Hanna M. Haverinen

Inkjet printing-process and its applications.

In this Progress Report we provide an update on recent developments in inkjet printing technology and its applications, which include organic thin-film transistors, light-emitting diodes, solar cells, conductive structures, memory devices, sensors, and biological/pharmaceutical tasks. Various classes of materials and device types are in turn examined and an opinion is offered about the nature of the progress that has been achieved.

Inkjet printing of light emitting quantum dots

We demonstrate the fabrication of diodes having inkjet printed light emitting quantum dots layer. Close packing of printed layer is shown to be influenced by surface morphology of the underlying polymer layer and size variance of quantum dots used. We extend our approach to printing quantum dots onto a quarter video graphics array substrate (76 800 monochrome pixels). The purity of emitted electroluminescent spectra of resulting devices is related to coverage integrity of printed layer, which in turn is shown to be affected by the number of printed drops per pixel.

Inkjet Printed RGB Quantum Dot-Hybrid LED

We report DC driven full color inkjet printed quantum-dots light-emitting devices. The inkjet was used to print monochromatic red, green, and blue, as well as integrate red-green-blue light-emitting quantum dots unto a substrate having QVGA display. The performance of the inkjet printed monochrome devices was on the same order as that of spin coated ones. For the full color RGB devices, a video brightness of 100 cd/m2 is achieved at 9.3 V.

Low-temperature amorphous-silicon backplane technology development for flexible displays in a manufacturing pilot-line environment

— A low-temperature amorphous-silicon (a-Si:H) thin-film-transistor (TFT) backplane technology for high-information-content flexible displays has been developed. Backplanes were integrated with frontplane technologies to produce high-performance active-matrix reflective electrophoretic ink, reflective cholesteric liquid crystal and emissive OLED flexible-display technology demonstrators (TDs). Backplanes up to 4 in. on the diagonal have been fabricated on a 6-in. wafer-scale pilot line. The critical steps in the evolution of backplane technology, from qualification of baseline low-temperature (180°C) a-Si:H process on the 6-in. line with rigid substrates, to transferring the process to flexible plastic and flexible stainless-steel substrates, to form factor scale-up of the TFT arrays, and finally manufacturing scale-up to a Gen 2 (370 × 470 mm) display-scale pilot line, will be reviewed.

Effect of molecular packing on interfacial recombination of organic solar cells based on palladium phthalocyanine and perylene derivatives

Planar heterojunction solar cells made of three different perylene tetracarboxylic diimide (PTCDI) derivatives as acceptor and palladium phthalocyanine as donor are demonstrated. Electron-hole pair recombination at donor/acceptor interface was compared for three PTCDI derivative solar cells by optical modeling and the effect of molecular packing of the PTCDI derivatives on charge dissociation is discussed. We observed that PTCDI with hexyl chains has the highest charge separation efficiency among three PTCDI derivatives, leading to a power conversion efficiency of 2.0% in solar cells.

Efficient organic light-emitting devices with platinum-complex emissive layer

We report efficient organic light-emitting devices having a platinum-complex emissive layer with the peak external quantum efficiency of 17.5% and power efficiency of 45 lm W−1. Variation in the device performance with platinum-complex layer thickness can be attributed to the interplay between carrier recombination and intermolecular interactions in the layer. Efficient white devices using double platinum-complex layers show the external quantum efficiency of 10%, the Commission Internationale d’Enclairage coordinates of (0.42, 0.41), and color rendering index of 84 at 1000 cd m−2.

Enhanced power conversion efficiency of p-i-n type organic solar cells by employing a p-layer of palladium phthalocyanine

We demonstrate an enhancement in the power conversion efficiency (PCE) of p-i-n type organic solar cells consisting of zinc phthalocyanine (ZnPc) and fullerene (C60) using a p-layer of palladium phthalocyanine (PdPc). Solar cells employing three different device structures such as ZnPc/ZnPc:C60/C60, PdPc/PdPc:C60/C60, and PdPc/ZnPc:C60/C60 with varying thickness of mixed interlayers were fabricated by thermal evaporation. The mixed i-layers were deposited by co-evaporation of MPc (M=Zn,Pd) and C60 by 1:1 ratio. PCE of 3.7% was obtained for optimized cells consisting of PdPc/ZnPc:C60/C60, while cells with device structure of ZnPc/ZnPc:C60/C60 showed PCE of 3.2%.

Polymer thin film transistor without surface pretreatment on silicon nitride gate dielectric

It is well known that surface modification of the gate dielectric in organic thin film transistors (TFTs) plays an important role in device performance, often giving rise to severalfold improvements in field-effect mobility. This paper reports on solution-processed polymer TFTs with mobilities comparable to high performance counterparts despite the absence of dielectric surface pretreatment. An effective mobility of 0.1cm2∕Vs was obtained with poly(2,5-bis(3-dodecylthiophene-2-yl)thieno[3,2-b]thiophene) transistors on silicon nitride gate dielectric. The results indicate that by judicious preparation of the device layers, one can mitigate the need for dielectric surface pretreatment, thereby reducing fabrication complexity without compromising TFT performance.

Short channel vertical transistors with excellent saturation characteristics

The use of a vertical thin film transistor (VTFT) topology in the flat panel active matrix array, opens up a plethora of new high performance applications. The VTFT is small in footprint by virtue of its stacked layer configuration, in which channel lengths can be conveniently scaled down to nanometer regime without having to resort to photolithography as would otherwise be needed when scaling lateral TFTs. More importantly, the VTFT is also fully compatible to the materials and processes used in flat panel technology, takes making it amenable to large area scaling.

CHAPTER 6:Reactive Inkjet Printing: From Oxidation of Conducting Polymers to Quantum Dots Synthesis

This chapter demonstrates the use of inkjet printing not only as a passive materials dispensing technique, but also as an active tool in materials fabrication. A survey of developments in this exciting area is discussed with examples showing the potential of RIJ printing in nanomaterials fabrication, the grey-scale sheet resistivity in conducting polymer of PEDOT : PSS, and the self-assembled synthesis of uniform size gold nanoparticles.