Pressure-Induced Polymorphic, Optical, and Electronic Transitions of Formamidinium Lead Iodide Perovskite

Pan Wang; Jiwen Guan; Draven T K Galeschuk; Yansun Yao; Cindy F He; Shan Jiang; Sijia Zhang; Ying Liu; Meiling Jin; Changqing Jin; Yang Song

doi:10.1021/acs.jpclett.7b00665

Pressure-Induced Polymorphic, Optical, and Electronic Transitions of Formamidinium Lead Iodide Perovskite

J Phys Chem Lett. 2017 May 18;8(10):2119-2125. doi: 10.1021/acs.jpclett.7b00665. Epub 2017 Apr 28.

Authors

Pan Wang¹, Jiwen Guan², Draven T K Galeschuk³, Yansun Yao^{3

4}, Cindy F He¹, Shan Jiang¹, Sijia Zhang⁵, Ying Liu⁵, Meiling Jin⁵, Changqing Jin⁵, Yang Song^{1

2

6}

Affiliations

¹ Department of Chemistry, The University of Western Ontario , London, Ontario N6A 5B7, Canada.
² Department of Physics and Astronomy, The University of Western Ontario , London, Ontario N6A 3K7, Canada.
³ Department of Physics and Engineering Physics, University of Saskatchewan , Saskatoon, Saskatchewan S7N 5E2, Canada.
⁴ Canadian Light Source Inc. , Saskatoon, Saskatchewan S7N 2V3, Canada.
⁵ Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China.
⁶ Soochow University-Western University Centre for Synchrotron Radiation Research, The University of Western Ontario , London, Ontario N6A 5B7, Canada.

PMID: 28440079
DOI: 10.1021/acs.jpclett.7b00665

Abstract

Formamidinium lead iodide (FAPbI₃) perovskite as a superior solar cell material was investigated in two polymorphs at high pressures using in situ synchrotron X-ray diffraction, FTIR spectroscopy, photoluminescence (PL) spectroscopy, electrical conductivity (EC) measurements, and ab initio calculations. We identified two new structures (i.e., Imm2 and Immm) for α-FAPbI₃ but only a structural distortion (in C2/c) for δ-FAPbI₃ upon compression. A pressure-enhanced hydrogen bond plays a prominent role in structural modifications, as corroborated by FTIR spectroscopy. PL measurements and calculations consistently show the structure and pressure dependences of the band gap energies. Finally, EC measurements reveal drastically different transport properties of α- and δ-FAPbI₃ at low pressures but a common trend to metallic states at high pressures. All of these observations suggest strongly contrasting structural stabilities and pressure-tuned optoelectric properties of the two FAPbI₃ polymorphs.