Electron injection versus charge recombination in photoelectrochemical solar cells using cis-[(dcbH2)2Ru(CNpy)(H2O)]Cl2 as a nanocrystalline TiO2 sensitizer

A transparent photoanode was prepared by immobilizing cis- [(dcbH(2))(2) Ru(CNpy)(H2O)](2+) (dcbH(2): 4,4'-(CO2H)(2)-2,2'-bipyridine; and CNpy: 4-cyanopyridine) in a TCO substrate coated with nanocrystalline TiO2 film for incident monochromatic photon-to-current conversion efficiency (IPCE) measurements. Time-resolved experiments were carried out and electron injection across the excited dye/semiconductor interface, as well as charge recombination and quenching processes were investigated. Transient absorption difference spectra revealed the formation of the oxidized complex [(dcbH(2))(2)Ru(III)(CNpy)(H2O)] upon light excitation. The recovery is a multiphasic process attributed to a charge recombination of the injected electron across the semiconductor/dye interface in the microsecond time domain. The presence of iodide results in a much faster quenching of the oxidized complex. Thus, an appropriate concentration of donor species in the redox mediator is essential to effectively recover the sensitizer closing the electric circuit so that a dye-sensitized solar cell works in a regenerative regime. Therefore, under proper experimental conditions, the compound performs successfully as the molecular sensitizer in photoelectrochemical solar cells based on dye sensitization of nanocrystalline n-type TiO2. Kinetics data of electron injection obtained by time-resolved experiments for cis-[(dcbH(2))(2)Ru(CNpy)(H2O)](2+) are discussed along with the properties of the sensitizer in photoelectrochernical solar cells. (C) 2002 Elsevier Science B.V. All rights reserved.