Pim Groen

Industrial-scale inkjet printed electronics manufacturing—production up-scaling from concept tools to a roll-to-roll pilot line

An efficient strategy for the up-scaling of processing technology for inkjet printing of silver nanoparticle inks towards industrially relevant manufacturing volumes is described. This has been demonstrated by the roll-to-roll production of fine conductive patterns on polymer foils. Starting with small-scale benchmarking to identify the most suitable ink–substrate combination from a range of commercial products, the processing conditions for inkjet printing and sintering were continuously optimized during three consecutive stages. During each iteration, the scale of the experiments in terms of complexity, time requirement and materials usage was increased, thereby more closely resembling the final industrial-scale production conditions. This increased effort was, however, counterbalanced by limiting the number of necessary experiments by purposeful selection based on the results obtained at the lower levels. In addition, the outcome of each previous iteration round served as a starting point for the optimization during the next higher stage. In this way, it was possible to strongly restrict the number of experiments to obtain valuable information about the most ideal conditions at the final stage, which was a roll-to-roll pilot production line. Following this approach, large-area functional conductive structures on plastic foils could be prepared in a continuous manner at process speeds of up to 10 m min–1. These samples showed promising properties for application in printed electronic devices.

X-Ray Detector-on-Plastic With High Sensitivity Using Low Cost, Solution-Processed Organic Photodiodes

We made and characterized an X-ray detector on a 25-μm-thick plastic substrate that is capable of medicalgrade performance. As an indirect conversion flat panel detector, it combined a standard scintillator with an organic photodetector (OPD) layer and oxide thin-film transistor backplane. Using solution-processed organic bulk heterojunction photodiode rather than the usual amorphous silicon, process temperature is reduced to be compatible with plastic film substrates, and a number of costly lithography steps are eliminated, opening the door to lower production costs. With dark currents as low as 1 pA/mm2 and sensitivity of 0.2 A/W the OPD also meets functional requirements: the proof-of-concept detector delivers high-resolution, dynamic images at 10 frames/s, and 200 pixels/in using X-ray doses as low as 3 μGy/frame.

Organic photovoltaic cells with all inkjet printed layers and freedom of form

Large volume production of organic photovoltaics by roll-to-roll compatible techniques is a field of intensive research. Inkjet printing is a well-known deposition technique in the graphical and textile industry, and has several advantages for the production of OPV as it is contactless and has economic materials use. More importantly, cells and modules can be directly patterned during R2R production and by digital fabrication of OPV altering the cell or module design does not require changes of hardware. This makes inkjet printing suitable for OPV with unconventional shapes, but also allows for customizable large scale production. Therefore, inkjet printing offers the flexibility required at this stage of technological and market development of OPV. We have been able, for the first time, to create fully inkjet printed OPVs with a performance of more than 75% of its reference prepared by spin coating and evaporation. Large areas were printed in single passes with an industrial printer head using non-halogenated solvents only. An inverted OPV stack of 6 layers was printed using 4 types of inks. ITO was replaced by an inkjet printed Ag current collecting grid combined with highly conducting PEDOT:PSS. In this contribution we will discuss the additive effect of printing multiple layers on the OPV performance. Furthermore, the performance of cells of different shapes and sizes (up to 6.5 cm2) will be discussed. This work confirms the potential of inkjet printing for OPV as well as printed electronics in general.

Functionally graded ferroelectric polyetherimide composites for high temperature sensing

High temperature ferroelectrics for thermally stable devices that can detect pressure and temperature are of great industrial interest. Here we describe composites of lead titanate (PT) particle-polyetherimide (PEI) polymers with stable dielectric and piezoelectric properties over a broad range of temperature and frequency. The reported materials have a low dielectric loss (tanδ ∼ 0.001 at 1 kHz) and a high piezoelectric voltage coefficient of 100 mV m N-1 at record temperatures of 175 °C. We demonstrate that a small ceramic loading leads to a significant change in thermally stable piezoelectric behavior, while the processability as well as mechanical properties remain comparable to those of the neat polymer. Careful design of the microstructure is performed by dielectrophoretic assembly of ferroelectric PT micro-particles to induce micro-wire configurations, which is shown to be a key element in attaining high functionality at low ceramic loading. Thermal imidization of the composites is performed in two steps, first partial imidization at 60 °C to form free standing films containing polyamic acid, followed by full imidization at 200 °C and 300 °C. The presence of highly polar polyamic acid results in higher dielectric permittivity and electrical conductivity that facilitate efficient poling. Upon complete imidization of the films at 300 °C the dielectric and piezoelectric properties are tested at elevated temperatures. A fully imidized composite contains completely closed imide groups, resulting in a thermally stable material with a very low dielectric loss that maintains more than 85% of its room temperature piezoelectric sensitivity up to 175 °C. The room temperature piezoelectric voltage coefficient shows more than 400% improvement over that of PT ceramics.

