title: Direct observation of intrinsic twin domains in tetragonal CH3NH3PbI3.
abstract: Organic-inorganic hybrid perovskites are exciting candidates for next-generation solar cells, with CH3NH3PbI3being one of the most widely studied. While there have been intense efforts to fabricate and optimize photovoltaic devices using CH3NH3PbI3, critical questions remain regarding the crystal structure that governs its unique properties of the hybrid perovskite material. Here we report unambiguous evidence for crystallographic twin domains in tetragonal CH3NH3PbI3, observed using low-dose transmission electron microscopy and selected area electron diffraction. The domains are around 100-300 nm wide, which disappear/reappear above/below the tetragonal-to-cubic phase transition temperature (approximate 57 °C) in a reversible process that often 'memorizes' the scale and orientation of the domains. Since these domains exist within the operational temperature range of solar cells, and have dimensions comparable to the thickness of typical CH3NH3PbI3films in the solar cells, understanding the twin geometry and orientation is essential for further improving perovskite solar cells.
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Mathias Uller
authors.initials: MU
authors.lastname: Rothmann
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.|Commonwealth Scientific and Industrial Research Organization, Manufacturing Flagship, Clayton, Victoria 3168, Australia.|Melbourne Centre for Nano Fabrication, 151 Wellington Road, Clayton, Victoria 3168, Australia.
authors.forename: Udo
authors.initials: U
authors.lastname: Bach
authors.affiliation: School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Leone
authors.initials: L
authors.lastname: Spiccia
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.|Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Joanne
authors.initials: J
authors.lastname: Etheridge
authors.affiliation: Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.|State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.
authors.forename: Yi-Bing
authors.initials: YB
authors.lastname: Cheng