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Competition between recombination and extraction of free charges determines the fill factor of organic solar cells

  • Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter theta, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor: acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor: acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires furtherAmong the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter theta, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor: acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor: acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires further improvements in charge transport while reducing recombination.show moreshow less

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Metadaten
Author:Davide Bartesaghi, Irene del Carmen Perez, Juliane Kniepert, Steffen RolandORCiDGND, Mathieu Turbiez, Dieter NeherORCiDGND, L. Jan Anton Koster
DOI:https://doi.org/10.1038/ncomms8083
ISSN:2041-1723 (print)
Pubmed Id:http://www.ncbi.nlm.nih.gov/pubmed?term=25947637
Parent Title (English):Nature Communications
Publisher:Nature Publ. Group
Place of publication:London
Document Type:Article
Language:English
Year of first Publication:2015
Year of Completion:2015
Release Date:2017/03/27
Volume:6
Pagenumber:10
Funder:STW/NWO (VENI) [11166]; Dutch Polymer Institute (DPI) [734]; Federal Ministry of Education and Research (BMBF) [FKZ 03|S2151D]; German Science Foundation (DFG) [SPP 1355]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer Review:Referiert
Publication Way:Open Access