Dye regeneration and charge recombination in dye-sensitized solar cells with ferrocene derivatives as redox mediators

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Energy & Environmental Science, ISSN: 1754-5692, Vol: 5, Issue: 5, Page: 7090-7099

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https://ro.uow.edu.au/scipapers/4263; https://publications.csiro.au/rpr/pub?list=SEA&pid=csiro:EP12176; http://scholarworks.unist.ac.kr/handle/201301/8684
Daeneke, Torben; Mozer, Attila J.; Kwon, Tae-Hyuk; Duffy, Noel W.; Holmes, Andrew B.; Bach, Udo; Spiccia, Leone
Royal Society of Chemistry (RSC); ROYAL SOC CHEMISTRY; The Royal Society of Chemistry
Environmental Science; Energy; mediators; charge; ferrocene; regeneration; dye; cells; derivatives; solar; sensitized; redox; recombination; Life Sciences; Physical Sciences and Mathematics; Social and Behavioral Sciences; Charge recombinations; Charge transfer process; Charge-transfer reactions; Cyclopentadienyl rings; Device operations; Driving forces; Dye regeneration; Dye-Sensitized solar cell; Ferrocene compounds; Ferrocene derivative; High energy; Higher efficiency; Open circuit potential; Recombination loss; Redox couple; Redox mediators; Redox potentials; Redox property; Redox shuttle; TiO
article description
Ferrocene compounds are promising redox shuttles for application in dye-sensitized solar cells (DSCs). Chemical modification of the cyclopentadienyl rings is easily achievable affording almost unlimited variation of the redox properties. This allows fine-tuning of the driving force for dye-regeneration and optimization of the energy conversion efficiency of DSCs. Herein, six ferrocene derivatives have been chosen for investigation which cover the large redox potential range of 0.85 V, by virtue of simple alkylation and halogenation of the cyclopentadienyl ring, and enable improved matching of the energy levels of the sensitizer and the electrolyte. Although the focus of this work was to examine the effect of the redox potential on charge transfer processes, DSCs were fabricated which achieved high energy conversion efficiencies of over 5%. Charge transfer reactions were studied to reveal the dependence of the dye regeneration rate, recombination losses and recombination pathways on the reaction driving force. An increase in redox potential led to a higher efficiency due to higher open circuit potentials until a threshold is reached. At this threshold, the driving force for dye regeneration (18 kJ mol , ΔE = 0.19 V) becomes too small for efficient device operation, leading to rapid recombination between the oxidized dye and electrons in the TiO conduction band. As a result of this work guidelines can be formulated to aid the selection of redox couples for a particular sensitizer in order to maximize the utilization of incident solar energy. © 2012 The Royal Society of Chemistry.