Perovskite is no longer afraid of humidity! The photoelectric conversion efficiency reached 24.1%! On March 26, the top international journal Science published an important study, Huang Wei, academician of the Chinese Academy of Sciences, and the team of Professor Chen Yonghua from the Institute of Advanced Materials of Nanjing University of Technology Pioneeringly proposed to use a multifunctional "ionic liquid" as a solvent to replace traditional organic solvents to prepare perovskite photovoltaic materials, and achieve the stability of black phase formamidine lead iodide perovskite at room temperature and high humidity , which solves the worldwide problem in the preparation process of traditional perovskite photovoltaic materials.
The ionic liquid developed by the research team, courtesy of Professor Chen Yonghua
Renew the solvent system, the perovskite material "breathes freely" in the air
Compared with traditional monocrystalline silicon cells, perovskite photovoltaic materials have become a research hotspot due to their advantages of lightness, thinness, low cost, environmental protection, and flexibility. Traditionally, perovskite photovoltaic materials are afraid of water and air, especially perovskite photovoltaic materials represented by formamidine-based perovskite are very "sensitive", prone to aging and functional degradation. Therefore, it can be prepared under the protection of inert gas.
At the same time, within the current scope of cognition, only no more than 5 solvents can be applied to perovskite materials. So many "pain points" make it difficult to expand the application of perovskite.
"Since the whole world is doing research in this area, we will do something different." Professor Chen Yonghua of Nanjing University of Technology believes that if we continue to do research in the traditional solvent system, there will always be a feeling of "tickling the boots". .
"Why not boldly imagine that 'perovskite can also be prepared in a high-humidity air environment'?" Everyone did what they said. Soon, the team focused on finding an environment-friendly, stable, and compatible solvent with physical and chemical properties.
In 2017, the team discovered a green proton-type ionic liquid, which was introduced into the preparation process due to the particularity of its functional group.
"The unique anion and cation structure of the ionic liquid can form a huge hydrogen bond network in the solution. At the same time, the organic anion and the metal halide form a chelate to adjust the properties of the precursor solution. Its unique chemical action can effectively control the crystallization kinetics process of the perovskite , so as to grow a high-quality perovskite film." said Luhui, the co-first author of the paper.
Based on the characteristics of ionic liquids, the research team constructed a highly efficient and stable layered perovskite solar cell in 2020, with a photoelectric conversion efficiency of 18.06%, breaking the record efficiency at the time.
Constructing a "fast track" of reaction, greatly improving the photoelectric conversion rate
Formamidine-based perovskite is considered to be the most promising material closest to the theoretical limit efficiency due to its excellent properties. However, its stability is poor and it is easily decomposed under high humidity conditions.
During the interview, Chen Yonghua drew a picture for reporters, a perovskite film made of formamidine-based perovskite material, the upper half of which is iodoformamidine and the lower half of lead iodide.
Chen Yonghua explained: "The key to achieving the stability of the formamidine-based perovskite is how to provide a strong lead iodide structure. The first step for a strong lead iodide structure is to prepare a stable lead iodide solution. "
Starting from the structure design and preparation of the multifunctional ionic liquid solvent, the research team found that the carbonyl group of the ionic liquid methylamine format can chelate with the lead in lead iodide, and the amine group forms a hydrogen bond with iodine.
"We are also delighted to find that during the process of forming the lead iodide film, this interaction pulls the lead iodide crystals into a regular arrangement, forming a series of nano-scale'ion channels' and vertically grown lead iodide crystal structures. These channels promote the penetration of iodoformamidine into the lead iodide film, which is quickly and robustly converted into a formamidine-based perovskite film." Chen Yonghua introduced.
The experimental results show that the device prepared by ionic liquid methylamine format as the solvent of the perovskite precursor finally achieved a photoelectric conversion efficiency as high as 24.1%, and the unencapsulated device was maintained under continuous heating and continuous light at 85°C. 80% and 90% of its initial efficiency reaches 500 hours.
Being green, non-toxic, stable and efficient, and low cost, such achievements created the prerequisites for the large-scale production and utilization of perovskite solar cells. However, Chen Yonghua held a perovskite solar cell with a size of 0.1 square centimeters. "The new abacus", he said: "In the next 5 years, we will be committed to achieving the enlargement from 0.1 square meter to 100 square centimeters, and truly realize the large-scale industrial application of perovskite batteries."