(Lecture) Correlating Polar Order, Ionic Migration, and Photocurrent in Organometallic Halide Perovskites
date:2019-12-16 pageviews:46

Speaker: Jiangyu Li

Time: 10:00, Dec. 16th, 2019

Venue: Room 502, Building of State Key Laboratory of Luminescent Materials and Devices, Wushan Campus

Abstract: Organometallic halide perovskite solar cell has emerged as one of the most exciting photovoltaic technologies in the last a few years, though many fundamental questions remain unanswered. In an attempt to resolving the intrinsic lattice structure of CH3NH3PbI3 by transmission electron microscopy, we identified a general decomposition pathway from CH3NH3PbI3 to PbI2 through an intermediate superstructure of CH3NH3PbI2.5, which appears to hold for CH3NH3PbBr3 and CsPbI3 as well. Importantly, the decomposition barrier is orientation-dependent, and the degradation can be slowed down substantially by carbon coating, enabling us to design a new perovskite solar cell with improved stability and reduced hysteresis. Detailed microscopy analysis reveals that the superstructure diffraction corresponds to ordered vacancies or vacancy-interstitial pairs of I, and interestingly, this Frenkel pair can be induced by electric field and stabilized in PVDF matrix, resulting in anomalously enhanced remnant polarization and electromechanical coupling in the nanocomposite that is also highly stable. Nevertheless, the intrinsic instability prevented us to acquire the atomic image of CH3NH3PbI3, and we have to resort to scanning probe to distinguish the fine structure difference between two competing space groups, revealing alternating polar and nonpolar orders in CH3NH3PbI3 and their effects on photocurrent. This presentation thus summarizes close collaborations in the last two years among Shenzhen Institutes of Advanced Technology, Peking University, Shijiazhuang Tiedao University, and Beihang University, among others, and we are continuing to explore the defect structures in halide perovskites and their far reaching implications.