Enhancement of quantum efficiency by co-adsorbing small julolidine dye and bulky triphenylamine dye in dye-sensitized solar cells

Abstract

Julolidine and benzothiadiazole have been employed separately as building blocks for sensitizers to widen absorption spectrum for dye-sensitized solar cells (DSSCs). We synthesize a new dye combining the two blocks. The DSSCs using the dye show incident photon-to-electron conversion efficiency (IPCE) spectrum up to 850 nm and the maximum IPCE value of about 80%. Then we examine various co-adsorbents and find that co-adsorbing with a bulky dye enhances the IPCE of the new dye even at the wavelengths that the bulky dye does not absorb. On the other hand, such effect is not observed with co-adsorption of chenodeoxycholic acid and a flat structured dye. The results suggest that even if small dyes do not have alkyl chains, the dyes can benefit from the blocking function of the alkyl chains attached to the co-adsorbed bulky dyes.