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Photophysics of Perovskite Nano- and Microcrystals

Chen, Junsheng LU (2018)
Abstract (Swedish)
Varje år ökar världens energiförbrukning på grund av befolkningstillväxt och ökande levnadsstandard. Vi står inför många stora problem, till exempel klimatförändringar, uttömning av fossila energikällor (t. ex. petroleum, kol och naturgas) och miljöföroreningar. Därför är det brådskande att söka efter förnyelsebar energi och hur människor kan använda energi så effektivt och ändamålsenligt som möjligt. Högeffektiva material är viktiga för att utvinna och använda energi ändamålsenligt. Under de senaste åren har blyhalogenidperovskitmaterial blivit en typ av lovande och mångsidiga material avsedda för förnyelsebar energiproduktion, till exempel solceller. Blyhalogenidperovskitmaterial kan användas för att tillverka effektivare... (More)
Varje år ökar världens energiförbrukning på grund av befolkningstillväxt och ökande levnadsstandard. Vi står inför många stora problem, till exempel klimatförändringar, uttömning av fossila energikällor (t. ex. petroleum, kol och naturgas) och miljöföroreningar. Därför är det brådskande att söka efter förnyelsebar energi och hur människor kan använda energi så effektivt och ändamålsenligt som möjligt. Högeffektiva material är viktiga för att utvinna och använda energi ändamålsenligt. Under de senaste åren har blyhalogenidperovskitmaterial blivit en typ av lovande och mångsidiga material avsedda för förnyelsebar energiproduktion, till exempel solceller. Blyhalogenidperovskitmaterial kan användas för att tillverka effektivare energiomvandlingsprodukter för vardagsbruk, t.ex. ljussättning (t.ex. lysdioder, LED:er), bildskärmar (t.ex. teveapparater), fotodetektorer (t.ex. kameror) och lasrar. Det finns absorption och emission av fotoner i alla produkterna. Under fotonabsorption och -emission sker många fotofysiska processer.

Omfattande kunskaper om blyhalogenidperovskitmaterialens fotofysik kommer att spela en viktig roll för att förbättra både materialens och produkternas funktion. I den här avhandlingen utforskade vi fotofysiken i perovskitkristaller av nanostorlek (1 nm = 0,000 000 001 m) och mikrostorlek (1 μm = 0,000 001 m) som kanske kan användas för LED:er, TV-apparater och fotodetektorer. Vi utforskade

blyhalogenidperovskitnanokristallers stabilitet under ljusbestrålning.

Blyhalogenidperovskitnanokristaller kan bli ett aktivt medium för lasrar med tvåfotonabsorption (där två fotoner absorberas samtidigt). Därför utforskade vi tvåfotonabsorptionsprocessen i blyhalogenidperovskitnanokristaller. Sedan tillverkade vi en högeffektiv fotodetektor baserad på blyhalogenidperovskitmikrokristallager.

Det finns stora miljöproblem med att använda blyhalogenidperovskitmaterial som innehåller giftigt bly. Därför ersatte vi det giftiga blyet med mindre giftig vismut i perovskitnanokristaller. De vismutbaserade kristallerna fotoluminescerar med synligt ljus. Emissionsintensiteten är dock väldigt svag på grund av att laddningsbärare fastnar i fälltillstånd. Det är möjligt att begränsa fällorna och öka emissionsintensiteten för användning i LED:er.

