Shulou(Shulou.com)11/24 Report--

CTOnews.com, November 2, according to the official news of Hefei Academy of material Sciences of the Chinese Academy of Sciences, Pan Xu and Tian Xingyou, researcher team of Institute of solid State Physics of Hefei Academy of material Sciences, key Laboratory of Photovoltaic and Energy Saving Materials of Chinese Academy of Sciences, and Professor Dai Songyuan of North China Electric Power University, worked together with Professor Nam-Gyu Park of Chengjunguan University of South Korea and Professor Dai Songyuan of North China Electric Power University. A new breakthrough has been successfully made in the research of trans-perovskite solar cells.

The research team found for the first time that the out-of-plane distribution of perovskite cations was the main reason affecting the battery performance, and the photoelectric conversion efficiency (PCE) of 26.1% was obtained by designing 1-(benzenesulfonyl) pyrrole (PSP) as an additive to homogenize the phase distribution of perovskite thin films.

The related results were published online on November 2 (AAP) in the journal nature, CTOnews.com attached a link to the paper:

Https://www.nature.com/articles/s41586-023-06784-0

According to reports, perovskite solar cells are solar cells that use perovskite-type organometallic halide semiconductors as light-absorbing materials. It belongs to a new concept of solar cells. After years of development, the traditional methods of interface passivation and crystallization regulation have greatly promoted the improvement of cell efficiency, but in recent years, the improvement rate of cell efficiency has obviously slowed down, and related research has encountered a "bottleneck".

Researchers have found that phase separation is inevitable in perovskite films. The previous work of the research team showed that effective management of halogen phase separation is helpful to improve the performance of devices. High efficiency perovskite materials are often obtained by using cationic doping components in pure iodine system, especially in FA1-xCsxPbI3 system. The distribution of different cationic components in the out-of-plane direction of perovskite body is very important for carrier diffusion and interface extraction of perovskite body. An in-depth study of the out-of-plane distribution of cations is not only helpful to understand the carrier dynamics of perovskite bodies, but also is expected to further improve the efficiency of perovskite solar cells. However, the distribution of different cationic components in perovskite phase and the reasons that affect the stability and efficiency loss of the battery are not clear.

Based on this, the team studied the longitudinal distribution of formamidine (FA) and cesium (Cs) cations through elemental quantitative analysis from the FA1-xCsxPbI3 system. Combined with time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS), depth analysis showed that inorganic Cs cations tended to be deposited at the bottom of the film and organic FA cations were enriched at the upper interface of the film. On this basis, the research team analyzed the crystal phase distribution of perovskite thin films in depth. Through grazing incidence X-ray diffraction (GIXRD) and transmission electron microscope (TEM) analysis of film cross section, it was proved that there was a crystal phase with small plane spacing at the bottom of the film, and the characteristic signal related to Cs-rich perovskite was shown at the bottom of the film. These experiments fully show the out-of-plane gradient uneven distribution of cations, and this is the first time to visually verify the out-of-plane non-uniform distribution of cationic components in perovskite films.

The research team further analyzed the reasons for the uneven distribution of the gradient through the in-situ test method, and found that the excessive rate difference of different cations in the process of crystallization and phase transformation was the main reason for the uneven composition. Furthermore, the team designed PSP molecules to make up for the difference in crystallization and phase transition rates between different cations to prepare homogenized perovskite films. The perovskite film with uniformly distributed cationic components effectively suppresses the quasi-I-type energy level arrangement caused by the bottom Cs-rich phase, greatly improves the carrier lifetime and diffusion length, and strengthens the carrier interface extraction.

The trans-perovskite solar cells prepared by the research team using PSP strategy achieved the highest efficiency of 26.1% and the certification efficiency of 25.8%. In addition, after 2500 hours of maximum power tracking (MPPT), the unpackaged devices still maintain 92% reliable operational stability of their initial PCE.

This research work shows that excellent cell performance can be obtained by homogenizing the out-of-plane distribution of perovskite components, which opens up a new way to improve the stability of cell devices, and is expected to break the efficiency bottleneck of perovskite solar cells. it provides a clear direction for further improving the efficient and stable perovskite solar cells, and is of great significance to promote the commercial development of PSCs.

Liang Zheng, a doctoral student from Hefei Institute of Physics, Chinese Academy of Sciences, is the first author of this paper, Dr. Zhang Yong of Southern University of Science and Technology and Xu Huifen, doctoral student of Institute of solids, Pan Xu, researcher of Institute of solids, Dr. Ye Jiaju of Institute of solids, Professor Nam-Gyu Park of Cheng Junguan University and Professor Dai Songyuan of North China Electric Power University are co-authors. This work has been supported by the National key Research and Development Program, the National Natural Science Foundation, the Outstanding Youth Fund of Anhui Province, and the President Fund of Hefei Institute of Materials.

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