, Xidian University, University of Electronic Science and Technology of China and Germany's Technical University of Munich recently reported a strategy to prompt the formation of homogenous 2D perovskite passivation layers in perovskite-based solar cells. Using their proposed method, they achieved good active-area efficiencies and stabilities in perovskite solar modules based on formamidinium and cesium.

Researchers from South China University of Technology, The Chinese University of Hong Kong, Chinese Academy of Sciences (CAS), National Center for Nanoscience and Technology, Friedrich-Alexander University Erlangen-Nürnberg and Linköping University set out to eliminate deep traps in inorganic narrow bandgap (NBG) perovskites, in order to enable the successful development of 2T inorganic perovskite tandem solar cells (IPTSCs).

The team explained that all-inorganic perovskites prepared by substituting the organic cations (e.g. methylammonium (MA⁺) and formamidinium (FA⁺)) with inorganic cations (e.g. Cs⁺) are effective concepts to enhance the long-term photo- and thermal-stability of perovskite solar cells (PSCs). Hence, inorganic perovskite tandem solar cells (IPTSCs) are promising candidates for breaking the efficiency bottleneck and addressing the stability issue as well. However, challenges in fabricating 2-terminal (2T) IPTSCs due to the inferior film formation and deep trap states induced by tin cations hinder that option.