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Harnessing sunlight to fuel the future through covalent organic frameworks

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Harnessing sunlight to fuel the future through covalent organic frameworks

Be it rising fuel prices or failures in electricity power grids, the consequences of global energy crisis are hard to ignore. The need for alternate fuel sources is greater than ever, but, despite the popularity of solar panels, a vast amount of solar energy goes untapped. Now, a multinational team of researchers explore existing research on covalent organic frameworks (COFs), a new class of light-absorbing compounds, as a potential solution for efficient solar-driven fuel production.

Photocatalysts absorb energy from light to make a chemical reaction happen. The best known photocatalyst is perhaps chlorophyll, the green pigment in plants that helps turn sunlight into carbohydrates. While carbohydrates may be falling out of favor, photocatalysis is garnering more attention than ever. In a photocatalytic process, light falls on a photocatalyst, increases the energy of its electrons and causes them to break their bonds and move freely through the catalyst.

These “excited” electrons then react with the raw materials of a chemical reaction to produce desired products. A top priority in the field of alternate energy research is using photocatalysts to convert solar energy to fuel, a process called “solar-to-fuel production.”

In an article published in Coordination Chemistry Reviews, Dr. Changlei Xia from Nanjing Forestry University, China; Dr. Kent Kirlikovali from Northwestern University, USA; Dr. Thi Hong Chuong Nguyen, Dr. Xuan Cuong Nguyen, Dr. Quoc Ba Tran, and Dr. Chinh Chien Nguyen from Duy Tan University, Vietnam; Dr. Minh Khoa Duong and Dr. Minh Tuan Nguyen Dinh from The University of Da Nang, Vietnam; Dr. Dang Le Tri Nguyen from Ton Duc Thang University, Vietnam; Dr. Pardeep Singh and Dr. Pankaj Raizada from Shoolini University, India; Dr. Van-Huy Nguyen from Binh Duong University, Vietnam; Dr. Soo Young Kim and Dr. Quyet Van Le from Korea University, South Korea; Dr. Laxman Singh from Patliputra University, India; and Dr. Mohammadreza Shokouhimer from Seoul National University, South Korea, have highlighted the potential of covalent organic frameworks (COFs), a new class of light-absorbing materials, in solar-to-fuel production.

As Dr. Pardeep Singh explains, “Solar energy has been successfully tapped to make electricity, but we are not yet able to efficiently make liquid fuels from it. These solar fuels, like hydrogen, could be an abundant supply of sustainable, storable, and portable energy.”

The specialty of COFs lies in their ability to improve catalysis and add special substituent molecules called “functional groups” to their structure, providing a way around the limitations of existing photocatalysts. This is due to certain favorable properties of COFs such as chemical stability, controllable porosity, and strong electron delocalization, which make them extra stable.

Like the name suggests, COFs consist of organic molecules that are bonded together into a structure that can be tailored to suit various applications. Moreover, strong electron delocalization means that, unlike in semiconductor photocatalysts, the excited electrons recombine midway only infrequently, resulting in more excited electrons for the chemical reaction. Since these reactions occur at the surface of the photocatalyst, the increased surface area and modifiable porosity of COFs is a huge advantage.

COF-photocatalysts find application in the conversion of water to hydrogen, and the production of methane from carbon dioxide, thus promising the dual benefit of producing fuel and mitigating global warming. Furthermore, they can even help with nitrogen fixation, plastics production, and storage of gases.

A new kind of COF, covalent triazine frameworks (CTFs), are currently at the cutting-edge of hydrogen production research. CTFs have 20-50 times the ability to produce hydrogen, compared to graphitic photocatalysts, making them a very promising option for future fuel production.

However, before we put the solar-powered cart before the horse, it is important to note that COF-based photocatalysts are at an early stage of development and still do not produce fuel as efficiently as their semiconductor-based counterparts. Nevertheless, their outstanding properties and structural diversity make them promising candidates for future solar-to-fuel research and a viable solution for the ongoing energy crisis. “The most essential issue is to explore robust COFs-derived catalysts for the desired applications. It can be expected that COF-based photocatalysts will achieve a new milestone in the coming years,” concludes an optimistic Dr. Pankaj Raizada.

Research Report: “The Emerging Covalent Organic Frameworks (COFs) for Solar-Driven Fuels Production”

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Innovative approach to perovskite solar cells achieves 24.5% efficiency

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Innovative approach to perovskite solar cells achieves 24.5% efficiency


Innovative approach to perovskite solar cells achieves 24.5% efficiency

by Simon Mansfield

Sydney, Australia (SPX) Mar 28, 2024






In groundbreaking research published in Nano Energy, a team led by Prof. CHEN Chong at the Hefei Institutes of Physical Science, part of the Chinese Academy of Sciences, has significantly improved the performance of perovskite solar cells (PSCs). By integrating inorganic nano-material tin sulfoxide (SnSO) as a dopant, they have boosted the photoelectric conversion efficiency (PCE) of PSCs to an impressive 24.5%.

Traditional methods of enhancing the charge transport in the critical hole transport layer (HTL) of PSCs involve the use of lithium trifluoromethanesulfonyl imide (Li-TFSI) to facilitate the oxidation of the HTL material spiro-OMeTAD. However, this method suffers from low doping efficiency and can leave excess Li-TFSI in the spiro-OMeTAD film, reducing its compactness and long-term conductivity. Additionally, the oxidation process typically requires 10-24 hours to achieve the desired electrical conductivity and work function.



The HFIPS team’s innovation lies in their development of a rapid and replicable method to control the oxidation of nanomaterials, using SnSO nanomaterial to pre-oxidize spiro-OMeTAD in precursor solutions. This novel approach not only enhances conductivity but also optimizes the energy level position of the HTL, culminating in a high PCE of 24.5%.



