| 1. |
|
|
| 2. |
- Ziółek, M., et al.
(författare)
-
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
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:50, s. 26227-26238
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Ziolek, Marcin, et al.
(författare)
-
Femtosecond to millisecond studies of electron transfer processes in a donor-(pi-spacer)-acceptor series of organic dyes for solar cells interacting with titania nanoparticles and ordered nanotube array films
- 2012
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:8, s. 2816-2831
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved emission and absorption spectroscopy are used to study the photoinduced dynamics of forward and back electron transfer processes taking place between a recently synthesized series of donor-(pi-spacer)-acceptor organic dyes and semiconductor films. Results are obtained for vertically oriented titania nanotube arrays (inner diameters 36 nm and 70 nm), standard titania nanoparticles (25 nm diameter) and, as a reference, alumina nanoparticle (13 nm diameter) films. The studied dyes contain a triphenylamine group as an electron donor, cyanoacrylic acid part as an electron acceptor, and differ by the substituents in a spacer group that causes a shift of its absorption spectra. Despite a red-shift of the dye absorption band resulting in an improved response to the solar spectrum, smaller electron injection rates and smaller extinction coefficients result in reduced dye sensitized solar cell (DSSC) conversion efficiencies. For the most efficient dye, TPC1, electron injection from the hot locally excited state to titania on a time scale of about 100 fs is suggested, while from the relaxed charge transfer state it proceeds in a non-exponential way with time constants from 1 ps to 50 ps. Our results imply that the latter process involves the trap states below the conduction band edge (or the sub-bandgap tail of the acceptor states), localized close to the dye radical cation, and is accompanied by fast electron recombination to the parent dye's ground state. This process should limit the efficiency of DSSCs made using these types of organic dyes. The residual, slower recombination can be described by a stretched exponential decay with a characteristic time of 0.5 ms and a dispersion parameter of 0.33. Both the electron injection and back electron transfer dynamics are similar in titania nanoparticles and nanotubes. Variations between the two film types are only found in the time resolved emission transients, which are explained in terms of the difference in local electric fields affecting the position of the emission bands.
|
|
