Jingsong Huang

Influence of thermal treatment on the conductivity and morphology of PEDOT/PSS films

Abstract The electrical properties of conducting polymers are strongly dependent on their film morphology and chemical and physical structure, which in turn can be strongly modified via a variety of post-deposition treatments. The aqueous dispersion of poly(3,4-ethylenedioxythiophene) with polyelectrolyte, poly(styrene sulfonic acid) (PEDOT/PSS) was used as the conducting polymer in our study. We report an investigation of the conductivity and morphology of spin-coated films and their dependence on heat treatment procedures in both air and N 2 atmospheres.

Patterning of organic devices by interlayer lithography

We report a new lithographic procedure that enables the patterning of as-received semiconducting polymers and small molecules at the near micron level without causing discernible degradation of the patterned material. The method involves a minimum of processing steps, requires no modification of the active layer, and is compatible with both rigid and flexible substrates. The technique makes use of an intermediate resist layer between the substrate and the active layer, i.e.underneath the active layer, and involves the simultaneous patterning of the resist and active layers in a single expose/develop step. The technique has been successfully applied to the fabrication of flexible ITO-free light-emitting diodes and photodiodes, yielding peak quantum efficiencies of 8.8 cd A−1 and 57% respectively comparable to similar devices fabricated on ITO-coated glass. It is also readily extendible to the patterning on a single substrate of multiple devices incorporating different component materials, e.g. the red, green and blue pixels of a colour display.

Efficient flexible polymer light emitting diodes with conducting polymer anodes

We report polymer light emitting diodes fabricated on flexible poly(ethyleneterephthalate) substrates coated with a layer of poly(3,4-ethylene-dioxythiophene) : poly(styrenesulfonate) that was lithographically patterned to define the anode structure. A blend of poly(9,9-dioctylfluorene-co-benzothiadiazole) and poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) was then spin-coated on top as the emissive layer and the device was completed by vacuum deposition of a LiF/Al bilayer cathode. The resulting yellow light emitting diodes had typical peak power and current efficiencies of 13.7 lm W−1 and 8.8 cd A−1 respectively, which compare well with values for similar devices fabricated on ITO-coated rigid glass substrates. A maximum luminance in excess of 7300 cd m−2 was achieved.

High efficiency flexible ITO-free polymer/fullerene photodiodes.

We report efficient polymer photodiodes fabricated on flexible polyethyleneterephthalate (PET) substrates. The PET substrates were coated with a layer of poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT:PSS) that was lithographically patterned to define the anode structure. A blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) was then spin-coated from a 1 : 1 mixture by weight of the two components in dichlorobenzene, and the device was completed by vacuum deposition of an aluminium electrode in vacuum. The resulting photodiodes had short-circuit quantum efficiencies of 45% and peak power efficiencies of 3%, which compare favourably with values for similar devices fabricated on rigid indium tin oxide (ITO) coated glass substrates.

Rapid Patterning of Single‐Wall Carbon Nanotubes by Interlayer Lithography

High resolution patterning of single-wall carbon nanotubes is achieved using interlayer lithography. Minimum feature sizes of 6 and 0.7 μm are demonstrated on glass and silicon, using the negative photoresist SU-8 and the positive photoresist AZ7220, respectively. Films patterned using SU-8 have a good balance of transparency and sheet-resistance, and are shown to be effective electrodes for organic solar cells. Copyright

Organic light emitting diodes and photodetectors: Toward applications in lab-on-a-chip portable devices

We report that polymer light emitting diodes (pLEDs) and polymer photodetectors can be integrated on disposable polydimethylsiloxane [PDMS] microfluidic flowcells to form hybrid microchips for bioluminescence applications. PLEDs were successfully employed as excitation light sources for microchip based fluorescence detection of microalbuminuria (MAU), an increased urinary albumin excretion indicative of renal disease. To circumvent the use of optical filters, fluorescence was detected perpendicular to the biolabel flow direction using a CCD spectrophotometer. Prior to investigating the suitability of polymer photodiodes as integrated detectors for fluorescence detection, their sensitivity was tested with on-chip chemiluminescence. The polymer photodetector was integrated with a PDMS microfluidic flowcell to monitor peroxyoxalate based chemiluminescence (CL) reactions on the chip. This work demonstrates that our polymer photodetectors exhibit sensitivities comparable to inorganic photodiodes. Here we prove the concept that thin film solution-processed polymer light sources and photodetectors can be integrated with PDMS microfluidic channel structures to form a hybrid microchip enabling the development of disposable low-cost diagnostic devices for point-of-care analysis.

Integrated sensors for point-of-care detection

We report a low cost device for performing chemiluminescent (CL) assays in a miniaturised format. The device comprises a poly(dimethylesiloxane) microfluidic chip for performing the CL assay coupled to a polymer photodiode based on a 1:1 blend by weight of poly(3-hexylthiophene) [P3HT] and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 [PCBM]. The integration of organic photodiodes with microfluidic chips offers a promising route to low cost fully integrated diagnostic devices for point-of-care applications.