Structural characterization, thermal properties, and molecular motions near the phase transition in hybrid perovskite [(CH2)3(NH3)2]CuCl4 crystals: 1H, 13C, and 14N nuclear magnetic resonance

Exploring the potential applications of lead-free organic-inorganic perovskite type [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals

The organic-inorganic hybrid perovskite compounds have been extensively studied since the dawn of a new era in the field of photovoltaic applications. Up to now, perovskites have proven to be the most promising in terms of power conversion efficiency; however, their main disadvantages for use in solar cells are toxicity and chemical instability. Therefore, it is essential to develop a hybrid perovskite that can be replaced with lead-free materials. This review focuses on the possibility of applying lead-free organic-inorganic perovskite types [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals. We are seeking organic-inorganic hybrid perovskite materials with very high temperature stability or without phase transition temperature, and thermal stability. Thus, by considering the characteristics according to the methylene lengths and the various transition metals, we aim to identify improved materials meeting the criteria mentioned above. Consequently, the physicochemical properties of organic-inorganic hybrid perovskite [NH3(CH2)nNH3]MCl4 regarding the effects of various transition metal ions of the anion and the methylene lengths of the cation are expected to promote the development and application of lead-free hybrid perovskite solar cells.

Crystal structures, phase transitions, and nuclear magnetic resonance of organic-inorganic hybrid [NH2(CH3)2]2ZnBr4 crystals

Organic-inorganic hybrid [NH₂(CH₃)₂]₂ZnBr₄ crystals were grown via slow evaporation, and their monoclinic structure was determined using single-crystal X-ray diffraction (XRD). The two phase transition temperatures at 401 K (T _C1) and 436 K (T _C2) were defined using differential scanning calorimetry and powder XRD. In the nuclear magnetic resonance spectra, a small change was observed in the ¹H chemical shifts for NH₂, ¹³C chemical shifts for CH₃, and ¹⁴N resonance frequency for NH₂ near T _C1. ¹H spin-lattice relaxation times T _1ρ and ¹³C T _1ρ for NH₂ and CH₃, respectively, rapidly decreased near T _C1, suggesting that energy was easily transferred. NH₂ in the [NH₂(CH₃)₂]⁺ cation was significantly influenced by the surrounding environments of ¹H and ¹⁴N, indicating a change in the N-H⋯Br hydrogen bond with the coordination geometry of the ZnBr₄ anion. These fundamental properties open efficient avenues for the development of organic-inorganic hybrids, thus qualifying them for practical applications.

Growth, structure, phase transition, thermal properties, and structural dynamics of organic-inorganic hybrid [NH3(CH2)5NH3]ZnCl4 crystal

In this study, the physicochemical properties of [NH₃(CH₂)₅NH₃]ZnCl₄ crystals were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and nuclear magnetic resonance (NMR). The crystals at 300 K had a monoclinic structure with C2/c space group and lattice constants are a = 21.4175 Å, b = 7.3574 Å, c = 19.1079 Å, β = 120.5190°, and Z = 8. Three endothermic peaks at 256, 390, and 481 K were observed in the DSC curve. From the single-crystal XRD patterns, powder XRD patterns, and optical microscopy results based on the temperature change, the phase transition and melting temperatures were determined to be 390 and 481 K, respectively. NMR studies indicated no change in ¹H chemical shifts, but a change in the chemical shifts for C2, located between C1 and C3 of the cation at 340 K. Increase in molecular motion caused an increase in the spin-lattice relaxation time, T_1ρ, at low spinning rates, under magic-angle spinning rate conditions. This crystal showed a minor change in the N-H···Cl hydrogen bond, related to the coordination geometry of the ZnCl₄ anion.

