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VERSION:2.0
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CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20261016T031124Z
UID:https://www.mpip-mainz.mpg.de/events/26645/536464
DTSTART:20200203T100000Z
DTEND:20200203T110000Z
CLASS:PUBLIC
CREATED:20201125T135811Z
DESCRIPTION:The invention of new materials combined with an improved knowle
 dge of structure-property relationships of organic donor-acceptor blends l
 ed to an impressive improvement in their energy conversion efficiency to 1
 7 % [1]. This success seems to contradict the simple view that the long ra
 nge Coulomb interaction between electrons and holes in organic semiconduct
 ors causes inefficient formation but efficient recombination of free charg
 e. An important characteristic of organic solar cells is that they compris
 e at least two organic components of different chemical structure\, introd
 ucing a large complexity of the morphology and electron landscape of the a
 ctive layer. In this talk\, I will present results regarding the generatio
 n and recombination of free charges in selected bulk heterojunction solar 
 cells\, with particular focus on the role of the interfacial CT state. We 
 show that free charge formation proceeds predominately through low energy 
 CT states\, ruling out the predominance of a hot CT dissociation pathway\,
  and that the same states dominate the subsequent recombination [2]. For f
 ullerene-based solar cells with a low donor content\, we find that the eff
 iciency of charge generation is limited by the same mechanism that limits 
 the VOC\, namely non-radiative recombination of the CT states via vibronic
  coupling [3]. Notably\, the rate of this recombination process obeys the 
 classical energy gap law\, implying that donor-acceptor blends benefit fro
 m a higher CT energy through longer CT lifetimes and more efficient photoc
 urrent generation [4]. Consistent with this result\, we observe that devic
 es suffer from inefficient CT dissociation also through a higher rate of n
 on-geminate recombination [5]. As a consequence\, it’s only the systems 
 with very efficient charge generation and very fast CT dissociation that t
 he free carrier recombination is strongly suppressed\, irrespective of the
  details of the spin statistics. We\, finally\, present recent results on 
 a highly efficient polymer:NFA blend\, where we find a surprisingly low ac
 tivation energy for free charge generation\, despite a low energy offset a
 t the heterojunction [6]. These results highlight the importance of a comp
 rehensive understanding of the energy landscape\, and how it affects the p
 athway from the bound CT exciton to the spatially separated electron-hole 
 pair.\nVortragende(r): Prof. Dieter Neher
LAST-MODIFIED:20201130T110904Z
LOCATION:Digital see link\, Raum: Digital see link
ORGANIZER;CN=Denis Andrienko:mailto:denis.andrienko@mpip-mainz.mpg.de
SUMMARY:Forth and Back and in Between: Free Charge Formation and Recombinat
 ion in Organic Solar Cells
URL;VALUE=URI:https://www.mpip-mainz.mpg.de/events/26645/536464
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