{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/140841"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/140841","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials","abstract":"Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim ABSTRACT Hybrid organic-inorganic perovskites (HOIPs) have emerged as promising semiconductors for optoelectronic applications. But their intrinsic instability limits practical applications. This dissertation explores dynamic crystallization as a design principle to enhance stability in halide perovskite materials through three studies. In Chapter 2, we developed a pH-controlled synthetic strategy for water-stable perovskitoid semiconductors using the zwitterionic molecule cysteamine (CYS). By varying pH conditions (acidic, neutral, and basic), we tuned the coordination environment to make Pb-S and Pb-N covalent bonds. Crystals synthesized under basic conditions maintainedtheir structure for over one month in direct contact with water. In contrast, crystals synthesized under acidic condition decomposed within one day. This approach represents a new synthetic method for making ionic perovskite structures. In Chapter 3, we investigated composition and passivation effects on thermochromic MAPbI3 (MA = methyl ammonium) thin films. Systematic variation of MAI:PbI2 ratios revealed that excess MAI is critical for complete reversible transitions between colored and colorless states. Chlorine incorporation from MACl accelerated structure transition kinetics by approximately 50%, with transition times of 52 seconds to 27 seconds. However, there was a trade-off between transition speed and long-term durability with chlorine incorporation. Passivation with 2-amino-4-methylpyridine improved thin film stability but extended transition times. This bifunctional additive coordinates with undercoordinated Pb2+ and Sn2+ sites at surfaces and grain boundaries. In Chapter 4, we developed color-neutral thermochromic perovskites through Pb-Sn compositional engineering and multi-layer encapsulation. Mixed Pb:Sn = 1:1 ratio produced neutral gray coloration by broadening absorption across the visible spectrum. We discovered that potassium halide additives (10% KF + 10% KI) showed better stability in Sn-mixed perovskites than with sodium halide additives. A tri-layer encapsulation architecture comprising hygroscopic polymers, the perovskite layer, and hydrophobic PMMA enabled reversible thermochromic cycling through moisture in the encapsulated system. Optimized films maintained stable optical property through 10 cycles. These works establish the methods to overcome intrinsic instability of halide perovskites into stable semiconductors for optical materials.","abstract_html":"Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim ABSTRACT Hybrid organic-inorganic perovskites (HOIPs) have emerged as promising semiconductors for optoelectronic applications. But their intrinsic instability limits practical applications. This dissertation explores dynamic crystallization as a design principle to enhance stability in halide perovskite materials through three studies. In Chapter 2, we developed a pH-controlled synthetic strategy for water-stable perovskitoid semiconductors using the zwitterionic molecule cysteamine (CYS). By varying pH conditions (acidic, neutral, and basic), we tuned the coordination environment to make Pb-S and Pb-N covalent bonds. Crystals synthesized under basic conditions maintainedtheir structure for over one month in direct contact with water. In contrast, crystals synthesized under acidic condition decomposed within one day. This approach represents a new synthetic method for making ionic perovskite structures. In Chapter 3, we investigated composition and passivation effects on thermochromic MAPbI3 (MA = methyl ammonium) thin films. Systematic variation of MAI:PbI2 ratios revealed that excess MAI is critical for complete reversible transitions between colored and colorless states. Chlorine incorporation from MACl accelerated structure transition kinetics by approximately 50%, with transition times of 52 seconds to 27 seconds. However, there was a trade-off between transition speed and long-term durability with chlorine incorporation. Passivation with 2-amino-4-methylpyridine improved thin film stability but extended transition times. This bifunctional additive coordinates with undercoordinated Pb2+ and Sn2+ sites at surfaces and grain boundaries. In Chapter 4, we developed color-neutral thermochromic perovskites through Pb-Sn compositional engineering and multi-layer encapsulation. Mixed Pb:Sn = 1:1 ratio produced neutral gray coloration by broadening absorption across the visible spectrum. We discovered that potassium halide additives (10% KF + 10% KI) showed better stability in Sn-mixed perovskites than with sodium halide additives. A tri-layer encapsulation architecture comprising hygroscopic polymers, the perovskite layer, and hydrophobic PMMA enabled reversible thermochromic cycling through moisture in the encapsulated system. Optimized films maintained stable optical property through 10 cycles. These works establish the methods to overcome intrinsic instability of halide perovskites into stable semiconductors for optical materials.","abstract_has_math":false,"creators":["Kim, Jiyoon"],"institution":"Virginia Tech","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Chemistry","degree_department":"Chemistry","school":null,"contributors":[],"advisors":[],"committee_chairs":["Quan, Lina"],"committee_members":["Slebodnick, Carla","Khodaparast, Giti","Morris, John R."],"year":2026,"date_issued":"2026-01-15","date_published":"2026-01-15","updated_at":"2026-07-22T22:20:34Z","subjects":["Dynamic crystallization","Stability of perovskite","Thermochromism"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45418"],"render_values":[{"text":"vt_gsexam:45418","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/140841","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Quan, Lina"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Slebodnick, Carla","Khodaparast, Giti","Morris, John R."]