Influence of dye chemistry and electrolyte solution on interfacial processes at nanostructured ZnO in dye-sensitized solar cells

A dye-sensitized solar cell is a complex system where an optimal interplay between three components, the semiconductor, dye and electrolyte, should be accomplished for good performance and stability. In this work, two dyes with different interaction with nanostructured ZnO are tested for application in ZnO-based dye-sensitized solar cells. The first dye is a perylene derivative, which adsorbs to the ZnO surface via an anhydride group. The short circuit photocurrent of the assembled solar cell increases with immersion time in the dye solution until it saturates and remains constant, indicating that the ZnO-dye interface is stable in the dye solution. However, it was found that the electrode bleaches at longer times in the redox electrolyte solution under illumination, both for organic solvent and ionic liquid-based systems, indicating a relatively weak bonding of the dye to the ZnO surface. The second dye is an indoline derivative, which has two carboxylic acid groups that can bond to the ZnO surface. In this case, the short circuit photocurrent is found to decrease strongly after a certain immersion time, indicating that the ZnO surface is attacked by the dye. In this case, however, for cells prepared with short immersion times, there is less bleaching after a prolonged time in the electrolyte solution indicating a stronger ZnO-dye bond. For both cases, ionic liquid electrolytes are observed to both exacerbate the bleaching process and to accelerate the recombination kinetics as compared to organic electrolyte solutions, thus illustrating the interaction of the ionic liquid with the semiconductor surface. The results highlight the importance of balanced dye interaction with the semiconductor surface, and the influence that the electrolyte solution can have. (c) 2013 Elsevier B.V. All rights reserved.