# Advances in the physicochemical characterization of lead-free hybrid perovskite [NH3(CH2)3NH3]CuBr4 Crystals – Scientific Reports

### crystal structure

Single crystal XRD analysis of [NH3(CH2)3NH3]CuBr4 was performed at 298 K. The structure, lattice constants and space group of this crystal were monoclinic, with a = 8.052 ± 0.009 , b = 7.560 ± 0.009 , c = 17.611 ± 0.190 , β = 96.920 ± 0.05°, Z = 4 and p21nand this result was in good agreement with an earlier report by Halvorson and Willett28

### Thermodynamic property:

In the DSC experiment, there was no phase transition temperature in the range of 200-500 K; however, large exothermic peaks were observed at 546 and 577 K (Supplementary Information) 1† To confirm that the DSC peaks at 546 and 577 K are related to the phase transition, TGA and differential thermal analysis (DTA) experiments were performed; the results are shown in fig. 2† The TGA results showed that this crystal is thermally stable up to 504 K. The initial weight loss of [NH3(CH2)3NH3]CuBr4 started at 504 K, and there was no weight loss before the decomposition temperature. In the TGA curve, [NH3(CH2)3NH3]CuBr4 showed a two-phase decomposition at high temperatures. The initial weight loss (17%) occurred in the 500-550 K range, which may be due to the breakdown of HBr in [NH3(CH2)3NH3]CuBr4† The decomposition in the second phase (63%) occurred due to the presence of an inorganic group in the range of 550-650 K. The amount remaining as a solid was calculated from the TGA data and chemical reactions. The weight losses of 17 and 35% at approximately 546 and 607 K are probably due to the decomposition of the HBr and 2HBr residues, respectively, which is consistent with the exothermic peak in the DSC curve. The molecular weight abruptly decreased between 550 and 650 K, with a corresponding weight loss of 63% at about 650 K.

Furthermore, optical polarization microscopy experiments were performed to understand the thermal decomposition and melting phenomena of the crystals. The crystal was brown at 300 K, as shown in the inset of FIG. 2† Although no changes were observed from 300 to 500 K, the crystal started to melt slightly and turned from brown to dark brown at about 543 K. The color change was probably due to decomposition due to the loss of HBr, as well as geometric changes in CuBr4† Above 600 K, the surface and edges melted significantly. The thermogram clearly indicated that 543 K was the melting point of the crystal. Hence the [NH3(CH2)3NH3]CuBr4 crystal is suitable for applications up to 504 K.

### 1H NMR chemical shifts and spin-lattice relaxation times

The 1H NMR chemical shifts of the [NH3(CH2)3NH3]CuBr4 crystals were recorded while the temperature was raised as shown in Fig. 3† Below 270K, only one 1H resonance signal was observed and the intensity and line width of the 1The H signal was very small and wide, respectively, which made detection challenging. The resonance signal showed asymmetrical shapes due to the overlap of the two types NH3 and CH2 signals. The 1H NMR chemical shift for CH2 was recorded at δ = 5.51 ppm at 300 K, while that for NH3 was recorded at δ = 10.94 ppm, which was then split into two resonance lines. The rotating side tires for CH2 are represented by open circles and those for NH3 are represented by crosses. The 1H chemical shifts for CH2represented by the dotted line in FIG. 3did not change significantly with increasing temperature, while the change in the 1H chemical shifts for NH3 to the lower chemical shift as the temperature increased. The greater shift in the 1H NMR chemical shift of the NH3 in the cation with changes in temperature, than that of the CH2 is reason for the big change in the N−H∙∙∙Br hydrogen bonding between the Br around Cu and the H of NH3

The relation of the decay rate of proton magnetization is determined by T and the Eq. †12736373839

$${\text{P}}(\tau ) = {\text{P}}(0){\text{exp}}( – \tau /{\text{T}}_{{{1}\ uprho }} ),$$

(1)

where P() and P(0) are sometimes the signal intensities and = 0, respectively. The intensity changes observed in the 1H NMR spectra were recorded with changing delay times at a given temperature, and at 300 K, the 1H NMR spectrum was plotted with a delay time ranging from 0.01 to 30 ms as shown in FIG. 4† From the slope of the intensities of the 1H signal indicated by the arrow vs. delay times, the 1HT can be calculated using Eq. †1† As a result, the 1HT values ​​for CH2 and NH3 are shown in FIG. 5 as a function of the inverse temperature. The 1HT values ​​were on the order of a few milliseconds for CH2 and NH3, and their values ​​were temperature dependent. As shown in the cation structure in FIG. 5the 1H from CH2 is expressed in red, and the 1H of NH3 is expressed in black, which is the same as the T values. the T values ​​decreased as the temperature increased and then rose sharply again at 210 K. Below 300 K, only the 1HT value for NH3 is displayed, and the 1HT values ​​of CH2 above 300 K have a longer T values ​​then 1H of NH3† the T vs. inverse temperature curve showed minima of 5.80 ms at 210 K, indicating the existence of clear molecular movements. the T values ​​can be explained by the correlation time τC for molecular motion. the T value for the molecular motion based on the Bloembergen-Purcell-Pound (BPP) theory is given by3536373839

