{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/375249"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/375249","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Charge and Thermoelectric Transport in Metal Halide Perovskite Semiconductors","abstract":"Metal halide perovskites exhibit optoelectronic properties that hold significant potential for applications in photovoltaics, light-emitting diodes, photodetectors, X-ray detectors, and field-effect transistors (FETs). Rapid and substantial enhancements in the performance of perovskite-based optoelectronic devices have been achieved, that recent records indicate power conversion efficiency (PCE) of single-junction solar cells exceeding 26%, and FET mobility surpassing 50 cm2V-1s-1. These advancements in metal halide perovskites have been paralleled by efforts to understand the material's fundamental chemistry and physical properties from a bottom-up perspective, providing extensive theoretical optimization guidance. In this thesis, efforts to improve device performance have been paralleled by a focus to understand the underlying charge transport physics in these lead-based and tin-based perovskite systems. In Chapter 3, we identified a strong causal relationship between metal contact reaction and non-ideal FET characteristics in CsFAMAPbI3 perovskite FETs. Prolonged channel bias leads to enhanced n-type doping at the contact interface, resulting in increased device conductivity. This research also extended to investigating electroactive A-site molecules on charge transport in alkyl-diammonium 2D/3D perovskite FETs (Chapter 4.1), and pure *n*=1 2D perovskite diodes (Chapter 4.2). Carbazole alkylammonium molecules were found to accept transferred holes and increase electron-hole pair separation, consequently enhancing charge carrier mobility in the out-of-plane direction. Tin-based perovskites have gained significant attention since 2022, as they are found to be less susceptible to ion migration and exhibit *p*-type FET mobility exceeding 10 cm2V-1s-1. Here, we optimized tin perovskite compositions with mixed A-site cations and de-doping additives, achieving *p*-type FET mobility above 2 cm2V-1s-1 at room temperature. However, the reported high FET mobility exceeding 10 cm2V-1s-1 in these tin-based perovskites is sometimes controversial. In Chapter 4.3, we conducted a comprehensive analysis of the impact of device geometry on mobility extraction and demonstrated more reliable mobility results using gated four-point probe measurements on tin perovskite FETs. In Chapter 5, we conducted a comprehensive analysis of charge transport characterization in tin-based perovskite systems. We precisely measured the hole concentration and mobility of CsSnI3 films across varying grain sizes and Pb-substitution ratios. A transition in charge transport mechanisms was observed, shifting from predominantly band-like in larger grains to being dominated by grain boundary effects in smaller grains and films alloyed with Pb. Films with the largest grains exhibited a Hall effect mobility of 60 cm2V-1s-1 at room temperature and between 100-160 cm-2V-1s-1 at low temperatures, while maintaining a constant hole density of 1.6x10-19 cm-3. This transition is thoroughly explained using a mixed transport model that integrates band-like, grain boundary thermal activation, and grain boundary site semi-metallic or impurity scattering mechanisms. To assess their thermoelectric performance and probe their electronic structure, we measured the temperature-dependent Seebeck coefficient. From a Seebeck coefficient of 85 μV K-1 in CsSnI3 we derived a DOS effective mass of 0.25 to 0.3*m*e, which remains consistent regardless of temperature and grain size and is slightly higher in samples with Pb-substitution. Finally, with thermal conductivity measurements, our best CsSnI3 film exhibited a high thermoelectric power factor of 118 μW m-1K-2 and a thermoelectric figure-of-merit of 0.11 at room temperature. We demonstrate that enhancing sample grain size and crystallinity is a viable strategy for optimizing the thermoelectric performance of tin perovskites.","abstract_html":"Metal halide perovskites exhibit optoelectronic properties that hold significant potential for applications in photovoltaics, light-emitting diodes, photodetectors, X-ray detectors, and field-effect transistors (FETs). Rapid and substantial enhancements in the performance of perovskite-based optoelectronic devices have been achieved, that recent records indicate power conversion efficiency (PCE) of single-junction solar cells exceeding 26%, and FET mobility surpassing 50 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>. These advancements in metal halide perovskites have been paralleled by efforts to understand the material's fundamental chemistry and physical properties from a bottom-up