Recently, under the leadership of Academician Zhuang Songlin, Jin Zianming, a young teacher from the School of Optoelectronics of University of Shanghai for Science and Technology, cooperated with scientists from Qingdao Institute of Bioenergy and Process Engineering, Chinese Academy of Sciences, Shanghai University, Shanghai Institute of Technical Physics, Shanghai Jiao Tong University, University of Wollongong, and Moscow University to innovatively use ultrashort terahertz coherent pulses. The quasiparticle-large polaron formed by the dynamic coupling of photogenerated carriers and low-frequency optical phonon modes was directly observed and measured in organic-inorganic hybrid metal halide perovskite CH3NH3PbI3 (MAPbI3) polycrystalline particles perovskite with terahertz probes", published in the journal Light: Science & Applications (Region I, impact factor 20.257), the first author of the paper is Jin Zianming, and the corresponding authors are Peng Yi and Zhu Yiming.
Organic-inorganic hybrid metal halide perovskite materials have attracted great attention because of their excellent photoelectric properties. Based on this material, optoelectronic devices including solar cells, solid-state lighting, memristors and ultrafast spin switches in spintronics have been designed and fabricated. Although the application prospect of organic-inorganic hybrid metal halide perovskite materials is broad, the experimental phenomenon of photo-induced charge carriers with "long lifetime and low mobility" in this material is still controversial and needs to be studied.
The researchers experimentally directly demonstrated the coupling of photogenerated carrier-optical phonon modes in MAPbI3 polycrystalline grains by ultrafast time-resolved optical pumping-terahertz electromagnetic detection spectroscopy. Photogenerated charge carriers and lattice distortions on several lattice constants around them form quasiparticles—large polarons. Using the Drude-Smith-Lorentz model and the Frӧhlich-type electron-phonon coupling model, the researchers obtained the effective mass and scattering parameters of photoexcited large polarons. Considering the effective mass increase caused by the large polaron effect, the polycrystalline properties of the material, and the inevitable defect state, the mobility of the large polaron is obtained in the order of ~80 cm2V-1s-1. In addition, the researchers found that the formation of large polarons in MAPbI3 protects charge carriers from scattering by grain boundaries or defects of polycrystalline particles, thus explaining the long-lived phenomenon of photoconductivity. The authors believe that this research work is helpful to understand the non-equilibrium physical process of photoexcited charge carrier and optical phonon coupling in organic-inorganic hybrid metal halide perovskite MAPbI3, which is of great significance for the basic physical property study and device design of perovskite materials.
Terahertz detection of quasiparticles-large polarons formed by photogenerated charge carriers and their surrounding lattice distortion (Image: Light website)
This work was supported by the National Natural Science Foundation of China Science Center Project (61988102).
Z. Jin, Y. Peng, Y. Fang, Z. Ye, Z. Fan, Z. Liu, X. Bao, H. Gao, W. Ren, J. Wu, G. Ma, Q. Chen, C. Zhang, A. V. Balakin, A. P. Shkurinov, Y. Zhu, S. Zhuang, Photoinduced large polaron transport and dynamics in organic-inorganic hybrid lead halide perovskite with terahertz probes, Light: Science & Applications 11, 209 (2022)