Aging process and solution of perovskite solution revealed by Qingdao Energy Institute

[ Instrument Network Instrument R & D ] In the past ten years, perovskite solar cell technology has developed rapidly, and its latest certified photoelectric conversion efficiency is as high as 25.2%. The efficiency of perovskite solar cells depends to a large extent on the crystalline quality of the perovskite photoactive layer, which is also the first issue to be considered in the preparation of perovskite films by the solution method.

Before the perovskite thin film is prepared by the solution method, a certain temperature and stirring are required to ensure that the precursor is fully dissolved. This process may be longer in the future industrial production process. Therefore, the composition of the perovskite precursor solution needs to be kept stable. For methylamine lead iodine single system, as long as the solution system is sufficiently sealed, the material itself is still very stable. However, when methylamine and formamidine coexist in the solution system, the decay of the solution is particularly obvious, resulting in the need to configure a fresh solution before each device, which not only brings tediousness to the device research work, but also It brings great uncontrollability, and has become an important obstacle to restrict the development of perovskite devices.

In response to this problem, Cui Guanglei and Qi Shuping, researchers at the Qingdao Institute of Bioenergy and Process Research, Chinese Academy of Sciences, have recently conducted in-depth research on the aging process of perovskite precursor solutions. The researchers found that significant side reactions occurred in the mixed organic cationic perovskite solution of methylamine ions and formazan ions, and found solutions to suppress these side reactions, which proved to improve the stability of the perovskite precursor solution It is the key to further improve the photoelectric efficiency of the battery and enhance the repeatability of the device. The research results were published in Chem.

Researchers used NMR technology to track the composition changes of the solution aging process, and found that with time, the components of methyl iodide and formamidine iodide in the perovskite solution gradually decreased, and some new compounds appeared. It was previously undiscovered. They finally determined the structure of the side reaction product and revealed the reaction mechanism. In fact, it was an addition-elimination reaction with methyl iodide after deprotonation of methyl iodide. In order to further confirm the accuracy of the conclusion, they synthesized this kind of substance by chemical means, which has the same nuclear magnetic signal.

The purpose of finding the problem was to solve this problem, the researchers then introduced triethyl borate into the solution, and used the empty orbital of boron to interact with the iodide ion of methylamine iodide to limit its deprotonation, thereby effectively limiting Further addition-elimination reaction with formazan iodide has achieved the purpose of improving the stability of the perovskite precursor solution. Triethyl borate is a commonly used low boiling point solvent. It can be completely evaporated during the subsequent heating of the film and will not remain in the perovskite film. This is particularly important for the preparation of high-quality perovskite films.

In addition, the researchers also studied other possible side reactions, such as the previously reported solvolysis to form dimethylamine, but such reactions usually occur at very high temperatures. In the conventional process of preparing perovskite films, side reactions between methylamine and formazan are predominant, which also explains why it is difficult to completely eliminate the heterogeneous phase in the methylamine formazan composite perovskite films.

The research was supported by the Shandong Talent Project, the Provincial Outstanding Youth Fund, the Innovation Research Institute Cooperation Fund, and the National Outstanding Youth Fund.