3차원 계층구조 형상의 TiO2 입자를 이용한 염료감응형 태양전지의 이중층 구조 제조

Abstract

The need for the development of renewable energy is growing because of the concern about environment and the running out of the conventional fossil fuels. Solar energy is one of the potential candidates, and has been received considerable attention because it is a permanent energy, and can be converted to electricity without environmental pollution. Since the discovery of photoelectric effect in 1839 by Edmond Becquerel, lots of researches have been conducted to develop high efficiency solar cell. In 1954, the silicon-based solar cell was developed at Bell Labs, after that, the cell is predominated the market for solar energy production. However, need for development of alternative solar cells which can replace the silicon-based solar cell arose is growing because of the high cost and complex process of production. Among the candidates, dye-sensitized solar cell (DSSC) is one of them. O’Regan and M. Grätzel reported an article about DSSC at first in 1991, and many researches have been conducted until now. TiO2 is one of the major components in DSSC because the morphology of TiO2 particle and the structure of semiconductor layer influence on power conversion efficiency critically. In general, 20-30 nm sized TiO2 nanoparticles are used as a semiconductor layer because of large surface area for anchoring dye molecules. However, light harvesting efficiency of the electrodes using nanosized TiO2 particles is poor because the light scattering ability is insufficient. Moreover, electron recombination phenomenon occurs during transport of photogenerated electrons to substrate by the direct contact between TiO2 surface and electrolyte and slow electron transport rate. Many researchers have been studied to overcome these drawbacks of the semiconductor layer to achieve high photovoltaic efficiency. In chapter 2, 3D hierarchical TiO2 particles were synthesized and applied to DSSC to obtain high photovoltaic efficiency. The hierarchically structured TiO2 particles with diameter of about 900 nm were synthesized using PVA, and used as bifunctional materials in DSSC because of its large surface area for the enhancement of dye loading and light scattering ability. For the comparison, spherical TiO2 particles with the size of about 1 μm were also tested as photoanode materials. It was observed by diffuse reflectance and IPCE data that the hierarchical particles could increase the light harvesting ability by light scattering effect. Meanwhile, more recombination occurrence was observed by EIS analysis compared with the beads particles because of the large surface area. However, much more dye loading on hierarchical particles led the dramatic increase in JSC, resulting in improvement of photovoltaic efficiency. In chapter 3, 1-dimensional (1D) TiO2 nanorods array electrode was prepared and hierarchical TiO2 particles were added on the film as a scattering layer. Nanorods array film was prepared by hydrothermal method and hierarchical particles were coated on nanorods array film by doctor blade method. The cell using hierarchical particles as a scattering layer showed higher efficiency compared with the cell using only nanorods array film. However, the efficiencies did not increase as increasing dye loading, because of the leakage of electron and weak connectivity between nanorods array film and hierarchical TiO2 particles layer.