A complementary electrochromic device based on polyaniline and poly(3,4-ethylenedioxythiophene)

In this study, two conducting polymers, polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), were used to construct an electrochromic device (ECD). PANI was employed as the anodic coloring polymer while PEDOT was used as the cathodic coloring polymer. The electrochemical and optical properties of PANI, which has a coloration efficiency of 25 cm²/C at 570 nm, were coupled with the complementary coloring material, PEDOT, which has a coloration efficiency of 206 cm²/C at 570 nm. A suitable operating potential window was switched between −0.6 and 1.0 V to explore the cycle life of the ECD. We tested the PANI–PEDOT ECD, which consisted of PANI, PEDOT, and an organic electrolyte containing 0.1 M LiClO₄ in propylene carbonate and 1 mM HClO₄. The transmittance of the ECD at 570 nm changed from 58% (−0.6 V) to 14% (1.0 V) with a coloration efficiency of 285 cm²/C. Within the selected operating voltage range, the PANI–PEDOT ECD could be cycled for up to 2×10⁴ cycles.     

Influence of coloring voltage on the optical performance and cycling stability of a polyaniline–indium hexacyanoferrate electrochromic system

An electrochromic system based on the multielectrochromic polyaniline (PANI) and pseudo-transparent indium hexacyanoferrate (InHCF) thin-film electrodes was studied in this work. In combination with a hybrid H⁺/K⁺-conducting solid polymer electrolyte—KCl-doped poly(2-acrylamido-2-methylpropanesulfonic acid) (K-PAMPS), a precoloring-free PANI–InHCF electrochromic device (ECD) with an active area of 3×3 cm² was fabricated and exhibited yellowish-green-blue multicolor electrochromism. From in situ spectroelectrochemical experiments, we found that the performance of a PANI/K-PAMPS/InHCF ECD was significantly affected by the operating voltages, especially by the coloring voltage. Both the bleached and yellowish state of the ECD could be attained reversibly by applying a voltage ranging from +1.5 to +1.7 V (InHCF vs. PANI). Different coloring voltages resulted in different optical properties and cycling stabilities, however. For instance, the device biased at −1.6 V (InHCF vs. PANI) showed a deep blue color, but the optical activity decayed quickly (less than 50 cycles) when the device was switched between +1.6 and −1.6 V. Nevertheless, the device could be reversibly operated between +1.6 and 0 V for several hundred cycles, although a narrower electrochromic extent (yellowish-to-green) was observed correspondingly. The optimization of the coloring voltage is therefore of paramount importance to the PANI/K-PAMPS/InHCF ECD.     

An all-thiophene electrochromic device fabricated with poly(3-methylthiophene) and poly(3,4-ethylenedioxythiophene)

A novel all-organic electrochromic device (ECD) is presented. By electrodepositing poly(3-methylthiophene) (PMeT) in boron fluoride ethyl ether (BFEE), a strong Lewis acid, a good-quality PMeT film was obtained. On the basis of studies of PMeT, it can be regarded as a pseudo-anodic coloring material for ECDs. On the other hand, poly(3,4-ethylenedioxythiophene) (PEDOT) is an ideal cathodic coloring electrochromic material known for its high optical contrast, long-term stability, and high coloration efficiency. By combining these two thiophene derivatives, the application potential of this device was determined. The color of the ECD switches between deep blue at −1.4 V (PEDOT vs. PMeT) and light red at 0.6 V. The device exhibits stable electrochromic performance, with a maximum optical attenuation (ΔT_max) at 655 nm reaching 46% (from 9% to 55%), and achieves a high coloration efficiency of 336 cm²/C. After 100 repeated cycles, the cell still retained at 91.3% of its ΔT_max at 655 nm.     

All-solid-state electrochromic device based on poly(butyl viologen), Prussian blue, and succinonitrile

A new complementary electrochromic device (ECD) is described; it is based on poly(butyl viologen) (PBV) and Prussian blue (PB) confined to the electrode surfaces. PBV is a cathodically colored organic polymer, while PB is an anodically colored inorganic material. The two electrochromic materials were individually characterized in a 0.5 M KCl aqueous solution. On the basis of their properties, a PBV–PB ECD containing a solid-state electrolyte prepared by adding lithium tetrafluoroborate (LiBF₄) as a salt to succinonitrile (SN) was investigated. This all-solid-state ECD system showed good optical contrast with a coloration efficiency of ca. 163 cm²/C at 650 nm and good stability during 4000 cycles. The transmittance of the ECD at 650 nm changed from 73% (bleached) to 8% (darkened), with an applied potential of 1.7 V (−1.0 to 0.7 V) across the two electrodes. After 4000 cycles, the transmittance attenuation (ΔT) of the device was still at 86% of its original value, i.e. the ΔT value had decreased from 65% to 56%.     

