Synthesis of the novel thienoisoindigo-based donor-acceptor type conjugated polymers and the stable switching performance of purple-to-transparent as the electrochromic materials

Three soluble conjugated polymers named PTINS-1, PTINS-2, and PTINS-3 were synthesized via Stille coupling reaction by employing different molar feed ratios of the donor units to the acceptor units. (E)-2,2′-dibromo-4,4′-bis(2-ethylhexyl)-[6,6′-bithieno [3,2-b]pyrrolylidene]-5,5′(4H, 4H′)-dione (TIIG, M2) was used as the acceptor unit, and 2,5-bis (trimethylstannyl)thieno [3,2-b] thiophene (M1) and tris(thienothiophene) (TTT, M3) were selected as the donor units. Electrochemical research demonstrates that three polymers could switch reversibly and stably between purple neutral states with different saturation and transparent oxidized states. Amid the three polymers, PTINS-1 exhibits the best comprehensive performance including the satisfying optical contrast of 41.28% in the visible region with the response time of coloring and bleaching in only 0.47 s and 0.93 s, respectively, and the optical contrasts up to 81.98% with the coloring and bleaching time in only 0.56 s and 1.18 s at the 1590 nm. Furthermore, the other two polymers display beyond 70% of the transmittance change in the near-infrared region (NIR), which endows three polymers with commendable prospects in NIR electrochromic applications, and deserves more attention and penetrating research.     

A Solution‐Processable High‐Coloration‐Efficiency Low‐Switching‐Voltage Electrochromic Polymer Based on Polycyclopentadithiophene

A solution‐processable electrochromic (EC) polymer, poly(4,4‐dioctyl‐cyclopenta[2,1‐b:3,4‐b′]‐dithiophene) (PDOCPDT) is prepared by means of chemical oxidative polymerization of the corresponding monomer. The UV‐vis spectrum of the spin‐coated PDOCPDT film displays an absorption maximum of 580 nm. Although the polymer is deep blue in its neutral state, it turns to transparent bluish after being oxidized. PDOCPDT film (thickness 120 nm) exhibits high coloration efficiency (CE)—as high as 932 C cm^–2 at 580 nm, low response time (0.75 s), high optical density (0.75 at 580 nm), and high‐level stability for long term switch (it switches repetitively 1000 times with less than 8 % contrast loss). The electrochemical stability and redox potentials of PDOCPDT films are independent of film thickness (50–180 nm) and active area (up to 2 cm × 2 cm). Nevertheless, optical contrast increases as the film thickness increases, although the CE and response time changes irregularly with the film thickness. The good EC properties combined with the easy film fabrication process make PDOCPDT a notable candidate for application in EC devices. (ECDs) A simple transmissive‐type ECD with good CE using PDOCPDT film as an active layer is also demonstrated.     

Effect of electrode surface on the electrochromic properties of electropolymerized poly(3,4-ethylenedioxythiophene) thin films

Electrochromism or electrochromic contrast in electropolymerized thin films of dioxythiophenes based conjugated polymers is known to be sensitive to the structure of monomer and the polymerizing conditions. However in our studies we found that it is also sensitive to the electrode surface wherein a significantly high electrochromic contrast is observed in the electropolymerized thin films of poly(3,4-ethylenedioxythiophene), PEDOT deposited on platinum (71%) as compared to that on indium tin oxide, ITO, coated glass surface (54%). This is attributed to the formation of more conjugated polymer on the metallic surfaces as confirmed by narrow and red shifted absorption peak for PEDOT on platinum compared to broad and blue shifted peak on ITO in the UV–vis absorption spectra. This difference in the electrochromic properties of electropolymerized PEDOT thin films on the two surfaces is investigated by studying their electrochemical growth using UV–vis absorption, Raman spectroscopy and atomic force microscopy techniques. These results suggest the deposition of more conjugated polymer in the initial stages of growth (≤3 mC/cm²) on both the substrates whereas it continues the same way into the intermediate stages (up to ∼15 mC/cm²) only on platinum, thereby, resulting in higher electrochromic contrast on platinum. The coloration efficiency of PEDOT thin film was also found to be improved on platinum (465 cm²/C) compared to that on ITO (230 cm²/C). Moreover, we observed that the EC contrast of electropolymerized PEDOT thin films on platinum was found to be insensitive to polymerizing solvent that is generally not the case when polymerized on ITO. The cyclic stability of PEDOT-Pt films are better compared to that of PEDOT-ITO which is attributed to the improved reversibility of these films with respect to potential switching.     

