Effect of ruthenium(II)-bipyridine complex photosensitizer on the panchromatic light absorption and electron transfer in N719-dye sensitized photoanodes

Abstract

It is known that the traditional N719 photosensitizer shows an insufficient light absorption from 400 to 500 nm in the visible region, which often limits the light harvesting efficiency (LHE) of its sensitized photoanodes and accordingly depresses the photoelectric conversion efficiency (PCE) of the resultant dye-sensitized solar cells (DSSCs). In this work, a type of [Ru (bpy)2 (dcbpy)](PF6)2 (labeled as Ru1) dyes was synthesized and used as a co-sensitizer for N719-dye sensitized photoanodes. Results show that Ru1 dye has a characteristic absorption peak within the range of 400–500 nm, accompanying with a higher molar extinction coefficient than N719 ones, which makes it well compensates for the insufficient LHE of N719 dye in this region. Moreover, the difference between the highest occupied molecular orbitals of Ru1 and N719 dyes can support a sufficient force for N719 dyes' regeneration. As a result, the DSSCs with Ru1/N719 composite photosensitizer show a 19%-improved PCE compared to the ones with N719 dyes. A series of tests and analysis indicate that the enhancement of PCE is mainly attributed to the complementary light absorption characteristics of N719/Ru1 in the visible light region, and a partial contribution to PCE could be due to the improved charge transfer within the photoanodes and the depressed competitive light absorption by I3− ions via energy band engineering.