Uniaxial Expansion of the 2D Ruddlesden–Popper Perovskite Family for Improved Environmental Stability

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Abstract
The unique hybrid nature of 2D Ruddlesden-Popper (R-P) perovskites has bestowed upon them not only tunability of their electronic properties but also high-performance electronic devices with improved environmental stability as compared to their 3D analogs. However, there is limited information about their inherent heat, light and air stability, and how different parameters such the inorganic layer number and length of organic spacer molecule affect stability. To gain deeper understanding of stability we have expanded the family of 2D R-P perovskites, by utilizing pentylamine (PA)2(MA)n-1PbnI3n+1 (n = 1-5, PA = CH3(CH2)4NH3+, C5) and hexylamine (HA)2(MA)n-1PbnI3n+1 (n = 1-4, HA = CH3(CH2)5NH3+, C6) as the organic spacer molecules between the inorganic slabs, creating two new series of layered materials, for up to n = 5 and 4 layers, respectively. The resulting compounds were extensively characterized through a combination of physical and spectroscopic methods, including single crystal X-ray analysis. High resolution powder X-ray diffraction studies using synchrotron radiation shed light for the first time to the phase transitions of the higher layer 2D R-P perovskites. The increase in the length of the organic spacer molecules did not affect their optical properties, however it has a pronounced effect on the air, heat and light stability of the fabricated thin films. An extensive study of heat, light and air stability, with and without encapsulation revealed that specific compounds can be air stable (RH 50-80%) for more than 450 days, while heat and light stability in air can be exponentially increased by encapsulating the corresponding films. Evaluation of the out of plane mechanical properties of the corresponding materials showed that their soft and flexible nature can be compared to current commercially available polymer substrates (e.g. PMMA), rendering them suitable for fabricating flexible and wearable electronic devices.
Funding Information
  • Argonne National Laboratory (DE-AC02-06CH1135)
  • Office of Naval Research (N00014-17-1-2231, N00014-18-1-2102)
  • Basic Energy Sciences (DE-SC0001059)
  • Brookhaven National Laboratory (DE-SC0012704)

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