Content

Organic and polymer semiconductors are revolutioning the consumer electronic market. Nowadays, mobile telephones and TV-sets are often equipped with OLED screens while wearable electronics is becoming more and more important. However, the knowledge of materials allowing for this revolution is poor. Aim of this class is to provide a knowledge of chemistry and physics fundamentals, the understanding of material properties and working principles of electronic devices made by organic semiconductors in order to face in a professional way the revolution of organic electronics.

Module 1: Electronic states and spectroscopy.

Extended p-electron systems both in molecules and polymers. Conjugation length: ionization potential, electron affinity and HOMO-LUMO gap in the series ranging from ethylene to polyene. Electronic states for the polyene: introduction to the Hückel method for the isolated chain and for interacting macromolecules. Dimerization and Peierls distorsion: metal and semiconducting polymers. Conducting conjugated polymers: doping and applications. Charge transport in semiconducting and conducting polymers. Spectroscopy of conjugated systems: electronic transitions, Franck-Condon principle and vibronic transitions, fluorescence and lifetime, singlet and triplet excitons, Jablonski diagram and photophysics.

Module 2: Synthesis and material properties.

Synthesis of main conjugated polymer families (polyacetylene, polythiophene, poly(p-phenylenevinylene)). Functionalization of chemical and physical properties of conjugated materials (solubility, ionization potential, electron affinity). Supramolecolar structure of conjugated polymers and role of aggregation in the solid state. Orientation techniques of conjugated polymers, optical and electronic properties anisotropy.

Module 3: Devices.

Working principles of devices made of conjugated molecules and polymers: sensors, devices for non-linear optics, organic/polymer light emitting diodes (OLED), organic field effect transistors (OFET), organic photovoltaic cells (OPV) and light harvesting based devices, wearable electronics. Role of the supramolecular structure on the main electronic properties of materials and of devices.

Module 4: Experiments

Simple classroom experiments will be done. Topics concern solution/film/materials spectroscopy (absorbance, reflectance and fluorescence). Simple electrical testing of OPV and luminescent solar concentrators

Aims

Basic knowledge of chemical and physical properties of conjugated polymers and organic semiconductors. Use of such materials in organic optoelectronics and photonic devices (sensors, transistor, led and photovoltaic cells)
At the end of the course, students are expected to understand:

• Main differences between the electronic structure of organic and inorganic semiconductors.
• Main qualitative differences of the electronic structure of isolated and interacting chains.
• The concept of energy gap, bandwidth, carrier mobility and intermolecular interactions.
• The meaning of conjugation length.
• The qualitative role of disorder in polymer semiconductors on the carrier mobility. The importance of solubility in processing.
• The qualitative effect of side chains on processability, controlling intermolecular interactions and solubility.
• Methods to make conjugated polymers oriented and the qualitative effect on the optical properties. Main synthetic strategies to prepare conjugated polymers.
• The role of regioregularity.
• Tuning of the ionization potential, electron affinity and energy gap.
• Fundamentals of spectroscopy and photophysics in organic semiconductors.
• The vibronic structure.
• Working principles of sensors, transistor, led and photovoltaic cells.
• Material strategies to improve their performances.

They have to be able to extract simple information on physical and chemical properties from absorption/fluorescence spectra of a conjugated polymer/molecule as described during the class with several examples.

Pre-requiste

Good knowledge in chemistry as well as physics

Recommended Books

1. M. Pope and C. Swemberg “Electronic processes in organic crystals and polymers”, Oxford Sci Publ. New York 1999. (Chapter 1).
2. M. Klessinger and J. Michl “Excited states and photochemistry of organic molecules”, VCH, New York 1995. (selected paragraphs).
3. J.B. Birks “Photophysics of Aromatic Molecules”, Wiley monographs in chemical physics, 1970. (selected paragraphs).
4. M.C. Petty "Molecular Electronics", Wiley 2007. (selected paragraphs).
5. Notes from the lecturer (available in advance on a web repository).
6. Selected papers published on international scientific journals.

Teaching Staff

Prof. Davide Comoretto

Hours

48 hours Lecture

Grading System

Oral exam held by two professors, one of them being D. Comoretto. The duration of the exam is no shorter than 30 minutes.

The student discusses an original power-point presentation or written relation on an item related to the course. The student selects the item more suitable to his/her aptitudes/needs with the help of the teacher among those reported in the scientific literature and/or provided on aula-web (usually one or two papers). The presentation has to be suitable for understanding by students of the same level.

The student must show to have understood main physical/chemical/technological fundamentals related to the topics and to use the suitable technical vocabulary (up to 20/30). The clarity of presentation (up to 5/30) and ability to answer questions (up 5/30) will be also evaluated.

Goal of the exam is to verify the achievement of the class aims. If aims are not achieved, the student is invited to make a deeper study and to ask the teacher for additional explanations before repeating the exam. In order to guarantee the correspondence between aims and exam topics, the detailed program is uploaded to aula web and described at the beginning of the course.