Search

Metal oxide semiconductors are promising interfacial materials for organic photovoltaics (OPVs) because of their electrical properties and solution processability. In this article, we report the fabrication of poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) OPV devices incorporating solution-based NiO interfacial layers that show promising enhancements of the device photocurrent and stability. We discuss the impact of parasitic shunt and series resistances on device performance as well as the ambient degradation of these devices, studied with intensity modulated photocurrent spectroscopy (IMPS). The results showed that charge extraction was predominantly affected by degradation via decrease in carrier mobility and increased trapping/recombination, revealing the physical mechanism behind the degradation observed. 2012 Elsevier Ltd. All rights reserved.

We present a solution-processed pseudo bi-layer organic solar cell with poly(3-hexyl thiophene) (P3HT) as donor and indene-C60 bisadduct (ICBA) as acceptor. The devices were fabricated by sequential processing of the active components followed by a thermal annealing treatment. An efficiency of 5.9% was achieved under AM 1.5G irradiation (1000 W/m2). The obtained efficiency is attributed to an enhanced nanomorphology that arises from the inter-diffusion of the ICBA molecules into a layer of pre-organised polymer (P3HT) and also due to the subsequent crystallisation of the ICBA molecules. These processes facilitate efficient charge generation and extraction. Time of flight-secondary ion mass spectroscopy (TOF-SIMS) depth profiling was carried out for different thermal annealing treatments of these pseudo bi-layer devices, which reveals full inter-diffusion of ICBA into the polymer P3HT. Photo-CELIV (charge extraction by linearly increasing voltage) studies elucidates that the thermal annealing imparts crystallinity to the fullerene phase which results in the improvement of charge carrier mobility.

A critical component in bulk-heterojunction (BHJ) organic photovoltaics (OPVs) is the charge-selective interfacial layer, which plays a vital role in achieving high device performance and stability. Here, we present the performance of molybdenum oxide (MoOx) hole selective interfacial layers for BHJ OPVs based on poly(3-hexylthiophene) (P3HT) donor and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) acceptor, prepared by a facile, low-temperature solution process. The results showed that the MoOx films enhanced device efficiency and stability in comparison to reference devices containing the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interfacial layer. Furthermore, a high fill factor (∼69%) close to the theoretical maximum value predicted for the P3HT:PCBM BHJ system was achieved. Despite their hole selective nature, ultraviolet photoemission spectroscopy (UPS) revealed that the MoOx films were n-type. This hole selective behavior can be explained by invoking band b...

The present work demonstrates the usefulness of nickel oxide as a hole transporting material in solid state dye-sensitized solar cells (SSDSSCs). We report on the photovoltaic performances of sensitized TiO2/NiO heterojunctions, and demonstrate that the TiO2 film thickness and morphology, as well as NiO film thickness, have significant effects on the photovoltaic behaviour of TiO2/NiO SSDSSC. Under 1 sun AM1.5G simulated illumination, the SSDSSCs demonstrated best photovoltaic performance with a short circuit photocurrent density, open circuit voltage, fill factor and efficiency of 0.91 mA cm−2, 780 mV, 40% and 0.3%, respectively. This study draws attention to the feasibility of enhancing the photovoltaic performance in SSDSSC devices through development of appropriately designed sensitized TiO2/NiO heterojunctions.

The copolymers of methacrylic acid with protoporphyrin IX (PPIX) and the metal complexes, zinc protoporphyrin IX and magnesium protoporphyrin IX were synthesised and characterised. Corresponding acrylic acid copolymers were also synthesised. The steady state absorption and fluorescence spectral properties of the macromolecular bound fluorophores PPIX, Zn-PPIX and Mg-PPIX were investigated. Poly(methacrylic acid) bound protoporphyrin IX, zinc protoporphyrin IX and magnesium protoporphyrin IX show an increase in the fluorescence intensity and lifetime with increase in the pH in the range 2-8 with a marked transition around pH 6.0-7.0. The fluorophore concentration in the dilute solution of the copolymers is micromolar and the fluorophore to the carboxylic acid monomer ratios in the copolymer is around 10 -3 . The molecular weight of the copolymers is 100 ± 10 kD. The fluorescence decay curves of all the fluorophore bound polymers follow biexponential decay fit independent of pH. Poly(MAA-co-PPIX) and poly(MAA-co-MgPPIX) undergo well marked pH induced structural transitions in the pH range of 6.0-7.0 whereas poly(MAA-co-ZnPPIX) undergoes pH induced structural transitions in the pH range of 4.0. In the case of polyacrylic acid copolymers the changes observed in the steady state and time resolved fluorescence studies are less marked. The distinct hydrophobic and hydrophilic environments experienced by the fluorophore bound to PMMA are attributed to the dynamics of the macromolecules in dilute aqueous solutions manifested by the α-methyl group present in the copolymer. The studies carried out using the fluorophores in the time windows from 2 ns to 12 ns indicate evolving trends in the dynamic coiling and reverse coiling of poly methacrylic acid chain.

