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Keywords:

  • dye-sensitized solar cells;
  • interfacial layers;
  • hole-transport materials;
  • conductive polymers;
  • iodine-free

Abstract

An iodine-free solid-state dye-sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency—one of the highest yet reported for N719 dye—as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO2 interfacial layer and the good hole conductivity of the solid-state-polymerized material. The organized mesoporous TiO2 (OM-TiO2) interfacial layer is prepared on large-area substrates by a sol-gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small-angle X-ray scattering (GISAXS). A 550-nm-thick OM-TiO2 film coated on fluorine-doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO2 film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO2/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM-TiO2 film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance (Ω), and enhanced electron lifetime (τ). The cell performance also depends on the conductivity of HTMs, which indicates that both highly conductive HTM and the transparent OM-TiO2 film interface are crucial for obtaining high-energy conversion efficiencies in I2-free ssDSSCs.