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Opto-Electrical Interactions in Next Generation Semiconductor Thin Films and Devices / ROBIN KERREMANS

Swansea University Author: ROBIN, KERREMANS

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DOI (Published version): 10.23889/SUthesis.58767

Abstract

The processes by which optical and electrical energies are transduced are at the heart of many modern technologies such as solar cells, light emitting diodes, photodetectors, imaging systems and displays. The basic functional element of these ‘opto-electrical’ devices are semiconductors, and the und...

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Published: Swansea 2021
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Meredith, Paul ; Armin, Ardalan
URI: https://cronfa.swan.ac.uk/Record/cronfa58767
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Abstract: The processes by which optical and electrical energies are transduced are at the heart of many modern technologies such as solar cells, light emitting diodes, photodetectors, imaging systems and displays. The basic functional element of these ‘opto-electrical’ devices are semiconductors, and the underpinning physics of how they transduce light and electricity is well understood for conventional inorganic materials such as silicon and gallium arsenide. However, new semiconductors such as the organics and the organohalide perovskites present additional opto-electrical questions and challenges since they are molecular solids with varying degrees of disorder and crystallinity. The work described in this thesis addresses these new questions and challenges, particularly in relation to how existing solid-state physics concepts must be adapted to reliably predict and model material-and-device-level structure-property relationships and performance. Two basic technology platforms are examined in detail – solar cells and light emitting diodes, with particular reference to so-called reciprocity. A second focus of the discussion is accurate determination of optical constants for these new semiconductors – a challenging endeavour due to factors such as morphological heterogeneity. Transfer matrix and drift diffusion formalisms are relied heavily upon to model, simulate and explain multi-layer device performance, and ellipsometry and spectrophotometry are utilised as the primary analysis and characterisation methodologies. A new approach to optical constant determination is presented and validated, as is an adapted reciprocity framework for the linking of absorption, emission and charge transfer state characterisation in the presence of cavity interference. Several ‘difficult’ solar cell systems are analysed in detail – in particular the previously mysterious working principles of the so-called carbon-stack perovskite system are elucidated for the first time. These findings explain how an electrically non-selective contact can still function as an effective photovoltaic electrode dependent upon the local minority and majority carrier concentration profile. The research described herein advances our understanding of next generation semiconductor opto-electrical physics and provides more practical means for the community to analyse optical constants.
Keywords: Opto-electronics, solar cells, transfer matrix
College: College of Science