Lecture by Neil Greenham from Cambridge University
date:2015-09-15 pageviews:14

Topic One: Triplet States in Organic Electronic Devices

 

Speaker: Professor Neil Greenham, Cavendish Laboratory of Cambridge University, UK

 

Time: 10:00 a.m., September 22, 2014

 

Venue: Conference Hall N308A, Building of State Key Laboratory of Luminescent Materials and Devices, SCUT North Campus

 

Sponsor: School of Materials Science and Engineering

 

Abstract:

Photoexcitation of organic semiconductors typically generates spin-zero singlet excitons. Triplet excitons, with a total spin of 1, also exist and their formation can provide an important loss mechanism in polymer light-emitting diodes and photovoltaics. In this tutorial-style talk I will review some old and some new work on triplet excitons in organic semiconductors. Some of the questions I will address include: how can we measure triplet excitons in devices; how can we determine the size of a triplet state; how quickly do excited triplet states relax; what determines the ratio of formation of singlet and triplet states by bimolecular recombination in a device, and how can we control this ratio?

 

 

Topic Two: Generation, separation and recombination of triplet excitons formed by singlet fission

 

Speaker: Professor Neil Greenham, Cavendish Laboratory of Cambridge University

 

Time: 4:00 p.m., September 22, 2014

 

Venue: Conference Hall N308A, Building of State Key Laboratory of Luminescent Materials and Devices, SCUT North Campus

 

Sponsor: School of Materials Science and Engineering

 

Abstract:

The process of singlet exciton fission allows solar cells to make efficient use of high-energy photons in the solar spectrum by rapidly generating two triplet excitons, each of which can be dissociated to generate photocurrent. After reviewing our work combining singlet-fission materials with low-bandgap semiconductor nanoparticles in solar cells, I will describe some very recent measurements to study the processes involved in a singlet-fission solar cell. Spectroscopic measurements on chemically coupled pentacene dimers allow us to study the effect of intermolecular interactions in the initial singlet-fission process. Optically detected magnetic resonance measurements allow us to observe triplet states directly, to demonstrate the roles of geminate and bimolecular recombination of triplet pairs, and to quantify the interaction between triplets in a pair. Finally, I will show how we can transfer energy (as opposed to charge) from triplet states in pentacene to PbSe nanoparticles, providing new opportunities for enhancing the efficiency of conventional solar cells using singlet fission.