STUDY OF DOPING IMPACT ON SUPRESSING CU-ZN DISORDERS IN CZTS SOLAR CELL ABSROBER LAYER BULK

• Main Author: Abdillah, Nurfauzi
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62496
• Institution: Institut Teknologi Bandung

CZTS (Cu2ZnSnS4) is a thin film solar cell material that is environmentally friendly and abundantly available in nature. Unfortunately, the energy conversion performance of CZTS solar cells has been hampered at 12.6% since 2014, despite having a relatively high theoretical efficiency at 28%. Most of the low efficiency causes in CZTS solar cells are Voc deficiency. The formation of Cu-Zn disorders in the CZTS bulk which is allegedly due to the presence of band tailings is one of the main contributors to this deficiency problem. Previous studies have reported that the use of isovalent dopants that have different ionic radius with Cu and Zn cations may improve Voc by suppressing the formation of Cu-Zn disorders. In this study, a Density Functional Theory (DFT) calculation was performed on eight isovalent dopants (Ag, Li, Na, K, Cd, Be, Mg, and Ca) having various radius size. The best dopant candidate is selected based on their potential to suppress Cu-Zn disorders formation. The calculations are implemented in the Vienna Ab-Initio Simulation Package (VASP) software through the GGA (Generalized Gradient Approximation) functional for system geometry optimization and GGA with U parameter correction to obtain the electronic structure. The system configuration used is pure CZTS system, CZTS with Cu-Zn defects, CZTS with substitutional and interstisial doping. All dopant showed thermodynamic stability at the substitutional site. Ag, Li, Na, and Be produce high Cu-Zn defect formation energy compared to other candidates, where Ag is the highest. These four dopants indicate different characteristics of the tail states. Group IA isovalent doping are able to prevent the formation of band tail in the VBM area, thereby increasing the value of the band gap which decreases due to the presence of Cu-Zn defects. In addition, the results of Bader charge analysis show that Li and Be are predicted to increase the concentration of charge carriers. Therefore, Li was chosen as the best dopant candidate that has the potential to overcome Voc deficiency in CZTS solar cells.