Guangfeng Wang

Flexible organic light-emitting diodes with a polymeric nanocomposite anode.

Flexible organic light-emitting diodes (FOLEDs) are facing mechanical issues arising from failure of the indium-tin oxide (ITO) films fabricated on flexible substrates. Polymeric nanocomposite anodes were fabricated by including single-wall carbon nanotubes (SWCNTs) in aqueous poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The conductivity, transmittance and flexibility of the polymeric nanocomposite anode were characterized. The polymeric nanocomposite anodes fabricated on a poly(ethylene terephthalate) (PET) substrate exhibited superior bending properties to ITO anodes on PET. The FOLEDs fabricated on the polymeric nanocomposite anodes had a low turn-on voltage and higher luminous intensity than those fabricated on ITO/PET anodes. This flexible nanocomposite polymeric anode is a very promising for fully FOLEDs and other optoelectronics.

Modification of Conductive Polymer for Polymeric Anodes of Flexible Organic Light-Emitting Diodes

A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), was modified with dimethyl sulfoxide (DMSO) in solution state, together with sub-sequential thermal treatment of its spin-coated film. The electrical conductivity increased by more than three orders of magnitude improvement was achieved. The mechanism for the conductivity improvement was studied at nanoscale by particle size analysis, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Smaller particle size was observed, resulting in larger contact area and better electrical conductive connections. Connection of conductive PEDOT increased on the surface of the PEDOT:PSS particles, which promoted high conductivity. Flexible anodes based on the modified PEDOT:PSS were fabricated. Flexible organic light-emitting diodes (FOLED) based the polymeric anodes have a comparable performance to those on indium–tin–oxide (ITO) anodes.

Light-emitting fabrics integrated with structured polymer optical fibers treated with an infrared CO2 laser:

This paper describes woven fabrics made from polymer optical fibers (POF), which are treated with a CO2 laser so that the resultant surface notches on the POFs facilitate side emission of light. The transmission and side-emitting behavior of POF with surface notches are studied in term of the variation in bending curvatures, which is related to end-usage of the woven fabrics as flexible displays, wearable phototherapy devices and fashion accessories. The measured power of transmission of light from the POF rapidly decreases with increasing bending curvature. However, the measured power of side-emission of light from the notched POFs remains almost constant at various bending curvatures within the experimental range. Theoretical analysis of the light propagation in a notched POF is conducted, which illustrates that more light is reflected from one side of the notch when the bending curvature is increased hence the transmission of the light is decreased. The theoretical and experimental results reach a good agreement.

Fabrication and evaluation of a notched polymer optical fiber fabric strain sensor and its application in human respiration monitoring

This paper describes an intensity-based notched polymer optical fiber (POF) fabric strain sensor and its application in human respiration monitoring. A mechanical analysis illustrates geometrical profiles of constrained fiber loops on the fabric substrate. V-shaped notches are made by laser ablation on the sides of the POFs. The effects of loop parameters and processing conditions on the sensing performance are investigated. The experimental results show that the fabric sensor is more sensitive to strain with notches on the outer side of the loops, a small radius of the loops and a low scanning speed of laser. This fabric sensor exhibits a large measurable strain range of up to 21%. The achieved strain sensitivity is 3.77. The temperature and relative humidity have little effect on strain sensitivity between 0℃ and 60℃. A belt has been fabricated by integrating the fabric sensor for monitoring human respiration. The evaluation trials show a strong correlation between the belt system and a clinic monitor.

Improvement of Organic Light-emitting Devices by Controlling Deposition Temperature and Inclusion of Carbon Nanotubes

Research was conducted to improve performance of organic light-emitting devices (OLEDs) on flexible polyethylene terephthalate (PET) substrates based on tris-(8-hydroxyquinoline)¨Caluminum (Alq3). Based on double layer structure, indium tin oxide(ITO)/N,N’Diphenyl-N-N’-di(m-tdyl) benzidine (TPD)/Alq3/Al, flexible OLEDs on polyethylene terephthalate (PET) substrates were fabricated by physical vapor deposition (PVD) method, with the Alq3 layer deposited at 90°C , 120°C and 150°C, respectively. It was found that the temperature had great effect on the surface morphology of Alq3 and the devices fabricated at high temperature (150°C) showed a higher external efficiency than those fabricated at low temperature (90°C , 120°C). Multi wall carbon nanotubes (MWCNTs) doping poly(3,4-ethylene dioxythiophene) (PEDOT) : poly(styrene sulfonate) (PSS) was used as hole injection layer to improve performance of OLEDs based on Alq3. PEDOT:PSS, which was doped by 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, 0.8 wt.% and 1 wt.% MWCNTs, was coated on clean PET substrate with ITO by spin- coating method. The light-emitting layer (Alq3) and cathode layer (Al) were deposited by PVD method. It was found that the electroluminescence (EL) intensity of the OLEDs were highly improved by adopting MWCNTs doping PEDOT:PSS as hole injection layer. The luminous intensity obtained from the device with a concentration of 0.4 wt.% MWCNTs in the PEDOT:PSS layer was three folds as those adopted from device without MWCNTS doping in the PEDOT:PSS layer.