Photovoltaics from discotic liquid crystalline HBCs & poly(2,7-carbazole)s [Elektronische Ressource] / Jiaoli Li

Lijiaoli

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2007
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

Photovoltaics
from
Discotic Liquid Crystalline HBCs
&
Poly(2,7-Carbazole)s



Dissertation zur Erlangung des Grades
‘Doktor der Naturwissenschaften’

am Fachbereich Chemie und Pharmazie
der Johannes Gutenberg-Universität in Mainz


Jiaoli Li
Geboren in Shaanxi Province / China
Mainz 2006
























Dedicated to my family



















I
CONTENTS




Chapter 1 INTRODUCTION 1
1.1 The Development of Organic Solar Cells…………………………...……………….…….2
1.2 Discotic Liquid Crystals as Active Semiconductors in Electronic and Optoelectronic
Devices………………………………………………………………………….…….………3
1.3 Conjugated Polymers as Active Components in Organic Solar
Cells…….………………………………….……………..………….…………………….….8
1.4 Motivation………………….……………………………………………………… .………..13
1.5 Contents of the Thesis……………………………………….……………….. ……..…….14


Chapter 2 ORGANIC SOLAR CELLS 15
2.1 The Organic Bulk Heterojunction Concept……………….…………..…… ….……..…..15
2.2 Fundamental Processes………………………….…………………..…………… ………16
2.2.1 The Absorption of Photons and the AM1.5 G Solar Light…………………… ……….17
2.2.2 Exciton Diffusion and Charge Separation at the D/A Interface………….………...…18
2.2.3 Charge Transport……………………..…………………………………………………22
2.2.4 Charge Recombination……………………………………………………………………24
2.2.5 The Organic Semiconductor/Metal Contact…………………………………………….25
2.3 Film Morphology……………………………………………….………… …………………26


Chapter 3 EXPERIMENTAL METHODS 29
3.1 Spectroscopy……………………………………………….………………………………..29
3.1.1 Absorption Spectra…………………………………………………...……….……….…..29
II Contents
3.1.2 Photoluminescence Measurements……………….………...…………………………..30
3.2 Cyclic Voltammetry……………….……………………………………...…..……………....30
3.3 Microscopic Techniques……………….………………………………………………..….32
3.3.1 Atomic Force Microscopy……………….…………………………………………....…..32
3.3.2 Scanning Electronic Microscopy……………….………………………………….……..34
3.4 X-ray………………………………………………………….………………… ……..……..34
3.5 Differential Scanning Calorimetry……….………………….……………………………..35
3.6 Fabrication and Characterization of Solar Cells……………….…………..….…...…….36
3.6.1 Device Fabrication……………….………………………………………………………..36
3.6.2 Device Testing…………..……….………………………………………….……………..38
3.6.3 Photovoltaic Parameters……………….…………………..………...…………………..40
3.6.3.1 I-λ Curve (EQE- λ Curve)……………….……………………………………….…40
3.6.3.2 I-V Curve………..…………….……………………………………………………..41


Chapter 4 APPLICATION OF HEXABENZOCORONENE (HBC) IN
SOLAR CELLS 43
4.1 Introduction………….………….…………..………………………………………………..44
4.2 Photodiodes Based on HBC-PhC …………….……………………………...……...…..46
12
4.2.1 Film Forming………………..……….……………………………………………………..47
4.2.2 Morphology Studies on PDI Crystals…….……….……………………………………..49
4.2.3 Device…………….………………………………………………………………………...54
4.2.3.1 Thermal Treatment……………….…………………………………………………54
4.2.3.2 HBC-PMI………..…………….……………………………………………………..56
4.2.4 Summary……….……………………………………………...…………………………...61
4.3 Photodiodes Based on Branched-alkyl Substituted HBCs……………….………...…..62
4.3.1 Introduction…………….…………………………………………………………….……..62
4.3.2 Optical Properties ………………………………….……………………………….……..65
4.3.3 Characterization of Energy Levels…………….…………….………….………………..67 III
4.3.4 Photovoltaic Device……..………….……………………………………………………..69
4.3.5 Morphology Investigation…………….…………………………………………………...72
4.3.6 Summary…………….…………………………………………………………………......78
4.4 HBC-C OC – A New Discotic Material for Solar Cells…………....….……....……..78 3 10,6


