Fabrication and characterization of AgBiS2 and BiSI light harvesting materials for thin film solar cell application

Recently, AgBiS2 and BiSI are both known as promising absorbing candidates for thin film solar cell application. Both compounds contain earth abundant and non-toxic elements, facilitating their low cost and large-scale production. In addition, due to the tuneable optical bandgaps by composition ratios (AgBiS2 Eg ~ 1.25-1.5 eV and BiSI Eg ~ 1.40-1.60 eV), both compounds can be used in tandem solar cell application, combined with lower optical bandgap materials (like Si (silicon)) to achieve higher power conversion efficiency beyond the single junction efficiency limit. Reaching a comprehensive study on both absorbers, investigating and optimizing single junction solar cells is the priority. This thesis focuses on thin film deposition, various properties investigation, and AgBiS2 and BiSI compounds' optimization for high-performance solar cell application. Firstly, the effects of solvent, composition ratio, and heat treatment temperature are carefully studied on the structural, optical, and electrical properties of the single phase AgBiS2 thin film prepared by the precursor method. Then AgBiS2-based solar cell is fabricated with different composition ratios (Ag/Bi = 0.8, 1.0, and 1.2) of the absorber to study the photovoltaic properties of the solar cells. The obtained optical bandgap and absorption coefficient are in the range of 1.20-1.32 eV and α > 2 ×105 cm-1 at 𝜆 =600 nm, respectively. Moreover, the best photovoltaic performance of AgBiS2-based solar cells is 1.40% PCE among all the composition ratios. Secondly, to improve the absorber performance, copper is doped into the AgBiS2, and the effect of copper presence is investigated on optical and electrical properties and photovoltaic behaviors. Doping copper increases the carrier concentration and optical bandgap of AgBiS2. This leads up to a 50% improvement of open circuit voltage of the copper doped solar cells. In addition, solar cell efficiency is improved from 0.99% PCE (without copper) up to 1.59% PCE (with 3% copper) mainly from voltage rising. Thirdly, BiSI thin film is successfully synthesized by two (precursor and hydrothermal) methods, obtaining randomly and vertically oriented crystals, respectively. Moreover, the stable ranges of the reacting temperature and composition ratio are investigated for achieving the pure phase of BiSI prepared by each of the above methods. Finally, considering the effects of composition ratio and synthesizing condition, optical properties and the photovoltaic performance of BiSI-based solar cells are studied; however, carrier concentration and mobility are not measured for BiSI. Optical indirect bandgaps are varied with a composition ratio in the proper range of 1.3 to 1.6 eV.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2022

Author dc:creator

• Tabari-Saadi, Yasaman

• Thin-film Solar cell
• AgBiS2
• BiSI

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/24277

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/100570