Low electrical percolation threshold and PL quenching in solution-blended MWNT–MEH PPV nanocomposites

Abstract

Pristine multiwall carbon nanotubes (MWNT) (synthesised using CVD approach) and poly[2-methoxy-5-(2 0 -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH PPV) based composites were prepared using a solution blending approach by employing various nanotube weight fractions. The prepared composites have been characterised using SEM, AFM, PL spectroscopy, UV-Vis studies and I-V characterisation. Increase in MWNT concentration has been found to quench the PL spectra of the composites suggesting photoinduced electron transfer from polymer to MWNT. The increase in MWNT concentration also increases the absorption of the composites. PL quenching and increase in absorption are desirable attributes for the design of photovoltaic systems. Also, the electrical conductivities of the composites can be described by the scaling law based on percolation theory and based upon the scaling law, a low electrical percolation threshold value (0.5 wt%) has been obtained for this composite system. The value of t (critical exponent) based on percolation theory is found to be 1.11. The low value of t is attributed to the aggregation and bundling of nanotubes in the prepared composites, as is evident from SEM and AFM micrographs. The turnon voltage is also found to be reduced in the case of polymer-nanotube composite system as compared to the pristine polymer system. Also, it has been observed that at higher weight percentages, the MWNTs form an immensely dense network and act as nanometric heat sinks, thus preventing the build up of large thermal effects, caused by the increased current in the pixels at higher voltages. Analysis of these optical and electrical properties is important before utilising the composite in organic electronics applications, in order to obtain more scientifically correct and repeatable results with fabricated devices.

Change in conformation of polymer PFO on addition of multiwall carbon nanotubes

“…Composites/blends of conducting polymers with carbon nanotubes [1][2][3] have caught the increasing attention of the scientific community in the last few years because of their potential applications in polymer light emitting diodes, 4,5 photovoltaic cells and photodiodes, 6 field effect transistors, 7 optical limiting devices, 8 supercapacitors, 9 sensors, 10 etc. Among polyphenylenebased materials, highly emissive poly(9,9-dioctylfluorenyl-2, 7diyl) end capped with dimethylphenyl (PFO) is a promising class of conjugated polymer, which can be used as blue light emitting material in polymer light emitting diodes.…”

Polymer Nanocomposites of Surface‐Modified Graphene. I: Thermal and Electrical Properties of Poly(Vinyl Alcohol)/Aminoacid‐Functionalized Graphene

“…Average contact number per conducting particle at the electrical percolation threshold, t , were 0.87 ± 0,12 for PVA/Phe‐RGO and 1.35 ± 0,19 for PVA/His‐RGO films, respectively. Expected Universal t values are between 1.5 and 2 contacts, but smaller values of 1.38 or 1.1 were reported for multiwalled nanotubes composites. In our case, such low t values may be attributed to multiple electrical conduction mechanisms, which includes electrons passing through aromatic conjugated sp 2 ‐bonds, which is the expected conducting mechanism, and through electrically charged aminoacyl groups at the sheets surface and edges, allowing electrical conduction without effective contact between the sp 2 carbon atoms of each neighboring sheet (Figure ).…”

Iodine doped multiwall carbon nanotubes in MEH-PPV:I-MWCNTs nanocomposite for organic solar cell applications

“…60 wt% shows the highest conductivity with 0.16 S/m. The change in conductivity is a result of the formation of an interconnected structure of IMWNTs and can be regarded as an electrical percolation threshold [17].…”