Design of highly stable and solution-processable electrochromic devices based on PEDOT:PSS

This study aimed to improve the repeatability of electrochromic devices(ECD) based on Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS); therefore, ferrocene was introduced as an anodic species. When 0.05 wt% ferrocene as compared to that of the electrolyte was contained in the electrolyte layer, the bleaching time significantly reduced from 110 s to 25 s without changing ΔT; consequently, repeatability markedly improved. However, ferrocenium cations, generated when ferrocene undergoes a reversible redox reaction, have high reactivity with oxygen, and hence, the stability of ECD is lowered over time. To overcome this problem, l-ascorbic acid, commonly known as vitamin C, was introduced as an antioxidant in the electrolyte layer. The repeatability of the ECD and the storage stability of the electrolyte solution were improved without side effects at an l-ascorbic acid ratio of 0.025 wt% as compared to that of the electrolyte. In addition, using cyclic voltammetry, it was confirmed that l-ascorbic acid did not affect the electrochemical properties of the ECD, and played only the role of an antioxidant for ferrocene. Furthermore, regarding encapsulated ECD, high repeatability could be maintained by preventing solvent evaporation and oxygen penetration into the electrolyte layer. When ECD of size 4 cm × 5 cm was glass encapsulated, there was no change in ΔT even after 5000 cycles for 139 h. We observed day-to-day changes in the response time and ΔT for 30 d; it maintained almost constant values from the beginning. Repeatability tests of 15 cm × 15 cm size large-area ECD for applications, such as smart windows, were conducted.     

Thiophene-2,5-diesters as electrochromic materials: The effect of ester groups on the device performance and stability

A series of thiophene-2,5-dicarboxylic acid diesters (R–Th, compounds 3–9) with linear and branched alkyl (3–7) and benzyl (8,9) ester groups have been synthesized and characterized by ¹H/¹³C NMR and MS. Their electrochemical reduction in cyclic voltammetry experiments proceed as two-step single-electron transfer process to form radical anions R–Th^•– (at −1.87 … −2.00 V vs Ag/Ag⁺) and dianions R–Th^2– (at −2.48 … −2.68 V vs Ag/Ag⁺). In spectroelectrochemical experiments in Bu₄NClO₄/N,N-dimethylformamide electrolyte solution, all compounds exhibit reversible color changes from colorless in their neutral state to blue colors in the reduced state, with two characteristic absorptions of radical anions R–Th^•– in the short-wavelength (ca. 406–420 nm) and long-wavelength regions (ca. 610–655 nm). The L*a*b* CIE color coordinates of th e sandwich-type electrochromic devices have been evaluated by colorimetry measurements and the devices demonstrated good coloration efficiency of up to 512 cm² C⁻¹. The cycling stability of the materials on electrochromic coloring/bleaching substantially depends on the structure of the R ester groups and increased with increasing the steric hindrances in the R. In the series of seven studies compounds, the best cycling stability was observed for R = 2-ethylhexyl and benzyl. The degradation mechanism during electrochromic cycling in an inert atmosphere (under nitrogen) and in air is discussed.     

