Two 1993 PhD directors teamed up to release Nature! His school has produced more than 40 young professors, including Wang Rui, Xue Jingjing, and Nature

Article | Reporter Han Yangmei and Li Chenyang from China Science Daily

In 2021, 28 year old Wang Rui and 27 year old Xue Jingjing returned to China after completing their studies and became the youngest doctoral supervisors at West Lake University and Zhejiang University, respectively. Not long ago, these two independent PIs, both born in 1993, jointly published papers in the journal Nature as co corresponding authors.

Screenshot of the paper

Upon closer examination of their resumes, one can discover more similarities in their academic experiences:

They have all studied at the University of California, Los Angeles and are doctoral students of the same level under Professor Yang Yang. The 2021 Forbes China 30Under30 list was released, and both individuals were included in the Science and Healthcare 30 list. In addition, they also made it to the MIT Technology Review Global "35 Technology Innovators Under 35" and Asia Pacific "35 Technology Innovators Under 35" rankings in 2022.

Wang Rui

When Xue Jingjing was in Professor Yang's laboratory, Wang Rui and Xue Jingjing had already become good research partners and had collaborated to publish two papers in Science. The recently released paper in Nature is the third top published paper jointly completed by the two, and it is also the first "double sword fusion" between the two after returning to China to become independent PI.

Even Yang Yang couldn't help but exclaim that it was not easy for work in the field of engineering to be published in main journals such as Nature and Science, but these two young people, when working together, were able to achieve "time and time again, time and time again.".

In fact, the Yang Yang research group has always been known for its high success rate. At present, this research group has trained at least 40 young professors, many of whom have returned to China for work.

Complementary expertise, jointly exploring the field of "perovskite"

The three top tier papers jointly published by Wang Rui and Xue Jingjing focus on the field of perovskite solar cells.

The famous work published in Science in 2019 was very impressive. They designed three similar alkaloids for perovskite solar cells: caffeine, theophylline, and theobromine to study their mechanisms for repairing surface defects in perovskite.

A collaborative paper on Science published by two individuals in 2019

Wang Rui once recalled in a media interview, "This idea first started with a joke while drinking coffee. One day, while we were discussing perovskite solar cells, we joked that if we needed coffee to replenish energy, what about perovskite? Do they need coffee to improve performance?" Later, they discovered the role of caffeine in enhancing perovskite solar cells. Later, they further collaborated and discovered through molecular structure optimization that theophylline could achieve superior battery performance.

Looking back now, this seemingly nonsensical joke not only opened up a meaningful research project, but also gave this young scientist duo a good start on their collaborative journey.

In 2021, another work they collaborated on was published again in Science.

A collaborative paper on Science published by two individuals in 2021

This time, they introduced organic conjugated cations to reconstruct the energy band edges and designed an organic ammonium containing pyrene, which once again improved the efficiency and stability of perovskite batteries.

This study, recently published in Nature, alters the "embryonic" structure of perovskite solar cells - by adding an additive called "pentamidine", a new method of oriented nucleation of lead iodide perovskite has been discovered, which can improve the overall crystallinity, photoelectric efficiency, and stability, and is applicable to all preparation methods and any size of perovskite solar cells.

Xue Jingjing told China Science Daily, "Although we are studying in the same research group, Wang Rui and I have different research focuses. My research direction focuses on fundamental research on analytical mechanisms, while Wang Rui is better at preparing devices and implementing an idea into a product. This complementary research direction has enabled us to maintain close cooperation in the United States."

Fortunately, the two returned to China and respectively joined West Lake University and Zhejiang University. Both universities are located in Hangzhou and are also very close, which allows their cooperation to continue more smoothly.

The first author of this Nature paper, Shi Pengju, is a doctoral student jointly trained by Wang Rui's research group and Xue Jingjing's research group.

0.18 second "capture"

Perovskite solar cells are a major category of third-generation solar cells, which have become a hot topic pursued by academia and industry due to their advantages such as light weight, high efficiency, and low preparation costs. Among them, FAPbI3 is considered one of the hopes of the perovskite material family - the most likely to achieve high photoelectric conversion efficiency.

However, the tricky aspect is that FAPbI3 can be divided into black phase FAPbI3 with photoactivity and other crystalline phases such as yellow that do not possess photoactivity. Scientists generally believe that "black phase" means that the perovskite crystal structure is more complete and ordered, allowing charge carriers to flow smoothly.

However, during the crystallization process, the black phase FAPbI3 does not have thermodynamic advantages, so a large amount of impurities from other crystal phases will always be generated, resulting in material performance loss.

