A regioregular head to tail thiophene based “double-cable” polymer with pendant anthraquinone functional groups: Preparation, spectroscopy and photovoltaic properties

We present an investigation into the electronic, photophysical and photovoltaic properties of a π-conjugated “double-cable” polymer based on regioregular head to tail poly(3-functionalized thiophene) with pendant anthraquinone acceptor groups (PT-AQ). This material was compared with model blends composed of a mixture of regioregular head to tail poly(3-hexylthiophene) (P3HT) as the polymer donor and anthraquinone-2-carboxylic acid octyl ester (AQ) as a small-molecule acceptor. We find that PT-AQ shows complete quenching of fluorescence whilst the donor/acceptor blend shows residual fluorescence emission and both phase separation and crystallization of the acceptor component. The operation of the double-cable based devices is however, dominated by geminate recombination and poor charge transport and extraction. Nevertheless, we show that the PT-AQ devices have a higher efficiency than devices based on representative bulk-heterojunction AQ:P3HT blends as the very coarse phase separation and crystallization is suppressed.     

Photo-electrocatalytic H2 evolution on poly(2,2′-bithiophene) at neutral pH

Vapour phase polymerised (VPP) polybithiophene (PBTh) on glassy carbon is revealed to be an efficient photo-electrocatalytic electrode for the hydrogen evolution reaction (HER). An onset potential of −0.03 V vs SCE for the HER is observed on illumination using visible light in 0.1 mol L⁻¹ phosphate buffer at pH 6.9, 600 mV lower in energy than E⁰. Hydrogen evolution is confirmed using gas chromatography with a calculated faradaic efficiency of 34% when holding at a potential of −0.5 V. Importantly, this process occurs without platinum and under neutral aqueous conditions thus revealing a significant but overlooked application for PBTh: a potential low-cost cathode material for the splitting of water.     

Multichromic conducting copolymer of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole with EDOT

Despite the significant progress made in the field of electrochromic polymers, the multichromic facility of current knowledge is restricted. Therefore, as previously proven, electrochemical copolymerization of 1-benzyl-2,5-di(thiophen-2-yl)-1H-pyrrole (SNBS) and 3,4-ethylenedioxythiophene (EDOT) was used as a strategy to achieve desired multichromic properties, where the resultant copolymer displayed distinct color changes between claret red, yellow, green, and blue colors with short switching times and high optical contrast. As an application, absorption/transmission type electrochromic device with indium tin oxide (ITO)/copolymer/gel electrolyte PEDOT/ITO configuration was constructed, where copolymer and PEDOT functioned as the anodically and the cathodically coloring layers, respectively. Results implied the successive use of this copolymer in electrochromic device applications, since the device exhibited short switching times with a wide color variation upon applied potential.     

Optical and electrical properties of hybrid photovoltaic devices from poly (3-phenyl hydrazone thiophene) (PPHT) and TiO2 blend films

Bulk heterojunction photovoltaic devices based on blends of a conjugated polymer poly (3-phenyl hydrazone thiophene) (PPHT) as electron donor and titanium dioxide (TiO₂) particles as an electron acceptor (n-type wide band gap semiconductor) have been studied. The blend films were spin coated from a common solvent mixture. The absorption peak and shape of the absorption spectra of PPHT:TiO₂ (40 vol%) indicate that it is a superposition of the absorption of PPHT and TiO₂. From the cyclic voltammetry measurements, we have estimated the values of levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for PPHT. A strong fluorescence quenching indicates that the exciton dissociation and charge separation occurs successfully at PPHT:TiO₂ interfaces formed in the bulk. This also enhances the possibility that the separated charges will reach the electrodes before recombining. Experimentally observed current–voltage characteristics of this device has been explained employing the metal–insulator–metal (MIM) model, where the intimate mixture of electron accepting and hole accepting materials is treated as a homogeneous intrinsic semiconductor. In this device, holes are solely transported along the pure donor phase and electrons transported along the paths of acceptor phase. Effect of TiO₂ concentrations in the blend and thermal annealing of device has been described is detail. For low concentration of TiO₂ below 20% the device performance is poor than that for pure PPHT, while for higher concentration of TiO₂ significant improvement was obtained. The thermal annealing of the device also improves the photovoltaic response of the device, which may be due to the reduction in the recombination process.     