Electrochemical synthesis and electrochromic application of a novel polymer based on carbazole

The compound containing carbazole and thiophene, named as B1 was synthesized with 4-(9H-carbazol-9-yl) phenol and 3,4-dibromo thiophene. Additionally, the electrochemical polymer of B1 was synthesized and coated onto an ITO-glass surface via electrochemical oxidative polymerization. The electrochemical synthesis of the polymer was performed both in 0.05 M LiClO₄ supporting electrolyte in AN/BF₃EtE (1:1, v/v) and an AN/LiClO₄ solvent/electrolyte solution. The compounds were characterized by FT-IR and NMR techniques. The spectroelectrochemical and electrochromic properties of this polymer were also investigated for two electrolyte solution systems. The switching ability of this polymer was measured as the percent transmittance (%T) at its point of maximum contrast. According to the electrochromic measurements, the synthesized polymer had a blue color when it was oxidized, and also when it was reduced, it had a transparent color. Additionally, redox stability measurements indicates that the polymer had a high stability and it could be used to produce new polymeric electrochromic devices and also, it was a good candidate for electrochromic devices (ECDs) applications.     

Effects of substitution position on electrochemical,electrochromic, optical,and photoresponsive properties of azobenzenecarboxylic acid alkyl ester derivatives

This study aimed to investigate the effects of substitution position on the electrochemical, electrochromic, optical, and photoresponsive properties of azobenzenecarboxylic acid alkyl ester derivatives. Therefore, a series of azobenzenen ester derivatives, including azobenzene-4,4′-dicarboxylic acid dialkyl ester derivatives (ADDEDs), azobenzene-3,3′-dicarboxylic acid dialkyl ester derivatives (ADADEs), and azobenzene-3,3′,5,5′-tetracarboxylic acid four alkyl ester derivatives (ATFAEDs), was synthesized in this work, and their electrochemical, electrochromic, optical, and photoresponsive properties were characterized. Substitution position significantly influenced the electrochemical, electrochromic, and optical properties but not the photoresponsive properties of azobenzenecarboxylic acid alkyl ester derivatives. With regard to stability and response time, the electrochromic properties of azobenzenecarboxylic acid alkyl ester derivatives decreased in the following order: ADDEDs > ATFAEDs > ADADEs. However, ADDEDs, ADADEs, and ATFAEDs can all be reversibly and efficiently photoswitched between trans and cis states upon alternate irradiation at 365 and 440 nm under electrochromic conditions.     

Geometric dependence in the electric response of electro-ionic polymer devices

Asymmetric and symmetric two-terminal PEDOT:PSS-electrolytic devices were fabricated and their electric response (current–voltage curve) was measured using an applied AC voltage source. The current–voltage curve for the symmetric devices was similar to a Bipolar Sigmoid function. By introducing asymmetry into the devices the current–voltage curve could be altered to resemble a linear ramp function. This work shows that the shape of the electrical response of these polymer devices can be used to implement activation transfer functions for artificial neurons, which are used to implement artificial neural networks.     

Bimodal functioning of a mesoporous,light sensitive polymer/electrolyte interface

Interfaces between conjugated polymers and aqueous electrolytes are gaining increasing interest for a number of different applications, including electrochemical cells, biosensors and functional organic devices for recording and stimulating the bioelectrical activity. In this field, devices sensitive to visible light are particularly interesting, both for inducing solar-driven photo-electrochemical reactions and for spatially selective, not-invasive optical control of living systems. We demonstrate that photoexcitation of the conjugated polymer leads to both capacitive and faradaic electrical signals at the interface with water. We introduce here a mesoporous, light sensitive polymer/electrolyte interface, we characterize its behavior and we reproduce the experimental data with an equivalent circuit model. Interestingly, we show that the use of polymer-based mesoporous devices offers a practical and simple handle for the modulation of the interface behavior. Device engineering allows to control the sign of charges at the polymer surface and to balance faradaic and capacitive currents established at the interface with water. This work opens up interesting opportunities towards applications in both photo-electrochemistry and biology.     

