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Title: Engineering and characterisation of silicon-based nanoscale interfaces and their impact in solar devices
Author: Rocks, Conor Joseph
ISNI:       0000 0004 6494 9709
Awarding Body: Ulster University
Current Institution: Ulster University
Date of Award: 2017
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The main objective of this work was to investigate silicon based nanoscale interfaces with other exciting materials and to investigate their applicability to photovoltaics. In this context, quantum confined silicon nanocrystals (Si NCs) were synthesised and methods used to manipulate surface properties in order to maintain desirable opto-electronic properties. Additionally, a spray deposition technique was developed in order to integrate Si NCs more effectively with organic-inorganic halide perovskite, for opto-electronic conversion and photovoltaic applications. One of the most important findings of this work is the control and understanding of Si NC oxidation that presented ideal conditions for the non-metallic growth of carbon nanotubes (CNTs), and the production of a Si NC-CNT nanocomposite. It was experimentally determined that the growth of CNTs was reliant on small nanocrystal assemblies (< 100 nm) coupled with an oxide shell thickness of at least 1 nm, before acting a suitable catalyst. Secondly, practicality of spray technique was demonstrated for perovskite solar devices where surface chemistry and subsequent change in electronic structure affected performance. Through optimizing the absorber thickness the short-circuit current density was increased from 4.9 mA/cm2 to 22.3 mA/cm2, increasing overall power conversion efficiency from 0.83% to 5.22%. Sprayed thin films however showed increased surface degradation that affected the stability under continued illumination, highlighting potential limitations existing for deposition technique. Following, third generation solar cells based on perovskite-quantum dot architectures with p-doped and n-doped Si NCs were fabricated for the first time. The Si NCs embedded within perovskite film absorbed diffusing moisture and became oxidized due to their hydrophilic nature which consequently slowed the chemical decomposition of the perovskite. The slowed degradation allowed composite perovskite-quantum dot devices to perform better under continued illumination with short- circuit current density reaching around 20 mA/cm2 and efficiencies above 6 %. Efforts were made towards an all Si NC heterojunction devices where mixing with perovskite in the solution phase allowed for more compact films that showed rectifying behaviour and demonstrated working devices.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available