The role of ion and solvent transport during the redox process of conducting polymers

The understanding of the redox behavior of conducting polymers is essential for a successful application of these so-called synthetic metals as functional coatings. The redox process involves the exchange of ions and solvent molecules. This so called doping/dedoping process involves changes of the mechanical and the electronic structure of the polymer. This paper discusses investigations at poly(3,4-ethylenedioxythiophene (PEDOT) and poly(pyrrole) (Ppy) by the electrochemical quartz crystal microbalance (EQCM) technique and electrochemical impedance spectroscopy (EIS). In the case of PEDOT a determination of the anion and the solvent fluxes was possible, and it was found that most anions replace solvent molecules upon their incorporation. The doping/dedoping mechanism of Ppy is more complicated. Here, the first redox cycles are characterized by a complex interplay of cation, anion and solvent fluxes with irreversible changes of the polymer structure. However, in combination with EIS new insights of the ion and solvent exchange and its influence on the electronic properties can be achieved.     

Time-Resolved Structural Kinetics of an Organic Mixed Ionic–Electronic Conductor

The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady-state and transient structure of the model organic mixed conductor, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time-resolved operando techniques. Steady-state operando X-ray scattering reveals a doping-induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time-resolved operando X-ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time-resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed-conductor-based devices, and present the first real-time observation of the structural changes during doping and dedoping of a conjugated polymer system via X-ray scattering.     

加热处理对十二烷基取代聚噻吩导电性能及结构的影响

以化学氧化法制备聚合物然后用碘进行掺杂处理使其导电,用表面电阻率、热失重分析、X射线光电子能谱研究了十二烷基取代聚噻吩在经反复加热和掺杂处理后的性能和结构变化。表面电阻率受温度的影响较大,在温度达到200℃以上时,该聚合物部分或全部丧失导电性。从X-射线光电子能谱可明显观察到空气中氧气参与了加热和掺杂过程并发生的物理化学反应。十二烷基取代聚噻吩掺杂后的热去掺杂过程在较低温度下(低于200℃)其导电性能可以恢复,但在高温下却不可恢复;而其结构经每一次热处理的破坏是不可逆转的,每一次加热处理都加速其老化降解。     

Studies of influence of naphthalene mono/disulfonic acid dopant on thermal stability of polypyrrole

Thermal stability of polypyrrole (PPY) synthesized by in situ doping polymerization in the presence of different naphthalene mono/disulfonic acid dopant like α-naphthalene sulfonic acid (α-NSA), β-naphthalene sulfonic acid (β-NSA), and 1,5-naphthalene disulfonic acid (1,5-NDSA) has been systematically investigated by thermogravimetric analysis (TG). It was found that the thermal stability of as-resulted PPY was greatly affected by type and concentration of dopant. In general, the order of their thermal stability was PPY-(β-NSA) > PPY-(α-NSA) ≈ PPY-(1,5-NDSA). And high concentration of dopant (e.g., 1.2 mol/L) had a negative effect on the thermal stability. Among those three dopants, 1,5-NDSA had a unique influence on thermal stability and crystallinity of as-resulted PPY. In addition, all of room-temperature conductivity and crystallinity of PPY-(1,5-NDSA) changed dramatically after aging for 9 h under N₂ atmosphere and at 230°C, which may be due to a partly dedoping process. These results were confirmed by elemental analysis, FTIR, X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Reversible Nanopatterning on Polypyrrole Films by Atomic Force Microscope Electrochemical Lithography

A reversible, erasable, and rewritable pattern at the nanoscale is inscribed on polypyrrole films doped with sodium dodecylbenzenesulfonate (PPy(DBS)) utilizing atomic force microscopy based electrochemical lithography. Nanopatterns are formed by applying a bias voltage between a conductive tip and the substrate. Afterward, the generated nanopatterns can be erased completely, followed by rewriting at the same location of the polymer film. Moreover, the alterations of PPy(DBS) during the lithography process are investigated by comparing the changes of the current intensity and surface potential depending on the lithography time.     

磷酸二次掺杂聚苯胺纳米纤维的合成及其性能的研究

采用无模板直接混合法制备了硫酸一次掺杂聚苯胺,经氨水解掺杂得到本征态聚苯胺,然后在磷酸体系中对本征态聚苯胺进行二次掺杂。研究了不同的磷酸浓度,反应时间,搅拌时间等对二次掺杂聚苯胺电导率和产率的影响,得到磷酸二次掺杂聚苯胺合成的优化条件,并通过四探针测试仪、扫描电镜、红外光谱、紫外光谱以及电化学测试技术,对掺杂态聚苯胺进行了研究与表征。结果表明,室温下磷酸浓度为1 mol·L-1,搅拌反应24 h时,磷酸二次掺杂聚苯胺的电导率以及产率达到最大值,电导率为0.25 S·cm·1,产率达到138.7%。扫描电镜表征显示,磷酸二次掺杂可获得形貌良好的聚苯胺纳米纤维,其长度可达400~600 nm,且纤维直径均匀;紫外谱图和红外谱图表明磷酸能有效的掺杂到本征态聚苯胺中,改善其电导率及产率;电化学测试结果表明磷酸二次掺杂聚苯胺较一次掺杂聚苯胺有着更好的防腐蚀性能。     

Electrosynthesis and characterization of polypyrrole/Au nanocomposite

Polypyrrole films containing gold nanoparticles (PPy/Au) were electrosynthesized on a glassy carbon electrode. This was done by applying a constant current of 1.43 mA cm⁻² in solutions containing colloidal Au particles and pyrrole monomer. A chloroaurate medium with a citrate/tannic acid reducing/protection agent was employed for generating the Au colloids. The PPy/Au films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Also, electrochemical behaviors of the PPy/Au films were characterized by cyclic voltammetry (CV) and AC impedance measurements. Experimental results demonstrate that PPy/Au has greater conductivity and better stability than PPy. The effect of incorporated Au nanoparticles in PPy matrix was studied and the mechanism was suggested.     

Field-Effect Transistors Based on Formamidinium Tin Triiodide Perovskite

To date, there are no reports of 3D tin perovskite being used as a semiconducting channel in field-effect transistors (FETs). This is probably due to the large amount of trap states and high p-doping typical of this material. Here, the first top-gate bottom-contact FET using formamidinium tin triiodide perovskite films is reported as a semiconducting channel. These FET devices show a hole mobility of up to 0.21 cm² V⁻¹ s⁻¹, an I_ON/OFF ratio of 10⁴, and a relatively small threshold voltage (V_TH) of 2.8 V. Besides the device geometry, the key factor explaining this performance is the reduced doping level of the active layer. In fact, by adding a small amount of the 2D material in the 3D tin perovskite, the crystallinity of FASnI₃ is enhanced, and the trap density and hole carrier density are reduced by one order of magnitude. Importantly, these transistors show enhanced parameters after 20 months of storage in a N₂ atmosphere.