Molecular engineering of push-pull porphyrin dyes for highly efficient dye-sensitized solar cells: The role of benzene spacers

Abstract

Porphyrins have drawn much attention as sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. In a donor and acceptor zinc porphyrin we applied a new strategy of introducing 2,1,3-benzothiadiazole (BTD) as a π-conjugated linker between the anchoring group and the porphyrin chromophore to broaden the absorption spectra to fill the valley between the Soret and Q bands. With this novel approach, we observed 12.75 % power-conversion efficiency under simulated one-sun illumination (AM1.5G, 100 mW cm-2). In this study, we showed the importance of introducing the phenyl group as a spacer between the BTD and the zinc porphyrin in achieving high power-conversion efficiencies. Time-resolved fluorescence, transient-photocurrent-decay, and transient-photovoltage-decay measurements were employed to determine the electron-injection dynamics and the lifetime of the photogenerated charge carriers. Not just to fill a gap: Porphyrins are promising sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. The incorporation of a 2,1,3-benzothiadiazole moiety in a donor-acceptor zinc porphyrin as a π-conjugated linker between the anchoring group and the chromophore (see structure) broadened the absorption spectra to fill the valley between the Soret and Q bands and led to efficient power conversion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.