Functional nano-structures using atomic layer deposition

• Main Author: Salgård Cunha, Pedro
• Published: University of Cambridge 2014
• Subjects: 621.3815
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607585

This thesis is a study of the crossover between the fields of atomic layer deposition, block copolymer self-assembly and photovoltaics. The central research question is how the technique of atomic layer deposition (ALD) can be incorporated into the creation of nano-structured functional materials and devices, specifically in the areas of photovoltaics and biomimetics. The work aims to explore the capabilities of ALD as a strategy for overcoming two main challenges: the creation of extremely thin conformal metal oxide layers and the replication of complex high surface area templates. In these areas of fabrication on the nano-scale, ALD has consistently been shown to achieve more conformal depositions of higher quality and with greater thickness control than other thin film experimental techniques. Rather than understanding these challenges in their narrowest sense, the thesis seeks to explore the full range of possibilities inherent to the ALD process for a number of quite different applications, all of which are linked by their reliance on self-assembled templates or the creation of functional photovoltaic structures. The thesis begins by providing three background chapters. Chapter 1 covers photovoltaics, with an emphasis on liquid and solid-state electrolyte dye-sensitised solar cells. Chapter 2 is concerned with the self-assembly of microphase separating diblock copolymers and covers the special case of the gyroid morphology which is utilised extensively in the thesis. Chapter 3 describes the ALD technique. It deals with the physical and chemical underpinnings of this process, as well as its application for the coating of non-ideal substrates such as polymeric and high-aspect-ratio structures. Chapter 4 then introduces the key experimental techniques and methods utilised throughout the research. These introductory sections serve as the foundation for the four major experimental chapters of the thesis. Chapter 5 reports on the formation of gyroid-structured coreshell Cu/Cu2O/CuO solar cells via the post-deposition thermal oxidation of electrodeposited copper. Chapter 6 deals with the replication of gyroid-structured polystyrene templates using metal oxides deposited via ALD, for use in dye-sensitised solar cells. The chapter presents a novel ozone-based functionalisation scheme which overcomes the inherent difficulty of ALD nucleation on polymer surfaces. Chapter 7 covers two projects which are ongoing. One is focused on the application of ALD for the deposition of metal sulphides, and primarily describes the safety and experimental considerations for the installation of H2S as the sulphur source for this process. The other is concerned with the deposition of ultra-thin titania compact layers for dye-sensitised solar cells using ALD. Chapter 8 reports on the use of ALD in the biomimetic replication of the spectral response of the wing scales of the Papilio Blumei butterfly.