 {1}/{\text{T}}_{{{1}\uprho }} = {\text{G}}(\gamma_{{\text{H}}} \gamma_{{\text{ C}}} \hbar /r^{{3}} )^{{2}} \left[ {{\text{4F}}_{{\text{a}}} + {\text{F}}_{{\text{b}}} + {\text{3F}}_{{\text{c}}} + {\text{6F}}_{{\text{d}}} + {\text{6F}}_{{\text{e}}} } \right] †

(2)

where FaC†[1 + ω12τC2]fbC†[1 + (ωC − ωH)2τC2]fcC†[1 + ωC2τC2]fdC†[1 + (ωC + ωH)2τC2]and FeC†[1 + ωH2τC2]† Here G is a coefficient, γhuh andC are the gyromagnetic ratios of the proton and carbon, respectively, ħ is Planck’s reduced constant, ωhuh andC are the Larmor frequencies of 1Hand 13C, respectively r is the distance between the proton and carbon, and ω1 is the spin-locking pulse sequence with a 71.42 kHz locking pulse. In the rotating frame, τC can be obtained when1C = 1, and the coefficient G in Eq. †2) can be obtained from Th, Cand1† Using this G-value, τC was obtained as a function of inverse temperature. The local field fluctuation is determined by the thermal movement, which is activated by thermal energy. Therefore,C is represented by the Arrhenius behavior: τCOexp(− Ea/kBT), where Ea and kB are the activation energy and Boltzmann constant, respectively36† theC vs. 1000/T was plotted on a logarithmic scale (inset of Fig. 5), and the Ea by 1H, depending on molecular dynamics, was obtained at 4.25 ± 0.25 kJ/mol per dot line.

### 13C NMR chemical shifts and spin-lattice relaxation times

The 13C NMR chemical shifts of [NH3(CH2)3NH3]CuBr4 were measured as a function of temperature, as shown in Fig. 6† The 13CMAS NMR spectra showed two resonance signals at all temperatures. The 13C NMR spectrum for TMS was recorded at 38.3 ppm at 300 K and used to determine the exact chemical shift of . to decide 13C27† Here, the CH2 between the two CH2 groups is labeled C1 and the CH2 close to NH3 is labeled C2, as shown in the inset of Fig. 6† The two resonance signals at 300 K were recorded at chemical shifts of = 33.54 and δ = 177.07 ppm for C1 and C2, respectively. The 13C chemical shifts for CH2 were different for C1 far from those of NH3 and C2 close to that of NH3† The 13C chemical shift for C1 changed slowly and did not vary significantly with increasing temperature, while that for C2 moved abruptly to the lower chemical shift side with increasing temperature compared to that for C1.

The changes in the intensity of the 13C NMR spectral peaks with increasing delay times were measured at a given temperature in the same way as the 1HT measuring method. The 13CT values ​​of the slope of the recovery traces are described by a single exponential function in Eq. †1† the T values ​​for C1 and C2 as a function of 1000/temperature are shown in fig. 7† In the cation structure, C1 is shown in green, C2 in red and T is displayed in the same way. 13CT values ​​for C2 showed no changes in the temperature range measured in this study, and the T for C1 according to the temperature change showed a similar trend as that for 1HT† The 13CT values ​​were about 10 times longer than the 1HT values. The 13CT values ​​were not affected by the spin diffusion due to the small dipolar coupling, which results from the low natural abundance. On the other hand, the T values ​​decreased as the temperature increased and then rose again at 200 K. Below 300 K, only the 13CT value for C1 vs. the inverse temperature showed a minimum of 28.58 ms at 200 K, implying the existence of active molecular movements at low temperatures.C values ​​on a logarithmic scale, as obtained by Eq. †2) versus 1000/T, were plotted (inset of Fig. 7† the Eadepending on the molecular dynamics of 13C, was measured as 8.59 ± 0.47 kJ/mol. The 13CEa value was about double that of 1HEa