From: Prof Nir Tessler <nir@ee.technion.ac.il>


COLLOQUIUM
 
You are invited to attend a lecture by
Professor Sir Richard Friend, FRS
Optoelectronics Group, Cavendish Laboratory
University of Cambridge

 
On:
 
Organic Semiconductor Devices: Charge injection, Transport, Recombination and Photoinduced Separation
 
I will report on several recent advances in the design and operation of organic semiconductor diodes:

Charge injection has traditionally been achieved with the use of metallic electrodes, but metal oxides are now known to provide excellent alternatives, providing ohmic injection of both electrons and holes. I will show that this provides interesting opportunities to redesign the architecture of light-emitting diodes.

Charge separation in organic solar cells requires the use of a heterojunction between two organic semiconductors that can be used to overcome the onsite Coulomb binding between electron and hole, but the formation of bound charge-transfer excitations across the heterojunction can limit the efficiency of simple heterojunction structures. These CT states can evolve to form spin-triplet excitons that then prevent long-time charge separation. The magnetic field dependence of the photoluminescence and photoconductivity provides information about these processes.

The possibility that a spin singlet exciton can split to form two triplet excitons when the exchange energy is large has been known for many years. However, the possible use of this process to improve efficiency for solar cells has now been appreciated. We have carried out transient optical absorption measurements that reveal that his process is present in pentacene/fullerene solar cells.
 
 
The lecture will take place
On Wednesday, 15/09/2010 at 12:30
 in Room 1003 Electrical Eng. Building
Technion City