Alkali elemental doping effects on Cu2CdSnS4 thin films

• Main Author: Widianto, Janet
• Other Authors: Lydia Helena Wong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Materials::Energy materials
• Online Access: https://hdl.handle.net/10356/166616
• Institution: Nanyang Technological University

Kesterite absorber, Cu2ZnSnS4 (CZTS), solar cells have received considerable attention due to structural similarity to high performing Cu(In,Ga)Se2 (CIGS), but with earth-abundant materials usage. However, the low open-circuit voltage (Voc) has hindered its progress in achieving theoretical power conversion efficiency. Substituting Zn with cation that has larger ionic size difference than Cu, such as cadmium has shown to alleviate defects problem. Nonetheless, the current efficiency of CCTS is still far lower than the theoretical Shockley Queisser limit of around 30%. As CCTS has a similar structure to CZTS and CIGS, the efficiency improvement methods used in CZTS and CIGS may work for CCTS, for instance alkali elements doping. In this work, solution-processed CCTS with various concentrations of alkali elements doping, such as lithium, sodium, potassium, rubidium, and caesium, were synthesized and investigated based on their photovoltaic performances and crystal structure. Through photovoltaic characterization, the best device was achieved with caesium doping, having 8.3% efficiency, current density (Jsc) 25.5 mA/cm2, Voc 0.56 V, and fill factor 57.6%. The doping shows peak shifts and smaller FWHM of CCTS peak in XRD spectra, implying an increase in crystallinity. Moreover, the intensity of the secondary phase CdS peaks reduced, suggesting less secondary phase formation.