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Nano-scale approaches for the development and optimization of state-of-the-art semiconductor photovoltaic devices

Garduno Nolasco, Edson

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

This project is concerned with both the study of different Multiple Quantum Wells (MQWs) structures using the In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP and a systematic investigation of the properties of InAs QD systems within GaAs with the aim of achieving enhancements of solar cell performance. The key challenge is the growth of QDs solar cell structures which exhibit sufficient absorption (enhanced infrared absorption) to increase short circuit current density (Jsc) but which can still maintains a high open circuit voltage (Voc). The research consists of epitaxial growth using state-of–the-art MBE, optical absorption, photoluminescence and high resolution x-ray diffraction measurements as well as device fabrication and characterization of novel solar cell structures. Optimization was performed on these novel cells to further improve their efficiency by inserting stacks of QD into different regions of the device. The effect of localized doping of such structures was used in an attempt to maintain and enhance the open-circuit voltage which in turn increases the device efficiency. The fabricated devices were characterized using measurements of the dark/light current-voltage (I-V) characteristics and spectral response (50-480 K). Solar cell external quantum efficiencies under standard air mass (AM) 1.5 spectrum were determined and the suitability of these new cells under solar concentration were assessed. Full physical simulations are performed using SILVACO semiconductors modelling software to generate models of multi-junction solar cells that were crucial in informing iterations to growth and fabrication and help to reconcile theory with experiment.One of the key findings, of this thesis, is the fact that Intermediate band photovoltaic devices using material based on InAs/GaAs vertically stacked quantum dot arrays, can be used in applications according to specific configuration criteria such as high temperature operation conditions. The intermediate band cell, including an inter-dot doped configuration, has been found to be a potential candidate as the inter dot doping profile reduces the efficiency degradation below the GaAs values including an enhancement in the open circuit voltage. It has been proved that these devices not only have a good performance at high temperatures but also by changing the vertical stacking QD layer periodicity can enhance the short circuit current density while keeping a large open circuit voltage. It was confirmed in practical device operation that thermal energy is required to enable the intermediate band in InAs/GaAs QD materials. The impact of this works can help in the future improvements of the intermediate band solar cells based on InAs on GaAs QD. The best overall efficiency of 11.6 % obtained in this work is an excellent value for so simple devices configuration. The Si3N4, tested for the first time on InAs/GaAs QD materials, reduces the reflectance on the device surface to a value of 2% and the operational wavelength can be tuned by controlling the layer thickness. A 100 nm Si3N4 antireflective coating proved to be an excellent coating from 700 to 1000 nm. In terms of short circuit current density a 37% enhancement was achieved.

Bibliographic metadata

Type of resource:
Content type:
Form of thesis:
Type of submission:
Degree type:
Doctor of Philosophy
Degree programme:
PhD Electrical and Electronic Engineering
Publication date:
Location:
Manchester, UK
Total pages:
179
Abstract:
This project is concerned with both the study of different Multiple Quantum Wells (MQWs) structures using the In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP and a systematic investigation of the properties of InAs QD systems within GaAs with the aim of achieving enhancements of solar cell performance. The key challenge is the growth of QDs solar cell structures which exhibit sufficient absorption (enhanced infrared absorption) to increase short circuit current density (Jsc) but which can still maintains a high open circuit voltage (Voc). The research consists of epitaxial growth using state-of–the-art MBE, optical absorption, photoluminescence and high resolution x-ray diffraction measurements as well as device fabrication and characterization of novel solar cell structures. Optimization was performed on these novel cells to further improve their efficiency by inserting stacks of QD into different regions of the device. The effect of localized doping of such structures was used in an attempt to maintain and enhance the open-circuit voltage which in turn increases the device efficiency. The fabricated devices were characterized using measurements of the dark/light current-voltage (I-V) characteristics and spectral response (50-480 K). Solar cell external quantum efficiencies under standard air mass (AM) 1.5 spectrum were determined and the suitability of these new cells under solar concentration were assessed. Full physical simulations are performed using SILVACO semiconductors modelling software to generate models of multi-junction solar cells that were crucial in informing iterations to growth and fabrication and help to reconcile theory with experiment.One of the key findings, of this thesis, is the fact that Intermediate band photovoltaic devices using material based on InAs/GaAs vertically stacked quantum dot arrays, can be used in applications according to specific configuration criteria such as high temperature operation conditions. The intermediate band cell, including an inter-dot doped configuration, has been found to be a potential candidate as the inter dot doping profile reduces the efficiency degradation below the GaAs values including an enhancement in the open circuit voltage. It has been proved that these devices not only have a good performance at high temperatures but also by changing the vertical stacking QD layer periodicity can enhance the short circuit current density while keeping a large open circuit voltage. It was confirmed in practical device operation that thermal energy is required to enable the intermediate band in InAs/GaAs QD materials. The impact of this works can help in the future improvements of the intermediate band solar cells based on InAs on GaAs QD. The best overall efficiency of 11.6 % obtained in this work is an excellent value for so simple devices configuration. The Si3N4, tested for the first time on InAs/GaAs QD materials, reduces the reflectance on the device surface to a value of 2% and the operational wavelength can be tuned by controlling the layer thickness. A 100 nm Si3N4 antireflective coating proved to be an excellent coating from 700 to 1000 nm. In terms of short circuit current density a 37% enhancement was achieved.
Thesis main supervisor(s):
Thesis advisor(s):
Funder(s):
Language:
en

Institutional metadata

University researcher(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:228176
Created by:
Garduno Nolasco, Edson
Created:
30th June, 2014, 15:28:03
Last modified by:
Garduno Nolasco, Edson
Last modified:
20th October, 2014, 12:56:23

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