Effect of modified ITO substrate on electrochromic properties of polyaniline films

In this work, we report the morphological and electrochromic properties of electrochemically synthesized polyaniline (PANI) thin films on bare and modified indium–tin oxide (ITO) glass substrates. In the last case, the surface of ITO glass was covered by a self-assembled monolayer of N-phenyl-γ-aminopropyl-trimethoxysilane (PAPTS). Atomic force microscopy images and perfilometry show that smoother and thinner PANI films were grown on PAPTS-modified ITO substrates. PANI-based electrochromic devices (ECDs) were assembled by using a viscous polymeric electrolyte (PE) of LiClO₄ and polymethyl methacrylate (PMMA) co-dissolved in a mixture of propylene and ethylene carbonate. The architectural design of the devices was glass/ITO/PANI/PE/ITO/glass. A dual ECD was also prepared by collocating a poly(3-methylthiophene) (P3MT) thin film as a complementary electrochromic element. The effect of the PAPTS-modified ITO substrate is reflected in a higher optical transmittance at bleach state and a little less color change at 550 nm of PANI-based ECDs.     

All-plastic electrochromic devices based on PEDOT as switchable optical attenuator in the near IR

Advanced materials for IR applications such as thermal control in spacecraft applications or variable optical attenuators which could replace the present systems have been sought. The use of electrochromic devices based on conducting polymers will add lightness and flexibility to the final device in order to overcome the limitations of the present materials used in IR applications. In this work, we present a new all-plastic electrochromic device with optical contrast (%ΔT) of 44% at 1971 nm in the IR region based on PEDOT formulations and ionic liquid blends as electrolytes. The switching time of the device is in the order of a few seconds, with a t_c 2.7 s and t_b 3.8 s.     

Electrochromic emissivity modulator for spacecraft thermal management

A novel electrochromic device (ECD) working in mid- to long-wave infrared (IR) region is presented, comprising of a solid-state monolithic thin film system for adjusting heat rejection/receiving levels on attached surfaces. The system is an electrically controllable active emissivity modulator. EclipseVED™, variable-emissivity ECD, is designed for satellite and spacecraft thermal control, using an active ECD system for long-wave infrared (LWIR) modulation and a passive cold mirror for solar rejection. Emissivity modulation of the system is 0.8 for 7–12 μm region while average solar rejection is 80% in the vis–NIR region. Device properties and initial space test results are also presented.     

Theoretical and experimental specific capacitance of polyaniline in sulfuric acid

The theoretical mass specific capacitance (C_s) of polyaniline (PANI) is firstly estimated by combining electrical double-layer capacitance and pseudocapacitance. The maximum C_s is 2.0 × 10³ F g⁻¹ for one single PANI electrode. In present work, the PANI nanofiber modified stainless-steel (SS) electrode (PANI/SS) was used to assemble supercapacitors. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicate that the PANI nanofiber has a coarse surface arising from the heterogeneous structure which likes an aggregation of nanoparticles. The performance of the assembled PANI/SS supercapacitors was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge methods in 1.0 M H₂SO₄. The maximum C_s obtained from these methods in present work is 608, 445.0, and 524.9 F g⁻¹, respectively, which is only 30%, 22%, and 26% of the theoretical one. The significant difference between the experimental and the theoretical value indicates that only a low percentage of PANI (effective) has contribution to capacitance. The percentage of effective PANI depends on both the diffusion of dopants (counter-anions) and the conductivity of PANI. Under practical conditions, the former factor makes PANI nanofiber behave like a concentric cable with only the shell part involved in the charge/discharge process. The latter one which determines the electron transfer rate in PANI has an influence on the degree of redox reaction. In present work, the heterogeneous structure of the PANI nanofiber has a negative effect on the conductivity.     

