两步掺杂-脱掺杂后处理制备PEDOT∶PSS薄膜及其热电性能研究

Study on two-step doping and de-doping post-treatment preparation of PEDOT∶PSS thin films and its thermoelectric properties

聚3,4-乙烯二氧噻吩:聚苯乙烯磺酸盐(PEDOT∶PSS)具有极低的热导率和优异的柔性,被认为是最有前景的有机热电聚合物之一.但由于PEDOT∶PSS的电导率(σ)和塞贝克系数(S)均较低,因而其热电性能仍有待于提高.本项工作报道了一种甲酰胺(CH_(3)NO)与抗坏血酸(LAA)连续掺杂-脱掺杂的两步滴涂法来同步增加PEDOT∶PSS的σ和S.研究结果表明,当LAA浓度为0.3 mol L^(-1)时,PEDOT∶PSS薄膜呈现出最大的室温功率因子(S~2σ)为49.50μW m^(-1)K^(-2),其中σ和S分别是993.79 S cm^(-1)和23.33μV K^(-1).薄膜呈现出的高σ得益于CH_(3)NO的掺杂削弱了PEDOT与PSS之间的库伦作用力,诱导PEDOT和PSS之间产生相分离,并去除了部分的绝缘PSS,增加了载流子的链间电荷传输;同时LAA脱掺杂导致PEDOT∶PSS氧化水平的降低,进而降低了载流子浓度提升S,最终使得σ和S同步增加.此外,当温度升高至456.65 K时,薄膜的S~2σ达到最大值78.36μW m^(-1)K^(-2),这一温度依赖的热电输运行为可以通过Mott变程跳变模型很好地解释.本项工作表明掺杂-脱掺杂的两步法能够同步增加σ和S,有效提升PEDOT∶PSS薄膜的S~2σ.

Poly3,4-ethylenedioxythiophene:polystyrene sulfonate(PEDOT∶PSS) is considered as one of the most promising organic thermoelectric and conductive polymers due to its extremely low thermal conductivity and excellent flexibility.However,the thermoelectric performance of PEDOT∶PSS is still not desired owing to its low electrical conductivity(σ) and Seebeck coefficient(S) of PEDOT∶PSS.This work reports a two-step preparation method of continuous doping and de-doping post-treatment of formamide(CH_(3)NO) and ascorbic acid(LAA) to improve the thermoelectric properties of PEDOT∶PSS.The results show that the optimum room temperature power factor(S~2σ) of PEDOT∶PSS films reached 49.50 μW m^(-1)K^(-2) at the LAA concentration of 0.3 mol L^(-1),where σ is 993.79 S cm^(-1) and S is 23.33 μV K^(-1).High σ can be attributed to the weaken coulomb force between PEDOT and PSS after CH_(3)NO doping,which further induces the phase separation between PEDOT and PSS and removes part of the insulating PSS,leading to the interchain carrier transport increases.At the same time,the oxidation level of PEDOT∶PSS decreased by the de-doping of LAA,thereby the carrier concentration was reduced and S increased.Therefore,σ and S of PEDOT∶PSS was simultaneous increased.In addition,S~2σ reaches the maximum value of 78.36 μW m^(-1)K^(-2) with increasing the temperature to 456.65 K,This temperature-dependent thermoelectric transport behavior can be well explained by the Mott range jump model.This work indicates that the two-step doping and de-doping post-treatment can increase σ and S simultaneously,which will further effectively improve the ultimate thermoelectric properties of PEDOT∶PSS films.