Perovskite solar cells have become a research hotspot in photovoltaic field due to their low cost and high conversion efficiency. However, its stability, large area manufacturing, efficiency conversion and other challenges are also the problems that domestic researchers must face.

Like most people, you Jingbi, a researcher at the Institute of Semiconductors at the Chinese Academy of Sciences, now works from home at a critical stage in the fight against COVID-19. "I didn't have time to sit down and take a good look at students' experiments, progress and reports. Now I can focus on new things and open up some new ideas."

Two years ago, You Jingbi's team successfully achieved China's world record in perovskite battery conversion efficiency.

Recently, advanced materials research institute of nanjing university of technology professor Chen yunhua and member of Chinese Academy of Sciences, northwestern polytechnical university professor stevie hoang, such as a number of partners, develop highly efficient and stable two-dimensional layered perovskite solar cells, and the relevant papers published in nature photonics, become ionic liquids used in another breakthrough in the field of perovskite.

In cooperation with Gong Qihuang and Huang Wei, academicians of The Chinese Academy of Sciences, Zhu Rui, a researcher from the School of Physics of Peking University, took the lead in the study on the stability of mixed cationic perovskite solar cells in adjacent space in China. The study was published as the cover article in the English edition of Chinese Science: Physics, Mechanics and Astronomy.

You jingbi is eager for them to start some more meaningful work as soon as possible.

Challenge 1: No application without stability

"There is no application without stability, and the main bottleneck for application is stability." You Jingbi told China Science Daily that although the stability of perovskite solar cells has been greatly improved, it is still a long way to go before they can fully meet the requirements of industrialization.

"To be industrialized, service life is important. The silicon battery life requirement is 25 years, perovskite battery life is still far away, we are also moving towards stability. Chen agreed on the importance of stability.

Silicon is an element found naturally in sand and stone, and because it's been around for hundreds of millions of years, silicon cells are remarkably stable. However, it has high energy consumption, serious environmental pollution and high cost in preparation.

The advantage of perovskite cells is that they can be prepared by solution method, such as inkjet printing, roll-to-roll printing, screen printing, etc., which greatly reduces the cost. If the silicon cells were replaced by perovskite cells, electricity would be cheap.

Chen yonghua said that stability studies have so far focused on the passivation of perovskite films and that innovative breakthroughs have yet to be made. In his view, in addition to the perovskite active layer itself, the design of other functional layers and the packaging technology of devices also need the integrated design of the whole chain, which requires the integration of resources and teams to concentrate on big things.

"Around 2016, stability was considered to be a serious problem, but with unremitting efforts and exploration in recent years, a lot of results have emerged, and the stability of devices has improved significantly." With enough time and commitment, He believes, stability is no longer a problem to solve.

Challenge 2: Large-area manufacturing, photoelectric conversion efficiency

As a new star in the field of photovoltaic, the commercialization process of perovskite solar cells is constantly advancing. Zhu Rui introduced that domestic companies, such as Suzhou GEXin Nano, Hubei Wandu Solar, Hangzhou Jinna, etc., are all focused on product-oriented RESEARCH and development exploration, especially in large area technology, stability, efficiency and other aspects.

"The large area is mainly a process problem, combined with the innovative results of basic research, led by photovoltaic enterprises, can significantly speed up the process of large-scale." You Jing Bi said. But he also pointed out that because the laboratory is currently doing small areas, and industrialization must develop to large modules, large-scale manufacturing has become another bottleneck restricting the industrialization of perovskite cells.

In addition to key issues such as battery stability and large area preparation, further improvements in battery efficiency are needed, you said. However, based on the current perovskite material system, there are many obstacles for further improvement of cell efficiency.

As for the problem between photoelectric conversion efficiency and large area preparation, Chen yonghua says his lab has done just one square centimeter. If the area is enlarged, the film process changes and many defects will occur, and the benefit and stability will also be reduced.

"Because of the excellent photoelectric conversion efficiency of perovskite under low light, indoor power supply application is also a major advantage of perovskite PHOTOVOLTAIC compared with traditional silicon-based cells, which can make use of indoor lighting and weak sunlight." Chen Yonghua believes that perovskite photovoltaic materials have irreplaceable advantages in flexible electronic energy supply in the future due to their characteristics of light, thin, soft and transparent.

He told China Science Daily that forming a laminated cell with a conventional silicon cell is expected to significantly improve the efficiency of the cell, which is currently 29.1 percent based on perovskite/silicon in the world. The industry believes that with the development of new thin film deposition technology, a large area perovskite cell module with higher conversion efficiency is just around the corner.

Integration with silicon cells is the direction

Referring to the future direction of perovskite solar cells, Zhu said the prevailing view now is that there are two ways to go. One is silicon, but the market is already so big that it may not be easy. The second is the combination with silicon cells, which may be an important development direction in the future.

Perovskite cells can improve the conversion efficiency of silicon cells by 26% to more than 30%, which has a great influence on the huge domestic photovoltaic market. Therefore, some silicon-based photovoltaic enterprises in China have also begun to advance the layout of perovskite photovoltaic direction.

Perovskite solar cells can be divided into formal and trans-device structures. Zhu's team has been working on trans-structures and made a breakthrough two years ago, when the results were published in Science. They set a record for the efficiency of this type of solar cell device, with a photoelectric efficiency of 20.9 percent.

A major advantage of the trans device is that it can be better integrated with silicon cells and can be made on silicon surfaces, enabling the entire device to achieve photoelectric conversion efficiencies of more than 30 percent, According to Zhu.

Zhu Rui also described a development prospect in the exploration for reporters -- perovskite solar cells have advantages such as low cost, flexible preparation, high energy to mass ratio, excellent radiation resistance performance, etc., and give full play to their advantages in adjacent space (airspace 20~100 kilometers above the ground) to provide energy supply for adjacent space aircraft. This could be an important way forward.

You jingbi pays more attention to the improvement of device performance, especially the improvement of photoelectric conversion efficiency. You jingbi said his team will continue to maintain its advantages in photoelectric conversion efficiency. The current world record of 25.2% conversion efficiency is set by South Korea. They will strive to develop new preparation technologies that will bring the efficiency of the battery to a better international level. In addition, the stability of the device and the preparation of large area batteries will be studied.

"Through the development of ionic liquid perovskite photovoltaic technology, our team has made great progress in stability and gradually achieved a higher level of efficiency by eliminating traditional highly toxic and unstable polar aprotic solvents. In addition, we are also working on a large area of craftsmanship that will hopefully give the industry some ideas and insights." Chen Yonghua said.