Amphiphilic acids as co-adsorbents of metal-free organic dyes for the efficient sensitization of nanostructured photoelectrode

Photoelectrode sensitization is an important step of metal-free organic dye-sensitized solar cell (DSSC) preparation. We describe an easy and flexible means for improving organic dye content of ZnO electrodes and avoiding the formation of aggregates by the use of amphiphilic fatty acids as co-adsorbents. A series of fatty acids with variable hydrophobic alkyl chain length has been studied and the D149 indoline dye loading and the recombination step have been optimized. The best performances were measured with butyric acid and octanoic acid. Computing and experimental results show that they present an alkyl chain length compatible with the dye molecule size and structure and provide an efficient re-generation of the oxidized dye by iodide. We also demonstrate that they act as efficient recombination barriers. Moreover the DSSC durability was markedly improved with octanoic acid compared to solar cells without co-adsorbent or with the common cholic acid co-adsorbent. The carrier lifetime increased upon the aging process irrespective of the co-adsorbant due to the increase of the photoelectrode chemical capacitance.