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Developing next generation, non-toxic, inorganic materials for photovoltaics and thin-film transistors



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Huq, Tahmida 


The focus of this thesis is on developing two next-generation inorganic materials for thin-film device applications, namely photovoltaics and thin-film transistors. Both of these device applications are crucial in today’s technology-based society with photovoltaics enabling sustainable generation of electricity whilst advancements in thin-film transistors allow for development of low-power, efficient electronic devices. BiOI, a non-toxic, perovskite-inspired material is investigated for photovoltaics (PVs) whilst Cu2O, with a reasonably high predicted hole mobility is developed for p-type thin-film transistors (TFTs). These novel materials are fabricated with scalable processing techniques which enable lower manufacturing costs and improve energy efficiency. In the first results chapter, the suitability of non-toxic BiOI as a photovoltaic material is investigated. Dense BiOI films grown by thermal chemical vapour deposition (CVD) incorporated into an all-inorganic ITO/NiOx/BiOI/ZnO/Al stack demonstrate high external quantum efficiencies (80% at 450 nm wavelength). However, the 1.9 eV band gap of BiOI is not matched to terrestrial solar spectra; the PVs achieve 1.8% power conversion efficiency. Owing to improved spectral matching with indoor light spectra, BiOI devices improve in efficiency to 4.37% under 1000 lux white light emitting diode indoor illumination, and millimetre-area BiOI devices are sufficient to power novel carbon nanotube inverters. The factor limiting further efficiency gains is downwards band-bending at the BiOI/NiOx interface owing to NiOx having a lower work function. In the second chapter, MoS2 is investigated as an alternative to NiOx where the work function of MoS2 is tuned through oxygen plasma treatment to increase its work function. The experimental examination of defect tolerance of BiOI is conducted in chapter three. BiOI films are vacuum-annealed to induce surface composition changes. Large changes in surface atomic fractions (reduction in iodine and bismuth by 40% and 5% respectively, and increase in oxygen by >45%) are observed. These significant changes do not affect the electronic and optoelectronic properties, in contrast to traditional covalent semiconductors. The applicability of low-temperature (≤ 200 °C) atmospheric pressure spatial atomic layer deposited (AP-SALD) Cu2O for use in p-type TFTs is explored in chapter four. The performance of AP-SALD Cu2O is comparable to atomic layer deposition (ALD) grown Cu2O with an ION/IOFF ratio of 103, and field-effect mobility between 10-4 - 10-3 cm2·V-1·s-1, illustrating the potential of AP-SALD grown films for integration with flexible substrates.





Driscoll, Judith


atmospheric pressure spatial atomic layer deposition, bismuth oxyiodide, copper oxide, indoor photovoltaics, nanotechnology, perovskite-inspired materials, photovoltaics, thin-film transistors


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
EPSRC (1647980)
EPSRC (1647980)
PragmatIC Aziz Foundation