Structural geometry and molecular dynamics by nuclear magnetic resonance of organic-inorganic perovskite [NH3(CH2)6NH3]CuBr4 crystal near phase transition temperature

Abstract

The structural, thermal, and physical properties of newly developed lead-free hybrid perovskite solar cells are discussed for [NH3(CH2)6NH3]CuBr4. The hybrid material undergoes a phase transition at 269 K (TC), and is thermodynamically stable until approximately 472 K. The crystal structure determined by single-crystal X-ray diffraction is monoclinic and triclinic above and below TC, respectively. The 1H and 13C nuclear magnetic resonance spectra, recorded as a function of the temperature, revealed considerable changes in the 1H chemical shifts of NH3 and the 13C chemical shifts of the carbon atoms close to N as a result of the structural phase transition. The large difference in the activation energy, obtained from the 13C spin-lattice relaxation time above and below TC, also appears to be related to energy transfer changes in 13C. The thermal stabilities of [NH3(CH2)nNH3]CuBr4 (n = 3, 4, and 6) were compared by varying the number of methylene units, and the temperature with 2 % weight loss was shown to decrease as the number of methylene units increases. This in-depth analysis of the physical properties is expected to promote the development and application of lead-free hybrid perovskite solar cells.