Using First-Principles Calculations and Molecular Dynamics to Investigate the Properties of Cesium-Based Halide Perovskites for Photovoltaic Applications
Open Access
- Author:
- Almishal, Saeed
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 18, 2021
- Committee Members:
- Ola Hamada Rashwan, Thesis Advisor/Co-Advisor
Brian Allen Maicke, Committee Member
Abdallah Ramini, Committee Member
Rick Ciocci, Special Signatory - Keywords:
- First-principles calculations
Density Functional Theory
Molecular Dynamics
Cs-based halide perovskite
Ge-based halide perovskite
structural properties
phase transformation
photovoltaic perovskites
electronic properties - Abstract:
- Halide perovskites have gained tremendous research attention since the first solid-state perovskite solar cell in 2012 due to their optoelectronic properties and low processing temperatures. Most of the current research focuses on improving these perovskites' stability, tuning their bandgaps, and optimizing their optical properties. Finding a stable, non-toxic, environmentally friendly alternative to Pb+2 cation in halide perovskites compounds for photovoltaic applications has become critical due to the huge environmental concerns. Cesium-based halide perovskites have great potential as nontoxic alternatives for efficient solar cells with improved stability. Computational materials simulations are needed to understand, study, and optimize their structures, stability, phase transformation, electronic and optical properties. In this thesis, the first-principles density functional theory (DFT) in VASP platform with two potential functionals PBE and PBEsol, were utilized to investigate the structural and electronic properties of CsPbI3 polymorphs and the trigonal inorganic CsGeI3-xBrx mixed-halide perovskites (x = 0.0, 1.0, 2.0 and 3.0) for photovoltaic applications. Our results showed that for both CsPbI3 and CsGeI3-xBrx, the bandgap edge states come mainly from B-X bonds. As the bromine content increases in CsGeI3-xBrx, the structural properties, such as the lattice parameters, Ge-X bond lengths, and volume, decrease. The bandgap calculations showed that the bandgap increased with the increase in the Br content. The electronic density of states revealed that only I 5p, Br 4p, and Ge 4s states contributed to the Valence Band Maximum (VBM) whereas, the Conduction Band Minimum (CBM) is mainly contributed by Ge 4p states in all compounds of CsGeI3-xBrx. Finally, a strong negative correlation was found between the Ge-X bond length and the bandgap. Molecular dynamics in LAMMPS software package was also utilized to investigate the structural properties and phase transformation of CsPbI3 by applying the appropriate force field. A novel hybrid force field was introduced, referred to as “Hybrid EABC,” where EABC stands for Embedded-Atomic-Method and Buckingham- Coulomb potential. The outcomes from employing both Buckingham- Coulomb potential and Hybrid EABC were compared. The new Hybrid EABC potential succeeded in reproducing the experimentally reported and the ab initio structure’s radial distribution functions and phase transitions of CsPbI3. Additionally, the novel Hybrid EABC molecular dynamics potential was able to detect the phase transformation from the orthorhombic to a cubic crystal structure and their melting temperatures at 594K and 750K, respectively, which agreed with the experimental values to within 1%. The new proposed hybrid potential proved to be accurate. It could potentially be used to infer the structure stability and the mechanical and thermal properties of the pure inorganic halide perovskites and the mixed halide perovskites which are used in various applications. The main findings confirmed the high potential of the inorganic Ge-based mixed halide perovskites for the photovoltaic applications as non-toxic, environmentally friendly alternatives and provided insights into their stability, structural properties, and electronic properties.