Photovoltaic and photophysical properties of a novel bis-3-hexylthiophene substituted quinoxaline derivative

We report on the photophysical properties and photovoltaic performance of a polythiophene derivative, poly-2,3-bis(4-tert-butylphenyl)-5,8-bis(4-hexylthiophen-2-yl)quinoxaline (PHTQ) as an electron donor in bulk heterojunction solar cells blended with the acceptor 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM). Devices were composed of PHTQ and varying amounts of PCBM (1:1, 1:2, 1:3, 1:4 w-w ratio). The components were spin cast from ortho-dichlorobenzene (ODCB) and characterized by measuring current–voltage characteristics under simulated AM 1.5 conditions. Efficiencies up to 0.3% have been reached. Incident photon to current efficiency (IPCE) is reported and the nanoscale morphology was investigated with atomic force microscopy (AFM). Photoinduced absorption spectroscopy confirms the photoinduced charge transfer in such donor acceptor blends.     

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.     

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 humidity on structure and electrochromic properties of sol–gel-derived tungsten oxide films

The influence of varying relative humidity (RH55 and 75%) during thin film deposition from an oxalato-acetylated peroxotungstic acid sol by dip coating, on the microstructure and electrochromic properties of pristine tungsten oxide (WO₃) films obtained upon annealing is presented. The films fabricated under a relative humidity of 55% are amorphous whereas the ones cast under a substantially humid atmosphere (RH75%) are characterized by interconnected nanocrystallites with a triclinic phase and a nanoporous surface morphology as well. Upon lithium insertion, larger integrated values of transmission modulation and coloration efficiency are observed over the photopic and solar regions, for the films prepared under a RH75% as compared to that observed for the films deposited under a RH of 55%. Functional improvements are due to the larger surface area of nanocrystallites and a porous microstructure, a consequence of a higher degree of hydration and hydroxylation in the former films in contrast to the non-porous and a rather featureless structure of the latter films. Faster switching kinetics between the clear and blue states, a greater current density for lithium intercalation, a higher diffusion coefficient for lithium and a superior cycling stability, again shown by the film fabricated under a 75% RH confirm that the WO₃ film microstructure is most conducive for a more facile ion insertion–extraction process, which hints at its potential for electrochromic window applications.     

Large-area photovoltaics based on low band gap copolymers of thiophene and benzothiadiazole or benzo-bis(thiadiazole)

Large-area solar cells (active area=3 and 10 cm²) were prepared with low band gap polymers based on thiophene and benzothiadiazole (1) or thiophene and benzo-bis(thiadiazole) (2). The band gaps of the polymers were 1.65 and 0.67 eV, respectively. The best photovoltaic performance was obtained for the device ITO/PEDOT/1:PCBM (1:2)/Al with an active area of 3 cm². The efficiency of the device was 0.62%. This is a high efficiency for a low band gap polymer in a large-area organic solar cell and thus polymer 1 is a very promising material for organic solar cells. The devices based on 2 were found to give poor devices when employed in bulk heterojunctions with PCBM. This was linked to a poor alignment of the energy levels in 2 with that of the electrodes and PCBM, showing that the requirement for a control of the positions of the energy levels becomes increasingly important as the band gap decreases.     

A complementary electrochromic device based on Prussian blue and poly(ProDOT-Et2) with high contrast and high coloration efficiency

A complementary electrochromic device (ECD) based on Prussian blue (PB) and poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et₂) has been systematically investigated. PB is regarded as an anodic coloring material with high electrochemical stability, while PProDOT-Et₂ is a cathodic coloring polymer with high contrast and high coloration efficiency (η). The electro-optical properties of the two electrochromic (EC) materials are characterized separately in a 0.1 M LiClO₄ in propylene carbonate (PC). A complementary ECD is assembled based on the two EC materials. The maximum transmittance of the ECD at 590 nm can be changed reversibly from 11.3% to 70.6% at the applied voltages of 1.2 and −1.3 V, and achieved a high coloration efficiency of 1214 cm²/C. Moreover, this ECD still remains at 98% of its maximum transmittance window (ΔT_max) even after 1,200 cycles, namely, the ΔT value decreases from 59% to 58%.     

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.     

Bulk heterojunctions based on a low band gap copolymer of thiophene and benzothiadiazole

We report on the incorporation of a low band gap copolymer based on thiophene and benzothiadiazole with a band gap of 1.65 eV into a bulk heterojunction device with the structure ITO/PEDOT:PSS/polymer:PCBM/Al. We have investigated the effects of process variable, including choice of solvent, polymer concentration and annealing temperature, on the photovoltaic device performance. The devices show spectral response down to the absorption edge of 1.65 eV and exhibit an efficiency of 1% under AM1.5 illumination and a peak external quantum efficiency of 18% at 600 nm.     

