The upper interface of perovskites , whether trans or formal. But as a thin film, there must be two interfaces, upper and lower. Since there are many problems in the upper interface that need to be solved, will there be similar or new problems in the lower interface that need to be paid attention to? In fact, the study of the lower interface is relatively difficult. As the buried interface of the device, it is difficult to be completely peeled off, which increases the difficulty of characterization. On August 19, 2021, Science published a paper online. The author found some reasons for limiting the performance of the device through the study of the lower interface of the trans device, and then optimized it accordingly.
By SEM characterization of the exposed perovskite lower interface, the author found that when the MA0.6FA0.4PbI3 film is deposited with 2ME-DMSO solvent, some holes will be generated in the lower interface, and the number of holes is related to the shape and the relative content of DMSO. : When the DMSO content is less than 13% or greater than 38%, there are many holes in the lower interface, and when the DMSO content is 25% and 38%, the number of holes is relatively small, but they still exist.
The authors speculate that when the DMSO content is low, the crystallization rate of the film is too fast, which leads to the generation of holes. When the DMSO content is too high, since the crystallization direction of the film is from top to bottom, the volatilization of DMSO will be delayed, resulting in about 2% DMSO remaining at the bottom of the perovskite, resulting in holes. Such a phenomenon exists in perovskites of different systems.
The degeneration of the area with holes is more obvious under the light, and some white substances will be produced around it, which is the non-conductive product of perovskite degradation. This exacerbates the degradation process of the device under operating conditions.
Based on this, the author replaced part of DMSO with solid carbohydrazide (CBH), which can still form coordination with Pb to delay crystallization, but due to its low volatility, it will not cause the volume shrinkage of the film, thus also The formation of holes in the lower interface is avoided.
In addition, CBH, as a reducing agent, can also effectively inhibit the formation of iodine in the film, thereby further improving the stability of the film.
In terms of stability, the small-area device has basically no efficiency attenuation (60 ℃) after 550 hours of operation at the maximum power point, and the module can maintain 85% of the initial efficiency after 1000 hours of light.
To sum up this article, the author improves the efficiency and stability of the device by solving the hole problem of the lower interface in the trans device, so that everyone has a better understanding of the lower interface. In addition, the article also puts the stability data of the module, which is also very important at the moment, because the stability problem of the module may be more than that of the small-area device, and we must find out and solve it as soon as possible. It is hoped that there will be more and more research on the lower interface of perovskite, so as to better improve the efficiency and stability of the device!
Source:Science