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Hot Exciton Dissociation at Organic Interfaces

Published online by Cambridge University Press:  20 June 2013

G. Grancini ,
D. Fazzi ,
M. Maiuri ,
A. Petrozza ,
H-J. Egelhaaf ,
D. Brida ,
G. Cerullo  and
G. Lanzani
G. Grancini*
Affiliation:
Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3 20133 Milano, Italy.
D. Fazzi
Affiliation:
Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3 20133 Milano, Italy.
M. Maiuri
Affiliation:
IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy.
A. Petrozza
Affiliation:
Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3 20133 Milano, Italy.
H-J. Egelhaaf
Affiliation:
BELECTRIC OPV GmbH, Landgrabenstrasse 94, 90443 Nürnberg, Germany.
D. Brida
Affiliation:
IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy.
G. Cerullo
Affiliation:
IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy.
G. Lanzani*
Affiliation:
Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, via Pascoli 70/3 20133 Milano, Italy.
*
*Email: giulia.grancini@iit.it
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Abstract

Interface physics is at the heart of organic photovoltaics (OPV). Here we reveal for the first time the actual charge generation mechanism in a low-band-gap polymer: fullerene blend as prototypical system for efficient OPV. We demonstrate that the photogenerated excitons dissociate into bound interfacial charge transfer states (CTS) and free charges in 20-50 fs, with a branching ratio that depends on the excess energy. Providing an excess energy, high energy singlet polymer states are excited, giving a direct hot electron transfer into the interfacial hot CTS* before internal energy dissipation occurs. This process ultimately leads to a higher fraction of free charges. Thanks to strong electronic coupling between high-energy-states and hot CTS, we demonstrate the opening of additional paths for charge generation that would otherwise be quenched by internal conversion to the lowest-lying states. Our results provide a new framework to understand charge generation in OPV system, suggesting that hot dissociation is a strategic option to enhance the photovoltaic conversion.

Keywords

energy generationoptoelectronicpolymer
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1537: Symposium B – Organic and Hybrid Photovoltaic Materials and Devices , 2013 , mrss13-1537-b09-02
Copyright
Copyright © Materials Research Society 2013 

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References

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