title: Analysis of dye degradation products and assessment of the dye purity in dye-sensitized solar cells.
abstract: BACKGROUND
  For commercialization of dye-sensitized solar cells (DSSCs), improvement of their long-term stability and efficiency is important. A key component in solar cells is the dye, its high purity and high stability. Here, methods for dye extraction and purification, and for determination of dye purity and dye degradation in DSSCs, were developed.
  
  
  METHODS
  A method was developed for extraction of the dye Z907 from intact solar cells using a water/ethanol mixture containing tetrabutylammonium hydroxide. The N719 dye synthesized in our laboratory was purified by gel filtration on Sephadex LH20. These dyes, along with the dyes N3 and RuL2 (NC)2, were analyzed using nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography coupled to an electrospray ionization quadrupole-time-of-flight mass analyzer (LC/MS) operating in negative ionization mode.
  
  
  RESULTS
  Purification of the synthesized N719 removed several impurities, including its undesired isomer with the thiocyanate ligand attached to ruthenium through sulfur instead of nitrogen. The dyes N719 and Z907 were successfully extracted from solar cells and together with N3 and RuL2 (NC)2 analyzed by LC/MS, although N719 isomerized almost immediately in basic aqueous solution. The [M-H](-1) ions were observed and the measured mass was within a ±6 ppm range from the exact mass.
  
  
  CONCLUSIONS
  LC/MS in combination with NMR spectroscopy was shown to provide useful information on dye structure, purity, and on the efficiency of the purification methods. These methods allow for further studies of solar cell dyes, which may provide the detailed information needed for the improvement and eventual commercialization of the solar cell technology.
authors.affiliation: Johan Gadolin Process Chemistry Centre, Laboratory of Organic Chemistry, Åbo Akademi University, FI-20500, Åbo, Finland.
authors.forename: Sabine M K
authors.identifier: http://orcid.org/0000-0002-7403-4831
authors.initials: SM
authors.lastname: Rendon
authors.affiliation: Johan Gadolin Process Chemistry Centre, Laboratory of Organic Chemistry, Åbo Akademi University, FI-20500, Åbo, Finland.
authors.forename: Denys
authors.initials: D
authors.lastname: Mavrynsky
authors.affiliation: Johan Gadolin Process Chemistry Centre, Laboratory of Organic Chemistry, Åbo Akademi University, FI-20500, Åbo, Finland.
authors.forename: Axel
authors.initials: A
authors.lastname: Meierjohann
authors.affiliation: Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland.
authors.forename: Armi
authors.initials: A
authors.lastname: Tiihonen
authors.affiliation: Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland.
authors.forename: Kati
authors.initials: K
authors.lastname: Miettunen
authors.affiliation: Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland.
authors.forename: Imran
authors.initials: I
authors.lastname: Asghar
authors.affiliation: Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Halme
authors.affiliation: Johan Gadolin Process Chemistry Centre, Laboratory of Organic Chemistry, Åbo Akademi University, FI-20500, Åbo, Finland.
authors.forename: Leif
authors.initials: L
authors.lastname: Kronberg
authors.affiliation: Johan Gadolin Process Chemistry Centre, Laboratory of Organic Chemistry, Åbo Akademi University, FI-20500, Åbo, Finland.
authors.forename: Reko
authors.initials: R
authors.lastname: Leino