8054
J. Phys. Chem. C 2010, 114, 8054–8061
Kinetic Competition in a Coumarin Dye-Sensitized Solar Cell: Injection and Recombination Limitations upon Device Performance Sara E. Koops, Piers R. F. Barnes, Brian C. O’Regan, and James R. Durrant* Department of Chemistry, Imperial College London, London SW7 2AY, United Kingdom ReceiVed: NoVember 18, 2009; ReVised Manuscript ReceiVed: February 22, 2010
There is great interest in synthesizing organic dyes to replace organometallic dyes as sensitizers in nanocrystalline TiO2 solar cells. We present a detailed comparison of interfacial electron transfer kinetics in dye-sensitized solar cells containing the coumarin based organic dye (NKX2677) against those observed for the ruthenium based organometallic dye, N719, including analysis of excited state lifetimes, injection kinetics, regeneration kinetics, and recombination to both oxidized dyes and electrolyte. We find three primary differences in behavior between these two dyes which limit the performance of NKX2677-sensitized solar cells: a shorter lifetime of the electron injecting state for NKX2677 versus N719 (primarily due to it being a singlet rather than triplet sensitizer); a faster rate constant for recombination to the electrolyte (RCE) for NKX2677-sensitized solar cells; and the greater tendency for NKX2677 to aggregate, reducing the electron injection efficiency. The shorter excited state lifetime results in relatively fast injection kinetics being required for efficient electron injection, with transient photoluminescence measurements indicating
