Addition Of Co-adsorbent Research Articles

The influence of alkyl chains on the performance of DSCs employing iron(II) N-heterocyclic carbene sensitizers.

The photovoltaic performances of DSCs employing two new iron(ii) N-heterocyclic carbene (NHC) sensitizers are presented. The presence of n-butyl side chains had a significant impact on DSC performace. The improvement in DSC performance up to 0.93–0.95% was observed for a new heteroleptic sensitizer bearing one carboxylic acid anchoring group. The photovoltaic performance was remarkably affected by sensitization time and by a presence/absence of coadsorbent on the semiconductor surface. The highest photoconversion efficiencies (PCE) were achieved for DSCs sensitized over 17.5 hours without addition of coadsorbents. However, for a shorter dipping time of 4 hours, the presence of chenodeoxycholic acid improved the PCE from 0.46% (no coadsorbents) to 0.74%, respectively. The performance of DSCs based on a new homoleptic complex bearing two n-butyl side chains and a carboxylic acid anchor on each NHC-ligand was improved from 0.05 to 0.29% via changes in dye-bath concentration and sensitization time. The changes in the dye load on the semiconductor surface depending on the sensitization conditions were confirmed using solid-state UV-Vis spectroscopy and thermogravimetric analysis. Electrochemical impedance spectroscopy was used to gain information about the processes occurring at the different interfaces in the DSCs. The impedance response was strongly affected by the immersion time of the photoanodes in the dye-bath solutions. In the case of the homoleptic iron(ii) complex, a Gerischer impedance was observed after 17.5 hours immersion. Shorter dipping times resulted in a decrease in the resistance in the system. For the heteroleptic complex, values of the chemical capacitance and electron lifetime were affected by the immersion time. However, the diffusion length was independent of sensitization conditions.

Factors Affecting the Performance of Champion Silyl-Anchor Carbazole Dye Revealed in the Femtosecond to Second Studies of Complete ADEKA-1 Sensitized Solar Cells.

Record laboratory efficiencies of dye-sensitized solar cells have been recently reported using an alkoxysilyl-anchor dye, ADEKA-1 (over 14 %). In this work we use time-resolved techniques to study the impact of key preparation factors (dye synthesis route, addition of co-adsorbent, use of cobalt-based electrolytes of different redox potential, creation of insulating Al2 O3 layers and molecule capping passivation of the electrode) on the partial charge separation efficiencies in ADEKA-1 solar cells. We have observed that unwanted fast recombination of electrons from titania to the dye, probably associated with the orientation of the dyes on the titania surface, plays a crucial role in the performance of the cells. This recombination, taking place on the sub-ns and ns time scales, is suppressed in the optimized dye synthesis methods and upon addition of the co-adsorbent. Capping treatment significantly reduces the charge recombination between titania and electrolyte, improving the electron lifetime from tens of ms to hundreds of ms, or even to single seconds. Similar increase in electron lifetime is observed for homogenous Al2 O3 over-layers on titania nanoparticles, however, in this case the total solar cells photocurrent is decreased due to smaller electron injection yield from the dye. Our studies should be important for a broader use of very promising silyl-anchor dyes and the further optimization and development of dye-sensitized solar cells.

Blocking recombination in Ru(II) complex-sensitized solar cells by incorporating co-adsorbents as additives in the Co(II)/(III)-based redox electrolytes

Ru(II) metallorganic complexes like the standard Z907 dye give easily efficiencies of more than 10% in dye solar cells employing the iodide/triiodide couple, however they struggle to provide decent performances in conjunction with the record beating Co(II)/(III) shuttle, due to an enormous increase of recombination under working operating conditions; a novel and pioneer strategy to control electron dynamics at the cobalt electrolyte/semiconductor interface is the addition of co-adsorbents, such as chenodeoxycholic acid (CHENO), in the electrolyte solution as additives, originally adopted in literature in the case of the ferrocene/ferrocenium mediator. In this work, we also employed CHENO and compared it with other typical co-adsorbents with similar structure such as bis(3,3-dimethylbutyl)phosphinic acid (DINHOP) and 3,3,3-triphenylpropionic acid (3PPA). Quite interestingly, we found that the initial efficiency, without any co-adsorbent, of only 1.9% (accompanied with a low open-circuit potential (Voc) of 0.67V, fully incompatible with the positive Nernst potential of the redox electrolyte) was enhanced systematically with the increase of the molecular size of the co-adsorbent added in electrolyte, reaching efficiency values for CHENO up to 5.7% along with a Voc of 0.82V. Photovoltage measurements with varying light intensity have proven that the ideality factor of the cell is dramatically decreased upon the addition of co-adsorbent, probably due to significant minimization of recombination. This was further confirmed by Electrochemical Impedance Spectroscopy measurements which have shown that the recombination resistance is systematically increased with the presence of co-adsorbents inside the electrolyte. Quite notably, we infer that recombination dominates the attainable values of Voc, rather than conduction-band edge shifts caused by the adsorption of the additives onto the titania surface, while simultaneously determines the electrons diffusion length and thus the photocurrent delivered by the Z907-solar cell.