Transparent Conductive CuI Films: Growth And Its Application In DSSC

Copper(I) iodide(CuI) has three main crystalline phases. γ-CuI is a p-type semiconductor with a large band gap of 3.1 eV. γ-CuI with low resistivity is transparent in the wavelength range of visible light. It is used in light emitting device(LED) and dye sensitized solar cell(DSSC). In this thesis, we have prepared the CuI films with copper film iodination and vacuum thermal evaporation methods. We have investigated the effect of different growth conditions on the physical properties. The CuI films with high transmittance and good conductivity was used to fabricate DSSC g. The main research contents and results are as follows.1. CuI films was prepared with iodination of thin copper films in iodine flux. The effect of various experimental conditions of copper film preparation and iodide process was studied. The results show that the preparation conditions of copper films has little influence on physical property of CuI films. The evaporated amount of iodine is the key factor, which is associate with conductive mechanism of CuI. The conductivity of CuI films is due to the excess of iodine ion and vacancy of copper. But when iodine is too high, the excess of iodine will attached on the surface of CuI films, which will destroy the semi- conductive property of CuI films.2. CuI films were prepared with vacuum thermal evaporation method. It was found that the substrate heating temperature is the main factor which influences the property of CuI films.The XRD patterns showed that the CuI films were polycrystalline thin films with γ-phase. The main diffraction peaks are identified as(111), exhibiting preferential growth along the<111>-direction. When the substrate heating temperature is 120 °C, the maximum transmittance is about 100%. The electrical property measured by Hall effect shows the lowest resistivity of 1.0×10-2Ω·cm with hole concentration of 3.0×1019cm-3and mobility of25 cm2/Vs.3. Different morphologies of ZnO like nanowire, nanosheet and dense film were prepared with electrochemical deposition by just changing the concentration of the precursor solution. The different types of ZnO nanostructures grown on the conductive substrate wereused as photoanodes for DSSC. The photovoltaic performance of DSSCs showed that ZnO nanowire has a large specific surface area to absorb a large amount of dye and enhanced scattering of nanowire arrays can improve the utilization of light and provide a direct path for the collection of photoexcited carriers. So the ZnO nanowires DSSC had the highest photoelectric conversion efficiency.4. The ZnO, N719 and CuI were suitable to assemble fully solid state dye sensitized solar cell according to their electron affinity and band gap. Vacuum thermal evaporation method is the best way to fill CuI into ZnO nanowire. The optimum nanowire length is 2 μm with a DSSC efficiency of 0.34%. The photocarriers recombination occurs when the ZnO nanowire is too long which will reduce the efficiency of DSSC.