| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 93 === In organic solar cell, many efforts have been devoted to increase the interfacial area between donor and acceptor, and thus increase the power efficiency of the device. However, the voids or the phase separation between heterogeneous phases are also a factor which may result in low cell efficiency. In our research, we developed a series of D-A linkers which were applied into layer structure, poly (3-hexylthiophene)/D-A linker/TiO2. The D-A linkers are composed of three parts including phosphonic acid, alkyl chain, and thiophene ring. Poly (3-hexylthiophene) could thus link to TiO2 by introducing D-A linkers whose phosphonic acid anchored to TiO2, and thiophene ring initialized electrochemical polymerization of 3-hexylthiophene. Therefore, the voids and phase separation between heterogeneous phases may be reduced. The interfacial distance between donor and acceptor can be controlled by introducing alkyl spacers with different length that may cause different packing behaviors or different conditions of electrochemical polymerization.
In this study, the D-A linkers, 2-thienyl phosphonic acid (TPA), 6-(2-thienyl)hexyl phosphonic acid (THPA), and 10-(2-thienyl)decyl phosphonic acid (TDPA) were self-assembled to TiO2 in ethanol solution containing D-A linkers. The contact angle measurements indicate the adsorptions onto TiO2 to reach saturation are around 8 hours for all D-A linkers. AFM images indicate the surface morphology of the self-assembled monolayer (SAM) is similar to that of TiO2 only. Besides, the direct evidence of the existence of D-A linkers on the TiO2 surface was obtained from the ESCA spectra of D-A linkers modified TiO2 substrates .
Electrochemical polymerization was carried out by the potential-static method using D-A linkers modified TiO2 or TiO2 only substrates as working electrodes. However, the electrochemical polymerization of poly(3-hexylthiophene) (P3HT) and poly(3-methylthiophene) (P3MT) did not proceed in THPA- and TDPA- modified TiO2 substrates, and the electrochemical polymerization of poly(2,2’-bithiophene) (PBT) did not proceed in TDPA-modified TiO2 substrates. These phenomena may be caused by the resistance of the insulting alkyl spacers of D-A linkers. From the AFM images of polymers on D-A linkers modified TiO2, P3HT showed a smoother surface than P3MT or PBT. GPC was employed to examine the molecular weight of the electrochemically polymerized P3HT on TiO2 only and TPA-modified TiO2. Because of the barrier caused by the D-A linker, the molecular weight of P3HT on TiO2 is larger than that on TPA-modified TiO2. However, the conjugation length didn’t change with the molecular weight of polymer from UV-vis measurements, and the positions of maximum emissions of polymers on D-A linker modified TiO2 or TiO2 only substrates were the same by PL measurements.
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