Since 2009, organic-inorganic hybrid perovskite materials have attracted wide attention in the fields of energy, photovoltaic, chemistry, material physics, etc. They have a continuously adjustable band gap, high light absorption coefficient, and long carrier diffusion distance. The excellent preparation characteristics and other excellent characteristics make it an ideal light absorbing material for the development of next-generation photovoltaic devices. Only after less than 10 years of development, the energy conversion efficiency record of perovskite thin-film solar cells has rapidly increased to 23.3%. The speed is the highest of all types of solar cells. In terms of chemical composition, the organic-inorganic hybrid perovskite material has a crystal structure of ABX3 type. The content of the A-form formazan ion is higher than 95%, and the content of the b-position of the X-position is lower than 5 % FAPbI3-based perovskite material with a band gap of less than 1.55 eV, which is the closest to the ideal band gap of a single-cell solar cell in the distribution ratio of various perovskite materials that have been developed. Currently, the two-step method is prepared. The long-term working stability of solar cell devices is generally lower than the one-step method, which is difficult to obtain a perovskite film containing alkali metal ions by the traditional two-step method.
The research team of 'Nanostructure and Low-dimensional Physics' of Peking University's School of Physics, led by Academician Yu Dapeng, made a series of progress on this issue. Professor Zhao Qing and his collaborators designed and proposed perovskite based on the traditional two-step method. A two-step spin coating method for seed crystal growth, by introducing a niobium-containing perovskite seed crystal into a lead iodide film, so that the seed crystal provides a nucleation site for subsequent perovskite growth, guiding high-quality film growth, solving two Effective doping of inorganic cations in the step method. Through seed crystal induction, precise regulation of nucleation and grain size can be achieved, and inorganic Cs ions are effectively incorporated, and the energy conversion efficiency of the device is improved to 21.7%. Meanwhile, the device is After 140 hours of continuous operation in AM1.5G sunlight, it still maintains an initial efficiency of more than 60%, which is far superior to the stability of the traditional two-step method. Related research results are 'Perovskite seeding growth of formamidinium-lead-iodide-based Perovskites for efficient and stable solar cells' was published in Nature Communications' Nature Communications 9, 1607 (2018). DOI: 10.1038/s41467-018-04029-7'. Zhao Yi Cheng, postdoctoral Tanhai Ren University of Toronto and the University of Leuven, Belgium Yuan Haifeng for postdoctoral research paper co-author Professor Edward H. Sargent University of Toronto and co-corresponding author for the Zhao Qing.
A schematic diagram of the process of preparing perovskite film by seed crystal method; b Photoluminescence microscopic in situ detection of real-time growth process of perovskite in seed crystal method
Zhao Qing's research group also designed a two-step method for cesium chloride to enhance the lead iodide precursor solution. While further increasing the alkali metal ion content in the perovskite film, the nucleation and growth process of the perovskite is slowed down. Large grain, lower defect density perovskite polycrystalline film. The planar formal perovskite thin film solar cell device based on this preparation has higher energy conversion efficiency (22.1%) and long-term operation stability of the device. It has also been improved to maintain 90% initial efficiency after 70 hours of operation in AM1.5G sunlight. This study is an efficient and efficient method for preparing alkali metal ions in a two-step process for preparing perovskite films and solar cell devices. Incorporation, improved device performance and other issues provide new ideas. Related research results are based on 'Efficient Perovskite Solar Cells Fabricated Through CsCl-Enhanced PbI2 Precursor via Sequential Deposition', published in the internationally renowned journal Advanced Materials' Advanced Materials 1803095 ( 2018). DOI: 10.1002/adma.201803095'. Peking University Ph.D. student Li Qi is the first author of the research paper, Zhao Qing made a communication The above research was supported by the National Natural Science Foundation of China, the State Key Laboratory of Artificial Microstructures and Mesoscopic Physics of Peking University, and the '2011 Plan' Collaborative Innovation Center for Quantum Matter Science.
