Preface

The world has seen a huge research development in the field of organic light emitting devices (OLEDs) (commonly known as the organic light emitting diodes) in the last two decades. This is because such devices exhibit a number of extra technical features in flat panel displays that conventional display devices do not. These advantageous features include high brightness and contrast, high luminous efficiency, fast response time, wide viewing angle, low power consumption, flexible structures, light weight and low cost manufacturing chemical technology. Furthermore, the advancement in developing the concept of rendering white light from OLEDs for domestic, commercial and street lighting has boosted the research activity in this field. The organic white light emitting devices (OWLEDs), traditionally known as the white organic light emitting devices (WOLEDs) show promise to have a major share in future ambient lighting due to their favourable properties mentioned above. In addition, as similar chemical technology can be used to fabricate both, WOLEDs and organic solar cells (OSCs), it opens new ways in lighting design such as light ceilings or luminous objects of almost any shape. A common flexible substrate can be used to fabricate WOLEDs on one side facing a room and OSCs on the other side facing the sun. The device thus fabricated can generate power in the day time and light a room/house at night. This book covers developments on OLEDs, WOLEDs and briefly on OSCs as well.

Several other books have recently appeared on OLEDs and related topics but the field is too active to cover up to date development in one volume for very long. Although the existing resources can provide valuable fundamental information on organic electroluminescence, this book provides the state-of-the-art advancement in the field of organic electroluminescence contributed by many established experts in the field.

This volume contains eight chapters contributed by many expert researchers worldwide. Chapter 1 introduces the mechanism of light extraction from the excited singlet and triplet exciton states. The concept of capturing the triplet exciton emission has been fully understood only recently through the invention of the new timedependent exciton-spin-orbit-photon interaction operator and its role is very critical in fabricating WOLEDs. Chapter 2 deals with the development of field emission organic light emitting diodes (FEOLEDs) which have a better balance (equality) in the number of injected electrons and holes and hence have higher luminous efficiency. Both fabrication and the performance of the resulting devices are discussed.

#### VIII Preface

Chapters 3 and 4 focus on the extraction of polarized light from OLEDs. In chapter 3 the fabrication of OLEDs for generating highly polarized electroluminescent (EL) through the innovative approach of using photonic reflective polarizers is presented and their electroluminescent properties are fully characterized. In chapter 4, the minimisation of trapping of light within OLEDs is described with a view to maximise the light extraction by incorporating nanostructures. The polarization of electroluminescence through the use of innovative reflectors is also covered.

Chapter 5 presents a very comprehensive study of the photophysical properties of two new donor-acceptor conjugated copolymers and their model compounds. These properties are measured as well as calculated and results are used to analyse possible applications in fabricating polymer light emitting diodes (PLEDs) and polymer photovoltaic cells (PPCs). Chapter 6 describes state-of-the-art advancement of charge carrier injection techniques that can be used for fabricating high-power OLEDs. Different designs of OLEDs have been fabricated and tested in order to optimise the injection.

Chapter 7 describes the role of exciplex electroluminescence of new organic materials which may be used for fabrication of WOLEDs. Many structures are explored and their electroluminescent properties are characterized. Finally in chapter 8 are described the synthesis and physical properties of pyranylidene and isophorene fragments containing donor-π-acceptor type chromphores which have the ability to emit light in the visible part of the spectrum. The chapter presents a very comprehensive study of many organic structures and discusses their potential applications in the fabrication of OLEDs.

This book has resulted from the sole effort of InTech from inviting the contributors to publication. I would like to express my gratitude to all the contributors for their enthusiasm and dedication in preparing their contributions. Without their efforts the realisation of this book would not have been possible. It is my great pleasure to acknowledge the support of Ms Mirna Cvijic and Ms Viktorija Zgela from InTech in completing my editorial job successfully and efficiently.

> **Prof. Jai Singh** Charles Darwin University, Darwin Australia

VIII Preface

injection.

applications in the fabrication of OLEDs.

completing my editorial job successfully and efficiently.

Chapters 3 and 4 focus on the extraction of polarized light from OLEDs. In chapter 3 the fabrication of OLEDs for generating highly polarized electroluminescent (EL) through the innovative approach of using photonic reflective polarizers is presented and their electroluminescent properties are fully characterized. In chapter 4, the minimisation of trapping of light within OLEDs is described with a view to maximise the light extraction by incorporating nanostructures. The polarization of

Chapter 5 presents a very comprehensive study of the photophysical properties of two new donor-acceptor conjugated copolymers and their model compounds. These properties are measured as well as calculated and results are used to analyse possible applications in fabricating polymer light emitting diodes (PLEDs) and polymer photovoltaic cells (PPCs). Chapter 6 describes state-of-the-art advancement of charge carrier injection techniques that can be used for fabricating high-power OLEDs. Different designs of OLEDs have been fabricated and tested in order to optimise the

Chapter 7 describes the role of exciplex electroluminescence of new organic materials which may be used for fabrication of WOLEDs. Many structures are explored and their electroluminescent properties are characterized. Finally in chapter 8 are described the synthesis and physical properties of pyranylidene and isophorene fragments containing donor-π-acceptor type chromphores which have the ability to emit light in the visible part of the spectrum. The chapter presents a very comprehensive study of many organic structures and discusses their potential

This book has resulted from the sole effort of InTech from inviting the contributors to publication. I would like to express my gratitude to all the contributors for their enthusiasm and dedication in preparing their contributions. Without their efforts the realisation of this book would not have been possible. It is my great pleasure to acknowledge the support of Ms Mirna Cvijic and Ms Viktorija Zgela from InTech in

**Prof. Jai Singh**

Australia

Charles Darwin University, Darwin

electroluminescence through the use of innovative reflectors is also covered.

**Chapter 1** 

© 2012 Singh, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Singh, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Harvesting Emission in White Organic Light** 

The current use of lighting in buildings and streets accounts for a significant percentage of the electricity consumed in the world at present and nearly 40% of that is consumed by inefficient thermoluscent incandescent lamps, only about 15 lm/W. This has created interest in investigating more efficient electroluminescent sources of white light for use in domestic,

int , *out ph*

int . *ex*

electron (e) and hole (h) pairs that recombine radiatively due to their Coulomb interaction.

, where *n* is the index of refraction of the substrate through which the light comes

The schematic of a very simple electroluminescent device can be envisaged as a single thin film of an electroluminescent layer sandwiched between anode and cathode electrodes, as

is the ratio of number of electrons to that of holes, or vice versa, injected from the

1 is maintained. *ex*

*ph* 20% .

is the ratio of number of radiative recombinations to the number of electrically

(1)

(2)

is the fraction of the injected

efficiency of an

and the

industrial and street lighting. The total light output efficieny *out*

as [1]:

electroluminescent lighting device depends on the internal qantum efficiency int

 

injected electrons and holes from opposite electrodes of the device and it is given by:

 

**Emitting Devices** 

http://dx.doi.org/10.5772/53130

photon out-coupling efficiency *ph*

opposite electrodes of a device so that

out. In the case of a glass substrate with *n* = 1.5,

**1. Introduction** 

where int 

Here 

2 1 2 *ph n* 

Additional information is available at the end of the chapter

Jai Singh
