Atomic Layer Deposition for Dye-Sensitized Photovoltaic Cells

Atomic layer deposition (ALD) is a thin film deposition method based on self-limiting reactions so that it enables to deposit high quality and ultra-thin films on complex structures with uniform thickness controlling thickness and chemical composition of films. ALD is available at low temperature around 100°C depending on precursors and co-reactants, which makes it possible to use plastic or biological substrates. The recent miniaturization in electronic devices and development in analytical tools accelerates the great interest in ALD and expands its applications from traditional semiconductor industries. Therefore, we made use of ALD to improve the performance of dye-sensitized solar cells (DSSCs) in our studies because DSSCs contain several interfaces based on mesoporous structure which need to engineer them for efficient electron transport system.;We synthesized ALD TiO2 on quartz fibers (QF) for the first time and investigated ALD TiO2 phase transition on QF upon annealing temperatures. Conformal and thin ALD TiO2 film is very stabilized even at 1050 °C and highly photocatalytic due to stable anatase TiO 2 phase. For DSSCs, we employed coated QF as a light scattering layer for DSSCs and it showed larger diffused reflectance than conventional light scattering layer improving power conversion efficiency of DSSCs.;Regarding to the interface between fluorine-doped tin oxide (FTO) and mesoporous TiO2 we deposited TiO2 film called as a blocking layer on FTO using ALD. Thus, conformal and dense ALD TiO2 film on FTO could efficiently inhibit charge recombination extending electron lifetime. We systemically examined how ALD TiO2 thickness affects the performance of DSSCs and found the optimal thickness, 5-10 nm which is the thinnest up to date.;ALD at low temperature enables us to deposit metal oxides on dyed TiO 2 and we showed that a few ALD cycle contribute to enhance the dye-attachment improving thermal stability of DSSCs especially under high temperature over 80 °C. We also introduced multicomponent ALD composed of TiO2 and Al2O3 ALD to optimize initial conversion efficiency and thermal stability so that the specific cycle ratio of TiO2 and Al2O3 ALD keeps the initial performance of DSSC and stabilized the performance under high temperature at the same time.;In terms of cathode for DSSCs, we tried to replace precious metal, Pt with PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) using oxidativemolecular layer deposition (o-MLD) for cathode. For better charge collection, we constructed mesoporous indium-doped tin oxide (In:SnO, ITO) on a cathode and then coated with PEDOT:PSS as an electrical catalyst. Compared to flat PEDOT:PSS film mesoporous PEDOT:PSS-ITO showed lower charge transfer resistance as well as higher conversion efficiency.;Lastly, we compared ALD Fe2O3 using oxygen and ozone as oxidants with ferrocene as a precursor and characterized ALD Fe 2O3.