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Title: | Energy-Gap Law for Photocurrent Generation in Fullerene-Based Organic Solar Cells: The Case of Low-Donor-Content Blends | Authors: | Collado-Fregoso, Elisa Pugliese, Silvina N. Wojcik, Mariusz Benduhn, Johannes Bar-Or, Eyal Toro, Lorena Perdigon Hoermann, Ulrich SPOLTORE, Donato VANDEWAL, Koen Hodgkiss, Justin M. Neher, Dieter |
Issue Date: | 2019 | Publisher: | AMER CHEMICAL SOC | Source: | JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141(6), p. 2329-2341 | Abstract: | 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 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. | Notes: | [Collado-Fregoso, Elisa; Bar-Or, Eyal; Toro, Lorena Perdigon; Hoermann, Ulrich; Neher, Dieter] Univ Potsdam, Dept Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany. [Pugliese, Silvina N.; Hodgkiss, Justin M.] Victoria Univ Wellington, Sch Chem & Phys Sci, Wellington 6040, New Zealand. [Pugliese, Silvina N.; Hodgkiss, Justin M.] MacDiarmid Inst Adv Mat & Nanotechnol, Wellington 6040, New Zealand. [Wojcik, Mariusz] Lodz Univ Technol, Inst Appl Radiat Chem, Wroblewskiego 15, PL-93590 Lodz, Poland. [Benduhn, Johannes; Spoltore, Donato] Tech Univ Dresden, Dresden Integrated Ctr Appl Phys & Photon Mat IAP, Nothnitzer Str 61, D-01187 Dresden, Germany. [Benduhn, Johannes; Spoltore, Donato] Tech Univ Dresden, Inst Appl Phys, Nothnitzer Str 61, D-01187 Dresden, Germany. [Vandewal, Koen] Hasselt Univ, Inst Mat Res IMO IMOMEC, Wetenschapspk 1, B-3590 Diepenbeek, Belgium. | Document URI: | http://hdl.handle.net/1942/29647 | ISSN: | 0002-7863 | e-ISSN: | 1520-5126 | DOI: | 10.1021/jacs.8b09820 | ISI #: | 000459222100024 | Rights: | 2019 American Chemical Society | Category: | A1 | Type: | Journal Contribution | Validations: | ecoom 2020 |
Appears in Collections: | Research publications |
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