{"id":{"repo_id":"toronto-retro","oai_identifier":"oai:utoronto.scholaris.ca:1807/150628"},"canonical_url":"https://search.dev.ndltd.org/etd/toronto-retro/oai:utoronto.scholaris.ca:1807/150628","repository":{"repo_id":"toronto-retro","name":"University of Toronto","base_url":"https://utoronto.scholaris.ca/server/oai/request"},"display":{"title":"Enhancing Stability in Quantum-Dot and Perovskite Optoelectronic Devices through Compositional Engineering and Surface Treatment","abstract":"Solution-processed quantum dots (QDs) and metal-halide perovskites are of interest inoptoelectronics because of their sharp color, high absorption, and bright emission. However, their further progress is hampered today by limited operating stability. In this thesis, I study how compositional engineering and surface treatment can address these stability challenges to increase durability at high efficiency. My investigation begins with stable, environment-friendly blue emitters for full-color displays. Vacancy-ordered double perovskites are lead-free, yet most are weakly emissive. I find that compositional engineering of a specific member, Rb2HfCl6, through Bi3+ doping and Cs+ alloying, transforms the non-emissive host into a moisture-resistant emitter at 466 nm with a 66% photoluminescence quantum yield. As material dimensions shrink to the QD scale, surfaces dominate, and the work then turns from engineering the bulk to focusing on the surface of QDs. A dual-ligand exchange assembles perovskite QDs into a densely-packed, ordered solid, which enhances conductivity and enables LEDs that generate 1000 cd m-2 at a voltage of 2.8 V. The reduced operating field extends the operating device stability 100-fold. With the emissive layer optimized, I then focus on charge transport layers. I address ETL instabilities from two complementary angles. First, I replace the conventional ZnMgO ETL with a bifunctional organic molecule that passivates QD surface traps and suppresses ion migration, thereby producing InP QD-LEDs with higher efficiency and improved stability. Secondly, I stabilize the ZnMgO with an ultrathin Al2O3 coating, which extended the operating lifetime tenfold. To achieve optimal device performance with balanced charge injection, I engineer the HTL via Li doping and oxygen treatment to tune the composition of the NiOₓ. The hole conductivity is improved, leading to balanced charge injection more efficient devices. Finally, I study how interfacial engineering can be applied to photovoltaics to address a large voltage loss due to interfacial traps and unfavorable band alignment in ultrawide-bandgap perovskite solar cells, a sublayer relevant to triple-junction solar cells. I find that a bifunctional molecule, positioned at a buried interface, simultaneously passivates traps and improves energy alignment, reclaiming ~30 mV of open-circuit voltage and providing a pathway to more efficient multi-junction solar cells.","abstract_html":"Solution-processed quantum dots (QDs) and metal-halide perovskites are of interest inoptoelectronics because of their sharp color, high absorption, and bright emission. However, their further progress is hampered today by limited operating stability. In this thesis, I study how compositional engineering and surface treatment can address these stability challenges to increase durability at high efficiency. My investigation begins with stable, environment-friendly blue emitters for full-color displays. Vacancy-ordered double perovskites are lead-free, yet most are weakly emissive. I find that compositional engineering of a specific member, Rb2HfCl6, through Bi3+ doping and Cs+ alloying, transforms the non-emissive host into a moisture-resistant emitter at 466 nm with a 66% photoluminescence quantum yield. As material dimensions shrink to the QD scale, surfaces dominate, and the work then turns from engineering the bulk to focusing on the surface of QDs. A dual-ligand exchange assembles perovskite QDs into a densely-packed, ordered solid, which enhances conductivity and enables LEDs that generate 1000 cd m-2 at a voltage of 2.8 V. The reduced operating field extends the operating device stability 100-fold. With the emissive layer optimized, I then focus on charge transport layers. I address ETL instabilities from two complementary angles. First, I replace the conventional ZnMgO ETL with a bifunctional organic molecule that passivates QD surface traps and suppresses ion migration, thereby producing InP QD-LEDs with higher efficiency and improved stability. Secondly, I stabilize the ZnMgO with an ultrathin Al2O3 coating, which extended the operating lifetime tenfold. To achieve optimal device performance with balanced charge injection, I engineer the HTL via Li doping and oxygen treatment to tune the composition of the NiOₓ. The hole conductivity is improved, leading to balanced charge injection more efficient devices. Finally, I study how interfacial engineering can be applied to photovoltaics to address a large voltage loss due to interfacial traps and unfavorable band alignment in ultrawide-bandgap perovskite solar cells, a sublayer relevant to triple-junction solar cells. I find that a bifunctional molecule, positioned at a buried interface, simultaneously passivates traps and improves energy alignment, reclaiming ~30 mV of open-circuit voltage and providing a pathway to more efficient multi-junction solar cells.","abstract_has_math":false,"creators":["Wan, Haoyue"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Electrical and Computer Engineering","school":null,"contributors":[],"advisors":["Sargent, Edward"],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-10","date_published":"2025-10","updated_at":"2026-07-27T21:27:56Z","subjects":["Light emitting devices","Optoelectronics","Perovskite","Quantum dots","Solar cells"],"languages":[],"rights":["Attribution-NonCommercial-NoDerivatives 4.0 International"],"rights_urls":["http://creativecommons.org/licenses/by-nc-nd/4.0/"],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1807/150628","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Sargent, Edward"]},{"key":"dc:contributor.department","label":"Department","values":["Electrical and Computer Engineering"]},{"key":"dc:creator","label":"Author","values":["Wan, Haoyue"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2025-10"]},{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-12-01T17:39:27Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-10"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Light emitting devices","Optoelectronics","Perovskite","Quantum dots","Solar cells"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["Attribution-NonCommercial-NoDerivatives 4.0 International"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://creativecommons.org/licenses/by-nc-nd/4.