Autor/a:
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Aumaitre, Cyril; Rodriguez-Seco, Cristina; Jover, Jesús; Bardagot, Olivier; Caffy, Florent; Kervella, Yann; López, Nuria; Palomares, Emilio; Demadrille, Renaud
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Abstract:
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The development of ruthenium-free organic photosensitizers showing panchromatic absorption up to the
near-infrared (NIR) region for application in dye-sensitized solar cells (DSSCs) is still scarce. Among the
sensitizers with absorption beyond 700 nm and developed for DSSCs, only zinc-phthalocyanine and
boron-dibenzopyrromethene-based dyes have been able to reach efficiencies as high as 6%. Here we
report metal-free organic dyes based on isoindigo, thieno-isoindigo or benzo-thieno-isoindigo
chromophores that absorb in the UV-visible and NIR spectral range up to 900 nm. These molecules, that
exhibit purple, blue, or green hues, were used to sensitize TiO2 mesoporous electrodes in order to
fabricate DSSCs with an iodide/triiodide-based electrolyte. Advanced photophysical characterizations,
including charge extraction, transient photovoltage, and laser transient absorption spectroscopy
experiments, combined with density functional theory modeling and computational investigations allow
us to fully unravel the interfacial processes at the origin of the solar cell performances and to identify the
limiting factors. A power conversion efficiency as high as 7% associated with a Jsc close to 19 mA cm!2
was obtained with one of the dyes, which is comparable to those of the best panchromatic organic dyes
reported so far. We also demonstrate in this work that the Voc of the solar cells is linearly correlated to
the dipolar moments of the oxidized dyes, the molecules possessing larger dipoles leading to the highest
Voc values. |