Effect of TiO2 mixtures on the optical, structural and electrochromic properties of Nb2O5 thin films

Metal oxide films are important for various optical devices and especially for solar energy materials. TiO₂-mixed Nb₂O₅ thin films have been produced by sol–gel dip-coating method. Several parameters such as heat treatment, thickness, and mixture percentages are studied for the effect of the optical, structural and electrochromic properties of the materials. Optical parameters of the films were calculated through transmission and reflection measurement by a refractive index, extinction coefficient and thickness analyzer. Structural, electrochromic and surface analyses of the films were done by X-ray diffractometer, potentiostat/galvanostat and atomic force microscope systems.     

Proton-conducting nanocomposite membranes based on P(VDF-co-CTFE)-g-PSSA graft copolymer and TiO2-PSSA nanoparticles

Bifunctional TiO₂ nanoparticles with hygroscopic and proton-conductive properties were synthesized by grafting proton-conducting polymer, i.e. poly(styrene sulfonic acid) (PSSA) from TiO₂ nanoparitlces via surface-initiated atom transfer radical polymerization (ATRP). These bifunctional TiO₂-PSSA nanoparticles were blended with poly(vinylidene fluoride-co-chlorotrifluoroethylene)-graft-poly(styrene sulfonic acid), i.e. P(VDF-co-CTFE)-g-PSSA to give proton-conducting membranes for high temperature fuel cells. FT-IR, UV-visible spectroscopy and X-ray diffraction (XRD) results revealed bifunctional properties of TiO₂-PSSA nanoparticles due to successful grafting of PSSA chains. Ion exchange capacity (IEC) of P(VDF-co-CTFE)-g-PSSA/TiO₂-PSSA membranes was not significantly changed irrespective of TiO₂-PSSA concentrations, representing almost fixed SO₃⁻ concentration in the membranes. In contrast, water uptake and proton conductivity of membranes continuously increased with increasing TiO₂-PSSA concentrations, presumably due to hygroscopic, soft conducting property of nanoparticles. The results of thermal gravimetric analysis (TGA) also showed that all the membranes were stable at least up to 280 °C.     

Measurements and predictions of solar radiation incident on horizontal surfaces at Santa Fe, Argentina (31° 39′S, 60° 43′W)

Measurements and predictions of solar radiation during a period of 10 years on horizontal surfaces at Santa Fe (31° 39′ S, 60° 43′ W), Argentina, reported as average daily global radiation for each month, are presented. Data are compared to those obtained with a previously published and verified model for computing solar radiation on horizontal planes at the earth's surface for cloudless sky days. Measurements show an important reduction of global radiation with respect to the cloudless sky model predictions for all months of the year. Conversely, averaged daily diffuse solar radiation calculated with Page's formula shows a small increment with respect to the predicted diffuse solar radiation for cloudless sky conditions. When direct solar radiation data, calculated from global and diffuse solar radiation values, are compared to theoretical prediction, a significant decrease is observed. This trend is similar to that obtained for global solar radiation.     

Effects of nanocrystal size and device aging on performance of hybrid poly(3-hexylthiophene):CdSe nanocrystal solar cells

We have studied hybrid solar cells based on the polymer poly(3-hexylthiophene) (P3HT) and colloidal CdSe nanocrystals. Using CdSe nanospheres with varying size, we have found that the power conversion efficiency (η_P) of these devices increases monotonically with the CdSe nanocrystal size, from η_P=(0.39±0.04)% under AM1.5G solar illumination for 4.0±0.2 nm size nanospheres to η_P=(1.9±0.2)% for 6.8±0.5 nm size nanospheres. The efficiency increase with nanocrystal size is mostly due to a significant increase in the short-circuit current, whereas the open-circuit voltage and fill factor of the solar cells are less affected. The devices also exhibit abnormal initial aging behavior when exposed to air, as an increase in both the short-circuit current and open-circuit voltage during the first 30 min leads to a significant increase in η_P.     

A study on the hydrogen-storage properties of La2−xTixMgNi9 (x = 0.1, 0.2, 0.3, 0.4) alloys

The La_2−xTi_xMgNi₉ (x = 0.1, 0.2, 0.3, 0.4) alloys were prepared by magnetic levitation melting under Ar atmosphere. The effects of partial substitution Ti for La on the phase structures, hydrogen-storage properties and electrochemical characteristics of the alloys were investigated systematically. For La_2−xTi_xMgNi₉ (x = 0.1, 0.2, 0.3, 0.4) alloys, LaNi₅, LaNi₃ and LaMg₂Ni₉ are the main phases, the maximum hydrogen-storage capacity is 1.51, 1.36, 1.35 and 1.22 wt%, respectively. The absorption–desorption plateau pressure of the alloys first decreases and then increases with increase of Ti content, and the La_1.8MgTi_0.2Ni₉ alloy has the lowest absorption–desorption plateau pressure. The discharge voltage of the alloy electrodes rises with increasing the amount of Ti content. The La_1.8Ti_0.2MgNi₉ alloy electrode presents good electrochemical performance.     

