| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 99 === Organic–inorganic hybrids have emerged as a novel class of optoelectronic materials for low cost and flexible photovoltaic applications. We have replaced PCBM acceptor by TiO2nanorods in the bulk heterojunction P3HT/PCBM solar cell system. The environmental friendly and low cost TiO2 can provide more thermal stable solar cell than that of P3HT/PCBM. In the bulk heterojunction structure, adequate phase separation provides not only large interfaces between donor and acceptor for efficient charge separation but also generates continuous conducting path for effective charge transport.
In our TiO2 nanorod system, the TiO2 nanorod were synthesized through sol-gel process in oleic acid, and then a part of insulating oleic acid was replaced by pyridine. Although the aromatic pyridine has improved the electron transport slightly as compared with insulating oleic acid, the compatibility between P3HT and TiO2nanorod was reduced. Therefore, we have done interface engineering using different organic molecules on the surface of TiO2 nanorod to improve the solar cell efficiency of P3HT/TiO2 nanorod hybrid. Pyridine was replaced by more hydrophobic pyridine derivatives such as 2,6-lutidine and 4-tertbutyl-pyridine. The Voc of the device was increased from 0.71V to 0.76 V and 0.78 V, respectively as compared with pyridine due to the reduced charge recombination at improved interfaces by using more compatible pyridine derivatives interface modifiers. We have designed two conducting metal-free dye, W4 and WF with conjugating and donor-acceptor structure. They exhibit bandgap between P3HT and TiO2 nanorod which can form a cascade energy level to facilitate charge transport. They were placed on the TiO2 after the pyridine derivatives treatment. Several device measurement analyses like power dependent method, electrochemistry impedance spectroscopy (EIS), charge extraction by linearly increasing voltage (CELIV) and space charge limited current (SCLC) method were used to study the device physics of P3HT/TiO2 nanorod solar cell fabricated from dye modified TiO2 nanorod.
The device efficiency is greatly improved using 4-tertbutylpyridine and W4 treated TiO2 nanorod on its surface because the TiO2 containing the least amount of insulating oleic acid and the most amount W4 dye. The device exhibits the performance of power conversion efficiency 1.36%, Voc=0.85 V, Jsc=2.48 mA/cm2, FF=64.40% as compares with device made from pyridine-treated TiO2 nanorod having PCE=0.40%, Voc=0.71 V, Jsc=1.17 mA/cm2, FF=48.23%.
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