Effect of Co-Adsorbate and Hole Transporting Layeron the Photoinduced Charge Separation at the TiO2–PhthalocyanineInterface

摘要

Understanding the primary processes of charge separation (CS) in solid-state dye-sensitized solar cells (DSSCs) and, in particular, analysis of the efficiency losses during these primary photoreactions is essential for designing new and efficient photosensitizers. Phthalocyanines (Pcs) are potentially interesting sensitizers having absorption in the red side of the optical spectrum and known to be efficient electron donors. However, the efficiencies of Pc-sensitized DSSCs are lower than that of the best DSSCs, which is commonly attributed to the aggregation tendency of Pcs. In this study, we employ ultrafast spectroscopy to discover why and how much does the aggregation affect the efficiency. The samples were prepared on a standard fluorine-doped tin oxide (FTO) substrates covered by a porous layer of TiO2 nanoparticles, functionalized by a Pc sensitizer and filled by a hole transporting material (Spiro-MeOTAD). The study demonstrates that the aggregation can be suppressed gradually by using co-adsorbates, such as chenodeoxycholic acid (CDCA) and oleic acid, but rather high concentrations of co-adsorbateis required. Gradually, a few times improvement of quantum efficiencywas observed at sensitizer/co-adsorbate ratio Pc/CDCA = 1:10 and higher.The time-resolved spectroscopy studies were complemented by standardphotocurrent measurements of the same sample structures, which alsoconfirmed gradual increase in photon-to-current conversion efficiencyon mixing Pc with CDCA.