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Charge Separation in Intermixed Polymer:PC70BM Photovoltaic Blends: Correlating Structural and Photophysical Length Scales as a Function of Blend Composition

Hendrik Utzat, Stoichko Dimitrov Orcid Logo, Scot Wheeler, Elisa Collado-Fregoso, Pabitra Shakya Tuladhar, Bob C. Schroeder, Iain McCulloch, James Durrant Orcid Logo

The Journal of Physical Chemistry C, Volume: 121, Issue: 18, Pages: 9790 - 9801

Swansea University Authors: Stoichko Dimitrov Orcid Logo, James Durrant Orcid Logo

Abstract

A key challenge in achieving control over photocurrent generation by bulk-heterojunction organic solar cells is understanding how the morphology of the active layer impacts charge separation and in particu-lar the separation dynamics within molecularly-intermixed donor-acceptor domains versus the dy...

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Published in: The Journal of Physical Chemistry C
ISSN: 1932-7447 1932-7455
Published: 2017
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa33171
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Abstract: A key challenge in achieving control over photocurrent generation by bulk-heterojunction organic solar cells is understanding how the morphology of the active layer impacts charge separation and in particu-lar the separation dynamics within molecularly-intermixed donor-acceptor domains versus the dynamics between phase-segregated domains. This paper addresses this issue by studying blends and devic-es of the amorphous silicon-indacenodithiophene polymer SiIDT-DTBT and the acceptor PC70BM. By changing the blend composition, we modulate the size and density of the pure and intermixed domains on the nanometre lengthscale. Laser spectroscopic studies show that these changes in morphology cor-relate quantitatively with the changes in charge separation dynamics on the nanosecond timescale, and with device photocurrent densities. At low fullerene compositions, where only a single, molecularly in-termixed polymer-fullerene phase is observed, photoexcitation results in a ~30% charge loss from gem-inate polaron pair recombination, which is further studied via light intensity experiments showing that the radius of the polaron pairs in the intermixed phase is 3-5 nm. At high fullerene compositions (≥ 67%), where the intermixed domains are 1-3 nm and the pure fullerene phases reach ~4 nm, the geminate recombination is suppressed by the reduction of the intermixed phase making the fullerene domains accessible for electron escape.
College: College of Engineering
Issue: 18
Start Page: 9790
End Page: 9801