Wang Chen, Liu Yucheng, Liu Shengzhong Frank, Li Bing, Chen Yue
Department of Mechanical Engineering , The University of Hong Kong , Pokfulam Road , Hong Kong SAR , China.
Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Institute for Advanced Energy Materials, School of Materials Science and Engineering , Shaanxi Normal University , Xian 710119 , China.
J Phys Chem Lett. 2018 Jun 7;9(11):3029-3034. doi: 10.1021/acs.jpclett.8b01101. Epub 2018 May 22.
Perovskite MAPbI that exhibits unique optoelectronic properties has emerged as a promising semiconductor material with a potential to revolutionize the photovoltaic industry. Inadequate understanding of the thermal instability and lattice dynamics of MAPbI, however, hinders its practical applications. Herein, combing molecular dynamics with a first-principles-based interatomic potential and inelastic neutron scattering measurements, we have performed an in-depth study of the lattice dynamics of MAPbI. The extremely large line widths of the optical phonons in the tetragonal phase, which prevent direct experimental measurement of the phonon lifetimes, have been obtained for the first time. Our atomic-level study also reveals a giant pressure tuning effect on phonon scattering, which is related to the four-fold rotation of the MA cations around the C-N axis. A hydrostatic pressure as low as 6 kbar can alter the phonon lifetime by more than 1 order of magnitude. This work is expected to pave the way for further phonon engineering and thermal optimization of MAPbI and related perovskites.
具有独特光电特性的钙钛矿MAPbI已成为一种有前途的半导体材料，有望给光伏产业带来变革。然而，对MAPbI的热不稳定性和晶格动力学认识不足，阻碍了其实际应用。在此，我们将分子动力学与基于第一性原理的原子间势以及非弹性中子散射测量相结合，对MAPbI的晶格动力学进行了深入研究。首次获得了四方相中光学声子极宽的线宽，这使得无法直接通过实验测量声子寿命。我们的原子尺度研究还揭示了声子散射的巨大压力调谐效应，这与MA阳离子围绕C-N轴的四重旋转有关。低至6千巴的静水压力可使声子寿命改变超过1个数量级。这项工作有望为MAPbI及相关钙钛矿的进一步声子工程和热优化铺平道路。