反射型聚苯胺基柔性电致变色器件的研制

采用循环扫描伏安法在Au/Cr/PET复合基底上聚合出聚苯胺(PAN)膜,设计并制备了基于PAN的反射型柔性电致变色器件(ECD)。研究了该ECD反射光谱的电压响应特性。结果显示,所得PAN具有晶体结构,微观上呈直径约60nm的纤维网形态,与Au/Cr/PET基底结合良好;该ECD的反射光谱曲线的波长选择性,在-0.4～+1.8V电压范围内随电压增加而逐渐明显,反射率峰值出现的位置由476nm移至584nm,表现出良好的电致变色响应特性。     

Electrical aspects of photovoltaic devices based on bi-layer organic semiconducting materials

Here we have investigated the opto-electrical properties of bi-layer sandwich devices based on polymer/C₆₀ hetero junctions. In this type of device the polymer acts as an electron donor to the second layers the C₆₀ which plays the role of an electron acceptor.     

Properties of solid-state electrochromic cells using Ta2O5 as electrolyte

Solid-state electrochromic (EC) cells (ITO/WO₃/Ta₂O₅/ITO), where ITO is indium-tin-oxide, were fabricated. Individual films were prepared by rf sputtering. The conduction mechanism in the Ta₂O₅ electrolyte was considered from the measurement of ac conductivity. Absorption spectra, coloration efficiency and memory characteristics of the EC cells were investigated. These results are compared with those of EC cells with liquid electrolytes.     

Solvent-vapor induced self-assembly of a conjugated polymer: A correlation between solvent nature and transistor performance

A systematical investigation on solvent-vapor annealing in polymer thin film transistors is performed using a thiazolothiazole-bithiazole conjugated polymer as the active layer. Film morphology, packing order and device performance are closely related to polarity and solubility parameter of the annealing solvent and annealing time. The formation of highly ordered and closely connected fibrillar domains is realized by using a solvent with similar solubility parameter and polarity to the conjugated polymer. Field-effect transistors based on pristine polymer films exhibit a highest charge carrier mobility of 0.0067 cm² V⁻¹ s⁻¹. After solvent vapor annealing with THF for 48 h, the mobility boosts up to 0.075 cm² V⁻¹ s⁻¹. This correlation between solvent polarity, solubility parameter and film morphology, packing order and mobility provides a useful guideline towards high performance polymer thin film transistors with solvent-vapor annealing method.     

Enhancing the performance of non-fullerene solar cells with polymer acceptors containing large-sized aromatic units

In this work, we develop four diketopyrrolopyrrole-based polymer acceptors for application in polymer-polymer solar cells. The polymer acceptors contain different-sized aromatic units, from small thiophene to benzodithiophene and large alkylthio-benzodithiophene units. Although the polymer acceptor with large-sized groups shows small LUMO offset and low energy loss when blended with the donor polymer PTB7-Th, the corresponding solar cells can achieve a high power conversion efficiency (PCE) of 3.1% due to high photocurrent. In contrast, the polymer acceptor with small thiophene units only provides a low PCE of 0.14% in solar cells. These results indicate that polymer acceptors with large-sized aromatic units can be potentially used into high performance non-fullerene solar cells.     

聚合物光纤与功能器件的研究与应用

本文综述了国内外聚合物光纤与功能器件研究工作的最近进展，并着重介绍本实验室相关的研究工作，同时讨论一些聚合物光纤器件和产品在通信与光电子方面的应用。     

Synthesis,electrochemical and electrochromic properties of novel 2,4,6-Tri(pyridine-4-yl)pyridilium derivatives

Four star-shaped like fused heterocyclic compounds multi-electrochromic materials 2,4,6-Tri(pyridine-4-yl)pyridilium derivatives (TPPDs) were successfully synthesized and characterized by NMR, Solid IR spectra, APCI-MS, and UV–vis spectroscopy. The electrochemical properties, electrochromic behavior, electro-optical properties, and electrochromic mechanism were investigated by thermogravimetric analysis, cyclic voltammetry and UV–vis absorption spectra. Electrochromic devices based on these compounds were fabricated with an active area of 3 cm × 4 cm and their electrochromic performances were further studied. It was found the ECDs presented a stable as well as multicolor electrochromic change from colorless to blue, then violet-blue and finally black-blue between 0 V and +4.0 V. In addition, the prepared electrochromic materials had high coloration efficiency, low switching time, and nice redox stability. This type of multi-electrochromic materials would thus be promising candidates for applications in electrochromic devices.     

