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Super-resolution Luminescence Micro-Spectroscopy : A nano-scale view of solar cell material photophysics

Merdasa, Aboma LU (2017)
Abstract (Swedish)
”Seeing is believing” är ett koncept fött ur människans oändliga nyfikenhet att veta mer. Otvivelaktigt så har modern vetenskap vuxit fram ur denna naturliga strävan efter att vilja veta mer. Från ett tidigt stadium har mikroskopi varit en hörnsten i många vetenskapsdiscipliner. Redan i ett tidigt skede filosoferade mikroskopister kring vad de minsta beståndselarna av naturen är och om vi ens kan beskåda dem med hjälp av ett mikroskop. År 1873 förklarade Ernst Abbe att naturens fundamentala lagar förhindrar direkt iakttagande av objekt som är mindra än halva våglängden av det ljus som objektet utstrålar – ljusets diffraktionsgräns. Nästan 150 år efter att denna gräns etablerats lyckades vetenskapsmän bryta denna gräns med hjälp av ett par... (More)
”Seeing is believing” är ett koncept fött ur människans oändliga nyfikenhet att veta mer. Otvivelaktigt så har modern vetenskap vuxit fram ur denna naturliga strävan efter att vilja veta mer. Från ett tidigt stadium har mikroskopi varit en hörnsten i många vetenskapsdiscipliner. Redan i ett tidigt skede filosoferade mikroskopister kring vad de minsta beståndselarna av naturen är och om vi ens kan beskåda dem med hjälp av ett mikroskop. År 1873 förklarade Ernst Abbe att naturens fundamentala lagar förhindrar direkt iakttagande av objekt som är mindra än halva våglängden av det ljus som objektet utstrålar – ljusets diffraktionsgräns. Nästan 150 år efter att denna gräns etablerats lyckades vetenskapsmän bryta denna gräns med hjälp av ett par fyndiga knep. Genom att på ett välkontrollerat sätt fästa enskilda molekyler på objektet av intresse och sen få dem att skina en åt gången så kunde man successivt lokalisera deras positioner och därmed skapa en så kallad ”super-upplöst” bild av objektet. Med dessa metoder kunde inre beståndsdelar av levande organismer på en nanometerskala studeras, vilket har under de senaste åren börjat ge svar på många frågor inom biologi och medicin. För denna bragd fick dessa vetenskapsmän Nobelpriset i Kemi år 2014.

Så vad mer kan dessa metoder användas till? Det har på senare tid vuxit fram ett intresse för att studera så kallade ”funktionella material”, som ofta används i solceller och ljusdioder. Dessa material är ofta långt större än en enskild molekyl men de processer som är intressanta att förstå kan inträffa på en väldigt liten storleksskala. Det är därför av större intresse att veta hur de små beståndsdelarna, som är del av en större ensemble ger upphov till diverse processer förknippade med exempelvis verkningsgraden av solceller.

Vi introducerar en ny metod som sammanbinder högupplöst optisk mikroskopi och spektroskopi vilket ger möjlighet att studera processer i större funktionella material på en nano-skala. Med denna metod, som vi kallar super-resolution luminescence micro- spectroscopy (SuperLuMS) har vi börjat studera material som kan användas för solceller och lyckats förstå vilka grundläggande processer som sker när materialet belyses med solljus. Vi har kunnat identifiera hur energin rör sig i materialet, samt förstå vilka processer som eventuellt skulle kunna hämma effektiviteten av solceller eller ljusdioder. Metoden är inte bara ämnad för solcellsmaterial utan vi är förvissade om att SuperLuMS kan hitta tillämpningar för funktionella material i allmänhet. (Less)
Abstract
Optical microscopy is a fundamental tool in a range of disciplines encompassed by the physical and biological sciences. At the dawn of this millennium, a break-through was made in optical microscopy where super-resolution methods emerged and declared imaging beyond the optical diffraction limit a possibility. Most of these methods are based on fluorescence detection of single molecules. These methods found particular prominence in the life sciences where small structures could be observed inside living organisms, due to the non-invasiveness of light.

Currently there is a growing notion that these methods can be applied in physics and chemistry to study photo-induced phenomena in materials with resolution at the nanoscale. The aim... (More)
Optical microscopy is a fundamental tool in a range of disciplines encompassed by the physical and biological sciences. At the dawn of this millennium, a break-through was made in optical microscopy where super-resolution methods emerged and declared imaging beyond the optical diffraction limit a possibility. Most of these methods are based on fluorescence detection of single molecules. These methods found particular prominence in the life sciences where small structures could be observed inside living organisms, due to the non-invasiveness of light.