One of the key advantages of the SnSO-regulated spiro-OMeTAD HTL is its pinhole-free, uniform, and smooth morphology, which maintains its performance and physical integrity even under challenging conditions of high temperature and humidity. Additionally, the oxidation process facilitated by this method is significantly faster, taking only a few hours- a crucial factor in improving the commercial production efficiency of PSCs.



Prof. CHEN Chong highlighted the importance of this breakthrough, stating, “Also, the oxidation process only takes a few hours, which is good for improving the commercial preparation efficiency of PSCs.” This advancement not only marks a significant leap in the efficiency and stability of PSCs but also holds substantial implications for their commercial viability.



Research Report:A nanomaterial-regulated oxidation of hole transporting layer for highly stable and efficient perovskite solar cells


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Revolutionary technique boosts flexible solar cell efficiency to record high

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Revolutionary technique boosts flexible solar cell efficiency to record high


Revolutionary technique boosts flexible solar cell efficiency to record high

by Simon Mansfield

Sydney, Australia (SPX) Mar 28, 2024






Researchers at Tsinghua University have made a significant breakthrough in the efficiency of flexible solar cells, leveraging a novel fabrication technique to set a new efficiency record. This advancement addresses the longstanding challenge of the lower energy conversion efficiency in flexible solar cells compared to their rigid counterparts, offering promising implications for aerospace and flexible electronics applications.

Flexible perovskite solar cells (FPSCs), despite their potential, have historically lagged in efficiency due to the polyethylene terephthalate (PET)-based flexible substrate’s inherent softness and inhomogeneity. This limitation, coupled with durability issues arising from the substrate’s susceptibility to water and oxygen infiltration, has hindered the practical deployment of FPSCs.



The team from the State Key Laboratory of Power System Operation and Control at Tsinghua University, alongside collaborators from the Center for Excellence in Nanoscience at the National Center for Nanoscience and Technology in Beijing, introduced a chemical bath deposition (CBD) technique. This method facilitates the deposition of tin oxide (SnO2) on flexible substrates without the need for strong acids, which are detrimental to such substrates. Tin oxide is essential for the FPSCs as it acts as an electron transport layer, crucial for the cells’ power conversion efficiency.



Associate Professor Chenyi Yi, a senior author of the study, explained, “Our method utilizes SnSO4 tin sulfate instead of SnCl2 tin chloride, making it suitable for acid-sensitive flexible substrates. This approach not only enhances the efficiency of FPSCs but also their durability, with a new power conversion efficiency benchmark set at 25.09%, certified at 24.90%.”



The novel fabrication technique also contributes to the FPSCs’ stability, as demonstrated by the cells maintaining 90% of their initial efficiency after being bent 10,000 times. The researchers noted an improved high-temperature stability in SnSO4-based FPSCs over those made with SnCl2, pointing towards the dual benefits of efficiency and durability enhancements.



The research signifies a leap towards industrial-scale production of high-efficiency FPSCs, with potential applications ranging from wearable technology and portable electronics to aerospace power sources and large-scale renewable energy solutions. The team’s findings, supported by Ningyu Ren, Liguo Tan, Minghao Li, Junjie Zhou, Yiran Ye, Boxin Jiao, and Liming Ding, mark a pivotal step in transitioning FPSCs from laboratory to commercial use.



Research Report:25% – Efficiency flexible perovskite solar cells via controllable growth of SnO2


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KAUST advances in perovskite-silicon tandem cells

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KAUST advances in perovskite-silicon tandem cells


KAUST advances in perovskite-silicon tandem cells

by Sophie Jenkins

London, UK (SPX) Mar 28, 2024






In 2009, researchers introduced perovskite-based solar cells, highlighting the potential of methylammonium lead bromide and methylammonium lead iodide-known as lead halide perovskites-for photovoltaic research. These materials, notable for their excellent light-absorbing properties, marked the beginning of an innovative direction in solar energy generation. Since then, the efficiency of perovskite solar cells has significantly increased, indicating a future where they are used alongside traditional silicon in solar panels.

Erkan Aydin, Stefaan De Wolf, and their team at King Abdullah University of Science and Technology (KAUST) have explored how this tandem technology could transition from experimental stages to commercial production. Perovskites are lauded for their low-temperature production process and their flexibility in application, offering a lighter, more adaptable, and potentially cost-effective alternative to silicon-based panels.



Combining perovskite with silicon in a single solar cell leverages the strengths of both materials, enhancing sunlight utilization and reducing losses that aren’t converted into electrical energy. “The synergy between perovskite and silicon technologies in tandem cells captures a broader spectrum of sunlight, minimizing energy loss and significantly boosting efficiency,” Aydin notes.



However, Aydin and his colleagues acknowledge challenges in scaling tandem solar-cell fabrication for the marketplace. For instance, the process of depositing perovskite on silicon surfaces is complicated by the silicon’s texture. Traditional laboratory methods like spin coating are not feasible for large-scale production due to their inefficiency and material wastage. Alternatives such as slot-die coating and physical vapor deposition present their own set of advantages and challenges.



Moreover, the durability of perovskite components under environmental stressors such as moisture, heat, and light remains a critical concern. Aydin emphasizes the need for focused research to enhance the reliability and lifespan of perovskite/silicon tandem cells, especially in harsh conditions.



Although tandem modules have already been demonstrated in proof-of-concept stages, the timeline for their market readiness is uncertain. Nonetheless, the successful development of efficient, commercial-grade perovskite/silicon solar cells is essential for meeting global energy demands sustainably.



Research Report:Pathways toward commercial perovskite/silicon tandem photovoltaics


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