Synthesis and organic photovoltaic (OPV) properties of triphenylamine derivatives based on a hexafluorocyclopentene “core”

A series of new “D-A-D” chromophores containing hexafluorocyclopentene thiophene as an acceptor and a triphenylamine unit as a donor, called TP-G1, TP-G2, TPB-G1 and TPB-G2, were designed and synthesized. Heterojunction organic photovoltaic (OPV) cells containing these chromophores were fabricated, and device 1, with the structure of ITO/PEDOT:PSS/TP-G1:P3HT/LiF/Al, displayed an open-circuit voltage (V_oc), short-circuit current (J_sc) and power-conversion efficiency (η) of 0.74 V, 1.178 mA/cm² and 0.22%, respectively. The triphenylamine group could effectively induce the open-ring isomer to close because the 4- and 4′- positions of the benzene rings were substituted by an electron-donating group and the value of the quantum yields of the closed-ring isomers increased. As a result, the closed-ring isomer facilitated intramolecular π-electron delocalization and exhibited a broad absorption band ranging from 200 to 850 nm. Due to the fluorine substitution of hexafluorocylopentene at the molecular center and the hole-transport characteristics of the triphenylamine moiety on the periphery, our chromophores showed obvious dual semiconductor properties, i.e., n- and p-type, which demonstrated a potential application for OPV devices.     

The doping effect on the crystal structure and electrochemical properties of LiMnxM1−xPO4 (M = Mg, V, Fe, Co, Gd)

To substitute minor Mn²⁺ by the transition metal ion M = Mg²⁺, V³⁺, Fe²⁺, Co²⁺, or Gd³⁺, LiMn_0.95M_0.05PO₄ samples are synthesized by a solid-state reaction route. The interpretation of doping effects is complicated by the interrelations between doping microstructure and morphology, because the crystal structure would be affected by the doped elements. The lattice structure and deviation of Li-O bond lengths of the doped LiMnPO₄ are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn³⁺/Mn²⁺ reaction coupled with the extraction/reinsertion process of Li⁺ in LiMnPO₄ structure. During charge/discharge process, the electron flowing and Li⁺ cation diffusion in the various doped LiMnPO₄ samples should be different thermodynamic and kinetic process. For further studying which step in thermodynamic and kinetic process would affect or control the electrochemical performance, the initial charge/discharge capacities and cycleability of doped LiMnPO₄ samples are obtained under different voltage range (from 2.7 to the upper cut-off voltage 4.4, 4.6 and 4.8 V, respectively) and different environment temperatures (0, 25, and 50 °C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO₄ shows 151.9 mAh g⁻¹.     

Electrochemical hydrogen storage properties of mechanically alloyed Mg0.8Ti0.2-xMnxNi (x = 0, 0.025, 0.05, 0.1) type alloys

Mechanical alloying was used in the synthesis of Mg_0.8Ti_0.2-xMn_xNi (x = 0, 0.025, 0.05, 0.1) quaternary alloys to analyze the effect of Mn substitution for Ti on the electrochemical performance of MgNi alloys. The milling was carried out for 25 h. By adding a small amount of Mn (x = 0.025) to the Mg_0.8Ti_0.2Ni alloy, a completely amorphous structure was obtained. The maximum discharge capacity of the Mg_0.8Ti_0.175Mn_0.025Ni alloy was observed as 543 mAh g^?1 at the initial charge/discharge cycle. When x = 0 and x = 0.05, the discharging performances of Mg_0.8Ti_0.2-xMn_xNi alloys were approximately the same. However, when x = 0.1, the lowest initial discharge capacity (401 mAh g^?1) and discharge capacity performance were observed. The capacity retention rates of Mg_0.8Ti_0.175Mn_0.025Ni, Mg_0.8Ti_0.2Ni, Mg_0.8Ti_0.05Mn_0.05Ni, and Mg_0.8Ti_0.1Mn_0.1Ni alloys were 81%, 68%, %67, and 47%, respectively, at the 20th cycle.