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Decoding Charge Recombination through Charge Generation in Organic Solar Cells

Safa Shoaee, Ardalan Armin Orcid Logo, Martin Stolterfoht, Seyed Mehrdad Hosseini, Jona Kurpiers, Dieter Neher

Solar RRL, Volume: 3, Issue: 11, Start page: 1900184

Swansea University Author: Ardalan Armin Orcid Logo

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DOI (Published version): 10.1002/solr.201900184

Abstract

The in‐depth understanding of charge carrier photogeneration and recombination mechanisms in organic solar cells is still an ongoing effort. In donor:acceptor (bulk) heterojunction organic solar cells, charge photogeneration and recombination are inter‐related via the kinetics of charge transfer sta...

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Published in: Solar RRL
ISSN: 2367-198X 2367-198X
Published: Wiley 2019
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa52737
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Abstract: The in‐depth understanding of charge carrier photogeneration and recombination mechanisms in organic solar cells is still an ongoing effort. In donor:acceptor (bulk) heterojunction organic solar cells, charge photogeneration and recombination are inter‐related via the kinetics of charge transfer states—being singlet or triplet states. Although high‐charge‐photogeneration quantum yields are achieved in many donor:acceptor systems, only very few systems show significantly reduced bimolecular recombination relative to the rate of free carrier encounters, in low‐mobility systems. This is a serious limitation for the industrialization of organic solar cells, in particular when aiming at thick active layers. Herein, a meta‐analysis of the device performance of numerous bulk heterojunction organic solar cells is presented for which field‐dependent photogeneration, charge carrier mobility, and fill factor are determined. Herein, a “spin‐related factor” that is dependent on the ratio of back electron transfer of the triplet charge transfer (CT) states to the decay rate of the singlet CT states is introduced. It is shown that this factor links the recombination reduction factor to charge‐generation efficiency. As a consequence, it is only in the systems with very efficient charge generation and very fast CT dissociation that free carrier recombination is strongly suppressed, regardless of the spin‐related factor.
Issue: 11
Start Page: 1900184