Electrochemical and Spectroelectrochemical Studies of Dyes used in Dye-sensitized Solar Cells

Abstract

Electrochemical and spectroelectrochemical techniques were employed to investigate the redox characteristics of dyes for dye sensitized solar cells (DSCs) adsorbed at the surface of fluorine-doped tin oxide (FTO) and FTO TiO2 electrodes. In this work are studied Ru-based dyes such as cis-bis(isothiocyanato)-bis(2,2’-bipyridyl- 4,4’dicarboxylato)-ruthenium(II) (N719) and (cis-RuLL'(SCN)2 with L=4,4'- dicarboxylic acid-2,2'-bipyridine and L'=4,4'-dinonyl-2,2'-bipyridine) known as Z907, and indoline organic dyes coded as D102, D131, D149, and D205. The adsorption, diffusion and stability of adsorbed dyes were studied using cyclic voltammetry in acetonitrile and 0.1 M NBu4PF6. The adsorption technique at FTO electrodes was optimized in order to be reproducible so that electrochemical studies as a function of dye coverage were carried out. Langmuirian binding constants were approximately estimated for all dyes adsorbed at FTO electrodes. Rate constants for the chemical degradation of the oxidized dye were also obtained. Is shown that degradation of the dyes mainly occurs at the surface of FTO and only insignificant degradation is evident once the dyes are adsorbed on TiO2. The degradation of dye adsorbed on FTO is shown to affect charge transport from the nonporous TiO2 via electron hopping. Spectroelectrochemical studies of indoline dyes adsorbed on FTO/TiO2 electrodes revealed a red shift of absorption peaks after oxidation and the presence of a strong charge transfer band in the near IR that suggest delocalization of holes in the dye layer. This is consistent with observation that the diffusion coefficient for hole conduction in the adsorbed dye layer is several orders of magnitude higher for the organic dyes compared to the Ru-based dyes. DSCs fabricated using indoline dyes showed good performance. Incident photon-tocurrent conversion efficiency (IPCE) spectra and I-V characteristics are presented.

Date of Award	1 Apr 2010
Original language	English
Awarding Institution	University of Bath
Supervisor	Laurie Peter (Supervisor)