以原子/分子層沉積之氧化鋅/高分子超晶格薄膜熱電性質研究

Abstract

本研究利用分子層沉積技術成長出聚(3,4-乙烯基二氧噻吩)與聚(3-噻吩乙醇)兩種高分子薄膜，且這是首次以分子層沉積技術合成出聚(3-噻吩乙醇)，我們將聚(3,4-乙烯基二氧噻吩)與聚(3-噻吩乙醇)薄膜應用於發展以原子層/分子層沉積技術製備氧化鋅/聚(3,4-乙烯基二氧噻吩)與氧化鋅/聚(3-噻吩乙醇)超晶格薄膜，並且分析這些不同結構之超晶格薄膜的熱電性質。藉由分子層沉積技術成長之聚(3,4-乙烯基二氧噻吩)與聚(3-噻吩乙醇)薄膜，其成長機制是在基板溫度150 °C的條件下，以五氯化銻作為氧化劑，分別利用表面介導氧化聚合3,4-乙烯基二氧噻吩與3-噻吩乙醇單體所聚合出之均勻且具有穩定成長速率的高分子薄膜。將分子層沉積技術成長之聚(3,4-乙烯基二氧噻吩)與聚(3-噻吩乙醇)高分子薄膜週期性地插入以原子層沉積技術成長出之氧化鋅薄膜中所構成的超晶格薄膜，會因為高分子薄膜中殘留的五氯化銻接觸到氧化鋅層而有n型摻雜效應，使得超晶格薄膜會擁有比氧化鋅薄膜還高的導電度與電子濃度，而且高分子層在超晶格中還能夠提供能量過濾效應以及使聲子散射，因此可以提升塞貝克係數以及降低熱導率。此外，由於具有羥基的聚(3-噻吩乙醇)能夠與氧化鋅薄膜形成Zn-O的鍵結，使得在超晶格薄膜中聚(3-噻吩乙醇)相較於聚(3,4-乙烯基二氧噻吩)能夠與氧化鋅層形成更完整的介面，而有更強的能量過濾效應以及聲子散射效應，因此氧化鋅/聚(3-噻吩乙醇)超晶格薄膜具有比氧化鋅/聚(3,4-乙烯基二氧噻吩)超晶格薄膜更優異的ZT值，且最佳的室溫ZT值可達0.0062，是氧化鋅的5倍。

This study investigated the molecular layer deposition (MLD) characteristics of poly(3,4-ethylenedioxythiophene) (PEDOT) and a novel poly(3-thiopheneethanol) (P3TE) thin films, developed integrated atomic layer deposition (ALD)/MLD methods for depositing ZnO/PEDOT and ZnO/P3TE superlattice thin films, and characterized the thermoelectric properties of the superlattice films with varied superlattice architectures. Uniform MLD PEDOT and P3TE thin films with steady growth rates per cycle was achieved through surface-mediated oxidation polymerization of 3,4-ethylenedioxythiophene (EDOT) and 3-thiopheneethanol (3TE), respectively, at a substrate temperature of 150 °C using SbCl5 as an oxidant. Incorporating the PEDOT or P3TE films with ALD ZnO films into superlattice films resulted in higher electrical conductivities and electron concentrations than those of the ZnO films, owing to the n-type doping effects that the SbCl5 contents used in the MLD processes imposed on the ZnO layers of the superlattice films. Additionally, the polymer layers served as energy-filtering and phonon-scattering barriers in the superlattice films, leading to higher Seebeck coefficients and lower thermal conductivities of the superlattice films compared with those of the ZnO films. The phonon-scattering and energy-filtering effects were stronger with P3TE than with PEDOT, because the hydroxyl side group of P3TE enabled formation of Zn-O bonds between the P3TE and ZnO layers, improving the quality of the P3TE-ZnO interfaces in the superlattice films. Examination of various superlattice architectures found that a ZnO/P3TE superlattice prepared by alternating 5 MLD cycles of P3TE (depositing 0.055 nm thickness) with 100 ALD cycles of ZnO (19.96 nm) yielded an optimal room-temperature ZT value of 0.0062, a ~5-fold increase over that of the ZnO film.