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SUMMARY:Organic semiconductor LEDs and solar cells: the role of spin
DTSTART:20130408T131500
DTSTAMP:20260406T103738Z
UID:8f5407eed2450f2f1423599de6a79d0967464934b5169b6a5fdecfa5
CATEGORIES:Conferences - Seminars
DESCRIPTION:Richard Friend\nUniversity of Cambridge\nBio : Richard Friend 
 is the Cavendish Professor of Physics in the University of Cambridge.  He
  has developed the semiconductor physics of pi-conjugated organic polymers
 \, and his research group has demonstrated that these materials can be use
 d in wide range of semiconductor devices\, including light-emitting diodes
  and transistors.  He co-founded Cambridge Display Technology Ltd in 1992
  to develop light-emitting diode displays\, Plastic Logic Ltd in 2000\, to
  develop polymer transistor circuits that are now being developed as flexi
 ble active-matrix backplanes for e-paper displays\, and Eight-19 Ltd in 20
 10 to develop plastic solar cells.\nExcitons in molecular semiconductors g
 enerally show high Coulomb binding energies\, of order 0.5 eV\, because di
 electric screening is low. They also show comparable values for the exchan
 ge energy between spin-singlet and spin-triplet configurations. These both
  present challenges and opportunities for the use of such materials in bot
 h light-emitting diodes and also in solar cells. Non-geminate electron-hol
 e collisions in organic semiconductor diodes should produce 25% spin singl
 et events and 75% spin triplet events. For systems designed to operate as 
 LEDs\, triplet excitons can decay efficiently through triplet-triplet coll
 isions to produce an emissive singlet exciton. Large exchange energies all
 ow scope for multiple exciton generation for materials for which the tripl
 et exciton energy is less than one half of the singlet exciton energy\, si
 nce this favours energetically the fission of a photogenerated singlet to 
 a pair of triplet excitons. If this process can be used in tandem with a l
 ower energy gap semiconductor that harvests singlet excitons directly then
  this may enhance solar energy conversion beyond the single-junction Shock
 ley-Queisser limit. We have shown that this can be achieved using a pentac
 ene/lead selenide hybrid solar cell device structure.
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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