MolecularEngineering of Organic Dyes for ImprovedRecombination Lifetime in Solid-State Dye-Sensitized Solar Cells.

A major limitation of solid-statedye-sensitized solar cells isa short electron diffusion length, which is due to fast recombinationbetween electrons in the TiO2electron-transporting layerand holes in the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene(Spiro-OMeTAD) hole-transporting layer. In this report, the sensitizingdye that separates the TiO2from the Spiro-OMeTAD was engineeredto slow recombination and increase device performance. Through thesynthesis and characterization of three new organic D-π-A sensitizingdyes (WN1, WN3, and WN3.1), the quantity and placement of alkyl chainson the sensitizing dye were found to play a significant role in thesuppression of recombination. In solid-state devices using Spiro-OMeTADas the hole-transport material, these dyes achieved the followingefficiencies: 4.9% for WN1, 5.9% for WN3, and 6.3% for WN3.1, comparedto 6.6% achieved with Y123 as a reference dye. Of the dyes investigatedin this study, WN3.1 is shown to be the most effective at suppressingrecombination in solid-state dye-sensitized solar cells, using transientphotovoltage and photocurrent measurements. [ABSTRACT FROM AUTHOR]