Interface modifications in solid state dye-sensitized TiO 2 solar cells

The concept of solid-state dye-sensitized TiO₂ solar cell in which the hole transport medium is an organic semiconductor is critically studied by examining the anode-TiO₂ interface and dye-hole conductor interface. The importance and the role of a compact hole-blocking TiO₂ layer in between the anode and the mesoporous layer is extensively studied by preparing this layer by spray pyrolysis using an automated procedure which guarantees reproducibility in obtaining constant thickness and quality of this crucial layer as seen in the current-voltage characteristics of the solar cells. To characterize the rectifying behavior of the blocking layer, cells with the structure, fluorinated tin oxide (FTO)/blocking TiO₂ layer/hole conductor/Au, were prepared and their current (I)-voltage (U) properties were investigated. Solid state solar cells were also prepared with different blocking layer thicknesses and their photovoltaic properties were investigated in order to study the influence of the blocking layer thickness on solar cell performance. In order to improve the dye-hole conductor interface, novel multifunctional molecules carrying dye units and triphenylamine moieties were synthesized and their influence as interface modifiers were studied. This interface modification results in doubling the external quantum efficiency of current conversion via improved charge transfer at the dye-hole conductor interface. Moreover, the recombination processes at this interface is drastically suppressed which leads to higher open circuit voltage and consequently higher power conversion efficiencies.