The team from Fuzhou Normal University reviewed the perovskite crosslinking strategy and provided guidance for solving the problem of cell stability

In recent years, with the strong rise of organic-inorganic hybrid perovskite photovoltaic technology, perovskite photovoltaic cells have become the most favored thin-film cells in academia and industry among the new generation of solution-processable photovoltaic cells.

Compared with traditional photovoltaic cells such as crystalline silicon cells or thin-film cells represented by copper indium gallium selenide, perovskite cells have low preparation costs, short industrial chains, easy availability of raw materials, and higher theoretical photoelectric conversion efficiency.

In addition, the perovskite material system has a larger space for scientific research and exploration due to its strong light absorption ability, easily adjustable photoelectric performance and strong defect tolerance, and it is precisely because of this that the efficiency iteration speed of perovskite cells has been the most significant in the past decade.

However, despite the advantages of high efficiency and low cost, the stability problem of perovskite cells has not been fundamentally solved, which also seriously restricts its commercialization process.

The instability of perovskite cells mainly comes from two aspects:

First, the perovskite material itself has the property of "soft lattice", which leads to its easy dissociation and degradation under external stimuli such as light, electricity, and heat;

Second, perovskite often forms more surface defects after film formation, which reduces the interfacial contact between perovskite and adjacent auxiliary functional layers, thus affecting the long-term working stability of the device.

In recent years, researchers have been seeking simple and efficient perovskite stabilization strategies, from chemical molecule design to material performance control, to device physical analysis and preparation process exploration, many methods to improve the stability of perovskite cells have been continuously reported.

Among them, the research group of Professor Wang Yang of Fujian Normal University noticed that the crosslinking strategy has been adopted by many teams in recent years, whether it is in the form of additive control, interface modification engineering, charge transport layer construction and packaging material selection, etc., which have significantly improved the wet/thermal stability and working stability of perovskite cells.

图 | 王漾（来源：王漾）

A crosslinkable material is a compound that can undergo a chemical reaction under specific conditions to form covalent bonds, or to form a three-dimensional network structure through interactions between molecules.

Cross-linked materials generally have excellent light/heat stability and good resistance to solvents. In fact, the crosslinking strategy has long been applied to the field of organic optoelectronic devices, such as organic light-emitting diodes and organic solar cells [1]. It is worth noting that the crosslinking strategy also has great potential to improve the efficiency and stability of perovskite cells, especially flexible large-area modules.

Therefore, in order to explore more cutting-edge research directions in the field of perovskite cells, and also to provide design ideas and guiding ideas for solving the stability problem of perovskite cells, the team summarized the work of predecessors in a timely manner, and put forward some views and insights based on the research work of this research group, so as to write a review paper.

日前，相关论文以《用于高效高稳定钙钛矿太阳能电池的交联策略》（Cross-linking strategies for efficient and highly stable perovskite solar cells）为题发在 Journal of Materials Chemistry C[2]，福建师范大学博士生王旭冉是第一作者，王漾教授和中国科学院院士黄维担任共同通讯作者。

图 | 相关论文（来源：Journal of Materials Chemistry Cm）

As mentioned above, this review paper mainly focuses on the application of crosslinking strategies in perovskite cells.

First, they analyzed several instability factors in perovskite cells, such as the instability of perovskite structure, humidity, heating, and light.

Then, they introduced the application value of the crosslinking strategy, including its definition, characteristics, and the structure and properties of the materials involved, as well as the reaction mechanism and processing methods.

Then, according to the specific application scenarios of the cross-linking strategy, the following aspects are discussed in detail:

The first aspect is that cross-linked molecules are used as additives, which can be applied to the perovskite active layer;

The second aspect is that the cross-linked molecule is used as a modification layer, which can improve the surface interface properties of perovskite.

The third aspect is the design and construction of cross-linked hole transport materials and electron transport materials.

The fourth aspect is the application of cross-linked molecules as encapsulation materials in perovskite cells.

Finally, they summarized the shortcomings of the crosslinking strategy in practical application and proposed the future development direction.

For example, further optimizing the properties of cross-linked materials, controlling the optoelectronic properties of materials through functional design, developing high-efficiency and stable charge transport materials that are in short supply, and synergistically using cross-linking strategies such as reasonably constructing cross-linked interface locks, etc., can help people achieve high-stability perovskite cell modules.

In order to systematically discuss the application of crosslinking strategies in perovskite cells, the research group spent a lot of time in literature collection, research, discussion, and writing.