},{"key":"dc:contributor.department","label":"Department","values":["Chemistry"]},{"key":"dc:creator","label":"Author","values":["Kim, Jiyoon"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-01-16T09:00:44Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-01-16T09:00:44Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-01-15"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Chemistry"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Dynamic crystallization","Stability of perovskite","Thermochromism"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45418"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/140841"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim ABSTRACT Hybrid organic-inorganic perovskites (HOIPs) have emerged as promising semiconductors for optoelectronic applications. But their intrinsic instability limits practical applications. This dissertation explores dynamic crystallization as a design principle to enhance stability in halide perovskite materials through three studies. In Chapter 2, we developed a pH-controlled synthetic strategy for water-stable perovskitoid semiconductors using the zwitterionic molecule cysteamine (CYS). By varying pH conditions (acidic, neutral, and basic), we tuned the coordination environment to make Pb-S and Pb-N covalent bonds. Crystals synthesized under basic conditions maintainedtheir structure for over one month in direct contact with water. In contrast, crystals synthesized under acidic condition decomposed within one day. This approach represents a new synthetic method for making ionic perovskite structures. In Chapter 3, we investigated composition and passivation effects on thermochromic MAPbI3 (MA = methyl ammonium) thin films. Systematic variation of MAI:PbI2 ratios revealed that excess MAI is critical for complete reversible transitions between colored and colorless states. Chlorine incorporation from MACl accelerated structure transition kinetics by approximately 50%, with transition times of 52 seconds to 27 seconds. However, there was a trade-off between transition speed and long-term durability with chlorine incorporation. Passivation with 2-amino-4-methylpyridine improved thin film stability but extended transition times. This bifunctional additive coordinates with undercoordinated Pb2+ and Sn2+ sites at surfaces and grain boundaries. In Chapter 4, we developed color-neutral thermochromic perovskites through Pb-Sn compositional engineering and multi-layer encapsulation. Mixed Pb:Sn = 1:1 ratio produced neutral gray coloration by broadening absorption across the visible spectrum. We discovered that potassium halide additives (10% KF + 10% KI) showed better stability in Sn-mixed perovskites than with sodium halide additives. A tri-layer encapsulation architecture comprising hygroscopic polymers, the perovskite layer, and hydrophobic PMMA enabled reversible thermochromic cycling through moisture in the encapsulated system. Optimized films maintained stable optical property through 10 cycles. These works establish the methods to overcome intrinsic instability of halide perovskites into stable semiconductors for optical materials."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim GENERAL AUDIENCE ABSTRACT Solar cells and smart windows could become cheaper and more efficient with materials called perovskites. These materials can turn sunlight into electricity or automatically adjust transmittance through windows to keep buildings cool and warm. However, these materials can break down quickly when exposed to water which makes them impractical for real-world applications. This research develops three different strategies to solve this stability problem. Think of it like developing better recipes and protective coatings to make something that would normally dissolve in water last for months or even years. The first strategy is changing the acidity to make materials. By adjusting the acidity, we created strong chemical bonds that act like waterproof glue even when submerged in water for over a month. Previous materials would fall apart in less than a day. The second strategy focuses on materials that change color with temperature. These materials are useful for smart windows that automatically darken in bright sunlight and clear up when it's cloudy. We discovered that adding specific ingredients speeds up the color change, but this comes with a trade-off of reduced durability. The third strategy makes materials with neutral gray color films instead of brown, which is a more useful color for windows and visors. By mixing two different metals and developing a three-layered coating system, we created films that can switch between dark and clear states through 10 cycles. These advances can build ways for affordable smart windows for buildings and adaptive visors for vehicles."