Preparation of Novel and Sustainable Transparent Conducting Electrodes for Photovoltaic Applications

Abstract

Transparent conducting electrodes (TCEs) are a unique class of materials that possess both low electrical resistivity and high optical transparency across the visible light range. Hence, they have been widely utilised in flat screen displays, photovoltaic cells, and light emitting diodes (LEDs). This thesis details the use of aerosol-assisted chemical vapour deposition (AACVD) to synthesise novel TCEs. Firstly, ZnO thin films were successfully deposited on glass substrates by AACVD and the effect of precursor solution concentration and post vacuum sintering on the film growth behaviour and electronic performance was thoroughly investigated. The results suggested that ZnO thin films derived from lower concentration were dense and compact with smaller and well-connected grains, as compared with those deposited from higher concentration which had larger but physically separate particles. Therefore, the films deposited from lower concentration had better optoelectronic performance (a resistivity of 6.38 Ω cm and a visible transmission of approximately 80%). The post vacuum sintering at 500 ℃ for 1 h improved the electrical conductivity (from 6.38 Ω cm to 2.28 Ω cm) but maintained the visible transparency which could be explained by the increase in the particle size and reduction of grain boundaries thereby enhancing the electron transport. Next, indium-free Mo-doped SnO2 thin layers were fabricated as alternative to ITO and the impact of Mo dopant levels upon the electro-optical properties was studied. The best-performing sample was achieved at 2.4 at.% of Mo which showed a low resistivity of 7.5 × 10^(-3) Ω cm and a transmission of 83% within the visible light range. This work presented the potential of synthesised Mo-doped SnO2 films by AACVD to substitute ITO to be employed in various fields. Moreover, the EDX measures demonstrated good agreement between theoretical Mo concentration in the solution and experimentally found amount of Mo in films, suggesting an exquisite control over doping levels by AACVD. Finally, indium-reduced multicomponent In-Sn-O thin films were investigated for the sustainability consideration. The thin films prepared at the optimal deposition temperature (450 ℃) exhibited a very low resistivity of 8.7 × 10^(-4) Ω cm and a transmittance of ca. 80% across the visible light spectra, which were comparative to the optoelectronic performance of commercial ITO substrates. More importantly, the indium content only accounted for approximately 70 at.% in the best-performing sample, which was much lower than that in ITO (commonly over 90 at.%). We believed that this work contributed a lot to the advancement of sustainable indium-reduced and indium-free TCEs. In addition, AACVD as a thin-film deposition method proved to have the potential to be used for standard industry production.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Allan Matthews (Supervisor) & David Lewis (Supervisor)