High-efficiency photovoltaics through mechanically stacked integration of solar cells based on the InP lattice constant

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dc.contributor.advisor Corbett, Brian en
dc.contributor.advisor Morrison, Alan P. en
dc.contributor.author Mathews, Ian P.
dc.date.accessioned 2014-11-10T12:06:43Z
dc.date.available 2014-11-10T12:06:43Z
dc.date.issued 2014
dc.date.submitted 2014
dc.identifier.citation Mathews, I. P. 2014. High-efficiency photovoltaics through mechanically stacked integration of solar cells based on the InP lattice constant. PhD Thesis, University College Cork. en
dc.identifier.endpage 163
dc.identifier.uri http://hdl.handle.net/10468/1705
dc.description.abstract Solar Energy is a clean and abundant energy source that can help reduce reliance on fossil fuels around which questions still persist about their contribution to climate and long-term availability. Monolithic triple-junction solar cells are currently the state of the art photovoltaic devices with champion cell efficiencies exceeding 40%, but their ultimate efficiency is restricted by the current-matching constraint of series-connected cells. The objective of this thesis was to investigate the use of solar cells with lattice constants equal to InP in order to reduce the constraint of current matching in multi-junction solar cells. This was addressed by two approaches: Firstly, the formation of mechanically stacked solar cells (MSSC) was investigated through the addition of separate connections to individual cells that make up a multi-junction device. An electrical and optical modelling approach identified separately connected InGaAs bottom cells stacked under dual-junction GaAs based top cells as a route to high efficiency. An InGaAs solar cell was fabricated on an InP substrate with a measured 1-Sun conversion efficiency of 9.3%. A comparative study of adhesives found benzocyclobutene to be the most suitable for bonding component cells in a mechanically stacked configuration owing to its higher thermal conductivity and refractive index when compared to other candidate adhesives. A flip-chip process was developed to bond single-junction GaAs and InGaAs cells with a measured 4-terminal MSSC efficiency of 25.2% under 1-Sun conditions. Additionally, a novel InAlAs solar cell was identified, which can be used to provide an alternative to the well established GaAs solar cell. As wide bandgap InAlAs solar cells have not been extensively investigated for use in photovoltaics, single-junction cells were fabricated and their properties relevant to PV operation analysed. Minority carrier diffusion lengths in the micrometre range were extracted, confirming InAlAs as a suitable material for use in III-V solar cells, and a 1-Sun conversion efficiency of 6.6% measured for cells with 800 nm thick absorber layers. Given the cost and small diameter of commercially available InP wafers, InGaAs and InAlAs solar cells were fabricated on alternative substrates, namely GaAs. As a first demonstration the lattice constant of a GaAs substrate was graded to InP using an InxGa1-xAs metamorphic buffer layer onto which cells were grown. This was the first demonstration of an InAlAs solar cell on an alternative substrate and an initial step towards fabricating these cells on Si. The results presented offer a route to developing multi-junction solar cell devices based on the InP lattice parameter, thus extending the range of available bandgaps for high efficiency cells. en
dc.description.sponsorship Enterprise Ireland (TD/08/338 for the project MODCON-PV); European Commission (European regional development fund) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2014, Ian P. Mathews en
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/3.0/ en
dc.subject Solar cell en
dc.subject InP en
dc.subject Indium phosphide en
dc.subject Multi-junction en
dc.subject Mechanical stack en
dc.subject InGaAs en
dc.subject InAlAs en
dc.subject CPV en
dc.title High-efficiency photovoltaics through mechanically stacked integration of solar cells based on the InP lattice constant en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PHD (Engineering) en
dc.internal.availability Full text available en
dc.check.info No embargo required en
dc.description.version Accepted Version
dc.contributor.funder Enterprise Ireland en
dc.contributor.funder European Commission en
dc.description.status Not peer reviewed en
dc.internal.school Electrical and Electronic Engineering en
dc.internal.school Tyndall National Institute en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.embargoformat Not applicable en
ucc.workflow.supervisor a.morrison@ucc.ie
dc.internal.conferring Autumn Conferring 2014

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