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    Home > Solving the mystery of delayed thermoluminescence of organic-inorganic hybrid perovskite ch3nh3pbbr3

    Solving the mystery of delayed thermoluminescence of organic-inorganic hybrid perovskite ch3nh3pbbr3

    • Last Update: 2018-01-19
    • Source: Internet
    • Author: User
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    Since the organic-inorganic hybrid lead halide perovskite solar cell was introduced in 2009, it has attracted great attention The photoelectric conversion efficiency soared from the initial 3.8% to 22.1% in 2017 Due to the unique structure of hybrid organic-inorganic perovskite, the movement of polar organic cations embedded in the rigid inorganic Pb br or pb-i framework greatly affects the photovoltaic and excited state charge properties of perovskite Zhu Xiaoyang, professor and collaborator of Columbia University (Science 2016, 353, 1409-1413), used time-resolved photoluminescence and optical Kerr effect spectra to observe long-lived high-energy charge thermoluminescence in mapbbr 3 and fapbbr 3, but not in inorganic perovskite cspbbr 3 High energy long-life electrons can greatly avoid energy loss and improve photoelectric conversion efficiency It is suggested that the relaxation of high energy hot electrons in the conduction band due to the reorientation of organic cations is the possible cause of long-life thermoluminescence A large number of ultrafast spectroscopic studies on inorganic and organic condensed materials show that the relaxation time of electrons in the conduction band is usually in the time scale of tens of femtoseconds to several picoseconds Therefore, it is very important to clarify the internal physical mechanism of delayed thermoluminescence for further optimizing the performance of perovskite photovoltaic solar cells Source: J am Chem SOC 2017, 139, 17327-17333 recently, through a large number of static electronic structure calculations, the research team of teacher long leap from the school of chemistry, Beijing Normal University designed two kinds of mapbbr 3 structures, free charge and local charge (polaron) formed by the rotation of Ma molecules, respectively, corresponding to systems with large band gap, high energy and small band gap, low energy Previous theoretical calculations also show that the stable energy of hole and electron polaron is only 0.06 EV and several MeV, which supports our hypothesis that free charge and polaron can coexist, while the energy provided by room temperature (0.025 EV) can simultaneously change the electron and hole polaron into free charge Based on the results of electronic structure calculation and rational analysis, the researchers used time-dependent density functional theory and non adiabatic dynamics simulation to study the non radiative electron hole composite dynamics of the two structures The results show that the electron hole recombination of mapbbr 3 structure (free charge) with large band gap and high energy is fast, and the formation of low energy local charge mapbbr 3 structure (polaron) with organic cation rotation is slow The calculated time scale is in good agreement with the experiment The difference of composite time scale is determined by non adiabatic coupling In the free electron structure, the superposition of electron and hole wave function is large, and the non adiabatic coupling strength is strong, so the recombination is fast On the contrary, the superposition of electron and hole wave functions in the local charge structure is small, and the diabatic coupling strength is weak, so the recombination is slow The researchers also used Einstein's natural emission model to calculate the radiation recombination time of the two structures, which is far from the experiment Therefore, the researchers infer that the free charge formed by the reorientation of organic molecules and the non radiative charge compound formed by the local charge structure correspond to the delayed thermoluminescence and the normal fluorescence respectively, which provides a possible explanation for the thermoluminescence phenomena found in organic-inorganic hybrid perovskite materials Paper link: profile of Professor long leap: teacher long leap
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