Advances in physicochemical characterization of lead-free hybrid perovskite [NH(3)(CH(2))(3)NH(3)]CuBr(4) crystals

To support the development of eco-friendly hybrid perovskite solar cells, structural, thermal, and physical properties of the lead-free hybrid perovskite [NH(3)(CH(2))(3)NH(3)]CuBr(4) were investigated using X-ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis, and nuclear magnetic resonance spectroscopy. The crystal structure confirmed by XRD was monoclinic, and thermodynamic stability was observed at approximately 500 K without any phase transition. The large changes in the (1)H chemical shifts of NH(3) and those in C2 close to N are affected by N–H∙∙∙Br hydrogen bonds because the structural geometry of CuBr(4) changed significantly. The (1)H and (13)C spin–lattice relaxation times (T(1ρ)) showed very similar molecular motions according to the Bloembergen–Purcell–Pound theory at low temperatures; however, the (1)H T(1ρ) values representing energy transfer were about 10 times lesser than those of (13)C T(1ρ). Finally, the (1)H and (13)C T(1ρ) values of [NH(3)(CH(2))(3)NH(3)]MeBr(4) (Me = Cu, Zn, and Cd) were compared with those reported previously. (1)H T(1ρ) was affected by the paramagnetic ion of the anion, while (13)C T(1ρ) was affected by the MeBr(4) structure of the anion; (13)C T(1ρ) values in Me = Cu and Cd with the octahedral MeBr(6) structure had longer values than those in Me = Zn with the tetrahedral MeBr(4) structure. We believe that these detailed insights on the physical properties will play a crucial role in the development of eco-friendly hybrid perovskite solar cells.