perspective, providing extensive theoretical optimization guidance. In this thesis, efforts to improve device performance have been paralleled by a focus to understand the underlying charge transport physics in these lead-based and tin-based perovskite systems. In Chapter 3, we identified a strong causal relationship between metal contact reaction and non-ideal FET characteristics in CsFAMAPbI<sub>3</sub> perovskite FETs. Prolonged channel bias leads to enhanced n-type doping at the contact interface, resulting in increased device conductivity. This research also extended to investigating electroactive A-site molecules on charge transport in alkyl-diammonium 2D/3D perovskite FETs (Chapter 4.1), and pure *n*=1 2D perovskite diodes (Chapter 4.2). Carbazole alkylammonium molecules were found to accept transferred holes and increase electron-hole pair separation, consequently enhancing charge carrier mobility in the out-of-plane direction. Tin-based perovskites have gained significant attention since 2022, as they are found to be less susceptible to ion migration and exhibit *p*-type FET mobility exceeding 10 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>. Here, we optimized tin perovskite compositions with mixed A-site cations and de-doping additives, achieving *p*-type FET mobility above 2 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup> at room temperature. However, the reported high FET mobility exceeding 10 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup> in these tin-based perovskites is sometimes controversial. In Chapter 4.3, we conducted a comprehensive analysis of the impact of device geometry on mobility extraction and demonstrated more reliable mobility results using gated four-point probe measurements on tin perovskite FETs. In Chapter 5, we conducted a comprehensive analysis of charge transport characterization in tin-based perovskite systems. We precisely measured the hole concentration and mobility of CsSnI<sub>3</sub> films across varying grain sizes and Pb-substitution ratios. A transition in charge transport mechanisms was observed, shifting from predominantly band-like in larger grains to being dominated by grain boundary effects in smaller grains and films alloyed with Pb. Films with the largest grains exhibited a Hall effect mobility of 60 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup> at room temperature and between 100-160 cm<sup>-2</sup>V<sup>-1</sup>s<sup>-1</sup> at low temperatures, while maintaining a constant hole density of 1.6x10<sup>-19</sup> cm<sup>-3</sup>. This transition is thoroughly explained using a mixed transport model that integrates band-like, grain boundary thermal activation, and grain boundary site semi-metallic or impurity scattering mechanisms. To assess their thermoelectric performance and probe their electronic structure, we measured the temperature-dependent Seebeck coefficient. From a Seebeck coefficient of 85 μV K<sup>-1</sup> in CsSnI<sub>3</sub> we derived a DOS effective mass of 0.25 to 0.3*m*<sub>e</sub>, which remains consistent regardless of temperature and grain size and is slightly higher in samples with Pb-substitution. Finally, with thermal conductivity measurements, our best CsSnI<sub>3</sub> film exhibited a high thermoelectric power factor of 118 μW m<sup>-1</sup>K<sup>-2</sup> and a thermoelectric figure-of-merit of 0.11 at room temperature. We demonstrate that enhancing sample grain size and crystallinity is a viable strategy for optimizing the thermoelectric performance of tin perovskites.","abstract_has_math":false,"creators":["Zhang, Youcheng"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Sirringhaus, Henning"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-06-15","date_published":"2024-06-15","updated_at":"2026-07-22T22:23:57Z","subjects":["Charge Transport Physics","Doping","Field-Effect Transistors","Hall-Effect","Metal Halide Perovskites","Optoelectronics","Thermoelectric Physics"],"languages":["eng"],"rights":[],"rights_urls":["https://www.repository.cam.ac.uk/bitstreams/52bec90c-8614-4f82-8a8d-e6d1107ef289/download","https://creativecommons.org/licenses/by/4.0/"],"identifier_entries":[{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000342339769"],"render_values":[{"text":"0000-0003-4233-9769","href":"https://orcid.org/0000-0003-4233-9769","code":true}]}]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.112999","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Sirringhaus, Henning"]},{"key":"dc:creator","label":"Author","values":["Zhang, Youcheng"]},{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000342339769"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2024-06-15"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/375249"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Charge Transport Physics","Doping","Field-Effect Transistors","Hall-Effect","Metal