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1807/150628"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Solution-processed quantum dots (QDs) and metal-halide perovskites are of interest inoptoelectronics because of their sharp color, high absorption, and bright emission. However, their further progress is hampered today by limited operating stability. In this thesis, I study how compositional engineering and surface treatment can address these stability challenges to increase durability at high efficiency. My investigation begins with stable, environment-friendly blue emitters for full-color displays. Vacancy-ordered double perovskites are lead-free, yet most are weakly emissive. I find that compositional engineering of a specific member, Rb2HfCl6, through Bi3+ doping and Cs+ alloying, transforms the non-emissive host into a moisture-resistant emitter at 466 nm with a 66% photoluminescence quantum yield. As material dimensions shrink to the QD scale, surfaces dominate, and the work then turns from engineering the bulk to focusing on the surface of QDs. A dual-ligand exchange assembles perovskite QDs into a densely-packed, ordered solid, which enhances conductivity and enables LEDs that generate 1000 cd m-2 at a voltage of 2.8 V. The reduced operating field extends the operating device stability 100-fold. With the emissive layer optimized, I then focus on charge transport layers. I address ETL instabilities from two complementary angles. First, I replace the conventional ZnMgO ETL with a bifunctional organic molecule that passivates QD surface traps and suppresses ion migration, thereby producing InP QD-LEDs with higher efficiency and improved stability. Secondly, I stabilize the ZnMgO with an ultrathin Al2O3 coating, which extended the operating lifetime tenfold. To achieve optimal device performance with balanced charge injection, I engineer the HTL via Li doping and oxygen treatment to tune the composition of the NiOₓ. The hole conductivity is improved, leading to balanced charge injection more efficient devices. Finally, I study how interfacial engineering can be applied to photovoltaics to address a large voltage loss due to interfacial traps and unfavorable band alignment in ultrawide-bandgap perovskite solar cells, a sublayer relevant to triple-junction solar cells. I find that a bifunctional molecule, positioned at a buried interface, simultaneously passivates traps and improves energy alignment, reclaiming ~30 mV of open-circuit voltage and providing a pathway to more efficient multi-junction solar cells."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:title","label":"Title","values":["Enhancing Stability in Quantum-Dot and Perovskite Optoelectronic Devices through Compositional Engineering and Surface Treatment"]}]}],"canonical_facts":{"dc:contributor.advisor":["Sargent, Edward"],"dc:contributor.department":["Electrical and Computer Engineering"],"dc:creator":["Wan, Haoyue"],"dc:date":["2025-10"],"dc:date.accessioned":["2025-12-01T17:39:27Z"],"dc:date.issued":["2025-10"],"dc:description.abstract":["Solution-processed quantum dots (QDs) and metal-halide perovskites are of interest inoptoelectronics because of their sharp color, high absorption, and bright emission. However, their further progress is hampered today by limited operating stability. In this thesis, I study how compositional engineering and surface treatment can address these stability challenges to increase durability at high efficiency. My investigation begins with stable, environment-friendly blue emitters for full-color displays. Vacancy-ordered double perovskites are lead-free, yet most are weakly emissive. I find that compositional engineering of a specific member, Rb2HfCl6, through Bi3+ doping and Cs+ alloying, transforms the non-emissive host into a moisture-resistant emitter at 466 nm with a 66% photoluminescence quantum yield. As material dimensions shrink to the QD scale, surfaces dominate, and the work then turns from engineering the bulk to focusing on the surface of QDs. A dual-ligand exchange assembles perovskite QDs into a densely-packed, ordered solid, which enhances conductivity and enables LEDs that generate 1000 cd m-2 at a voltage of 2.8 V. The reduced operating field extends the operating device stability 100-fold. With the emissive layer optimized, I then focus on charge transport layers. I address ETL instabilities from two complementary angles. First, I replace the conventional ZnMgO ETL with a bifunctional organic molecule that passivates QD surface traps and suppresses ion migration, thereby producing InP QD-LEDs with higher efficiency and improved stability. Secondly, I stabilize the ZnMgO with an ultrathin Al2O3 coating, which extended the operating lifetime tenfold. To achieve optimal device performance with balanced charge injection, I engineer the HTL via Li doping and oxygen treatment to tune the composition of the NiOₓ. The hole conductivity is improved, leading to balanced charge injection more efficient devices. Finally, I study how interfacial engineering can be applied to photovoltaics to address a large voltage loss due to interfacial traps and unfavorable band alignment in ultrawide-bandgap perovskite solar cells, a sublayer relevant to triple-junction solar cells. I find that a bifunctional molecule, positioned at a buried interface, simultaneously passivates traps and improves energy alignment, reclaiming ~30 mV of open-circuit voltage and providing a pathway to more efficient multi-junction solar cells."],"dc:description.degree":["Ph.D."],"dc:identifier.uri":["https://hdl.handle.net/1807/150628"],"dc:rights":["Attribution-NonCommercial-NoDerivatives 4.0 International"],"dc:rights.uri":["http://creativecommons.org/licenses/by-nc-nd/4.0/"],"dc:subject":["Light emitting devices","Optoelectronics","Perovskite","Quantum dots","Solar cells"],"dc:title":["Enhancing Stability in Quantum-Dot and Perovskite Optoelectronic Devices through Compositional Engineering and Surface Treatment"],"dc:type":["Thesis"]},"updated_at":"2026-07-27T21:27:56Z"}