Electronic energy transfer processes and charge carrier transport in {π-conjugated [pi-conjugated] polymers [Elektronische Ressource] / vorgelegt von Frédéric Laquai

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2006
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Electronic energy transfer processes
and charge carrier transport in
…-conjugated polymers
Dissertation
zur Erlangung des Grades
"Doktor der Naturwissenschaften"
am Fachbereich Chemie, Pharmazie und Geowissenschaften
der Johannes-Gutenberg-Universit˜at Mainz
vorgelegt von
Fr¶ed¶eric Laquai
geboren in Wilhelmshaven
Mainz, im Jahr 2006Non exiguum temporis habemus, sed multum perdidimus.
(Lucius Annaeus Seneca)Contents
1 Introduction 1
1.1 Organic electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Motivation and Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Theoretical Basics 5
2.1 Light absorption and emission . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Electronic transitions in organic molecules . . . . . . . . . . . . . . . . 9
2.2.1 Transition dipole moment . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 The selection rules . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.3 Electronic transitions - Conflguration-Coordinate Diagram . . . 12
2.3 Energy transfer processes . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 From small molecules to conjugated polymers . . . . . . . . . . . . . . 18
2.4.1 Aggregates, excimers and exciplexes . . . . . . . . . . . . . . . . 18
2.4.2 Band-model versus exciton model . . . . . . . . . . . . . . . . . 19
2.4.3 Exciton models . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.5 The fate of excited states . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.1 Exciton migration and relaxation . . . . . . . . . . . . . . . . . 26
2.5.2 decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.2.1 Singlet exciton decay . . . . . . . . . . . . . . . . . . . 28
2.5.2.2 Triplet decay . . . . . . . . . . . . . . . . . . . 30
3 Photophysical properties of blue light emitting polyspirobi uorene
homo- and copolymers 35
3.1 Introduction - Light-emitting polymers . . . . . . . . . . . . . . . . . . 35
3.1.1 Poly-phenylene-vinylene (PPV) derivatives . . . . . . . . . . . . 35
3.1.2 Poly-p-phenylene (PPP) derivatives . . . . . . . . . . . . . . . . 37
3.1.3 Polyspirobi uorene polymers: Towards a stable blue . . . . . . . 39
3.2 A dielectric spectroscopy study on a spirobi uorene homopolymer . . . 41
3.2.1 Dielectric spectroscopy data . . . . . . . . . . . . . . . . . . . . 41
3.2.2 Ionic mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2.3 Molecular mobility . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3 On the morphology of Poly-spirobi uorene homopolymer fllms . . . . . 46
3.4 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.5.1 Polyspirobi uorene Homopolymer . . . . . . . . . . . . . . . . . 51
3.5.1.1 Fluorescence dynamics . . . . . . . . . . . . . . . . . . 51
iContents
3.5.1.2 Delayed uorescence and phosphorescence in thin fllms 55
3.5.1.3 Delayed and in frozen so-
lution . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.5.1.4 Stability against oxidation . . . . . . . . . . . . . . . . 60
3.5.2 Polyspirobi uorene Copolymers . . . . . . . . . . . . . . . . . . 62
3.5.2.1 Fluorescence energies and kinetics . . . . . . . . . . . 63
3.5.2.2 Delayed uorescence and phosphorescence in thin fllms 64
3.5.2.3 Delayed and in solution . 68
3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4 Energy transfer in polymer blends and doped polymer matrices 73
4.1 Introduction - Why blends and copolymers? . . . . . . . . . . . . . . . 73
4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.2.1 Blends of Spiro-co-TAD with S-NRS-PPV . . . . . . . . . . . . 76
4.2.2 Energy transfer in PSBF polymers doped with a triplet emitter 79
4.2.3 Temperature dependence of energy transfer in PtOEP doped
PSBF-co-TAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.4 Comparison of energy transfer in triplet-emitter doped PSBF
matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.3 Photon energy upconversion in PtOEP doped PSBF matrices . . . . . 85
4.3.1 Introduction - The phenomenon of energy upconversion . . . . . 85
4.3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3.2.2 Sample preparation . . . . . . . . . . . . . . . . . . . . 87
4.3.2.3 Instrumentation . . . . . . . . . . . . . . . . . . . . . 88