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Quan, Lina"],"dc:contributor.committeemember":["Slebodnick, Carla","Khodaparast, Giti","Morris, John R."],"dc:contributor.department":["Chemistry"],"dc:creator":["Kim, Jiyoon"],"dc:date.accessioned":["2026-01-16T09:00:44Z"],"dc:date.available":["2026-01-16T09:00:44Z"],"dc:date.issued":["2026-01-15"],"dc:description.abstract":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim ABSTRACT Hybrid organic-inorganic perovskites (HOIPs) have emerged as promising semiconductors for optoelectronic applications. But their intrinsic instability limits practical applications. This dissertation explores dynamic crystallization as a design principle to enhance stability in halide perovskite materials through three studies. In Chapter 2, we developed a pH-controlled synthetic strategy for water-stable perovskitoid semiconductors using the zwitterionic molecule cysteamine (CYS). By varying pH conditions (acidic, neutral, and basic), we tuned the coordination environment to make Pb-S and Pb-N covalent bonds. Crystals synthesized under basic conditions maintainedtheir structure for over one month in direct contact with water. In contrast, crystals synthesized under acidic condition decomposed within one day. This approach represents a new synthetic method for making ionic perovskite structures. In Chapter 3, we investigated composition and passivation effects on thermochromic MAPbI3 (MA = methyl ammonium) thin films. Systematic variation of MAI:PbI2 ratios revealed that excess MAI is critical for complete reversible transitions between colored and colorless states. Chlorine incorporation from MACl accelerated structure transition kinetics by approximately 50%, with transition times of 52 seconds to 27 seconds. However, there was a trade-off between transition speed and long-term durability with chlorine incorporation. Passivation with 2-amino-4-methylpyridine improved thin film stability but extended transition times. This bifunctional additive coordinates with undercoordinated Pb2+ and Sn2+ sites at surfaces and grain boundaries. In Chapter 4, we developed color-neutral thermochromic perovskites through Pb-Sn compositional engineering and multi-layer encapsulation. Mixed Pb:Sn = 1:1 ratio produced neutral gray coloration by broadening absorption across the visible spectrum. We discovered that potassium halide additives (10% KF + 10% KI) showed better stability in Sn-mixed perovskites than with sodium halide additives. A tri-layer encapsulation architecture comprising hygroscopic polymers, the perovskite layer, and hydrophobic PMMA enabled reversible thermochromic cycling through moisture in the encapsulated system. Optimized films maintained stable optical property through 10 cycles. These works establish the methods to overcome intrinsic instability of halide perovskites into stable semiconductors for optical materials."],"dc:description.abstractgeneral":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials Jiyoon Kim GENERAL AUDIENCE ABSTRACT Solar cells and smart windows could become cheaper and more efficient with materials called perovskites. These materials can turn sunlight into electricity or automatically adjust transmittance through windows to keep buildings cool and warm. However, these materials can break down quickly when exposed to water which makes them impractical for real-world applications. This research develops three different strategies to solve this stability problem. Think of it like developing better recipes and protective coatings to make something that would normally dissolve in water last for months or even years. The first strategy is changing the acidity to make materials. By adjusting the acidity, we created strong chemical bonds that act like waterproof glue even when submerged in water for over a month. Previous materials would fall apart in less than a day. The second strategy focuses on materials that change color with temperature. These materials are useful for smart windows that automatically darken in bright sunlight and clear up when it's cloudy. We discovered that adding specific ingredients speeds up the color change, but this comes with a trade-off of reduced durability. The third strategy makes materials with neutral gray color films instead of brown, which is a more useful color for windows and visors. By mixing two different metals and developing a three-layered coating system, we created films that can switch between dark and clear states through 10 cycles. These advances can build ways for affordable smart windows for buildings and adaptive visors for vehicles."],"dc:description.degree":["Doctor of Philosophy"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:45418"],"dc:identifier.uri":["https://hdl.handle.net/10919/140841"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Dynamic crystallization","Stability of perovskite","Thermochromism"],"dc:title":["Dynamic Crystallization and Stability Engineering in Hybrid Organic-Inorganic Perovskites: Towards Water-Stable and Thermochromic Materials"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Chemistry"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:20:34Z"}