Halide Perovskites","Optoelectronics","Thermoelectric Physics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.repository.cam.ac.uk/bitstreams/52bec90c-8614-4f82-8a8d-e6d1107ef289/download","https://creativecommons.org/licenses/by/4.0/"]},{"key":"dc:rights.embargodate","label":"Dc Rights Embargodate","values":["2026-10-24"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["embargo"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.112999"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://www.repository.cam.ac.uk/bitstreams/c80c4f2b-3991-45d4-8d21-5a54752d64b2/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Metal halide perovskites exhibit optoelectronic properties that hold significant potential for applications in photovoltaics, light-emitting diodes, photodetectors, X-ray detectors, and field-effect transistors (FETs). Rapid and substantial enhancements in the performance of perovskite-based optoelectronic devices have been achieved, that recent records indicate power conversion efficiency (PCE) of single-junction solar cells exceeding 26%, and FET mobility surpassing 50 cm2V-1s-1. These advancements in metal halide perovskites have been paralleled by efforts to understand the material's fundamental chemistry and physical properties from a bottom-up perspective, providing extensive theoretical optimization guidance. In this thesis, efforts to improve device performance have been paralleled by a focus to understand the underlying charge transport physics in these lead-based and tin-based perovskite systems. In Chapter 3, we identified a strong causal relationship between metal contact reaction and non-ideal FET characteristics in CsFAMAPbI3 perovskite FETs. Prolonged channel bias leads to enhanced n-type doping at the contact interface, resulting in increased device conductivity. This research also extended to investigating electroactive A-site molecules on charge transport in alkyl-diammonium 2D/3D perovskite FETs (Chapter 4.1), and pure *n*=1 2D perovskite diodes (Chapter 4.2). Carbazole alkylammonium molecules were found to accept transferred holes and increase electron-hole pair separation, consequently enhancing charge carrier mobility in the out-of-plane direction. Tin-based perovskites have gained significant attention since 2022, as they are found to be less susceptible to ion migration and exhibit *p*-type FET mobility exceeding 10 cm2V-1s-1. Here, we optimized tin perovskite compositions with mixed A-site cations and de-doping additives, achieving *p*-type FET mobility above 2 cm2V-1s-1 at room temperature. However, the reported high FET mobility exceeding 10 cm2V-1s-1 in these tin-based perovskites is sometimes controversial. In Chapter 4.3, we conducted a comprehensive analysis of the impact of device geometry on mobility extraction and demonstrated more reliable mobility results using gated four-point probe measurements on tin perovskite FETs. In Chapter 5, we conducted a comprehensive analysis of charge transport characterization in tin-based perovskite systems. We precisely measured the hole concentration and mobility of CsSnI3 films across varying grain sizes and Pb-substitution ratios. A transition in charge transport mechanisms was observed, shifting from predominantly band-like in larger grains to being dominated by grain boundary effects in smaller grains and films alloyed with Pb. Films with the largest grains exhibited a Hall effect mobility of 60 cm2V-1s-1 at room temperature and between 100-160 cm-2V-1s-1 at low temperatures, while maintaining a constant hole density of 1.6x10-19 cm-3. This transition is thoroughly explained using a mixed transport model that integrates band-like, grain boundary thermal activation, and grain boundary site semi-metallic or impurity scattering mechanisms. To assess their thermoelectric performance and probe their electronic structure, we measured the temperature-dependent Seebeck coefficient. From a Seebeck coefficient of 85 μV K-1 in CsSnI3 we derived a DOS effective mass of 0.25 to 0.3*m*e, which remains consistent regardless of temperature and grain size and is slightly higher in samples with Pb-substitution. Finally, with thermal conductivity measurements, our best CsSnI3 film exhibited a high thermoelectric power factor of 118 μW m-1K-2 and a thermoelectric figure-of-merit of 0.11 at room temperature. We demonstrate that enhancing sample grain size and crystallinity is a viable strategy for optimizing the thermoelectric performance of tin perovskites."