In this research, we have studied CH3NH3PbI3 perovskite at ambient conditions and at high pressure by using the density functional method. The simulation cell of CH3NH3PbI3 perovskite at ambient conditions is shown in Figure 1.6.1. We have investigated the essential of the van der Waals interaction and found that it plays a major role in the lattice structure and also in the rotation dynamics of the methyl-ammonia (MA) molecules.
At high pressure, we found that phase transition from a tetragonal I4/mcm structure to a cubic Im3 structure, as shown in Figure 1.6.2. The orientation of the MA molecules play a major role in the lowest energy structure. The different orientation of the MA are labeled as Config1, Config2, Config3 and Config4. The red-dotted line marks the lowest energy structure. Furthermore, the volume-pressure relation is in good agreement with the experimental data (green diamonds) .
Next, we will study the physical properties, such as band gap, optical absorption and so on. This would lead to a suggestion to improve the efficiency of the perovskite as a solar energy material.
Principal Investigator: Associate Professor Dr. Udomsilp Pinsuk 1)