Beijing Institute of Technology, Nov 8th, 2020:Recently, Energy & Environmental Science (impact factor 30.289), a top international journal in the field of chemistry and materials, reported the new progress in the research on the stability of high efficiency organic-inorganic hybrid metal halide perovskite solar cells by the research group of Cui Binbin from Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology. Related research results were published online under the title “In-situ Cross-linked 1D/3D Perovskite Heterostructure Improves Stability of Hybrid Perovskite Solar Cells for Over 3000h Operation”. The first author of this work is Yang Ning, a Ph. D. candidate of BIT; corresponding author is Cui Binbin, the special associate researcher from Advanced Research Institute of Multidisciplinary Science, BIT. This work was completed jointly with Professor Chen Qin’s research group from School of Materials Science and Engineering, BIT.

　　In recent years, organic-inorganic hybrid metal halide perovskite has attracted extensive attention and research due to its extraordinary photovoltaic conversion properties, diverse components, adjustable band gap and low cost. At present, the power conversion efficiency of a single perovskite solar cell has been boosted from 3.8% to 25.5%, which demonstrates a great commercial prospect for green and clean energy. However, hybrid metal halide perovskite materials are commonly sensitive to moisture, oxygen, heat, and light in the ambient environment. Therefore, the main challenge for the commercialization of perovskite solar cells is to improve the stability of the absorbing layer and carrier transport interface. Compared with 3D organic-inorganic hybrid metal halide perovskite, the hydrophobicity of organic cations in low-dimensional perovskite gives it superior moisture stability. 1D, 2D perovskite and 3D perovskite build 1D / 3D or 2D / 3D heterojunctions, which can significantly enhance the stability of perovskite solar devices. However, the insulation of organic cations in low-dimensional perovskite will reduce the carrier transport performance of perovskite devices. Therefore, this method usually prolongs the life of perovskite solar cells at the expense of the power conversion efficiency (PCE). If it is possible to enhance the stability of the device as in this strategy and at the mean time ensure the capacity of low-dimensional perovskite carrier transport, then efficient and stable perovskite solar cells are expected to be realized.

Fig. 1 Structure principle and NMR characterization of 1D perovskite

　　The team builds 1D ultrathin perovskite with in situ cross-linkable organic cations on the organic-inorganic hybrid metal halide 3D perovskite active layer (Fig. 1a), which not only passivates the iodine vacancy defects on grain boundaries and interfaces, but also improves the anti-aging ability of perovskite films through the polymerization of organic cations. Most importantly, the electron conjugation structure formed by cross-linking reaction can improve the carrier transport performance, improving the power conversion efficiency of perovskite solar cells effectively. In the meantime, the 1D perovskite crystalline material from the reaction of PAI with excess PbI2, composed of [PbI6]4-octahedral surface coplanar, has relatively good stability in moisture and light. The PA+ cations around inorganic 1D chain are polymerized and crosslinked in situ by heating at 150 ℃ for 15 min to form polymeric organic compounds with electron conjugation structure, which can effectively transport carriers in 1D layers of heterostructures, thus enhancing the current transmission between interfaces.

Fig. 2 Improved interface carrier transport behavior and stress-strain correlation characterization

　　In addition, the residual strain of mixed phase perovskite polycrystalline films is studied by depth-resolved grazing incidence X-ray strain test. In 1D / 3D perovskite heterostructure, the residual tensile strain of the perovskite active layer changes into compressive strain after polymerization and cross-linking of propargylamine cation in 1D type perovskite films during heating (Fig. 2), which is beneficial to the improvement of photovoltaic performance and stability of PSCs. This feature provides a feasible method for the modulation of perovskite materials interface strain. The results show that the highest power conversion efficiency of cross-linked 1D/3D perovskite solar devices is 21.19%, the open-circuit voltage(VOC) is 1.11 V, the short-circuit photocurrent density (JSC) is 23.69 mA·cm−2, and the fill factor (FF) is 80.76%. Compared with standard devices, the short-circuit current of cross-linked 1D / 3D devices is significantly increased.

Fig. 3 Stability test of PSCs under various conditions

　　As to study the stability of the devices, it is found that the content ratio of PbI2 to perovskite in cross-linked 1D / 3D perovskite heterostructure films is almost unchanged after 1000 hours aging of dark state storage in ambient air (humidity 40-70%, temperature 25-40 ℃). Under a nitrogen atmosphere (humidity 20-40%), before and after cross-linking 1D / 3D PSCs stored in dark state remained 97% of the original efficiency. Under a nitrogen atmosphere, after 840 hours of continuous 0.8 sun illumination, the cross-linked 1D / 3D heterostructure perovskite solar cell devices almost maintain 95.9% of its original efficiency. In this paper, the stability of perovskite devices is evaluated according to the standard of ISOS-L-1. Under a nitrogen atmosphere, after 3055 hours of MPP measurement, the cross-linked 1D / 3D PSCs can still maintain 93% of their initial efficiency after 3055 hours of continuous operation.

Brief introduction to the author:
Cui Binbin, member of Jiusan Society, assistant professor. From 2011 to 2016, he studied in Institute of Chemistry Chinese Academy of Sciences and received a doctor degree in Science. From September 2015 to April 2016, he visited Nanyang Technological University in Singapore. He is currently a pre-appointed assistant professor (special associate researcher) and doctoral supervisor in Advanced Research Institute of Multidisciplinary Science, BIT. The main research direction is organic-inorganic hybrid optoelectronic functional materials, including metal halide perovskite photovoltaic devices and low-dimensional perovskite crystal luminescent materials. In recent years, more than 20 research papers have been published in NAT. Commun., J. am. Chem. SOC., angelw. Chem. Int. ed., J. mater. Chem. A, adv. optical mate, ACS, appl. Mater. Interfaces. Besides, he has presided over the general program and youth program of National Natural Science Foundation of China.

Paper details:
Ning Yang, Cheng Zhu, Yihua Chen, Huachao Zai, Chenyue Wang, Xi Wang, Hao Wang, Sai Ma, Ziyan Gao, Xueyun Wang, Jiawang Hong, Yang Bai, Huanping Zhou, Bin-Bin Cui* and Qi Chen. In-situ Cross-linked 1D/3D Perovskite Heterostructure Improves Stability of Hybrid Perovskite Solar Cells for Over 3000h Operation, doi: 10.1039/D0EE01736A.
Homepage of the teacher: http://arims.bit.edu.cn/xzdw/qnggjs/tbfyjy/104331.htm
Link to the paper：https://doi.org/10.1039/D0EE01736A