Probing structure–property relationship in chemical vapor deposited hybrid perovskites by pressure and temperature

Temperature-Dependent Phase Stable Hybrid Halide Perovskite Films by Chemical Vapor Deposition

“…Figure shows three representative GIXRD patterns at different temperatures along with their Le Bail fits. All three show a similar diffraction pattern with the tetragonal symmetry (SG I 4/ mcm ), demonstrating a remarkable stability over the temperature range of 20–300 K. The calculated lattice parameters at 300 K are found to be a = b = 8.900 (1) Å, c = 12.577 (5) Å, in agreement with other reports of MAPbI 3 at 300 K. , The unique feature here is that, unlike the case of MAPbI 3 , there is no change to the orthorhombic phase in MAPbI 3– x Cl x at temperatures lower than 160 K. At all temperatures, the sample remains in the tetragonal symmetry. In each case for the fits, the R wp value was less than 5%.…”

“…Transport measurements from MAPbI 3 films can be complicated due to the dominance of ionic conductivity over electronic conductivity under dark conditions . In a prior work, we were successful in the synthesis of cubic phase MAPbI 3 films (at room temperature) and four-probe resistivity measurements yielded orders of magnitude lower values for resistance compared with MAPbI 3 films that are in the tetragonal phase at room temperature . We believe that the occurrence of the cubic phase under ambient conditions could induce some self-doping process due to the presence of local charge defects, similar to what has been observed in MASnI 3 .…”

“…The phase transition from orthorhombic (<160 K) ↔ tetragonal (160–320 K) ↔ cubic (>320 K) perovskite structures in MAPbI 3 has been determined by several structural and spectroscopic techniques. ,, However, insights into structural phase transformation, thus far, have been obtained from either spin-coated films or single crystals. In a prior work, we found that the CVD growth substantially increases the air stability while also inducing the stable cubic phase in MAPbI 3 at room temperature and at pressures as low as 0.25 GPa …”

“…More importantly, the trend in the resistance versus temperature showed a one-to-one correlation with the structural phase transitions (at 160 K from orthorhombic to the tetragonal phase and at 290 K from the tetragonal to the cubic phase). When MAPbI 3 is in the tetragonal phase under ambient conditions, the resistance typically decreases with increasing temperature …”

“…In a prior work, we found that the CVD growth substantially increases the air stability while also inducing the stable cubic phase in MAPbI 3 at room temperature and at pressures as low as 0.25 GPa. 24 Figure 2 displays a stacked GIXRD pattern from a MAPbI 3−x Cl x film at temperature steps of 10 K from 20 to 300 K. A quick observation highlights that the diffraction pattern undergoes minimal changes in MAPbI 3−x Cl x , suggesting a uniform phase across the entire temperature region. This is contrary to what has been observed in MAPbI 3 , where a distinct structural transformation from the tetragonal to the orthorhombic phase is observed in the range 140−170 K. 8,23 Figure 3 shows three representative GIXRD patterns at different temperatures along with their Le Bail fits.…”