Up-scaling perovskite solar cell manufacturing from sheet-to-sheet to roll-to-roll: Challenges and solutions

Organometallic halide perovskite solar cells (PSCs) are extremely promising novel materials for thin-film photovoltaics, exhibiting efficiencies over 22% on glass and over 17% on foil 1, 2 . First, a sheet-to-sheet (S2S) production of PSCs and modules on 152x152 mm2 substrates was established, using a combination of sputtering, e-beam evaporation, slot die coating and thermal evaporation (average PCE of 14.6 ± 1.3 % over 64 devices, more than 10% initial PCE on modules). Later the steps towards a roll-to-roll production will be investigated, starting from the optimization of the stack to make it compatible with a faster production at low temperature. A water based SnOx nanoparticles dispersion was used as solution processable ETL, and the deposition process was scaled-up from spin coating to R2R slot die coating on a 300 mm wide roll of PET/ITO. R2R production is often carried out in ambient atmosphere and involve the use of large volumes of materials, thus a first point is the development of a green solvent and precursor system for the perovskite layer to prevent the emission of toxic compound in the environment. The first results on device fabrication are encouraging, which allow partial R2R manufacturing of flexible PSC (R2R coating of SnOx and perovskite, S2S for Spiro-OMeTAD and gold) with stabilized PCE of 12.6%, a remarkable value for these novel devices. This result can be considered an important milestone towards the production of efficient, low cost, lightweight, flexible PSC on large area.

Investigation of interfacial instabilities with a two-layer slide coating process

Organic electronics have been thoroughly investigated due to their broad application potential, ranging from light-emitting diodes to photovoltaics. The processing of organic electronics is trending from vacuum toward wet chemical deposition, which allows fast low-cost mass production of devices with scalable dimension. One of the current challenges of wet film processing is the redissolution of already dried active materials when applying a liquid top layer. Further, increasing overall process efficiency by coating multiple liquid layers in one step raises such challenges as liquid–liquid mixing or dewetting. This article describes the experimental investigation of these instabilities for two-layer flows with organic solvents. A modified slide coating device was chosen where an extended plate after the slot exit allows prolonged observation of the flow while it travels down the plate. During experimentation, stable and unstable two-layer flows as well as different types of instabilities were detected. The key finding is a correlation of flow stability with the spreading coefficient, a combined measure of surface and interfacial tensions. Focusing on fluid properties, this paper succeeds in defining a three-dimensional stability window for a dual-layer flow.

Setup for EMI Shielding Effectiveness Tests of Electrically Conductive Polymer Composites at Frequencies up to 3.0 GHz

Conductive polymer composites have been receiving increased interest both from the scientific community and industry with a special focus on electromagnetic interference (EMI) shielding applications. In this paper, we present the design, EM wave simulation, and validation through S-parameters measurements of an EMI shielding effectiveness (SE) tester based on the ASTM D4935 standard, to be used in the development of such materials. EM wave simulations and computer aided design were used in parallel to improve the SE test setup performance, which resulted in a unique low-loss coaxial–spherical–conical smooth transition design that ensured the best tradeoff between sample size and performance. The proposed SE tester has an insertion loss smaller than 1 dB, with good reproducibility and a setup-independent frequency response in the frequency range from a few kHz up to 3 GHz.

Thin-film flexible barriers for PV applications and OLED lighting

To protect organic flexible devices from the ambient, they have to be encapsulated. Depending on the application in mind (OLED lighting, PV) different thin-film encapsulation methodology can be chosen. Each encapsulation process has different requirements and fabrication process freedom might be restricted, for example by mechanical reliability requirements or the total cost of the end product. Here we will show our recent investigations into different thin-film barriers with respect to their application and the route to production.