Alexander Lange

High performance indium tin oxide-free solution-processed organic light emitting diodes based on inkjet-printed fine silver grid lines

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.

Inkjet-printed embedded Ag-PEDOT:PSS electrodes with improved light out coupling effects for highly efficient ITO-free blue polymer light emitting diodes

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. Inkjet-printed 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®-based material. A detailed performance analysis of PLEDs fabricated on ITO, non-embedded 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 refer...

Tailor-made absorber polymers for OPV: from synthesis to formulation development

Organic solar cells are a favorable alternative to their inorganic counterparts because the functional layers of these devices can be processed with printing or coating on a large scale. In this study, a novel absorber polymer was synthesized, blended with fullerene and deposited with inkjet printing for solar cell applications. A fluorene based terpolymer with dialkyl substituted diphenyl-dithienylbenzopyrazine and triphenylamine units was synthesized by Suzuki polymerization with high molecular weights. The introduction of dialkyl substituted diphenyldithienylbenzopyrazine in the fluorene main chain leads to LUMO-energy level of -3.1 eV and to an open circuit voltage of 0.96 V in solar cells. All the requirements were fulfilled to achieve absorber polymers with high efficiencies including a HOMO energy level which is lower than -5.2 eV, a band gap in the range of 1.3-1.9 eV and a hole mobility in OTFTs greater than 1 x 10-3cm2/Vs. Solar cells with printed layers were compared to those with spin coated films in order to evaluate inkjet printing as a thin film deposition method. Efficiency values of 3.7% were found for devices with inkjet printed layers or spin coated layers when using chlorinated solvents. In order to be able to use inkjet printing on a large scale, hazardous, chlorinated solvents should be avoided when depositing the functional materials. Anisol/tetralin was used as an alternative solvent system. It was found that devices prepared from the chlorine-free system showed only slightly lower efficiencies of 2.7% with respect to the chlorinated system. A coarser phase separation was found with energy filtered transmission electron microscopy plasmon mapping which most likely resulted in the performance differences for the chlorinated and chlorine-free solvent systems.