In recent years, organic-inorganic hybrid perovskite materials have set off photovoltaics due to their excellent photoelectric characteristics such as adjustable band gap, high absorption coefficient, bipolar carrier transmission properties, long carrier diffusion length and low defect state density Research wave in the energy field. After only nine years of technological development, the device performance of polycrystalline perovskite thin-film solar cells has been comparable to that of crystalline silicon cells with 60 years of research history, and its development rate is far faster than any solar cell technology in history. From 2009 to the present, researchers around the world have developed a variety of thin film preparation processes such as one-step spin coating, two-step spin coating, steam-assisted method, blade coating, and many other devices such as solvent engineering, composition engineering, interface engineering, etc. The optimization criteria continue to promote solar cells to high conversion efficiency at the macro level of improving the quality of perovskite polycrystalline thin films and the optimization of device structure design. However, at present, there are still few in-depth studies on perovskite materials and devices at the micro and meso scales. The lack of a mechanistic understanding of the structure-effect relationship between the material microstructure, carrier transport characteristics and device performance directly hinders device efficiency Based on this, exploring the potential law between the microstructure of the material and the photovoltaic performance will be a key step in improving the performance of perovskite solar cells.
The Huanping Zhou team at the School of Engineering, Peking University used the synchrotron radiation X-ray grazing incidence wide-angle scattering technology (GIWAXS) of the Shanghai Light Source of the National Science Center to systematically study the crystal plane selection of the perovskite polycrystalline thin film of the mixed cation system that maintains the highest efficiency. Orientation rules, on this basis, through the fine doping of multiple cation cascades, the direction of the specific crystal plane relative to the stacking arrangement of the substrate is controllably adjusted, resulting in more excellent device performance. Further, the team studied the internal law between polycrystalline thin films with different preferred orientation relationships and device performance from the perspective of carrier transport characteristics, and found that a strong preferred orientation of the (001) crystal plane family parallel to the substrate will promote current carrying The high-speed migration of electrons in the film improves the transmission rate and collection efficiency of carriers at the interface between the perovskite and the transport layer. The specific crystal plane stacking method and the preferred orientation relationship provide more efficient carrier transport operations. Therefore, the performance of the battery device is greatly improved. The results of this study confirmed that the cascade doping of multiple cations can effectively control the preferred orientation of the polycrystalline thin film crystal plane, which brings a mechanistic understanding of the structure-activity relationship between the microstructure of the material and the photovoltaic performance and provides a breakthrough for the current battery efficiency bottleneck. New design ideas. The result was published in the famous journal Nature Communications [Nature Communications 9, 2793 (2018). The title is "Manipulation of facet orientation in hybrid perovskite polycrystalline films by cation cascade". DOI: 10.1038 / s41467-018-05076-w], Peking University The co-first author of the paper is to jointly train the doctoral student Zheng Guanhaojie with the Shanghai Institute of Applied Physics and the doctoral student Zhu Cheng of Beijing Institute of Technology. Peking University is the first unit.
Orientation evolution analysis of multiple cascade doping of alkali metal cations: (a) FAMA, FAMA-Cs, FAMA-CsRb, FAMA-CsRbK cascade doped polycrystalline thin film GIWAXS pattern; (b) FAMA, FAMA-Cs, FAMA -CsRb, FAMA-CsRbK cascade-doped polycrystalline thin film (001) azimuthal integrated intensity graph; (c) cascade-doped polycrystalline thin film crystal orientation orientation evolution
This research system investigated the effect of multi-stage cascade doping of alkali metal cations Cs +, Rb +, and K + on the crystal stack orientation. Through fine doping to achieve controllable orientation control, it was revealed that the preferred orientation at the microstructure level greatly affects calcium The photoelectric characteristics of the titanium material confirm that the strongly preferred orientation of the (001) crystal plane parallel to the substrate will promote the high-speed migration of carriers in the film and improve the carrier at the interface between the perovskite and the transport layer The transmission rate and collection efficiency establish a clear and clear potential structure-effect relationship between the perovskite polycrystalline microstructure, device performance and carrier transport characteristics, which provides new design ideas for the current battery to break through the efficiency bottleneck .
The research was completed in collaboration with Professor Chen Qi of Beijing Institute of Technology, Researcher Xingyu Yu of Shanghai Institute of Applied Physics, Researcher Hu Jinsong of Institute of Chemistry, Chinese Academy of Sciences, and Professor Hong Jiawang of School of Aeronautics and Astronautics, Beijing Institute of Technology. The research was supported by funding from the National Natural Science Foundation of China, the National Key R & D Program, and the Youth Thousand Talents Program.
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