Highly efficient blue and all-phosphorescent white polymer light-emitting devices based on polyfluorene host

We report efficient blue electrophosphorescent polymer light emitting devices with polyfluorene (PFO) as the host and iridium bis[2-(4,6-difluorophenyl)-pyridinato-N,C²] picolinate (FIrpic) as the dopant. Despite the low-lying triplet energy level of the polyfluorene polymer host, phosphorescent quenching can be suppressed by using poly(N-vinylcarbazole) (PVK) as anode buffer layer, resulting in a high luminous efficiency of 26.4 cd A^?1, which is one of the best results in the literature based on conjugated polymer reported to date. The reduced phosphorescent quenching is found to be associated with the exciton formation and charge carrier recombination within the PVK layer and the PVK/PFO interface due to the accumulation of holes. As compared with the devices based on non-conjugated host polymer PVK, the devices based on PFO showed a lower turn-on voltage (3.6 V vs. 4.4 V) and higher power efficiency (17 lm W^?1 vs. 8.3 lm W^?1) due to the higher mobility of PFO. When doubly doped with a newly synthesized yellow-emitting metallophosphor, white polymer light-emitting devices with superior device performance (a peak device efficiency of 40.9 cd A^?1, a CIE coordinates of (0.32, 0.48), and a power efficiency of 31.4 lm W^?1) was achieved. These findings can broaden our selection in polymer hosts for highly efficient phosphorescent blue emitting devices and can find potential applications in full color displays and solid-state lighting applications in the future.     

MLPB-PEG400/LiClO4固体聚合物电解质的电化学性能研究

采用溶液浇铸法,以聚乙二醇400(PEG400)接枝马来酸酐聚丁二烯(MLPB)为基体,高氯酸锂(LiClO4)为碱金属盐,制备了MLPB-PEG400/LiClO4固体聚合物电解质.研究了MLPB-PEG400/LiClO4电解质的电化学性能.结果表明,所制氧锂摩尔比为8的MLPB-PEG400/LiClO4固体聚合...     

Improvement in polymer solar cell performance and eliminating light soaking effect via UV-light treatment on conjugated polyelectrolyte interlayer

A new conjugated polyelectrolyte material, namely, poly [9,9-bis((6′-N,N,N-trimethylamino)hexyl)-fluorene-alt-co-benzoxadiazole dibromide] (PFBD) is reported as electron transport layer (ETL) in polymer solar cells. We observed a light-soaking effect and described how a pre-UV light treatment on PFBD ETL is essential for attaining higher efficiencies (>7%) and negate the light-soaking problem. The pre-UV light treatment on PFBD layer is found to directly influence its molecular structure and result in reduction of the work function and increased electron mobility in PFBD which corroborates well with the observed lower series resistances obtained from dark current analysis and impedance spectra, and therefore enhancement in open-circuit voltage and fill factor. Moreover, after the pre-UV light treatment, the maximal efficiency of the solar cells retains at a nearly similar level for at least 26 days.     

Surface effects on network formation of conjugated polymer wrapped semiconducting single walled carbon nanotubes and thin film transistor performance

SWCNT network morphology and TFT performance of polyfluorene wrapped sc-SWCNT on different substrates is reported. The polymer/tube weight ratio and concentration impacts network formation and device performance. Hydrophilic SiO₂ surfaces show stronger adsorption compared to poly-l-lysine treated SiO₂, which leads to more uniform and higher density networks. TFTs with mobility up to 38 cm²/Vs with <10% variability and on/off ratios on the order of 10⁵ were obtained using an iterative dip-coating process.