掺杂态PEDOT的热电性能研究

发布时间：2018-03-02 07:18

本文关键词： 有机热电材料热电优值电导率 Seebeck系数热导率　出处：《中国工程物理研究院》2015年硕士论文　论文类型：学位论文

【摘要】：热电材料是一类可以直接将热能转化为电能的能源转化材料,由于其无运动部件、寿命长、无噪声、环境友好等优势而被广泛关注。然而目前常用的无机热电材料由于其合成元素稀缺、工业大规模合成困难、样品易碎等因素而难以在生活中被广泛应用。有机热电材料相比于无机热电材料具有柔韧性好、合成元素丰富、工业合成容易、易于大规模应用等优势而被认为是室温下最具有广泛应用前景的热电材料。其中导电聚合物由于其较高的电导率以及比大多数无机热电材料更低的热导率而被广泛关注。作为导电聚合物之一,掺杂态的PEDOT在溶剂处理下获得了目前有机热电应用领域内最高的热电优值0.42,较大地促进了有机热电器件的应用步伐。然而掺杂对PEDOT热电特性改善的内部机制并不明确,相关的研究也少见报道。因此本研究主要基于第一性原理来探讨掺杂对PEDOT热电性能影响的内部机制。首先我们基于实验数据构建了结晶化的本征态PEDOT晶格结构以及各种掺杂态PEDOT晶格结构的结构模型并基于第一性原理进行几何优化；其次基于已优化的晶格结构,对其电学、热学、热电性质进行了详细的研究。获得如下结论：(1)本征态的PEDOT晶格结构呈现出半导体特性,其能带结构具有一个0.452eV的小的带隙；Tos-离子掺杂下的PEDOT晶格结构呈现出金属特性,费米能级由价带顶部被迁移到价带内部。这种由于掺杂而引起的PEDOT晶格结构性质的转变可能是由于以下原因造成：1)Tos-离子掺杂引起了PEDOT晶格内电荷的转移和重新分布,PEDOT层中的电荷被转移到被掺杂的Tos-离子上,从而使得PEDOT带正电荷而增加其电荷载流子浓度；2)Tos-离子掺杂促使了PEDOT链内的主链结构发生了变化,由本征态的芳香型结构转变为半醌式结构,因此更有利于电荷载流子沿着链延伸的方向进行传输。(2)Tos-离子掺杂下的PEDOT晶格结构比本征态的PEDOT具有更高的电导率且电导率的大小与掺杂浓度息息相关。掺杂浓度越高半导体-金属转变越剧烈,电导率的提升就越明显。(3)Tos-离子掺杂有效地影响了PEDOT晶格结构Seebeck系数的大小,一个适当的Tos-离子掺杂浓度对最优化PEDOT的Seebeck系数尤为重要。由态密度分析我们发现12.5% Tos-离子掺杂浓度的PEDOT晶格结构能够获得最大的Seebeck系数,从而有助于获得高的热电优值；同时相关的结论也表明Tos-离子掺杂的浓度并非越高越好,过高的掺杂浓度可能会降低Seebeck系数的大小。(4)Tos分子掺杂表现出完全不同于Tos-离子掺杂的结果：Tos分子掺并不引起PEDOT晶格内电荷的转移和结构转变,同时Tos分子掺也并不利于提高其电导率和Seebeck系数。(5)基于能带理论以及分态密度的分析,我们发现PEDOT晶格结构的Seebeck系数、电导率、热导率等呈现出明显的各向异性,其中沿着链延伸的方向具有最优的传输特性,其次是沿着链间堆叠的方向,而沿着PEDOT层间堆叠的方向几乎很难传输。此外,为了探索PEDOT在有机热电材料实际应用中的制热制冷效果,我们通过有限元模拟软件对以PEDOT为基础材料的有机热电器件单元进行了模拟。结果发现有机热电器件的热电制热制冷效果与PEDOT的热电性能密切相关,热电性能越好器件的制热制冷性能越优越；另外,在热电器件的应用中热电效应与热阻效应同时起到作用,只有在适当的条件下才能获得最优的热电制热制冷效果。
[Abstract]:Thermoelectric material is a kind of can directly convert heat into electricity energy conversion materials, because of its no moving parts, long life, no noise, environmental friendliness and widespread concern. However, the commonly used inorganic thermoelectric materials because of its scarcity of synthetic elements, a large industrial scale synthesis difficult, fragile factors such as sample the difficulty in life has been widely used. Compared to the inorganic organic thermoelectric materials, thermoelectric materials with good flexibility, synthesis of rich elements, the industrial synthesis of easy, easy large-scale applications and is considered to be the most thermoelectric materials has broad application foreground at room temperature. The conductive polymer because of its high conductivity and thermal conductivity of thermoelectric materials is lower than most inorganic the rate was widespread concern. As one of the conductive polymer, doped PEDOT was the highest in the current application of organic solvent treatment in thermal power The ZT value of 0.42, to promote the application of organic thermoelectric devices greatly. However, the internal mechanism of doping on the thermoelectric properties of PEDOT improvement is not clear, the related research is rarely reported. Therefore this research is mainly based on the first principle to explore the internal mechanism of PEDOT doping on the thermoelectric properties of impact. First we constructed based on experimental data the crystallization of the intrinsic lattice structure and structure model of various states of PEDOT doped PEDOT lattice structure and geometry optimization based on first principle; secondly the lattice structure has been optimized