Atomic layer deposition and metal organic chemical vapour deposition of materials for photovoltaic applications

Hindley, Sarah Atomic layer deposition and metal organic chemical vapour deposition of materials for photovoltaic applications. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

In this thesis, the development of thin films and nanostructures prepared with chemical vapour techniques are investigated for applications in photovoltaics. The deposition of both p-type and n-type oxides are investigated as a means of preparing all oxide p-n junctions. Both CVD and ALD precursors and processes have been developed. Zinc oxide nanowires are of interest as an n-type absorber layer with high surface area. In this thesis, the crystal structures of DEZn and DMZn were revisited and a new understanding of conventional zinc CVD precursors is presented. For DEZn a single structure was isolated and characterised with single crystal XRD. In the case of DMZn two temperature dependant structures were identified: namely α and β at 200K and 150K respectively. The DMZn precursor was subsequently exploited in a series of adduct-based precursors of the notation [DMZn.L] (where L = 1,2-dimethoxyethane, 1,4-dioxane and 1,4-thioxane). The crystal structures of these precursors were determined, and they were subsequently used to grow ZnO and sulphur doped ZnO across a range of CVD growth conditions. The microstructure and electronic properties of the nanowires have been characterised with electron microscopy, x-ray diffraction, Raman spectroscopy and photoluminescence. The II:VI ratio and substrate temperatures were both confirmed as playing a significant role in determining the microstructure of the nanowires. It has been demonstrated that the use of [DMZn.L] can avoid the pre-reaction between DMZn and oxygen. The studies with the thioxane adduct suggests the involvement of the ligand and hence sulphur incorporation in the nanowires. Two copper precursors were selected as the basis of p-type copper oxide film studies. The first Cu(hfac)(COD) has been used previously to deposit copper oxide by conventional CVD. In this thesis it is demonstrated for the first time that a pulsed LI-ALD approach can be exploited to deposit CuO with ozone as the co-reagent. An unexpected outcome of the research was the successful growth of electrically conductive copper metal films with a sheet resistance of 0.83Ω/□ when the precursor was thermally decomposed. The second copper precursor, namely CpCu(tBuNC) was used in atomic layer deposition to successfully deposit CuO or Cu2O with oxygen plasma and water respectively. Having identified that the β-diketonate compound yielded copper, the cyclopentadienyl based precursor was investigated as a route for the deposition of conductive copper metal films. Both thermal decomposition and a hydrogen plasma ALD process have been shown to deposit copper. With the plasma process, deposition of copper was demonstrated as low as 75˚C with a sheet resistance of only 0.55Ω/□. This thesis has demonstrated novel deposition routes for p- and n-type oxide materials which have potential future applications in thin film or nanostructured photovoltaic technology.

Item Type:	Thesis (Doctor of Philosophy)
Additional Information:	Date: 2014-01 (completed)
Uncontrolled Keywords:	ALD, CVD, photovoltaics, all-oxide
Subjects:	?? TA ??
Divisions:	Faculty of Science and Engineering > School of Engineering
Depositing User:	Symplectic Admin
Date Deposited:	07 Aug 2014 09:03
Last Modified:	16 Dec 2022 04:41
DOI:	10.17638/00016313
Supervisors:	Chalker, Paul
URI:	https://livrepository.liverpool.ac.uk/id/eprint/16313