New Diketopyrrolopyrrole (DPP) Dyes for Efficient Dye-Sensitized Solar Cells

Two novel metal-free dyes (DPP-I and DPP-II) with a diketopyrrolopyrrole (DPP) core were synthesized for dye-sensitized solar cells (DSSCs). The absorption spectra and electrochemical and photovoltaic properties of DPP-I and DPP-II were extensively investigated. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels call be conveniently accomplished by alternating the pi-conjugated systems. Besides, coadsorption of chenodeoxycholic acid (CDCA) can hinder the formation of dye aggregates and might improve electron injection yield and, thus, J(sc). This has also led to a rise in the photovoltage, which is attributed to the decrease of charge recombination. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80%, a short-circuit photocurrent density (J(sc)) of 9.78 mA cm(-2), an open-circuit photovoltage (V-oc) of 605 mV, and a fill factor (FF) of 0.69, corresponding to an overall conversion efficiency of 4.14% under standard global AM 1.5 solar light condition. This work suggests that the metal-free dyes based on a DPP core are promising candidates for improvement of the performance of DSSCs.