based on the electrical, thermal, and thermoelectric properties were studied in detail. The conclusion was as follows: (1) the eigenstates of PEDOT lattice structure showing the characteristics of semiconductor. It has a 0.452eV structure with small band gap; crystal structure of PEDOT doped Tos- by showing the characteristics of metal, the Fermi level by the valence band The top is migrating to the inside. The valence band due to the structural properties of PEDOT doped lattice changes may be due to the following reasons: 1) Tos- ion doping caused the transfer of PEDOT lattice charge and re distribution of charge in the PEDOT layer is transferred to be doped Tos-, which makes PEDOT with positive charge increasing the charge carrier concentration; 2) doped Tos- to PEDOT within the chain backbone structure changed, changed from aromatic structure eigenstates for semiquinoid structure, which is helpful to the charge carrier for transmission along the chain direction. (2) crystal structure of PEDOT doped Tos- under this eigenstates of PEDOT has higher conductivity and the size of conductivity and doping concentration are closely related. The higher the concentration of doped semiconductor metal transition windspeed, enhance the conductivity is more obvious. (3) Tos- ion The effect of doping effectively PEDOT lattice structure Seebeck coefficient, Seebeck coefficient of a proper Tos- doping concentration on the optimization of PEDOT is very important. By the analysis of density of states we found that the crystal structure of PEDOT Tos- 12.5% doping concentration of Seebeck can be the largest coefficient, thus helping to obtain high ZT value; at the same time the results suggest that the concentration of Tos- is not doped higher, high doping concentration may be reduced the Seebeck coefficient (4). The results showed the Tos molecule doping is completely different from the doped Tos-: Tos doped molecules do not cause change of transfer and charge structure of PEDOT lattice, while Tos molecules doped it is not conducive to improve the electrical conductivity and Seebeck coefficient. (5) analysis of the band theory and based on the density of States, we find that the Seebeck coefficients of the PEDOT lattice structure, conductivity, Thermal conductivity shows obvious anisotropy, which has the best transmission characteristics along the chain direction, then along the chain between the stacking direction, and along the PEDOT layer stack direction is almost difficult to transfer. In addition, in order to explore PEDOT actual heating and cooling effect in organic thermoelectric materials, we is simulated by the finite element software unit of organic thermoelectric devices based on PEDOT material. The results showed that the closely related thermoelectric properties of thermoelectric refrigerating effect and PEDOT organic thermoelectric devices, heating and cooling performance of thermoelectric devices better performance more superior; in addition, the application of thermoelectric devices in thermoelectric and thermal resistance effect at the same time play a role only in appropriate conditions in order to obtain the thermoelectric refrigerating effect is optimal.

【学位授予单位】：中国工程物理研究院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

【共引文献】