OPV devices based on functionalized lanthanide complexes for application in UV–light detection

Organic photovoltaic (OPV) devices with the general structure of ITO/PEDOT: PSS (60 nm)/m-MTDATA (40 nm)/(OXD-Pybm)Ln(DBM)₃ (20 nm)/LiF (1 nm)/Al (120 nm) are demonstrated by utilizing (OXD–Pybm)Ln(DBM)₃ (Ln=Pr, Sm, Eu, Gd, and Tb) as electron acceptors and 4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamino) triphenylamine (m-MTDATA) as an electron donor. The performances of these devices are experimentally improved by the introduction of 2,5-diphenyl-1,3,4-oxadiazole (OXD) group into the electron acceptors. Besides, it is found that (OXD–Pybm)Pr(DBM)₃ based device holds the potential application in UV-light detection due to the absence of dark current with the compensatory voltage lower than 1.65 V. The highest power conversion efficiency (η) and the maximum fill factor (FF) among these OPV devices are 2.60% and 0.33, respectively.     

Cycling and at-rest stabilities of a complementary electrochromic device containing poly(3,4-ethylenedioxythiophene) and Prussian blue

PEDOT-based electrochromic devices (ECDs) have been investigated intensively in recent years. In order to obtain an ECD having long cycle life, the counter electrode and electrolyte used should be compatible in the electrochemical environment. Prussian blue (PB) is proven to be electrochemically stable when cycling in non-aqueous solutions. Thus a new organic-inorganic complementary ECD was assembled in combination with a PMMA-based gel polymer electrolyte. This ECD exhibited deep blue-violet when applying −2.1 V and became light blue when applying 0.6 V. Under these conditions, the transmittance of the ECD at 590 nm changed from 13.8% (−2.1 V) to 60.5% (+0.6 V) with a coloration efficiency of 338 cm²/C. The cell retained 55% of its maximum transmittance window (ΔT_max) after 50,640 repeated cycles. Moreover, the at-rest stability test revealed a transmittance window (ΔT) decay of 9.6% over a period of 107 days. Therefore, the proposed PEDOT-PB ECD may have potential for practical applications.     

Formation of ultrafast-switching viologen-anchored TiO2 electrochromic device by introducing Sb-doped SnO2 nanoparticles

Ultrafast-switching viologen-anchored TiO₂ electrochromic device (ECD) was developed by introducing Sb-doped SnO₂ (Sb_xSn_1−xO₂, ATO) as counter electrode (CE), and the switching behavior of the fabricated ECD was investigated as a function of Sb-doping concentration. About 9-nm-sized Sb_xSn_1−xO₂ (x=0–0.3) nanoparticles were synthesized by a solvothermal reaction of tin (IV) chloride and antimony (III) chloride at 240 °C, and employed to fabricate 2.4-μm-thick transparent CE. Working electrode (WE) was formed from the 7-nm-sized TiO₂ nanoparticle by a doctor blade method, and the thickness of the nanoporous TiO₂ electrode was 4.5 μm. The phosphonated viologen, bis(2-phosphonylethyl)-4,4′-bipyridinium dibromide, was then adsorbed on the prepared films for the construction of the ECD. The response time was strongly dependent on the doping concentration of Sb in ATO, and the fastest switching response was observed at 3 mol%. At this composition, the coloration time was 5.7 ms, and the bleaching time was 14.4 ms, which is regarded as one of the best results so far reported.     

Enhancement of photovoltaic characteristics using a PEDOT interlayer in TiO2/MEHPPV heterojunction devices

The effect of inserting a PEDOT interlayer between the MEHPPV layer and the Au electrode of a nanocrystalline ITO/TiO₂/MEHPPV/Au heterojunction device on the photovoltaic characteristics of the device has been studied. The MEHPPV layer has both a light-sensitizing role and a hole-transporting function. The overall conversion efficiency of the device with a PEDOT layer is better by more than 80% than that obtainable without a PEDOT layer. The modified device shows improved photocurrent density–voltage (J–V) characteristics, in that there is a strong reduction of the roll-over behavior in the forward bias region, and an increase in the fill factor. These improvements are due to the reduction of junction resistance across the MEHPPV/Au interface in the presence of the PEDOT interlayer, which results in improved hole injection.     

π-Conjugated polymer/GaN Schottky solar cells

We developed heterojunction-based Schottky solar cells consisting of π-conjugated polymers and n-type GaN. Poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) was used as the transparent Schottky contact material and their electrical properties were investigated in comparison with those of a polyaniline (PANI) Schottky contact. The PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample exhibited high-quality rectifying characteristics with a low reverse leakage current of less than 10⁻⁸ A/cm² at a reverse bias voltage of −3 V. While investigating the photovoltaic performance, it was observed that the open-circuit voltage of the PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample reached 0.8 V, which was much superior to the photovoltage reported for a conventional metal/GaN Schottky photodetector. We also confirmed that the PEDOT:PSS is as promising a material as PANI for π-conjugated polymer/GaN Schottky solar cells.     