Organic-inorganic hybrid [NH3(CH2)6NH3]ZnBr4 crystal: structural characterization, phase transitions, thermal properties, and structural dynamics

Organic–inorganic hybrid [NH₃(CH₂)₆NH₃]ZnBr₄ crystals were prepared by slow evaporation; the crystals had a monoclinic structure with space group P2₁/c and lattice constants a = 7.7833 Å, b = 14.5312 Å, c = 13.2396 Å, β = 90.8650°, and Z = 4. They underwent two phase transitions, at 370 K (T_C1) and 430 K (T_C2), as confirmed by powder X-ray diffraction patterns at various temperatures; the crystals were stable up to 600 K. The nuclear magnetic resonance spectra, obtained using the magic-angle spinning method, demonstrated changes in the ¹H and ¹³C chemical shifts were observed near T_C1, indicating changing structural environments around ¹H and ¹³C. The spin–lattice relaxation time, T_1ρ, increased rapidly near T_C1 suggesting very large energy transfer, as indicated by a large thermal displacement around the ¹³C atoms of the cation. However, the environments of ¹H, ¹⁴N, and C1 located close to NH₃ in the [NH₃(CH₂)₆NH₃] cation did not influence it significantly, indicating a minor change in the N–H⋯Br hydrogen bond with the coordination geometry of the ZnBr₄ anion. We believe that the information on the physiochemical properties and thermal stability of [NH₃(CH₂)₆NH₃]ZnBr₄, as discussed in this study, would be key to exploring its application in stable, environment friendly solar cells.

Organic–inorganic hybrid [NH₃(CH₂)₆NH₃]ZnBr₄ crystals were prepared by slow evaporation; the crystals had a monoclinic structure with space group P2₁/c and lattice constants a = 7.7833 Å, b = 14.5312 Å, c = 13.2396 Å, β = 90.8650°, and Z = 4.

Characterization on Lead-Free Hybrid Perovskite [NH3(CH2)5NH3]CuCl4: Thermodynamic Properties and Molecular Dynamics

It is essential to develop novel zero- and two-dimensional hybrid perovskites to facilitate the development of eco-friendly solar cells. In this study, we investigated the structure and dynamics of [NH₃(CH₂)₅NH₃]CuCl₄ via various characterization techniques. Nuclear magnetic resonance (NMR) results indicated that the crystallographic environments of ¹H in NH₃ and ¹³C on C3, located close to NH₃ at both ends of the cation, were changed, indicating a large structural change of CuCl₆ connected to N–H···Cl. The thermal properties and structural dynamics of the [NH₃(CH₂)_nNH₃] cation in [NH₃(CH₂)_nNH₃]CuCl₄ (n = 2, 3, 4, and 5) crystals were compared using thermogravimetric analysis (TGA) and NMR results for the methylene chain. The ¹H and ¹³C spin-lattice relaxation times (T_1ρ) exhibited similar trends upon the variation of the methylene chain length, with n = 2 exhibiting shorter T_1ρ values than n = 3, 4, and 5. The difference in T_1ρ values was related to the length of the cation, and the shorter chain length (n = 2) exhibited a shorter T_1ρ owing to the one closest to the paramagnetic Cu²⁺ ions.

Phase transition, thermal stability, and molecular dynamics of organic-inorganic hybrid perovskite [NH3(CH2)6NH3]CuCl4 crystals

Organic-inorganic hybrid perovskites have various potential applications in fuel cells and solar cells. In this regard, the physicochemical properties of an organic-inorganic [NH3(CH2)6NH3]CuCl4 crystal was conducted. The crystals had a monoclinic structure with space group P21/n and lattice constants a = 7.2224 Å, b = 7.6112 Å, c = 23.3315 Å, β = 91.930°, and Z = 4 at 300 K, and the phase transition temperature (T C) was determined to be 363 K by X-ray diffraction and differential scanning calorimetry experiments. From the nuclear magnetic resonance experimental results, the changes in the 1H chemical shifts in NH3 and the influence of C1 located close to NH3 in the [NH3(CH2)6NH3] cation near T C are determined to be large, which implies that the structural change of CuCl4 linked to N-H⋯Cl is large. The 1H spin-lattice relaxation time (T 1ρ) in NH3 is shorter than that of CH2, and the 13C T 1ρ values for C1 close to NH3 are shorter than those of C2 and C3 due to the influence of the paramagnetic Cu2+ ion in square planar geometry CuCl4. The structural mechanism for the phase transition was the change in the N-H⋯Cl hydrogen bond and was associated with the structural dynamics of the CuCl4 anion.