Surface Traps in Colloidal Quantum Dot Solar Cells, their Mitigation and Impact on Manufacturability

Handle URI:
http://hdl.handle.net/10754/625510
Title:
Surface Traps in Colloidal Quantum Dot Solar Cells, their Mitigation and Impact on Manufacturability
Authors:
Kirmani, Ahmad R. ( 0000-0002-8351-3762 )
Abstract:
Colloidal quantum dots (CQDs) are potentially low-cost, solution-processable semiconductors which are endowed, through their nanoscale dimensions, with strong absorption, band gap tunability, high dielectric constants and enhanced stability. CQDs are contenders as a standalone PV technology as well as a potential back layer for augmenting established photovoltaic (PV) technologies, such as Si. However, owing to their small size (ca. few nanometers), CQDs are prone to surface trap states that inhibit charge transport and threaten their otherwise wonderful optoelectronic properties. Surface traps have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells, as all of the reports, to date, have relied on spin-coating with sophisticated and tedious ligand exchange schemes, some of which need to be performed in low humidity environments. In this thesis, we posit that an in-depth understanding of the process-structure-property-performance relationship in CQDs can usher in fresh insights into the nature and origin of surface traps, lead to novel ways to mitigate them, and finally help achieve scalable fabrication. To this end, we probe the CQD surfaces and their interactions with process solvents, linkers, and ambient environment employing a suite of spectroscopic techniques. These fundamental insights help us develop facile chemical and physical protocols to mitigate surface traps such as solvent engineering, remote molecular doping, and oxygen doping, directly leading to better-performing solar cells. Our efforts finally culminate in the realization of >10% efficient, air-stable CQD solar cells scalably fabricated in an ambient environment of high, uncontrolled R.H. (50-65%). As-prepared solar cells fabricated in high humidity ambient conditions are found to underperform, however, an oxygen-doping recipe is devised to mitigate the moisture-induced surface traps and recover device performances. Importantly, these solar cells are fabricated at coating speeds of >15 m min-1 with roll-to-roll compatible techniques such as blade and bar coating requiring 1/25th the CQD material consumed by the standard spin-coated devices, overcoming the two major challenges of manufacturability and scalability faced by CQD PV.
Advisors:
Amassian, Aram ( 0000-0002-5734-1194 )
Committee Member:
Bakr, Osman M. ( 0000-0002-3428-1002 ) ; Inal, Sahika ( 0000-0002-1166-1512 ) ; Kamat, Prashant V.
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Program:
Materials Science and Engineering
Issue Date:
30-Jul-2017
Type:
Dissertation
Appears in Collections:
Dissertations

Full metadata record

DC FieldValue Language
dc.contributor.advisorAmassian, Aramen
dc.contributor.authorKirmani, Ahmad R.en
dc.date.accessioned2017-09-27T13:26:31Z-
dc.date.available2017-09-27T13:26:31Z-
dc.date.issued2017-07-30-
dc.identifier.urihttp://hdl.handle.net/10754/625510-
dc.description.abstractColloidal quantum dots (CQDs) are potentially low-cost, solution-processable semiconductors which are endowed, through their nanoscale dimensions, with strong absorption, band gap tunability, high dielectric constants and enhanced stability. CQDs are contenders as a standalone PV technology as well as a potential back layer for augmenting established photovoltaic (PV) technologies, such as Si. However, owing to their small size (ca. few nanometers), CQDs are prone to surface trap states that inhibit charge transport and threaten their otherwise wonderful optoelectronic properties. Surface traps have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells, as all of the reports, to date, have relied on spin-coating with sophisticated and tedious ligand exchange schemes, some of which need to be performed in low humidity environments. In this thesis, we posit that an in-depth understanding of the process-structure-property-performance relationship in CQDs can usher in fresh insights into the nature and origin of surface traps, lead to novel ways to mitigate them, and finally help achieve scalable fabrication. To this end, we probe the CQD surfaces and their interactions with process solvents, linkers, and ambient environment employing a suite of spectroscopic techniques. These fundamental insights help us develop facile chemical and physical protocols to mitigate surface traps such as solvent engineering, remote molecular doping, and oxygen doping, directly leading to better-performing solar cells. Our efforts finally culminate in the realization of >10% efficient, air-stable CQD solar cells scalably fabricated in an ambient environment of high, uncontrolled R.H. (50-65%). As-prepared solar cells fabricated in high humidity ambient conditions are found to underperform, however, an oxygen-doping recipe is devised to mitigate the moisture-induced surface traps and recover device performances. Importantly, these solar cells are fabricated at coating speeds of >15 m min-1 with roll-to-roll compatible techniques such as blade and bar coating requiring 1/25th the CQD material consumed by the standard spin-coated devices, overcoming the two major challenges of manufacturability and scalability faced by CQD PV.en
dc.language.isoenen
dc.subjectSolar Cellsen
dc.subjectColloidal Quantum Dotsen
dc.subjectNanoparticlesen
dc.subjectSurface Trap Statesen
dc.subjectLead Sulfideen
dc.subjectDopingen
dc.titleSurface Traps in Colloidal Quantum Dot Solar Cells, their Mitigation and Impact on Manufacturabilityen
dc.typeDissertationen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
thesis.degree.grantorKing Abdullah University of Science and Technologyen
dc.contributor.committeememberBakr, Osman M.en
dc.contributor.committeememberInal, Sahikaen
dc.contributor.committeememberKamat, Prashant V.en
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.nameDoctor of Philosophyen
dc.person.id118519en
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