Energy-gap law for photocurrent generation in fullerene-based organic solar cells

  • The involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C-60 and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy. Using a combination of steady-state photocurrent measurements and time-delayed collection field experiments, we demonstrate that the power conversion efficiency, and more specifically, the fill factor of these devices, is mainly determined by the bias dependence of photocurrent generation. By combining these findings with the results from ultrafast transient absorption spectroscopy, we show that blends with small CT energies perform poorly because of an increased nonradiative CT state decay rate and that thisThe involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C-60 and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy. Using a combination of steady-state photocurrent measurements and time-delayed collection field experiments, we demonstrate that the power conversion efficiency, and more specifically, the fill factor of these devices, is mainly determined by the bias dependence of photocurrent generation. By combining these findings with the results from ultrafast transient absorption spectroscopy, we show that blends with small CT energies perform poorly because of an increased nonradiative CT state decay rate and that this decay obeys an energy-gap law. Our work challenges the common view that a large energy offset at the heterojunction and/or the presence of fullerene clusters guarantee efficient CT dissociation and rather indicates that charge generation benefits from high CT state energies through a slower decay to the ground state.show moreshow less

Export metadata

Additional Services

Share in Twitter Search Google Scholar Statistics
Metadaten
Author details:Elisa Collado-FregosoORCiD, Silvina N. Pugliese, Mariusz WojcikORCiD, Johannes BenduhnORCiD, Eyal Bar-Or, Lorena Perdigon ToroORCiD, Ulrich HörmannORCiDGND, Donato SpoltoreORCiD, Koen VandewalORCiD, Justin M. HodgkissORCiD, Dieter NeherORCiDGND
DOI:https://doi.org/10.1021/jacs.8b09820
ISSN:0002-7863
Pubmed ID:http://www.ncbi.nlm.nih.gov/pubmed?term=30620190
Title of parent work (English):Journal of the American Chemical Society
Subtitle (English):the case of low-donor-content blends
Publisher:American Chemical Society
Place of publishing:Washington
Publication type:Article
Language:English
Date of first publication:2019/02/13
Completion year:2019
Release date:2021/04/08
Volume:141
Issue:6
Page number:13
First page:2329
Last Page:2341
Funding institution:German Ministry of Science and Education (BMBF)Federal Ministry of Education & Research (BMBF) [FKZ 13N13719]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [182087777-SFB 951]; New Zealand Ministry of Business, Innovation, and Employment, via a Catalyst grant; BMBFFederal Ministry of Education & Research (BMBF) [03IPT602X]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
DDC classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Peer review:Referiert