Toward Efficient Solid-State p‑Type Dye-Sensitized Solar Cells: The Dye Matters

Photoelectrochemical devices based on p-type nanostructured semiconducting materials show strong potentialities for various applications, such as photovoltaics and photocatalysis. While only one study was reported on the use of the reference dye P1 for solid-state p-type dye-sensitized solar cells (DSSC), in this work we have systematically investigated two diketopyrrolopyrrole (DPP) derivatives as sensitizers for solid-state p-type DSSC based on NiO and [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM) as solid-state electron transporter material. We report on the performance in solid-state p-type DSSC of a simple DPP dye bearing a thienyl carboxylic acid as the binding group and a parent compound substituted by a pyromellitimide (PYRO) playing the role of a secondary inner electron acceptor. By focusing on the dye/PCBM interface, we specifically show using transient photoluminescence measurements that the presence of a secondary electron acceptor unit can efficiently favor the formation of the (dye+/PCBM-) state, owing to its significant reducing ability and lifetime of the charge separated state. As a consequence, using these DPP derivatives leads to unprecedented photocurrents up to 0.45 mA cm<sup>–2</sup>, which are 10 times larger than previously reported values for the system based on P1. Our analysis also demonstrates the strong correlation between the ability of the dyes to efficiently generate charge carriers and the resulting photocurrents.