Introduction to organic semiconductors and applications

Prof. Franco Cacialli
Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, London, U.K.

20 hours, 5 credits (final test)

May 14 - May 18, 2007
Dipartimento di Ingegneria dell'Informazione: Elettronica, Informatica, Telecomunicazioni, via Caruso 16, meeting room, ground floor

Contacts: Prof. Andrea Nannini

Syllabus

Introduction

• Inorganic semiconductors
• Organic semiconductors
• Π-orbitals and conjugation
  
• Excitations: excitons and polarons
  
• Exciton spin: singlets and triplets
  
• Synopsis electronic and optical processes
  
• Optical properties: a few examples
  Energy gap vs. molecular weight; electron-phonon coupling: vibrational structure and thermochromism; Förster transfer and site selective spectroscopy
• Summary of optical properties

Polymer-based light-emitting diodes (LEDs)

• Structure
• Fundamental processes
• Charge injection
• Charge transport
• Exciton formation
  Mutual capture; Exciton characteristics (binding energy, spin-multiplicity, capture cross-section
• Exciton decay
  Radiative and non-radiative decay; Exciton lifetime; Efficiency
• Characterisation of PLEDs
• Relevant performance parameters
• Characterising metal-semiconductor contacts: electroabsorption measurements as a non-invasive tool for the study of the energy level line up in finished devices
• Practical implementations
• Anodes
• Cathodes
• Active materials
  Singlet emitters; Triplet emitters - enhanced spin-orbit coupling via doping with rare-earth ligands; Blends: trying to achieve the best of all worlds; Prototypical materials for red, green and blue emission (singlet emitters)
• Fabrication technology: the advantage of solution processability
  Spin-coating; Ink-jet printing (IJP); Screen-printing and other examples
• State of the art devices and future prospects

Polymer-based photovoltaic diodes (PVDs)

• Fundamental process
• Exciton absorption
• Exciton dissociation
• Charge collection
• Characterisation of PVDs
• Relevant performance parameters
• Most important examples of polymer-based PVDs
• Polymer-polymer heterojunctions
  Enhanced dissociation at type II heterojunctions; Preparation methods: polymer blends and spontaneous phase separation
• C60-polymer structures
• Heterojunctions with nanocrystals, nanorods, etc.
• State of the art devices and future prospects

Polymer-based field-effect transistors (FETs)

• Structure
• Fundamental processes
• Channel formation
• Charge transport
• Characterisation
• Relevant performance parameters
• Examples of successful strategies
• State of the art devices and future prospects