Chapter 5 POLY(2,7-CARBAZOLE)S AS DONOR MATERIALS IN
PHOTOVOLTAICS 84
5.1 Introduction…….………………………………………………………...…………………..84
5.1.1 Synthesis of Poly(2,7-carbazole) (PCz)….……………………………………………...84
5.1.2 Optical Properties………………….……………………….…………….………………..85
5.1.3 Characterization of Energy Levels….…………………………………………… ……...86
5.1.4 Comparison of PCz and PF in Solar Cell…..…………………………………………...87
5.2 Photodiodes based on PCz…….……………………………………………..….………..89
5.2.1 Pairing PCz with PDI or PCBM…………………………………………………………..89
5.2.1.1 Optical Properties of the Blends.…………………….…….………………..…….90
5.2.1.2 Matching Energy Levels of D/A.…………….……………………………………..91
5.2.1.3 Charge Transfer from the Donor to the Acceptor…………..………...………...91
5.2.1.4 Photovoltaic Device………..………..…………………………...……………......93
5.2.2 Optimization of Device PCz/PDI…….……………………………… …………………...94
5.2.2.1 D/A Ratio……………………….………………..…….……… …………………….94
5.2.2.2 Thermal Treatment….……….………………………….… ……………………..102
5.2.3 Summary…….…………………………………………………………….. …………….105
5.3 Photodiodes based on Ladder Type Poly(2,7-Carbazole)s……………..…………….105
5.3.1 Optical Properties…….………………………………………………….……………… 107
5.3.2 Characterization of Energy Levels……………………………………..……….…...…109
5.3.3 Self-organization Properties………………………………………….…….…………...110
5.3.4 Photovoltaic Device…………………….………………………………………………..117
5.3.4.1 PCBM based Device.……………………...………………………………….…..117
IV Contents
5.3.4.2 PDI based Device.…………….…………………………………………………..123
5.3.5 Summary…………………….……………………………………………………………132
5.4 Low Band-gap Materials containing 2,7-linked Carbazole………….……….……....…133
5.4.1 Copolymer of PCz and PDI………………………….…….……………….…………....134
5.4.2 Conjugated Copolymers of 2,7-linked Carbazole and Ladderized Pentaphenylene
with Diketone Bridge (LPPK)…………………………………………………………..139
5.4.3 Small Molecule based on Carbazole and Diketone………. …..….………….….…...142


Chapter 6 GUIDELINES FOR SOLAR CELL DESIGN 146
6.1 Absorption of Solar Light………………………………………………..………...………146
6.2 Relative Energy Levels……………………………………………...…………….. ……..150
6.3 Charge Transport and D/A Interfacial Area……………………….…..………… ……..152
6.4 Film Forming…………………….……………………………………………..…………..157


CONCLUSIONS AND OUTLOOK 161

REFERENCES 164

ACKNOWLEDGEMENT 178

LIST OF PUBLICATIONS 180

CURRICULUM VITAE 182 Index of Abbreviations V
Index of Abbreviations




AFM atomic force microscopy
DSC differential scanning calorimetry
FET field effect transistor
g gram
HBC hexa-peri-hexabenzocoronene
h hour
LED light emitting diode
min minute
m.p. melting point
MALDI-TOF matrix-assisted laser desorption ionization-time of flight
NIR near infrared
NMR nuclear magnetic resonance
PAH polycyclic aromatic hydrocarbons
POM polarized optical microscopy
PR-TRMC p ulse radiolysis time-resolved microwave conductivity
RT room temperature
STM scanning tunneling microscopy
THF tetrahydrofuran
UV-vis ultraviolet/visible