In Wang Rui's view, although they have conducted many research works in the field of perovskite in the past, most of these studies have focused on "surface issues", namely interface research, and have rarely truly explored the "innermost" mechanism of perovskite batteries - the crystallization process.

It should be noted that the crystallization process of perovskite is very fast and can be completed in a few seconds or more, and nucleation is the first step of crystallization, equivalent to the "embryonic stage". Understanding the mechanism of nucleation process is of great significance for improving battery efficiency and stability. However, due to the lack of research methods, they have not been able to officially carry out related work before.

"Our original intention and greatest motivation for this work is to make every effort to see what exactly happened in the first few seconds of crystallization," said Xue Jingjing.

As early as 2019, when Wang Rui and Xue Jingjing were still pursuing their PhD in the United States, they noticed a substance called "oil ammonium iodine" that could help crystals grow better. From a molecular structure perspective, "ammonium iodide" has a "long tail" - an "alkyl chain.". The research team speculates that this tail may be the key factor affecting crystal growth.

After returning to China, the team prepared and synthesized three organic molecules with the same "alkyl chain" - propamidine, butymidine, and pentamidine - which were added to the growth process of FAPbI3 crystals. It was found that adding pentamidine with the longest alkyl chain resulted in the formation of a "pure black phase" FAPbI3 at room temperature.

How did this process occur? To analyze the mechanism, it is necessary to use some advanced equipment.

They learned that Dr. Carolin Sutter Fella's team at Lawrence Berkeley Laboratory has two instruments - fluorescence in situ synchrotron radiation and X-ray diffraction of in situ synchrotron radiation. These two instruments were commonly used in the past to characterize and test the crystallization process of polymers, which excited Wang Rui and Xue Jingjing, and their collaboration was immediate.

The research team fully utilized various experimental observation methods such as X-ray diffraction, Fourier transform spectroscopy, in situ photoluminescence measurement, and conductive atomic force microscopy to capture and measure at a frequency of 0.18 seconds per measurement, which is close to the pause time of human vision.

Through in-situ characterization, researchers captured all the information about FAPbI3 from the moment of nucleation to the gradual growth of the crystal, and understood the principle and mechanism of the nucleation process.

The Bole research group is known for its high success rate

On the path of Wang Rui and Xue Jingjing's success, mentor Yang Yang played a crucial role.

The Yangyang research group has always been known for its high yield. At present, at least 40 young professors have been trained. Zhou Huanping, a professor of Peking University, Chen Qi, a professor of Beijing Institute of Technology, You Jingbi, a researcher of the Institute of Semiconductor Research of the Chinese Academy of Sciences, Yang Yang, a professor of Zhejiang University, Huang Jinsong, a professor of the University of North Carolina at Chapel Hill, Li Gang, a professor of Hong Kong Polytechnic University, Dou Letian, a professor of Purdue University, Yao Yan, a professor of the University of Houston, etc. are all from this research group.

Yang Yang summarized his approach to education as: establishing mutual trust between teachers and students; Identify the special talents of students; Encourage students to undertake challenging projects; Outline a beautiful blueprint for their future; Unleash their potential.

He said, "When we cultivate students as talents and stimulate their inner potential, students are likely to become thousands of miles away in the future; when we manipulate students as labor force, they will become labor force in the future."

Wang Rui said that Professor Yang Yang always treats doctoral students as postdoctoral students and postdoctoral students as professors, encouraging them to actively communicate with collaborators and participate in all scientific research processes, from the generation of ideas to submission and review, supervisor supervision, and student leadership. This made him familiar with any details when he later became the head of an independent research group.

In addition to specific scientific research work, what benefited Wang Rui more was his mentor's guidance on his conduct and knowledge. "He subtly influenced my research taste and wanted to do research that others had not studied before, not follow the trend. He told us that data must withstand scrutiny, and everything given to readers must be solid." In Wang Rui's view, joining the Yangyang research group was a turning point in his growth.

When Xue Jingjing first joined the team, Yang Yang's words have been unforgettable to her ever since, "You must go as deep as you can.". Xue Jingjing said that this is a training for problem-solving. "When facing a problem, it's not just about staying on the surface. You keep asking yourself why, until your mentor can't answer it, the textbook can't answer it, or you can't answer it even after consulting all the literature. This indicates that you think deeply enough, and often this point may not be well researched in the field."

Xue Jingjing said that it was the good atmosphere of the mentor team that facilitated her cooperation with Wang Rui. "What we want to research, who we want to collaborate with, and so on, the mentor gave us enough freedom."

This is the secret behind the collaboration of "golden partners".