Both good and bad: a perovskite solar cell with higher efficiency and stability was prepared by Zhou huanping's research group and collaborators of Peking University

The vacancy defects of organic cations and halogen anions are the main factors restricting the high efficiency and long-term stability of perovskite solar cells How to eliminate these two defects at the same time is the current problem Based on this, Zhou huanping, researcher group of Beijing University of technology, put forward a new elimination mechanism, that is, introducing fluoride into perovskite active layer, using the extremely high electronegativity of fluoride, achieving the double effects of fluoride forming strong hydrogen bond with organic cation and strong ion bond with lead ion at the same time Thus, the vacancy defects of organic cations and halogen anions are effectively eliminated, and the photoelectric conversion efficiency and long-term stability of the battery are greatly improved Recently, relevant research was published in the international top academic journal Nature energy, entitled: catch and anion mobilization through chemical binding enhancement with flurides for stable halide perovskite solar cells (DOI: 10.1038 / s41560-019-0382-6) As an inexhaustible clean energy, solar energy has attracted the attention of researchers, and the solar cells which convert solar energy into electric energy are also the materials favored by many research groups in the world In recent years, organic-inorganic hybrid perovskite solar cells have attracted a lot of attention in academia and industry due to its advantages of high efficiency and low cost, and its photoelectric conversion efficiency has also rapidly increased to 24.2% in just a few years, which is the most efficient membrane solar cell in a single cell However, the poor stability of these batteries is a major obstacle to their commercial application Compared with the traditional inorganic photovoltaic materials, the lattice of organic-inorganic hybrid perovskite materials is soft, and it is an ionic crystal, which is easy to transfer ions under the interference of external environment, forming a large number of vacancy defects, so as to induce lattice collapse and component decomposition, making it no longer have excellent photoelectric conversion ability Among many vacancy defects, halogen anion and organic cation vacancy exist on the surface and grain boundary of perovskite because of their low defect formation energy These two vacancy defects not only affect the efficiency of solar cell, but also induce the further degradation of perovskite crystal and form more bulk defects In view of these two defects, the previous work mainly focused on passivation of single defect, i.e organic cation or halide vacancy, which can not achieve "both good and bad" How to eliminate these two defects at the same time and achieve higher efficiency and stability of perovskite solar cells is the most difficult problem at present In view of the above important problems, Zhou huanping's group proposed a new elimination mechanism by introducing sodium fluoride into the active layer of perovskite By using the extremely high electronegativity of fluorine, the double effects of fluoride forming strong hydrogen bond with organic cation and strong ion bond with lead ion are realized Based on the chemical bond modulation of this ion bond and hydrogen bond, the organic cations and halogen anions in perovskite can be fixed, so that the corresponding vacancy defects can be eliminated, and the efficiency and stability of the battery are significantly improved The highest efficiency of NaF battery device is 21.92% (certified value is 21.7%), and there is no obvious hysteresis At the same time, the device with sodium fluoride shows excellent thermal and optical stability After 1000 hours of continuous solar irradiation or 85 ° C heating, the device can still maintain 95% and 90% of the original efficiency, respectively After 1000 hours of continuous operation at the maximum power point, the device can maintain 90% of the original efficiency This method can solve two important factors that restrict the stability of titanium dioxide solar cells: organic cation and halogen anion vacancy, and can be extended to other perovskite optoelectronic devices; and the method of chemical bond modulation has important reference significance for other inorganic semiconductor devices facing similar problems Long term stability of perovskite battery: (a) performance change of perovskite battery under continuous sunlight; (b) performance change of perovskite battery under continuous heating at 85 ° C; (c) performance change of perovskite battery under long-term storage in air; (d) performance change of perovskite battery under continuous operation at maximum power point (source: nature) Energy) the first author of this paper is Li nengxu, a 2017 level doctoral student of Zhou huanping's research group, and Zhou huanping's special researcher is the corresponding author The partners also include Shuxia Tao Group of Eindhoven University of technology, Chen Qi group of Beijing University of technology, Hong Jiawang group of Beijing University of technology, Yang Shihe group of Hong Kong University, Xie Haipeng, Professor Geert Brocks of Central South University, etc The work was jointly supported by the National Natural Science Foundation of China, the Ministry of science and technology, the Beijing Natural Science Foundation, the Beijing Science and Technology Commission, the Beijing Key Laboratory of advanced battery material theory and technology, etc Zhou huanping's research group has recently been committed to improving the efficiency and stability of perovskite solar cells, successively in Science (DOI: 10.1126 / science Aau5701), nature energy (DOI: 10.1038 / s41560-019-0382-6), A series of important progresses were reported on NAT Commun (DOI: 10.1038/s41467-019-09093-1; doi: 10.1038/s41467-019-08507-4; doi: 10.1038/s41467-018-05076-w), adv mater (DOI: 10.1002/adma.201900390), J am Chem SOC (DOI: 10.1021 / JACS 7b1157).