4.3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.3.4 Discussion and Outlook . . . . . . . . . . . . . . . . . . . . . . 96
5 Charge carrier transport in …-conjugated polymers 99
5.1 Introduction - Theoretical background . . . . . . . . . . . . . . . . . . 99
5.1.1 Charge carrier generation . . . . . . . . . . . . . . . . . . . . . 99
5.1.2 transport . . . . . . . . . . . . . . . . . . . . . . 101
5.1.3 Time-of- ight (TOF) technique . . . . . . . . . . . . . . . . . . 103
5.1.4 Charge-generation-layer TOF technique . . . . . . . . . . . . . . 105
5.1.5 Other techniques to determine the charge carrier mobility. . . . 108
5.1.5.1 Dark-injectionspace-charge-limitedcurrenttransientmethod108
5.1.5.2 Space-charge-limited current-voltage measurements . . 108
5.1.5.3 Time-resolved microwave conductivityts . 109
5.1.5.4 Field-efiect transistor mobilities . . . . . . . . . . . . . 109
5.1.6 Models of charge carrier transport . . . . . . . . . . . . . . . . . 111
5.1.6.1 Dispersive and nondispersive charge carrier transport . 112
5.1.6.2 The disorder model of charge carrier transport . . . . . 114
5.1.7 Charge carrier mobility in organic materials . . . . . . . . . . . 118
5.2 Experimental part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.2.2 Sample preparation and instrumentation . . . . . . . . . . . . . 122
iiContents
5.3 Cyclic voltammetry measurements. . . . . . . . . . . . . . . . . . . . . 124
5.3.1 Cyclic voltammetry - Background . . . . . . . . . . . . . . . . . 124
5.3.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 125
5.4 Results and interpretation of TOF measurements . . . . . . . . . . . . 128
5.4.1 TOF measurements on the PSBF-homopolymer and Spiro-co-
(10%)TAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
5.4.1.1 Temperature and fleld-dependence of hole mobility . . 128
5.4.1.2 Temp dependence of zero-fleld mobility . . . . . 129
5.4.1.3 Interpretation of charge carrier transport parameters . 133
5.4.1.4 Hole mobility in an annealed sample . . . . . . . . . . 136
5.4.2 TOF measurements on Spiro-co-(10%)anthracene and Spiro-co-
(10%)carbazole . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
5.4.2.1 Temperature and fleld-dependence of hole mobility . . 139
5.4.2.2 Temp dependence of the zero-fleldy . . 142
5.4.2.3 The occurrence of a cusp at higher temperatures . . . 146
5.5 Discussion and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6 Amplifled spontaneous emission in polymer waveguides 151
6.1 Introduction - Theoretical background . . . . . . . . . . . . . . . . . . 151
6.1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
6.1.2 Stimulated emission in organic materials . . . . . . . . . . . . . 152
6.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
6.2.1 Material and sample preparation . . . . . . . . . . . . . . . . . 156
6.2.2 Experimental setup and techniques . . . . . . . . . . . . . . . . 157
6.3 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7 Conclusions and Outlook 168
References 172
A Abbreviations 186
B List of scientiflc publications 189
iiiivChapter 1
Introduction
1.1 Organic electronics
The electronic and optical properties of conjugated polymers have attracted tremen-
dous academic and industrial research interest over the past decades due to the ap-
pealing advantages that organic / polymeric materials ofier for electronic applications
and devices such as organic light emitting diodes (OLED), organic fleld efiect transis-
tors (OFET), organic solar cells (OSC), photodiodes and plastic lasers [MF05] [For05].
From the afore mentioned devices organic / polymer light emitting diodes have been
developed furthest and some products have already entered the market as precursors
of the next generation of display and lighting technology. A simplifled scheme of an
organic light emitting diode is shown in Figure 1.1. The research fleld of organic
Counter electrode
Light emitting
material
Transparent
Electrode
Substrate
Emitted Light
Figure 1.1: Simple scheme of an organic light emitting diode (OLED).
light emitting diodes is traditionally divided into the small molecule based devices
which were flrst reported by a team from Kodak [TvS87] and polymer based LEDs
(also PLEDs) flrst demonstrated by the research group of Friend from the University
11.1. Organic electronics
+of Cambridge (UK) [BBB 90]. The former have already proven their applicability
from simple monochrome OLEDs up to full-color displays which have already been
introduced int