We report on solution processed polymer light emitting diodes (PLEDs) using inkjet-printed embedded and non-embedded metal grid anodes. Metal grids were inkjet-printed in a honeycomb layout. Honeycomb dimensions were varied from 3 mm to 8 mm to optimize device performance. Inkjetprinted grids were then coated with a highly conductive PEDOT:PSS formulation. First experiments on PEDOT:PSS coated, non-embedded metal grid anodes showed that grids with a 3 mm honeycomb diameter have a similar efficiency as optimized indium tin oxide (ITO) based reference devices. To further improve the efficiency of the devices, the honeycomb Ag-grids were embedded in an Ormocer V R-based material. A detailed performance analysis of PLEDs fabricated on ITO, nonembedded and embedded grids was carried out. It is shown that reduced leakage current and enhanced light outcoupling by embedding result in a significant efficiency enhancement of 250% in inkjet-printed embedded Ag-PEDOT:PSS ITO-free PLEDs, compared to the ITO-based reference PLEDs.
We report on the grid design requirements and inkjet-printing processing conditions of well-defined silver nanoparticles combined with poly(3,4-ethylenedioxylthiophene):poly(styrenesulfonate) PEDOT:PSS as indium tin oxide (ITO) replacement for ITO-free organic light emitting diodes (OLEDs). Solution-processed ITO-free OLEDs based on the 5BTF8 blend of poly(9,9-dioctylfluorene-alt-benzothiadiazole (F8BT) and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) light-emitting layers, processed in ambient conditions, showed comparable luminance efficiency and power efficiency values to reference devices based on ITO and near identical efficiencies at low luminance values.
The chemical design of a polymer can be tailored by a random or a block sequence of the comonomers in order to influence the properties of the final material. In this work, two sequences, PCPDTBT and F8BT (F8), were polymerized to form a block or a random copolymer. Differences between the various polymers were examined by exploring the surface topography and charge carrier mobility. A distinct surface texture and a higher charge carrier mobility was found for the block copolymer with respect to the other materials. Solar cells were prepared with polymer:PC 71BM blend active layers and the best performance of up to 2% was found for the block copolymer, which was a direct result of the fill factor. Overall, the sequences of different copolymers for solar cell applications were varied and a positive impact on efficiency was found when the block copolymer structure was utilized
We report efficiency enhancement of indium phosphide (InP) quantum dot-based light-emitting diodes (QD-LEDs) by using an polyethylenimine (PEI) surface modifier. By adapting a solution processed PEI layer on top of a aluminum doped zinc oxide (Al:ZnO) nanoparticle (NP) film, the leakage current of the inverted device was substantially suppressed. In addition, the electron injection into the conduction band edge (CBE) of InP/ZnSe/ZnS QDs was also facilitated by the low work function (WF) of the Al:ZnO film which was realized by the strong interfacial dipoles of the thin film of PEI. As a result, the charge balance in the inverted devices was controlled by the change of surface roughness, the WF and the thickness of neighboring layers via spin-coating the PEI dissolved in alcohol mixture on the Al:ZnO layer such that the current efficiency was dramatically increased from 0.07 cd/A to 3.17 cd/A. The performance of our device is not comparable to Cd-based devices; however, it shows the great potential for using an interfacial dipole layer to develop highly efficient InP-based inverted QD-LEDs
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