Fabrications and Properties of Poly(3-hexylthiophene) / w-(2-Thienyl) Alkylphosphonic Acids / Titania Layer Heterojunction
Date Issued
2007
Date
2007
Author(s)
Yu, Chia-Feng
DOI
zh-TW
Abstract
The heterojunction of organic solar cell is combined by two semiconductor materials which have different energy band gap. We can use the different electron affinities of these two materials to favor exciton separation, then to generate current. However, the incompatibility between organic and inorganic materials would cause voids in the face of the heterojunction. And it will block the electron transfer. So we developed a series of donor-accepter linkers which were applied into layer structure. The using of D-A Linkers has led to the synthesis of covalently linked donor-acceptor system.
In our research, the D-A linker structure consists of three major parts : phosphonic acid, alkyl chain and thiophene ring. Poly (3-hexylthiophene) could thus link to TiO2 by introducing D-A linkers whose phosephonic acid anchored to TiO2, and thiophene ring initialized electrochemical polymerization of 3-hexylthiophene. The interfacial distance between donor and acceptor can be controlled by introducing alkyl spacers with different length that may cause different conditions of electrochemical polymerization.
First, we use NMR spectrum to characterize the chemical structures of three different D-A linkers. After the linkers form the self-assembled monolayers on TiO2, we can measure the contact angle to realize the relationship with immersing time. And it indicated the adsorptions onto TiO2 to reach saturation are around one hour for all D-A linkers. Besides, the analysis of XPS spectra identified the bonding structure of all D-A linkers on TiO2 particles. And the use of TGA and UV-vis spectra calculated the content of linkers on the TiO2 particles. AFM images indicate the surface morphology of the self-assembled monolayers is similar to that of TiO2.
In the electrochemical polymerization process, by the chronopotential method, the chronopotentiogram analysis showed the longer alkyl chain brings the bigger resistance. Also, the molecular weight measuring by GPC proved that the resistance resulting from alkyl chain blocked the polymerization on the self-assembled monolayers.
However, from the AFM images of polymers, weather alkyl chain or resistance exist or not, it has no influence on the surface morphology of P3HT. Though the measurement from UV-vis and PL, although the different alkyl chain length caused the different molecular weight of P3HT, it didn’t affect the maximum of absorption wavelength and the emissions positions.
We found out the P3HT propagating from linker-modified TiO2 substrates have higher quenching efficiency though the measurement of quantum yield. And the shorter length the alkyl chain is, the higher efficiency it results. As we believed, D-A linkers covalently linked TiO2 and conjugated polymers. This phenomenon avoided the generation of pin holes, and raised the considerable efficiency of the electron transfer between donor and acceptor.
Subjects
自組裝單層膜
二氧化鈦
磷酸
太陽能電池
異質界面
界面連接劑
self-assembled monolayers (SAMs)
titanium dioxide (TiO2)
phosphonic acid
solar cell
heterojunction
donor-acceptor linker
Type
thesis
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