Mechanical properties of APbX 3 ( A = Cs or CH 3 NH 3 ; X= I or Br) perovskite single crystals
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esearch Letters
Mechanical properties of APbX3 (A = Cs or CH3NH3; X = I or Br) perovskite single crystals Yevgeny Rakita, Materials and Interfaces Department, Weizmann Institute of Science, Rehovot 76100, Israel Sidney R. Cohen, Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel Nir Klein Kedem, Gary Hodes, David Cahen, Materials and Interfaces Department, Weizmann Institute of Science, Rehovot 76100, Israel Address all correspondence to Sidney R. Cohen at [email protected] and David Cahen at [email protected] (Received 13 August 2015; accepted 21 September 2015)
Abstract The remarkable optoelectronic and especially photovoltaic performance of hybrid organic–inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX3 (A = Cs, CH3NH3; X = I, Br). The Young’s moduli are ∼14, 19.5, and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3, and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss the possible relevance of our results to suggested “self-healing”, ion diffusion, and ease of manufacturing. Using our results, together with literature data on elastic moduli, we classified HOIPs amongst the relevant material groups, based on their elastomechanical properties.
Hybrid organic–inorganic perovskite (HOIP)—structured materials, mostly CH3NH3PbI3 and CH3NH3PbBr3, and the latter’s inorganic analog CsPbBr[31] are of interest primarily for their remarkable photovoltaic properties.[2] The remarkable solar cell characteristics of HOIPs can be ascribed, at least in part, to the long lifetimes and good charge carrier mobilities, especially for materials, prepared from solution at low temperatures. It has been speculated that this combination of features can be explained by “self-healing” or low kinetic formation barriers.[3,4] Such low barriers could support the suggested occurrence of ion migration, which has been invoked to explain hysteresis[5] observed in current–voltage characteristics of some of the devices.[6–9] The ability of HOIPs to support elastic local deformations is germane to these phenomena. However, despite the great interest in HOIPs in recent years, only limited information exists on their mechanical properties. To try to clarify this matter, we carried out measurements and analyses of elastomechanical properties of single crystals of the methylammonium iodide (CH3NH3I) and bromide and the all-inorganic Cs lead bromide; the corresponding iodide does not have a perovskite(-like) structure at standard temperature and pressure (STP). Because we include CsPbBr3 in our study we will use the abbreviation HaP, Halide Perovskite, rather than HOIP, where appropriate. To investigate the mechanical properties, we performed nano-indentation on single crystals of CH3NH3PbI3, CH3NH3PbBr3, and CsPbBr3 to determine their Young’s modulus (E) and nano-hardness (H ), and co
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