Effect of electrolyte composition on electron injection and dye regeneration dynamics in complete organic dye sensitized solar cells probed by time-resolved laser spectroscopy
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 50, 26227-26238 p.Article in journal (Refereed) Published
Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, real titania nanoparticle solar cells sensitized with an efficient organic dye (TH305) were performed in order to investigate the role of the electrolyte composition on the charge transfer dynamics. The electron injection rate constants were found to range from 0.4 to 3.5 ps-1 in iodide-based electrolyte, and they well correlate with the shift of the conduction band edge potential of titania. The lithium cation additives resulted in 2 times faster electron injection rate constant (3.55 ps-1) with respect to that when larger sodium cations were used (1.86 ps-1). However, in the presence of a pyridine derivative component in the electrolyte solution, the electron injection rate constant decreased several times (0.38 ps-1 for Li+ and 0.54 ps-1 for Na+), while the electron injection efficiency was found to be still very high, 96-100%. The dye regeneration by the redox couple under relatively low fluence of excitation beam (0.4 mJ/cm2 giving about 4 electrons per titania nanoparticle) proceeds with an average rate constant of about 40 × 10 3 s-1 and efficiency close to 100%, independent of the electron composition. However, for a larger fluence (2 mJ/cm2) excitation, a titania-dye electron recombination process competes with the dye regeneration and lowers the solar cell efficiency. The effect of self-quenching, high vibrational levels of the dye excited state, and the neat solvent on the electron injection process are also discussed. This study clearly shows that for TH350-based DSSCs the best performance is obtained using Li+ and TBP as additives to the iodide electrolyte, giving the highest open circuit voltage and almost 100% efficiency of electron injection and dye regeneration.
Place, publisher, year, edition, pages
2012. Vol. 116, no 50, 26227-26238 p.
Charge-transfer dynamics, Conduction band edge, Dye regeneration, Electrolyte compositions, Electrolyte solutions, Electron recombinations, Excitation beams, Femtoseconds, Flash photolysis, Fluences, Injection efficiency, Lithium cations, Organic dye, Pyridine derivatives, Redox couple, Self-quenching, Sodium cations, Solar cell efficiencies, Time-resolved, Titania, Titania nanoparticles, Vibrational levels
IdentifiersURN: urn:nbn:se:kth:diva-116645DOI: 10.1021/jp3097988ISI: 000312519600015ScopusID: 2-s2.0-84871606047OAI: oai:DiVA.org:kth-116645DiVA: diva2:600295
QC 201301242013-01-242013-01-222013-02-04Bibliographically approved