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