Currently there is a growing notion that these methods can be applied in physics and chemistry to study photo-induced phenomena in materials with resolution at the nanoscale. The aim of this thesis is to explore and develop these possibilities to study energy and charge transport in functional materials interesting for light harvesting and solar-energy conversion. We present a novel wide-field super-resolution microscopy method adapted from localization microscopy. In combination with fluorescence spectroscopy it allows for an interrogation of a material’s photophysical properties down to the nanometer scale. We call the method super-resolution luminescence micro-spectroscopy (SuperLuMS).

One of the examples that we present here is a study of energy migration and trapping in individual molecular J-aggregates. We show that so-called ‘outliers’ (seldomly occurring trapping states) completely determine the exciton transport and dominate the fluorescence response. We also show that hybrid organic-inorganic perovskites are ideal objects for luminescence microscopy. These “hot” solar cell and light-emitting materials possess rich structures at scales just beyond optical diffraction limit making them an ideal “playground” for employing SuperLuMS and demonstrating its abilities.

The dynamics of charge carrier recombination in these materials is controlled by trapping and, as we demonstrate here, possess a great spatial inhomogeniety. For the first time we showed that one single trap can control the fate of charge carries in micrometer sized perovskite crystals which has important consequences for optical design of solar cells and other optoelectronic devices. We were also able to observe details of light-induced degradation and crystal phase transition in individual hybrid organic-inorganic perovskite crystals.

We believe SuperLuMS is an approach which will continue to evolve and find more diverse applications in material science.
(Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Dr. Loi, Maria Antonietta, University College Groningen, The Netherlands
organization
publishing date
type
Thesis
publication status
published
subject
keywords
super-resolution microscopy, Single Molecule Spectroscopy, J-aggregates, perovskites, photophysics
pages
171 pages
publisher
Lund University, Faculty of Science, Department of Chemistry, Division of Chemical Physics
defense location
Lecture hall B, Department of Chemistry, Naturvetarvägen 14, Lund
defense date
2017-01-27 10:15
ISBN
978-91-7422-497-9
978-91-7422-496-2
language
English
LU publication?
yes
id
204a9d56-c957-43a6-b08e-95ca8de6bd54
date added to LUP
2017-01-10 13:17:26
date last changed
2017-01-19 11:12:21
@phdthesis{204a9d56-c957-43a6-b08e-95ca8de6bd54,
  abstract     = {Optical microscopy is a fundamental tool in a range of disciplines encompassed by the physical and biological sciences. At the dawn of this millennium, a break-through was made in optical microscopy where super-resolution methods emerged and declared imaging beyond the optical diffraction limit a possibility. Most of these methods are based on fluorescence detection of single molecules. These methods found particular prominence in the life sciences where small structures could be observed inside living organisms, due to the non-invasiveness of light.<br/> <br/>Currently there is a growing notion that these methods can be applied in physics and chemistry to study photo-induced phenomena in materials with resolution at the nanoscale. The aim of this thesis is to explore and develop these possibilities to study energy and charge transport in functional materials interesting for light harvesting and solar-energy conversion. We present a novel wide-field super-resolution microscopy method adapted from localization microscopy. In combination with fluorescence spectroscopy it allows for an interrogation of a material’s photophysical properties down to the nanometer scale. We call the method super-resolution luminescence micro-spectroscopy (SuperLuMS). <br/><br/>One of the examples that we present here is a study of energy migration and trapping in individual molecular J-aggregates. We show that so-called ‘outliers’ (seldomly occurring trapping states) completely determine the exciton transport and dominate the fluorescence response. We also show that hybrid organic-inorganic perovskites are ideal objects for luminescence microscopy. These “hot” solar cell and light-emitting materials possess rich structures at scales just beyond optical diffraction limit making them an ideal “playground” for employing SuperLuMS and demonstrating its abilities.<br/><br/>The dynamics of charge carrier recombination in these materials is controlled by trapping and, as we demonstrate here, possess a great spatial inhomogeniety. For the first time we showed that one single trap can control the fate of charge carries in micrometer sized perovskite crystals which has important consequences for optical design of solar cells and other optoelectronic devices. We were also able to observe details of light-induced degradation and crystal phase transition in individual hybrid organic-inorganic perovskite crystals. <br/><br/>We believe SuperLuMS is an approach which will continue to evolve and find more diverse applications in material science.<br/>},
  author       = {Merdasa, Aboma},
  isbn         = {978-91-7422-497-9},
  keyword      = {super-resolution microscopy,Single Molecule Spectroscopy,J-aggregates,perovskites,photophysics},
  language     = {eng},
  pages        = {171},
  publisher    = {Lund University, Faculty of Science, Department of Chemistry, Division of Chemical Physics},
  school       = {Lund University},
  title        = {Super-resolution Luminescence Micro-Spectroscopy : A nano-scale view of solar cell material photophysics},
  year         = {2017},
}