3 resultados para Organic Acid
em Cambridge University Engineering Department Publications Database
Resumo:
A simple and cheap procedure for flexible electronics fabrication was demonstrated by imprinting metallic nanoparticles (NPs) on flexible substrates. Silver NPs with an average diameter of 10 nm were prepared via an improved chemical approach and Ag Np ink was produced in α-terpineol with a concentration up to 15%. Silver micro/nanostructures with a dimension varying from nanometres to microns were produced on a flexible substrate (polyimide) by imprinting the as-prepared silver ink. The fine fluidic properties of an Ag NP/α-terpineol solution and low melting temperatures of silver nanoparticles render a low pressure and low temperature procedure, which is well suited for flexible electronics fabrication. The effects of sintering and mechanical bending on the conductivity of imprinted silver contacts were also investigated. Large area organic field effect transistors (OFET) on flexible substrates were fabricated using an imprinted silver electrode and semiconducting polymer. The OFET with silver electrodes imprinted from our prepared oleic acid stabilized Ag nanoparticle ink show an ideal ohmic contact; therefore, the OFET exhibit high performance (Ion/Ioff ratio: 1 × 103; mobility: 0.071 cm2 V-1 s-1). © 2010 IOP Publishing Ltd.
Resumo:
The performance of polymer-fullerene bulk heterojunction (BHJ) solar cells is strongly dependent on the vertical distribution of the donor and acceptor regions within the BHJ layer. In this work, we investigate in detail the effect of the hole transport layer (HTL) physical properties and the thermal annealing on the BHJ morphology and the solar cell performance. For this purpose, we have prepared solar cells with four distinct formulations of poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) buffer layers. The samples were subjected to thermal annealing, applied either before (pre-annealing) or after (post-annealing) the cathode metal deposition. The effect of the HTL and the annealing process on the BHJ ingredient distribution - namely, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) - has been studied by spectroscopic ellipsometry and atomic force microscopy. The results revealed P3HT segregation at the top region of the films, which had a detrimental effect on all pre-annealed devices, whereas PCBM was found to accumulate at the bottom interface. This demixing process depends on the PEDOT:PSS surface energy; the more hydrophilic the surface the more profound is the vertical phase separation within the BHJ. At the same time those samples suffer from high recombination losses as evident from the analysis of the J-V measurements obtained in the dark. Our results underline the significant effect of the HTL-active and active-ETL (electron transport layer) interfacial composition that should be taken into account during the optimization of all polymer-fullerene solar cells. © 2012 The Royal Society of Chemistry.
Resumo:
The dithiophene donor-acceptor copolymers that are bridged either with carbon (C-PCPDTBT) or silicon atoms (Si-PCPDTBT) belong to a promising family of materials for use in photoactive layers for organic photovoltaic cells (OPVs). In this work, we implement the non-destructive Spectroscopic Ellipsometry technique in the near infrared to the far ultraviolet spectral region in combination with advanced theoretical modeling to investigate the vertical distribution of the C-PCPDTBT and Si-PCPDTBT polymer and fullerene ([6,6]-phenyl C71-butyric acid methyl ester - PC70BM) phases in the blend, as well as the effect of the polymer-to-fullerene ratio on the distribution mechanism. It was found that the C-PCPDTBT:PC70BM blends have donor-enriched top regions and acceptor-enriched bottom regions, whereas the donor and acceptor phases are more homogeneously intermixed in the Si-PCPDTBT:PC70BM blends. We suggest that the chemical incompatibility of the two phases as expressed by the difference in their surface energy, may be a key element in promoting the segregation of the lower surface phase to the top region of the photoactive layer. We found that the increase of the photoactive layer thickness reduces the polymer enrichment at the cathode, producing a more homogeneous phase distribution of donor and acceptor in the bulk that leads to the increase of the OPV efficiency. © 2014 Elsevier B.V.