The Energy crisis happens to be one of the greatest challenges we are facing today. In this view, much effort has been made in developing new, cost effective, environmentally friendly energy conversion and storage devices. The performance of such devices is fundamentally related to material properties. Hence, innovative materials engineering is important in solving the energy crisis problem. One such innovation in materials engineering is porous materials for energy storage. Porous electrode materials for lithium-ion batteries (LIBs) offer a high degree of electrolyte-electrode wettability, thus enhancing the electrochemical activity within the material. Among the porous materials, mesoporous materials draw special attention, owing to shorter diffusion lengths for Li + and electronic movement. Nanostructured mesoporous materials also offer better packing density compared to their nanostructured counterparts such as nanopowders, nanowires, nanotubes etc., thus opening a window for developing electrode materials with high volumetric energy densities. This would directly translate into a scenario of building batteries which are much lighter than today's commercial LIBs. In this article, the authors present a simple, soft template approach for preparing both cathode and anode materials with high packing density for LIBs. The impact of porosity on the electrochemical storage performance is highlighted.

The current state of the art solution processed organic photovoltaic (OPV) cells are based on the bulk heterojunction (BHJ) architecture, consisting of an active layer, in which the donor and the acceptor material are dissolved in a common solvent. In this report, we show that by sequential processing of the active components and by subsequent annealing a “pseudo-bilayer” can be formed which results in an enhanced nanomorphology for efficient charge generation and extraction. The enhanced nanomorphology arises from the inter-diffusion of the PCBM nanoparticles into a layer of pre-organised polymer P3HT instead of a phase separation that happens at the time of spin-coating and annealing in the case of conventional BHJ devices. To get a further insight into the inter-diffusion process, TOF-SIMS depth profiling and XPS measurements were carried out for different thermal annealing treatments of these pseudo-bilayer devices, which show full inter-diffusion after only seconds of annealing at 140°C. The optimised photovoltaic devices that were fabricated showed an efficiency of 4.1%.

Polymer solar cells fabricated through sequential-solution-processing of donor and acceptor materials consist of partially intermixed heterojunctions and are therefore termed as organic “pseudo-bilayer” solar cells. A steady-state model for such organic pseudo-bilayer solar cells, which generalizes the bulk-heterojunction and the bilayer solar cell models, is derived based on a donor-blend-acceptor structure for the active layer. In short, the model considers intrinsic solar cell physics such as optical generation, charge carrier transport, generation, and recombination, as well as the space charge effect. Parameter fitting and model validation are carried out with current-voltage measurements from in-house fabricated pseudo-bilayer solar cells. The model shows that even with a large exciton diffusion length, a pure large-molecule bilayer cell is unable to produce the photocurrents seen in the measurements. This confirms the experimental observation that an intermixed region, instead of a well-defined interface, exists between the donor and acceptor phases in pseudo-bilayer solar cells. In addition, the effect of blend region thickness on device performance is explored. Local features, such as the electric field and charge carrier concentrations, are also discussed.

not Available.

Micrometre-sized mesoporous materials have characteristic grains as well as pores nearly in the same scale. Electrodes of mesoporous materials for lithium batteries have short transport lengths for Li+ ions due to their nano-sized grains (10–20 nm), and easy access for electrolytes due to their nanopores (5–10 nm). Such mesoporous materials have high packing densities unlike nanopowders, nanowires, nanorods and nanotubes. Despite such advantages, electronic conduction over micrometre-sized particles limits the rate performance of mesporous materials. Occasionally counductive thin layers (2–5 nm) of carbon or RuO2 have been used to overcome such kinetic limitations and to achieve high storage performances. In this manuscript, we present a simple approach for the synthesis of mesoporous TiO2 anatase using a soft-template method, which shows superior storage performance without such conductive surface layers. Various cationic surfactants with different chain lengths have been selected for this investigation to assist the formation of the mesoporous TiO2 structure. Among these, cetyl trimethylammoniumbromide templated C16-TiO2 has the highest surface area of 135 m2 g−1 and reversible capacity of 288, 220, 138,134 and 107 mAh g−1 at 0.2, 1, 5, 10 and 30C respectively. The storage performance of the as-synthesized mesoporous TiO2 is nearly five times better than the commercially available TiO2 nanopowder. The packing density of meso-TiO2 is found to be 6.6 times higher than the TiO2 nanopowder. In addition, battery testing using mesoporous TiO2 electrodes without the 15% carbon additive exhibits nearly the same performance at low rate as the meso-TiO2 with carbon additives. These exciting results suggest a facile conduction path for electrons, a unique character of micrometre-sized mesoporous TiO2 with highly interconnected nanograins of 15–20 nm.

The present work demonstrates the usefulness of the soft-template directed approach in preparing mesoporous titanium dioxide and applying it in dye-sensitized solar cells (DSSCs). Mesoporous titanium dioxide with nanograins of dimension in the range, 16-20 nm were prepared through the soft-templating approach using various cationic surfactants such as octyl-, dodecyl-, cetyl trimethylammonium bromide with different surfactant compositions and titania precursor concentrations. As-synthesized mesoporous titanium dioxide samples were characterized by TGA, PXRD, FESEM, HRTEM and surface area measurements, used as photo-electrode material in DSSCs. Under global AM 1.5 solar irradiation, the best photovoltaic performance of 7.5% with a short circuit photocurrent density of 14.2 mA/cm(-2), an open circuit voltage of 748 mV, and a fill factor of 70.83% were obtained for the DSSC using a film of mesoporous TiO2 synthesized from the cetyl trimethylammoniumbromide surfactant. In contrast, the use of commercial titania powder P25 resulted in an efficiency of 5.0% under similar conditions. The structural and morphological merits of these template-directed materials will be especially addressed in comparison with their traditional bulk forms.