• Energy Research

Abstract To realize the full gamut of functions that are envisaged for electronic textiles (e-textiles) a range of semiconducting, conducting and electrochemically active materials are needed. This article will discuss how metals, conducting polymers, carbon nanotubes, and two-dimensional (2D) materials, including graphene and MXenes, can be used in concert to create e-textile materials, from fibers and yarns to patterned fabrics. Many of the most promising architectures utilize several classes of materials (e.g., elastic fibers composed of a conducting material and a stretchable polymer, or textile devices constructed with conducting polymers or 2D materials and metal electrodes). While an increasing number of materials and devices display a promising degree of wash and wear resistance, sustainability aspects of e-textiles will require greater attention. Graphical abstract

Ternary blends of poly(3-hexylthiophene): Photovoltaic Devices [6,6]-phenyl C(61)-butyric acid methyl ester (P3HT:PC(61)BM) and the insulating bulk polymers high-density polyethylene (HDPE), isotactic- and atactic polystyrene (i-PS, a-PS), are investigated. Addition of up to approximate to 50 wt% of the electronically inert, semicrystalline HDPE and i-PS to the organic semiconducting system does not significantly degrade the performance of photovoltaic devices fabricated with these ternary blends.

Composite films of poly(3-hexylthiophene) and single- as well as multi-walled carbon nanotubes are demonstrated to offer a competitive thermoelectric performance. The power factor significantly exceeds values obtained with either constituent alone provided that the conjugated polymer is sufficiently p-doped. The use of single-walled carbon nanotubes consistently results in a higher electrical conductivity with a maximum value above 10 3 S cm-1 and thus gives rise to a power factor of 25 ± 6 μW m-1 K-2 for a filler content of only 8 wt% and a maximum 95 ± 12 μW m-1 K-2 for 42-81 wt%. Moreover, a carbon nanotube content of 8-10 wt% does not compromise the low bulk thermal conductivity of the polymer matrix, which promises a high figure of merit of at least ZT > 10-2 at room-temperature. All samples are cast on plastic substrates, emphasising their suitability for large-area, flexible thermoelectric applications. © 2013 The Royal Society of Chemistry. This work was supported by the Ministerio de Economía y Competitividad through Grant CSD2010-00044 (Consolider NANOTHERM). C.M. gratefully acknowledges financial support from the CSIC through the JAE-Doc program (European Social Fund). M.C.-Q. thanks the Ministerio de Economía y Competitividad for funding through a Ramón y Cajal fellowship. M.S.M.-G. acknowledges the ERC for funding through an ERC 2008 Starting Grant “Nano-TEC” number 240497. Peer Reviewed

AbstractThe power conversion efficiency of ternary organic solar cells (TOSCs), consisting of one host binary blend and one guest component, remains limited by large voltage losses. The fundamental understanding of the open-circuit voltage (VOC) in TOSCs is controversial, limiting rational design of the guest component. In this study, we systematically investigate how the guest component affects the radiative and non-radiative related parts of VOC of a series of TOSCs using the detailed balanced principle. We highlight that the thermal population of charge-transfer and local exciton states provided by the guest binary blend (that is, the guest-component-based binary blend) has a significant influence on the non-radiative voltage losses. Ultimately, we provide two design rules for enhancing the VOC in TOSCs: high emission yield for the guest binary blend and similar charge-transfer-state energies for host/guest binary blends; high miscibility of the guest component with the low gap component in the host binary blend.

The recently published quinoxaline/thiophene-based polymer TQ1 has been modified on its acceptor unit, either altering the acceptor strength by incorporating a pyridopyrazine, substitution of the acceptor-hydrogens by fluorine, or substitution of the alkoxy side chain by alkyl. The changes in physical, electronic and device properties are discussed. For the polymers incorporating the stronger acceptors a decreased performance is found, where in both cases the current in the devices is compromised. Incorporation of the pyridopyrazine-based acceptor seems to result in more severe or additional loss mechanisms compared to the polymer that incorporates the fluorine atoms. A similar performing material is obtained when changing the alkoxy side chain in TQ1 to an alkyl, where the solar cell performance is mainly improved on the fill factor. It is demonstrated that the standard TQ1 structure is easily modified in a number of ways, showing the versatility and robustness of the standard TQ1 structure and synthesis.

Diketopyrrolopyrrole (DPP)-based organic semiconductors EH-DPP-TFP and EH-DPP-TFPV with branched ethyl-hexyl solubilizing alkyl chains and end capped with trifluoromethyl phenyl groups were designed and synthesized via Suzuki coupling. These compounds show intense absorptions up to 700 nm, and thin film-forming characteristics that sensitively depend on the solvent and coating conditions. Both materials have been used as electron donors in bulk heterojunction and bilayer organic photovoltaic (OPV) devices with fullerenes as acceptors and their performance has been studied in detail. The best power conversion efficiency of 3.3% under AM1.5G illumination (100 mW cm−2) was achieved for bilayer solar cells when EH-DPP-TFPV was used with C60, after a thermal annealing step to induce dye aggregation and interdiffusion of C60 with the donor material. To date, this is one of the highest efficiencies reported for simple bilayer OPV devices.

Electronic properties of organic semiconductors are often critically dependent upon their ability to order from the molecular level to the macro-scale, as is true for many other materials attributes of macromolecular matter such as mechanical characteristics. Therefore, understanding of the molecular assembly process and the resulting solid-state short- and long-range order is critical to further advance the field of organic electronics. Here, we will discuss the structure development as a function of molecular weight in thin films of a model conjugated polymer, poly(3-hexylthiophene) (P3HT), when processed from solution and the melt. While focus is on the microstructural manipulation and characterization, we also treat the influence of molecular arrangement and order on electronic processes such as charge transport and show, based on classical polymer science arguments, how accounting for the structural complexity of polymers can provide a basis for establishing relevant processing/structure/property-interrelationships to explain some of their electronic features. Such relationships can assist with the design of new materials and definition of processing protocols that account for the molecular length, chain rigidity and propensity to order of a given system.

AbstractDevices that can capture and convert sunlight into stored chemical energy are attractive candidates for future energy technologies. A general challenge is to combine efficient solar energy capture with high energy densities and energy storage time into a processable composite for device application. Here, norbornadiene (NBD)–quadricyclane (QC) molecular photoswitches are embedded into polymer matrices, with possible applications in energy storing coatings. The NBD–QC photoswitches that are capable of absorbing sunlight with estimated solar energy storage efficiencies of up to 3.8% combined with attractive energy storage densities of up to 0.48 MJ kg−1. The combination of donor and acceptor units leads to an improved solar spectrum match with an onset of absorption of up to 529 nm and a lifetime (t1/2) of up to 10 months. The NBD–QC systems with properties matched to a daily energy storage cycle are further investigated in the solid state by embedding the molecules into a series of polymer matrices revealing that polystyrene is the preferred choice of matrix. These polymer devices, which can absorb sunlight and over a daily cycle release the energy as heat, are investigated for their cyclability, showing multicycle reusability with limited degradation that might allow them to be applied as window laminates.