Felix Hermerschmidt

Highly efficient indium tin oxide-free organic photovoltaics using inkjet-printed silver nanoparticle current collecting grids

We report an in-depth investigation of an inkjet-printed silver (Ag) nanoparticle grid combined with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) of different conductivities as an alternative to an indium tin oxide (ITO)-based transparent anode for organic solar cell applications. The reported measurements revealed higher transparency of the inkjet-printed Ag nanoparticle-based grid when compared to different thicknesses of ITO on glass substrates. Based on the proposed current collecting grid, a record power conversion efficiency of 2% is achieved for ITO-free organic solar cells.

4H-1,2,6-Thiadiazin-4-one-containing small molecule donors and additive effects on their performance in solution-processed organic solar cells

The optical, electrochemical, morphological and transport properties of a series of thiadiazinone (acceptor) and (thienyl)carbazoles (donor) containing π-extended donor–acceptor–donors (D–A–D) are presented. Systematic variations in the number of the thienyl units, the choice of branched or straight alkyl side chains and the use of a processing additive demonstrate their use as electron donors in bulk heterojunction solar cells blended with fullerene acceptors. The best power conversion efficiency (PCE) of 2.7% is achieved by adding to the D–A–D 3 : fullerene blend a polydimethylsiloxane (PDMS) additive, that improves the morphology and doubles the hole mobility within the D–A–D : fullerene blend.

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...

Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols

High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3 interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.

Evaporation-free inverted organic photovoltaics using a mixture of silver nanoparticle ink formulations for solution-processed top electrodes

We report an investigation of inkjet-printed silver (Ag) nanoparticle inks combined with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) formulation for solution-processed top electrodes in inverted organic photovoltaics (OPVs) employing the poly(3-hexylthiopehene):phenyl-C61-butyric acid methyl ester material system. We propose a suitable mixture of Ag nanoparticle inks to control the printability and electrical conductivity of the solution-processed top electrode. Based on the proposed solution-processed hole-selective contact, a power conversion efficiency in the range of 3% is reported for evaporation-free inverted OPVs.

Beyond solar radiation management – the strategic role of low-cost photovoltaics in solar energy production

This paper examines the role of renewable energy sources (RES), especially the sun, as a potential solution for solar radiation management concerns. It states how photovoltaic (PV), especially low-cost PV and other thin film technology, can be applied and what impact and share they can have on the European market – using the Cyprus market as an example of strategic implementation. The Energy Service of the Ministry of Energy, Commerce, Industry and Tourism currently reports a 7.5% share (as at end of 2012) of RES in overall final energy consumption and suggests ways in which that share can increase. In the near future, PVs will be the most significant electricity source if the cost per kWh produced is further reduced, as was proven recently during the award procedures for PV systems.

Large area processing and printing of conducting copper structures for use in (opto)electronics (Conference Presentation)

Most current electronics manufacturing technologies utilise subtractive processing that is expensive, wasteful and energy intensive. Printed electronics is revolutionising the electronics industry by enabling additive processing that significantly reduces expense, waste and energy consumption. The EU-funded PLASMAS project demonstrates the capability of printed electronics based on novel nanoparticle Cu inks with favourable cost to performance ratios, through development of large area printed circuit boards and printed logic as well as OLED and OPV elements with printed Cu nanoparticle electrodes. However, a number of challenges need to be overcome when printing these metal nanoparticle inks – the typical feature height of printed structures of several 100 nm tend to exhibit a rough surface, which can lead to shorts in the device after subsequent overcoating of the organic active layer materials. Furthermore, the sintering temperature of the nanoparticle inks needs to be low (< 130 °C) in order to allow deposition and curing on transparent flexible substrates such as PET. We therefore present the process development of solution-processed electrodes based on inkjet-printed Cu grids, by embedding the inkjet-printed metal grids to yield ITO-free optoelectronic devices. Secondly, we present roll-to-roll inkjet-printed RFID antennas based on Cu inks. Finally, we demonstrate a truly low-temperature sintering route for a Cu nanoparticle ink by using a reducing atmosphere of formic acid, yielding stable highly conducting layers. The results of the project highlight overall parameters for solution processing and implementation of novel metal nanoparticle materials and architectures in printed electronics.