Wang Yang said: "I would also like to thank my first PhD student, Xuran Wang, and my first master's students, Ziwu Ding, Xingyu Liu, and Zhenzhen Huang. ”

In fact, while the review paper was still under review, the Fudan University team and the Institute of Chemistry of the Chinese Academy of Sciences had already published a review paper on a similar topic in top international journals [3,4].

This shows that scholars in the field generally recognize and have high hopes for the application potential of crosslinking strategy in stabilizing perovskite cells.

It is also reported that Wang Yang's research group has long been engaged in the research of new organic conjugated molecule design, synthesis of optoelectronic functional materials and device application.

In the near future and in the next few years, their research focus will focus on the design and development of key organic functional materials in flexible large-area perovskite cells.

In order to promote the industrialization process of photovoltaic technology, the past achievements of the research group have always reflected the guiding ideology of "high performance, low cost and high stability". Their main representative achievements in the past can be summarized in the following three aspects:

First, they have proposed molecular integration design strategies and dendritic engineering strategies, developed high-performance organic interface materials, and set a record for the highest energy conversion efficiency of trans-perovskite cells in the same period, and related papers were published in Advanced Materials and Science China Chemistry.

Second, they developed high-performance, low-cost organic interfacial materials using anchor group assisted strategies and fluorination strategies, and enhanced the green solvent processing characteristics and universal application value of the materials, which were published in Nature Energy and the Journal of the American Chemical Society.

Third, they used the cross-linking design strategy to develop organic interface materials with high performance, low cost, and high stability, and achieved high efficiency and stability of perovskite photovoltaic cells, which were published in Advanced Materials.

It is also reported that before joining Fujian Normal University, Wang Yang did postdoctoral research in Taiwan, China. He said that during his Ph.D., he was mainly engaged in the research and development of light-emitting materials in organic light-emitting diodes.

After coming to Tsinghua University in Taiwan, he began to study charge transport materials in perovskite cells with Ji Yun, an academician of the Asia-Pacific Academy of Materials Sciences and a distinguished chair professor in Taiwan, which is equivalent to shifting from electroluminescence to photovoltaic power generation.

Although there are some changes in the direction, the core of the research is still the design and synthesis of organic semiconductor materials, but the application side is different.

Fortunately, Wang Yang paid more attention to the different optoelectronic properties of organic semiconductor materials and their device applications during his Ph.D., so the direction change in the postdoctoral stage did not cause him great trouble, but on the contrary, it aroused his research interest in the field of organic optoelectronic functional materials.

He said: "At that time, it was the initial stage of the rise of perovskite cell research, and I was able to catch the early train in this research field. Of course, I was fortunate enough to publish my first paper with an impact factor greater than 20 in Advanced Energy Materials during my time in Taiwan. ”

He continued, thanks to the accumulation of work as a postdoctoral fellow in Taiwan, China, and then when he went to Southern University of Science and Technology as a postdoctoral fellow, he was able to expand and extend the relevant work with ease, and began to make some breakthroughs in the field.

The Strait School of Flexible Electronics (Future Technology) of Fujian Normal University, where he currently works, was established in July 2021 and is also the co-construction platform of the Strait Innovation Laboratory, the fourth provincial laboratory in Fujian Province, led by Academician Huang Wei.

At the beginning of 2022, Wang Yang joined Fujian Normal University. He said that although he has not been on the job for a long time, he has received strong support from schools and colleges.

At present, he has a 200-square-meter laboratory, sufficient research funds, 2-4 master's students per year, and assists Academician Huang Wei to supervise 2 doctoral students, and recently the team has also introduced 1 "young talent" associate professor.

"Fujian Normal University is a century-old provincial institution of higher learning, with 21 doctoral degrees in chemistry, physics, optical engineering, etc., and Fuzhou is indeed a good place to settle down with a pleasant climate," he said. We sincerely welcome students who have a strong interest in scientific research, are diligent and practical, and have good team spirit to join our team ([email protected]). ”

Resources:

1. J. Mater. Chem. A, 2022, 10, 18542

2. Wang, Y., Wang, X., Ding, Z., Wang, Y., & Huang, W. (2023). Cross-linking strategies for efficient and highly stable perovskite solar cells. Journal of Materials Chemistry C.

3. Small, 2023, 19, 2304189

4. Energy Environ. Sci., 2023, 16, 4251

Website: https://sife.fjnu.edu.cn/main.htm

Webpage: https://www.x-mol.com/groups/steven_wangyang

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