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Abstract
The demand and consumption of energy is increasing dramatically all around the world. Broad adoption of fossil fuels has triggered an enormous threat to the environment. To ensure sustainability of our species and habitat, new solutions to fulfill the energy demand have to be found. Innovative materials offer the possibility to generate scalable renewable energy, which is efficient and environmentally friendly. In recent years, it was demonstrated that lead halide perovskite (LHP) materials prepared with superior optoelectronic properties which are desirable for solar-cell applications. Moreover, the solution processing ensures cheap production of those materials. In order to optimize and widely adopt LHPs as a key component for solar... (More)
The demand and consumption of energy is increasing dramatically all around the world. Broad adoption of fossil fuels has triggered an enormous threat to the environment. To ensure sustainability of our species and habitat, new solutions to fulfill the energy demand have to be found. Innovative materials offer the possibility to generate scalable renewable energy, which is efficient and environmentally friendly. In recent years, it was demonstrated that lead halide perovskite (LHP) materials prepared with superior optoelectronic properties which are desirable for solar-cell applications. Moreover, the solution processing ensures cheap production of those materials. In order to optimize and widely adopt LHPs as a key component for solar energy generators, it is important to understand the fundamental photophysical processes governing their unique behavior.
In this thesis we studied the photophysics of LHP nano- (NC) and microcrystals (MC) using spectroscopic methods. We investigated the photostability of NCs, and found the light irradiation induced particle aggregation. Furthermore, we revealed large two-photon absorption cross sections of these NCs, and we conclude that the two-photon absorption process populates the exciton band through a virtual state. Moreover, we have demonstrated the crucial role of size distribution in explaining the difference between the one-photon excited and two-photon excited photoluminescence (PL).
We fabricated photodetectors using micrometer-sized LHP crystals as building blocks, which show high responsivity as well as fast response in both the visible (one-photon absorption process) and the near infrared (NIR) region (two-photon absorption process). We also elucidated the underlying mechanism for the enhanced photoresponse by efficient charge collection, low trap density and high charge carrier mobility in the MCs.
In order to develop environmentally friendly materials, we replaced the lead element with less toxic bismuth in LHP structures to form the bismuth-based perovskite NCs, which exhibit tunable PL but with low quantum yield. The photophysical studies in such NCs with time-resolved spectroscopy attributed the low PL emission intensity to a fast trapping process. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Dr. Lian, Tianquan, Department of Chemistry, Emory University, Atlanta, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Ultrafast spectroscopy, Two-photon absorption, Perovskite, Nanocrystals, Photostability, Lead free perovskite
pages
146 pages
publisher
Lund University, Faculty of Science, Department of Chemistry, Division of Chemical Physics
defense location
Lecture hall F, Center for chemistry and chemical engineering, Naturvetarvägen 14, Lund
defense date
2018-03-16 13:15
ISBN
978-91-7422-568-6
978-91-7422-567-9
language
English
LU publication?
yes
id
d78ae248-b401-43a3-98eb-c1d7caa862ce
date added to LUP
2018-02-20 15:07:54
date last changed
2018-05-29 10:52:26
@phdthesis{d78ae248-b401-43a3-98eb-c1d7caa862ce,
  abstract     = {The demand and consumption of energy is increasing dramatically all around the world. Broad adoption of fossil fuels has triggered an enormous threat to the environment. To ensure sustainability of our species and habitat, new solutions to fulfill the energy demand have to be found. Innovative materials offer the possibility to generate scalable renewable energy, which is efficient and environmentally friendly. In recent years, it was demonstrated that lead halide perovskite (LHP) materials prepared with superior optoelectronic properties which are desirable for solar-cell applications. Moreover, the solution processing ensures cheap production of those materials. In order to optimize and widely adopt LHPs as a key component for solar energy generators, it is important to understand the fundamental photophysical processes governing their unique behavior. <br/>In this thesis we studied the photophysics of LHP nano- (NC) and microcrystals (MC) using spectroscopic methods. We investigated the photostability of NCs, and found the light irradiation induced particle aggregation. Furthermore, we revealed large two-photon absorption cross sections of these NCs, and we conclude that the two-photon absorption process populates the exciton band through a virtual state. Moreover, we have demonstrated the crucial role of size distribution in explaining the difference between the one-photon excited and two-photon excited photoluminescence (PL).<br/>We fabricated photodetectors using micrometer-sized LHP crystals as building blocks, which show high responsivity as well as fast response in both the visible (one-photon absorption process) and the near infrared (NIR) region (two-photon absorption process). We also elucidated the underlying mechanism for the enhanced photoresponse by efficient charge collection, low trap density and high charge carrier mobility in the MCs.<br/>In order to develop environmentally friendly materials, we replaced the lead element with less toxic bismuth in LHP structures to form the bismuth-based perovskite NCs, which exhibit tunable PL but with low quantum yield. The photophysical studies in such NCs with time-resolved spectroscopy attributed the low PL emission intensity to a fast trapping process.},
  author       = {Chen, Junsheng},
  isbn         = {978-91-7422-568-6},
  keyword      = {Ultrafast spectroscopy,Two-photon absorption,Perovskite,Nanocrystals,Photostability,Lead free perovskite},
  language     = {eng},
  pages        = {146},
  publisher    = {Lund University, Faculty of Science, Department of Chemistry, Division of Chemical Physics},
  school       = {Lund University},
  title        = {Photophysics of Perovskite Nano- and Microcrystals},
  year         = {2018},
}