Chemically stable conducting polyaniline composite coatings

Aniline monomer was dispersed in polymethyl methacrylate (PMMA) and polyvinyl carbazole (PVK) solutions. The resulting mixtures were coated on substrates, dried in toluene atmosphere and enclosed later on in a chamber containing an oxidized atmosphere of HCl and (NH₄)₂S₂O₈. Electrical and optical characterizations indicate that polyaniline (PANI) was formed in the PMMA and PVK matrixes. Sheet resistance as a function of the pH value demonstrates that both PANI–PMMA and PANI–PVK composite coatings keep their R_□ almost unchanged when they are immersed in a moderate basic solution (pH9). Especially, PANI–PVK coatings are more stable than PANI–PMMA samples for longer time of immersion and also in solutions with a higher pH value. Scanning electron micrographs show different surface morphologies of these two composite materials suggesting a possible explanation of their chemical stability.     

Low methanol-permeable polyaniline/Nafion composite membrane for direct methanol fuel cells

Protonated polyaniline (PANI) is directly polymerized on Nafion 117 (N117), forming a composite membrane, to act as a methanol-blocking layer to reduce the methanol crossover in the direct methanol fuel cell (DMFC), which is beneficial for the DMFC operating at high methanol concentration. The PANI layer grown on the N117 with a thickness of 100 nm has an electrical conductivity of 13.2 S cm⁻¹. The methanol permeability of the PANI/N117 membrane is reduced to 59% of that of the N117 alone, suggesting that the PANI/N117 can effectively reduce the methanol crossover in the DMFC. Comparison of membrane-electrode-assemblies (MEA) using the conventional N117 and the newly developed PANI/N117 composite shows that the PANI/N117-based MEA outputs higher power at high methanol concentration, while the output power of the N117-based MEA is reduced at high methanol concentration due to the methanol crossover. The maximum power density of the PANI/N117-based MEA at 60 °C is 70 mW cm⁻² at 6 M methanol solution, which is double the N117-based MEA at the same methanol concentration. The resistance of PANI/N117 composite membrane is reduced at elevated methanol concentration, due to the hydrogen bonding between methanol and PANI pushes the polymer chains apart. It is concluded that the PANI/N117-based MEA performs well at elevated methanol concentration, which is suitable for the long-term operation of the DMFC.     

Energy auditing of diversified rice–wheat cropping systems in Indo-gangetic plains

The field investigations were carried out for energy use analysis in terms of different input requirements and outputs harvested under the diversified rice–wheat cropping systems at the research farm of Project Directorate for Cropping Systems Research, Modipuram, Meerut, India during the year 2000–2004. The experiments were conducted on rice (Oryza sativa L.)–wheat (Triticum aestivum L. emend. Fiori and Paol) system involving 8 sequences using diversification, furrow irrigated raised bed system (FIRB) of sowing wheat, use of summer period for deep ploughing or raising legume crops for seed or green manure to study the energy dynamics of different diversified cropping systems. Results revealed that total energy use was highest in rice–potato–wheat (i.e. 77,601 MJ/ha in flat bed & 75,697 MJ/ha in raised bed) followed by rice–wheat–sesbania (i.e. 48,770 MJ/ha in flat & 47,830 MJ/ha in raised bed) and rice–wheat–greengram (i.e. 48,414 MJ/ha in flat & 47,482 MJ/ha in raised bed). In overall, the raised bed sowing of wheat in the cropping system consumed 6–11% less fertilizer energy than flat bed while saved up to 4.2% energy through irrigation. The total output energy of the system was recorded significantly higher in rice–potato–wheat system (i.e. 222,836 MJ/ha in flat bed & 218,065 MJ/ha in raised bed) in comparison to rice–wheat–greengram (i.e. 177,477 MJ/ha in flat bed & 175,125 MJ/ha in raised bed), rice–wheat–sesbania (i.e. 172,000 MJ/ha in flat bed & 168,919 MJ/ha in raised bed) and rice–wheat system (i.e. 156,085 MJ/ha in flat bed & 151,862 MJ/ha in raised bed). The significantly higher net return of energy was obtained in rice–potato–wheat system as compared to other systems. This system required about 75% more input energy but provided about 42% more output energy compared to conventional rice–wheat system. About 10% higher output energy was obtained through growing greengram in summer for grain and foliage incorporation while 14% gain obtained by green manuring sesbania, when compared to deep summer ploughing after wheat harvest.     

