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Limitations of Charge Transfer State Parameterization Using Photovoltaic External Quantum Efficiency

Ardalan Armin Orcid Logo, Nasim Zarrabi, Oskar Sandberg Orcid Logo, Christina Kaiser, Stefan Zeiske, Wei Li, Paul Meredith Orcid Logo

Advanced Energy Materials, Volume: 10, Issue: 41, Start page: 2001828

Swansea University Authors: Ardalan Armin Orcid Logo, Oskar Sandberg Orcid Logo, Paul Meredith Orcid Logo

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DOI (Published version): 10.1002/aenm.202001828

Abstract

Free carrier photogeneration in bulk‐heterojunction solar cells composed of blends of acceptor and donor organic semiconductors proceeds via intermolecular charge transfer (CT) states. Non‐adiabatic Marcus theory has proven valid to explain the absorption and emission of these sub‐gap states which h...

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Published in: Advanced Energy Materials
ISSN: 1614-6832 1614-6840
Published: Wiley 2020
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa55526
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Abstract: Free carrier photogeneration in bulk‐heterojunction solar cells composed of blends of acceptor and donor organic semiconductors proceeds via intermolecular charge transfer (CT) states. Non‐adiabatic Marcus theory has proven valid to explain the absorption and emission of these sub‐gap states which have extremely weak emission probabilities and absorption cross sections making them difficult to probe directly using optical spectroscopy. Therefore, the CT state parameters involved in the Marcus model are often extracted from fittings on the photovoltaic external quantum efficiency (EQEPV) and electroluminescence. These two spectra are (ideally) interrelated via the so‐called reciprocity principle. In this paper, the limitations of such an approach are demonstrated, in particular the impact of simple low finesse cavity interference effects acting as an uneven spectral filter for emission and absorption. This can produce almost spurious CT state parameterization with, for example, relative errors as large as 90% in absorption coefficients obtained from EQEPV. It is shown how these limitations can be partially lifted using an iterative transfer matrix approach applied to the EQEPV.
Keywords: charge transfer states; electroluminescence; external quantum efficiency; organic photovoltaics; reciprocity principle
College: College of Science
Funders: EPSRC, WEFO
Issue: 41
Start Page: 2001828