Hybrid solar cells from the Blend of Poly(3-hexylthiophene) and ligand-capped TiO2 nanorods.

International audienceHybrid bulk heterojunction solar cells based on nanocrystalline TiO2 (nc-TiO2) nanorods capped with trioctylphosphine oxide (TOPO) and regioregular poly(3-hexylthiophene) (P3HT) are processed from solution and characterized in order to relate the device function (optical absorption, charge separation, and transport and photovoltaic properties) to active-layer properties and device parameters. Annealing the blend films is found to greatly improve the polymer-metal oxide interaction at the nc-TiO2/ P3HT interface, resulting in a six-fold increase of the charge separation yield and improved photovoltaic device performance under simulated solar illumination. In addition, the influence of the organic ligand at the nc-TiO2 particle surface is found to be crucial for charge separation. Ligand-exchange procedures applied on the TOPO-capped nc-TiO2 nanorods with an amphiphilic ruthenium-based dye are found to further improve the charge-separation yield at the polymer-nanocrystal interface. However, the poor photocurrents generated in the hybrid blend devices, before and after ligand exchange, suggest that transport within or between nanoparticles limits performance. By comparison with other donor-acceptor bulk heterojunction systems, we conclude that charge transport in the nc-TiO2:P3HT blend films is limited by the presence of an intrinsic trap distribution mainly associated with the nc-TiO2 particles

Hybrid bulk heterojunction solar cells based on blends of TiO2 nanorods and P3HT.

International audienceOver the past decades, organic solar cells based on semiconducting polymers or small molecules have become a promising alternative to traditional inorganic photovoltaic devices. However, to address the intrinsic limitations of organic materials, such as charge separation yield, charge transport and durability, new strategies based on hybrid organic/inorganic materials have been explored. One such approach exploits mesoporous inorganic nanostructures as electron acceptors, which takes advantage of the potential to control the active layer structure and interface morphology through nanoparticle synthesis and processing. In this work, the potential of hybrid photovoltaics will be discussed and illustrated through a recent study of bulk heterojunction systems based on the blend of TiO2 nanorods with a conjugated polymer

Activation of structural carbon fibres for potential applications in multifunctional structural supercapacitors

The feasibility of modifying conventional structural carbon fibres via activation has been studied to create fibres, which can be used simultaneously as electrode and reinforcement in structural composite supercapacitors. Both physical and chemical activation, including using steam, carbon dioxide, acid and potassium hydroxide, were conducted and the resulting fibre properties compared. It was proven that the chemical activation using potassium hydroxide is an effective method to prepare activated structural carbon fibres that possess both good electrochemical and mechanical properties. The optimal activation conditions, such as the loading of activating agent and the burn-off of carbon fibres, was identified and delivered a 100-fold increase in specific surface area and 50-fold improvement in specific electrochemical capacitance without any degradation of the fibre mechanical properties. The activation process was successfully scaled-up, showing good uniformity and reproducibility. These activated structural carbon fibres are promising candidates as reinforcement/electrodes for multifunctional structural energy storage devices

Hierarchically porous carbon foams from pickering high internal phase emulsions

Carbon foams were produced from a macroporous poly(divinylbenzene) (poly(DVB) precursor, synthesized by polymerizing the continuous but minority phase of water-in-oil high internal phase emulsions (HIPEs) stabilized by molecular and/or particulate emulsifiers. Both permeable and non-permeable hierarchically porous carbon foams, or ‘carboHIPEs’, were prepared by carbonization of the resulting macroporous polymers at 800 °C. The carbon yields were as high as 26 wt.% of the original polymer. CarboHIPEs retain the pore structure of the macroporous polymer precursor, but with surface areas of up to 505 m2/g and excellent electrical conductivities of 81 S/m. Contrary to some previous reports, the method does not require further modification, such as sulfonation or additional crosslinking of the polyHIPE prior to carbonization, due to the inherently crosslinked structure of poly(DVB). The use of a pourable, aqueous emulsion-template enables simple moulding, minimises waste and avoids the strong acid treatments used to remove many conventional solid-templates. The retention of the macroporous structure is coupled with the introduction of micropores during carbonization, producing hierarchically porous carboHIPEs, suitable for a wide range of applications as sorbents and electrodes

Structural composite supercapacitors

This paper presents the development of multifunctional materials that perform a structural role whilst simultaneously storing electrical energy as a supercapacitor. Two structural carbon fibre woven electrodes were separated by a woven glass fibre layer, and infused with a multifunctional polymer electrolyte. Following characterisation of electrochemical and compressive performance, working structural supercapacitor prototypes were demonstrated. Since the relative mechanical and electrical demands are application specific, an optimisation methodology is proposed. Multifunctional composites were achieved, which had compressive moduli of up to 39 GPa and capacitances of up to 52 mF g−1

Multifunctional structural energy storage composite supercapacitors

This paper addresses the challenge of producing multifunctional composites that can simultaneously carry mechanical loads whilst storing (and delivering) electrical energy. The embodiment is a structural supercapacitor built around laminated structural carbon fibre (CF) fabrics. Each cell consists of two modified structural CF fabric electrodes, separated by a structural glass fibre fabric or polymer membrane, infused with a multifunctional polymeric electrolyte. Rather than using conventional activated carbon fibres, structural carbon fibres were treated to produce a mechanically robust, high surface area material, using a variety of methods, including direct etching, carbon nanotube sizing, and carbon nanotube in situ growth. One of the most promising approaches is to integrate a porous bicontinuous monolithic carbon aerogel (CAG) throughout the matrix. This nanostructured matrix both provides a dramatic increase in active surface area of the electrodes, and has the potential to address mechanical issues associated with matrix-dominated failures. The effect of the initial reaction mixture composition is assessed for both the CAG modified carbon fibre electrodes and resulting devices. A low temperature CAG modification of carbon fibres was evaluated using poly(3,4-ethylenedioxythiophene) (PEDOT) to enhance the electrochemical performance. For the multifunctional structural electrolyte, simple crosslinked gels have been replaced with bicontinuous structural epoxy–ionic liquid hybrids that offer a much better balance between the conflicting demands of rigidity and molecular motion. The formation of both aerogel precursors and the multifunctional electrolyte are described, including the influence of key components, and the defining characteristics of the products. Working structural supercapacitor composite prototypes have been produced and characterised electrochemically. The effect of introducing the necessary multifunctional resin on the mechanical properties has also been assessed. Larger scale demonstrators have been produced including a full size car boot/trunk lid