A complementary electrochromic device based on polyaniline tethered polyhedral oligomeric silsesquioxane and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid)

A high-contrast complementary electrochromic device based on polyaniline (PANI) tethered polyhedral oligomeric silsesquioxane (POSS) (POSS-PANI) and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid) (PEDOT:PSS) is assembled. The electrochromic properties, cyclic voltammetry behavior and coloration efficiency of the device are studied. Due to the loosely packed structure, POSS-PANI gives rise to a significantly higher electrochromic contrast, coloration efficiency and faster switching speed than PANI. Despite its high contrast, the combination of POSS-PANI with PEDOT:PSS still shows synergy in terms of contrast enhancement, which can be attributed to the additional driving force for the diffusion of dopants into PEDOT:PSS provided by the dedoping of POSS-PANI.     

Electrosyntheses, characterizations and electrochromic properties of a copolymer based on 4,4′-di(N-carbazoyl)biphenyl and 2,2′-bithiophene

Electrochemical copolymerization of 4,4′-di(N-carbazoyl)biphenyl (CBP) with 2,2′-bithiophene (BT) is carried out in acetonitrile (ACN)/dichloromethane (DCM) (1:1, by volume) solution containing sodium perchlorate (NaClO₄) as a supporting electrolyte. Characterizations of the resulting copolymer P(CBP-co-BT) are performed by cyclic voltammetry (CV), UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetry (TG). The P(CBP-co-BT) film has distinct electrochromic properties and exhibits four different colors (orange yellow, blue, yellowish green and greenish blue) under various potentials. Maximum contrast (ΔT%) and response time of the copolymer film are measured as 51.6% and 0.94 s at 667 nm. An electrochromic device (ECD) based on P(CBP-co-BT) and poly(3,4-ethylenedioxythiophene) (PEDOT) is constructed and characterized. The optical contrast (ΔT%) at 700 nm is found to be 28.6% and the response time is measured as 0.47 s. The coloration efficiency (CE) of the device is calculated to be 234 cm² C⁻¹ at 700 nm. An ECD also has good optical memories and redox stability.     

Using modified poly(3,4-ethylene dioxythiophene): Poly(styrene sulfonate) film as a counter electrode in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs), assembling with nano-crystalline TiO₂ adsorbed cis-Ru(dcb)₂(NCS)₂ dye (known as N3) using polar solvent-treated poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) coating on a conductive glass (fluorine-doped tin oxide, FTO) as a counter electrode, were studied. The conductivity of a bare PEDOT:PSS film was only 2±0.05 S/cm. However, the conductivities of PEDOT:PSS films treated with dimethyl sulfoxide (DMSO), N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), and dichloromethane (DMC) reached 85±15, 45±10, 36±7, and 20±6 S/cm, respectively. In addition, carbon blacks (0.02, 0.1, 0.5, 1.0, 2.0 wt% with respect to PEDOT:PSS aqueous solution) were added into the DMSO-treated PEDOT:PSS solution (denoted as DMSO-PEDOT:PSS) to enhance the conductivity. Atomic force microscopy (AFM) images of PEDOT:PSS and various DMSO-PEDOT:PSS films coated on the FTO glasses were examined. The topographical images reveal that the increased surface roughness is responsible for the enhanced electrochemical property of the DMSO-PEDOT:PSS films. AC impedance technique was also employed to analyze the kinetics at the electrolyte/counter electrode interface. The DSSC using carbon black (0.1 wt%)-modified DMSO-PEDOT:PSS conductive coating as a counter electrode reached a cell efficiency of 5.81% under 100 mW/cm². This efficiency is higher than a DSSC using Pt as a counter electrode (5.66%).     

Optical characterization of a-C:N thin films deposited by RF sputtering

In this work we present the main results of the optical properties study of amorphous carbon nitride (a-C:N) thin films prepared by reactive radio frequency (RF) sputtering. The a-C:N films were deposited, at room temperature, onto glass substrates, from a graphite target, in a pure nitrogen plasma. During the deposition, the pressure of nitrogen and the power density were maintained at 10⁻² mbar and 0.79 W cm⁻², respectively. Optical properties of these films were deduced from optical transmission spectra in the ultraviolet–visible–near infrared (UV–Vis–NIR) range. The refractive index follows well the Cauchy law with an extrapolated value of 1.68 in the far IR region. The optical band gap of the a-C:N films is about 1.2 eV. This value is relatively high in comparison with that of amorphous carbon films (0.8 eV) obtained in similar conditions. The incorporation of nitrogen in the amorphous carbon network leads to an increase of the optical band gap.