| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 102 === The bismuth-based metal oxides, such as BiFeO3 (BFO) and Bi/B-doped TiO2 are potential candidates for electrolyte of low temperature solid oxide fuel cell and solution processable hybrid solar cell, respectively. In this study, we synthesize bismuth-based metal oxides, and investigate the material characteristics and the cell characteristics.
For low temperature solid oxide fuel cells, we prepared BFO as electrolyte. The material was synthesized using solution approach. Bismuth nitrate pentahydrate (Bi(NO3)3．5H2O) and iron nitrate nonahydrate (Fe(NO3)3．9H2O) were dissolved in the mixture of 2-ethoxyethanol and acetic acid at 70°C for 30 min. After evaporating the solvent, the BFO was calcined at 500°C for 2 hrs in air. The air calcined BFO was pressed into a disk which showed a pure BFO perovskite structure after sintered at either 850°C or 900°C. The BFO was coated with 100 micron yttria-stabilized zirconia (YSZ) buffer layer to avoid hydrogen reduction of BFO. This bilayer electrolyte exhibits 1.6 times increasing in maximum power density as compared with pure YSZ due to its perovskite structure, when Ni-YSZ anode and lanthanum strontium cobalt ferrite cathode were used in the fuel cell at 650°C.
TiO2 nanorods were synthesized to fabricate hybrid P3HT:TiO2 solar cells. The TiO2 nanorods were synthesized using sol-gel process in the presence of oleic acid surfactant at 98℃ for 9 hrs. The size of TiO2 nanocrystal is about 35 nm in length and 5 nm in diameter. The insulating oleic acid on TiO2 nanorods was replaced by pyridine (as-synthesized TiO2) for good charge transport between P3HT and TiO2 in the application of hybrid P3HT:TiO2 nanorods solar cells. In order to improve the power conversion efficiency (PCE) of P3HT:TiO2 solar cell, we have further increased the crystallinity of anatase TiO2 nanorods. Two novel approaches: (1) ripening and (2) bismuth/boron doping for TiO2 nanorods were explored. The crystallinity of the as-synthesized TiO2 nanorods was increased through ripening (120℃, 24 hrs) by using an autoclave reactor while the size of nanocrystal was not significantly changed. The bismuth doped TiO2 (Bi-doped TiO2) and boron doped TiO2 nanorods (B-doped TiO2) were synthesized using the same sol-gel process of as synthesized TiO2 nanorods. The PCE of P3HT:TiO2 solar cells was increased by 1.31 times and 1.79 times under A. M. 1.5 illumination for ripened and B-doped TiO2, respectively, as compared with as-synthesized TiO2. The B-doped TiO2 has the highest mobility and PCE, mainly due to the presence of partially reduced Ti4+ by boron atom with delocalized electrons. W4-dye is a promising way for modifying the interface between P3HT and TiO2 charge transport further. The Bi-doped TiO2 has higher Jsc as compared with B-doped TiO2, mainly due to the presence of improvement of electron density under TiO2. The PCE of solar cell made of W4-dye modified TiO2 nanorods has been increased by 1.33 times and 1.30 times for Bi-doped TiO2 and B-doped TiO2, respectively, as compared with that of as-synthesized TiO2.
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