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["6fd51b5cb5083702b71e4ad04c4ac111","87eda9de84448d1f82354d60eee3eb5f"]},{"key":"dc:title","label":"Title","values":["Charge and Thermoelectric Transport in Metal Halide Perovskite Semiconductors"]}]}],"canonical_facts":{"dc:contributor.advisor":["Sirringhaus, Henning"],"dc:creator":["Zhang, Youcheng"],"dc:creator.authoridentifier":["0000000342339769"],"dc:date.issued":["2024-06-15"],"dc:description.abstract":["Metal halide perovskites exhibit optoelectronic properties that hold significant potential for applications in photovoltaics, light-emitting diodes, photodetectors, X-ray detectors, and field-effect transistors (FETs). Rapid and substantial enhancements in the performance of perovskite-based optoelectronic devices have been achieved, that recent records indicate power conversion efficiency (PCE) of single-junction solar cells exceeding 26%, and FET mobility surpassing 50 cm2V-1s-1. These advancements in metal halide perovskites have been paralleled by efforts to understand the material's fundamental chemistry and physical properties from a bottom-up perspective, providing extensive theoretical optimization guidance. In this thesis, efforts to improve device performance have been paralleled by a focus to understand the underlying charge transport physics in these lead-based and tin-based perovskite systems. In Chapter 3, we identified a strong causal relationship between metal contact reaction and non-ideal FET characteristics in CsFAMAPbI3 perovskite FETs. Prolonged channel bias leads to enhanced n-type doping at the contact interface, resulting in increased device conductivity. This research also extended to investigating electroactive A-site molecules on charge transport in alkyl-diammonium 2D/3D perovskite FETs (Chapter 4.1), and pure *n*=1 2D perovskite diodes (Chapter 4.2). Carbazole alkylammonium molecules were found to accept transferred holes and increase electron-hole pair separation, consequently enhancing charge carrier mobility in the out-of-plane direction. Tin-based perovskites have gained significant attention since 2022, as they are found to be less susceptible to ion migration and exhibit *p*-type FET mobility exceeding 10 cm2V-1s-1. Here, we optimized tin perovskite compositions with mixed A-site cations and de-doping additives, achieving *p*-type FET mobility above 2 cm2V-1s-1 at room temperature. However, the reported high FET mobility exceeding 10 cm2V-1s-1 in these tin-based perovskites is sometimes controversial. In Chapter 4.3, we conducted a comprehensive analysis of the impact of device geometry on mobility extraction and demonstrated more reliable mobility results using gated four-point probe measurements on tin perovskite FETs. In Chapter 5, we conducted a comprehensive analysis of charge transport characterization in tin-based perovskite systems. We precisely measured the hole concentration and mobility of CsSnI3 films across varying grain sizes and Pb-substitution ratios. A transition in charge transport mechanisms was observed, shifting from predominantly band-like in larger grains to being dominated by grain boundary effects in smaller grains and films alloyed with Pb. Films with the largest grains exhibited a Hall effect mobility of 60 cm2V-1s-1 at room temperature and between 100-160 cm-2V-1s-1 at low temperatures, while maintaining a constant hole density of 1.6x10-19 cm-3. This transition is thoroughly explained using a mixed transport model that integrates band-like, grain boundary thermal activation, and grain boundary site semi-metallic or impurity scattering mechanisms. To assess their thermoelectric performance and probe their electronic structure, we measured the temperature-dependent Seebeck coefficient. From a Seebeck coefficient of 85 μV K-1 in CsSnI3 we derived a DOS effective mass of 0.25 to 0.3*m*e, which remains consistent regardless of temperature and grain size and is slightly higher in samples with Pb-substitution. Finally, with thermal conductivity measurements, our best CsSnI3 film exhibited a high thermoelectric power factor of 118 μW m-1K-2 and a thermoelectric figure-of-merit of 0.11 at room temperature. We demonstrate that enhancing sample grain size and crystallinity is a viable strategy for optimizing the thermoelectric performance of tin perovskites."],"dc:format.checksum.md5":["6fd51b5cb5083702b71e4ad04c4ac111","87eda9de84448d1f82354d60eee3eb5f"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.112999"],"dc:identifier.uri":["https://www.repository.cam.ac.uk/bitstreams/c80c4f2b-3991-45d4-8d21-5a54752d64b2/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/375249"],"dc:rights":["https://www.repository.cam.ac.uk/bitstreams/52bec90c-8614-4f82-8a8d-e6d1107ef289/download","https://creativecommons.org/licenses/by/4.0/"],"dc:rights.embargodate":["2026-10-24"],"dc:rights.embargotype":["embargo"],"dc:subject":["Charge Transport Physics","Doping","Field-Effect Transistors","Hall-Effect","Metal Halide Perovskites","Optoelectronics","Thermoelectric Physics"],"dc:title":["Charge and Thermoelectric Transport in Metal Halide Perovskite Semiconductors"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:23:57Z"}