The Investigation Of Regeneration Kinatics Of Mesocopic Solar Cells With Scanning Electrochemical Microscopy

The operation principle of dye sensitized solar cells (DSSCs) is based on charge separation and kinetic competition in different components. The overall process will be determined by electron flow in incident light induced electron or hole injection, diffusion and the dye regeneration. The regeneration kinetics of DSSCs depends on kinetic competition between electron transfer reaction and dye regeneration processes by the redox electrolyte. The working mechanism of mesocopic solar cells depend on photon excitation of the senstizer leads to the formation of excited state, which decays by hole injection into valence band of the semiconductor (p-SC) to form the charge separated state.The aim of this research is to investigate regeneration kinetics parameters of mesocopic Solar Cells. Regeneration is critical charge transfer reaction which significantly relay on reaction rate factors such as heterogeneous rate constant (Keff), reduction rate constant (Kred), absorption cross section (Φhv) and incident photo light intensity.The power conversion efficiency of p-type DSSCs is determined by the kinetics of hole/electron transfer reaction and dye-regeneration reaction at the dye/electrolyte interface.This dissertation present series of experiments involving local measurements of dye regeneration kinetics investigated by scanning electrochemical microscopy (SECM). The reduction of photo-reduced dye molecules by iodide ions and organic thiolate-based electrolytes investigated using the feedback mode of SECM.In this work we investigated the photochemical regeneration kinetics of dye adsorbed on CuCrO2mesoporous film by using SECM feedback mode. Organic P1and C343sensitizers with iodide-based and thiolate-based electrolytes were used to understand the effect of sensitizers and redox shuttles on dye-regeneration process. In order to compare effect of electrolyte nature on regeneration kinetics we extract regeneration constant in different electrolytes.A fast regeneration kinetic rate constant was confirmed in thiolate-based electrolyte compared with iodide-based electrolyte, i.e. indicating that organic redox was an efficient mediator to optimize the fast regeneration of p-type DSSCs. And also SECM feedback mode has been used to investigate regeneration kinetics of P1dye sensitized NiO electrodes in contact with reduced iodide liquid electrolyte. In this case we analyzed the effect of light intensity, electrolyte concentration and solvent nature on regeneration kinetics of organic dye.In addition we investigate new donor-π-acceptor organic chrophroms with pyridine ring as anchoring group are designed and synthesized for p type dye-sensitized solar cells (p-DSC). The investigation demonstrates that the pyridine ring, works effectively as anchoring group for organic sensitizers. SECM investigation of regeneration kinetics inorganic pyridine ring group dyes sensitized NiO electrode with iodide-based and organic thiolate-based electrolytes. These dyes have showed promising performance in p-type dye-sensitized solar cells. The results reveal that the anchoring group affects the effective rate constant, showing that an efficient dye-regeneration process for the dye with carboxylic acid anchoring group. Meanwhile, it is worthy to note that the regeneration process between the reduced dye and oxidized state of thiolate-based electrolyte is much faster than that of iodide-based electrolyte.Furthermore the interesting application of SECM investigation on regeneration kinetics of organo-metal halide perovskite (MAPbI3) sensitized onto various semiconductor oxides nanocrystal, including n-type titanium dioxide and p-type nickel oxide. We have found the regeneration rate constant, and absorption cross section of MAPbl3are significantly higher than the conventional sensitizers.Finally SECM investigation show clear evidence for variation of regeneration kinetic parameters, heterogeneous rate constant (Keff), reduction rate constant (Kred),absorption crossection (Φhv) in different illumination intensity, in light harvesting capacity of sensitizer, in different sensitizer, electrolyte, electrolyte concentration and electrolyte solvent. Therefore SECM to be new novel technique to select appropriate hole transfer material (electrolyte) and effective sensitizer to enhance light harvesting capacity and performance of P-type DSSCs.