STUDY OF CALCIUM (CA) AND MANGANESE (MN) EFFECT ON DOPED-PEROVSKITE CSSNI3 STABILITY USING DENSITY FUNCTIONAL THEORY

• Main Author: Hanif Tejo Baskoro, Fakhrian
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/57529
• Institution: Institut Teknologi Bandung

The increase in human needs makes energy consumption also increase. To compensate, energy sources need to be increased. However, most of the energy sources still come from non-renewable energy, which can be depleted and is not environmentally friendly. Therefore an increase in non-renewable energy sources is needed. Solar cells are one of the most developed renewable energy sources. They are expected to be able to replace non-renewable energy sources so that efforts to increase efficiency and reduce costs continue to be carried out. Perovskite halide materials such as MAPbI3 are one of the advanced materials that are widely developed as optoelectronic material applications, due to their high absorbance and band gap energy values that are suitable for solar cells. However, the use of Pb has the potential to pollute the environment and the changes in the structure and electronic properties observed in atmospheric conditions have made this perovskite not yet commercialized. Sn-based perovskite halide is an alternative material, with good electronic properties and low pollution levels. However, the oxidation of Sn2+ to Sn4+ raises new instability problems that need to be solved. This oxidation transforms the structure and electronic properties of CsSnI3 and hinders its application in solar cells. In several previous studies, it is known that the use of doping can increase the stability of perovskite materials. In this study, doping simulations are carried out on cubic phase CsSnI3 perovskite material to prove the theoretical ability of the doping method in increasing the stability of CsSnI3. The materials used as dopants are Ca and Mn. The research is conducted by optimizing the CsSnI3 perovskite structure using interpolation method, with the obtained lattice constant for the CsSnI3 perovskite structure used to be 6.28 ?. This structure is then expanded to be able to carry out vacancy and doping modeling. Sn vacancies are known to cause changes in the oxidation state of Sn in CsSnI3. In this study, we found that the Bader Sn charge on the vacant structure increased to +0.934 which indicates the presence of Sn4+. Furthermore, doping modeling is carried out to identify the effect of doping in inhibiting the appearance of Sn4+ in the perovskite structure. The dopant concentrations are varied by 3.7% and 7.4% to determine the concentration that gives the highest stability. Based on the Bader charge analysis, it is observed that the doped structures still maintain the Sn2+ state because the value of the Sn bader charge on the structures is still below the value of the Sn4+ and Sn bader charges in the vacancy structure. From the calculation of the formation energy, CsSnI3:Ca has negative formation energy, which indicates that the structure is easier to form. Meanwhile, CsSnI3:Mn has a positive formation energy so it can be said that the structure is more difficult to form. Then we model the Sn vacancy in the doped structure as in the pure structure. We find that the formation energy of the Sn vacancy in CsSnI3:Ca and CsSnI3:Mn tends to be lower than in the pure structure. However, the Ca dopant with a concentration of 7.4% obtains a positive Sn vacancy formation energy which indicates that the Sn vacancy tends to be inhibited in this structure. From the DOS and band structure analysis, an increase in band gap energy in CsSnI3:Ca is obtained. Meanwhile, in CsSnI3:Mn, a state appears near the Fermi energy originating from the 3d Mn orbital. This state becomes the minimum conduction band of CsSnI3:Mn. From the calculation of the band gap on the band structure, the band gap energy increases in CsSnI3:Mn, with the highest band gap value at 3.7% Mn. This band gap energy data is then used to estimate the efficiency of solar cells from each structural variation and the highest efficiency was achieved by CsSnI3:Ca with a Ca concentration of 7.4%. Based on the results obtained, CsSnI3:Ca with a dopant concentration of 7.4% gives a better increase in stability. This is supported by the low formation energy of the structure with the formation energy of the Sn vacancy is higher than in the pure structure. Then from the calculation of the efficiency of solar cells, it is found that CsSnI3:Ca with a concentration of 7.4% produces the highest solar cell efficiency so that by reviewing performance and stability, the use of Ca dopant with a concentration of 7.4% can be a solution to obtain a stable and high-performance CsSnI3.