In this work, we report the synthesis of all-conjugated donor-acceptor block copolymers via a externally initiated Kumada catalyst-transfer polycondensation (KCTP) method. In the first step, electron acceptor blocks, poly(naphthalene diimide)s (PNDIs), were prepared via the Stille coupling polycondensation. Then, P3HT blocks were polymerized by KCTP initiated by Ni(COD)2 activated PNDI complexes. Therefore, a series of ABA (P3HTs were initiated from both ends of PNDI) and AB-type (P3HT was initiated from one end of PNDI) block copolymers were successfully synthesized. Before fabrication of all-polymer solar cells, the morphologies and crystalline behaviors of the block copolymers were extensively investigated as a function of thermal annealing and the main chain composition of PNDI block. As a control, the crystalline behaviors of the physical blends of P3HT and PNDIs were also reported. Finally, all-polymer solar cells were fabricated by using the block copolymers as the single active component or as surfactants. A PCE of 0.11 % with Voc=0.46 V, Jsc=0.50 mA/cm2, and FF=0.46 was recorded by using the donor-acceptor all-conjugated block copolymer as the single active component.

Inkjet printing is a well-accepted deposition technology for functional materials in the area of printed electronics. It allows the precise deposition of patterned functional layers on both, rigid and flexible substrates. Furthermore, inkjet printing is considered as up-scalable technology towards industrial applications. Many electronic devices manufactured with inkjet printing have been reported in the recent years. Some of the evident examples are capacitors, resistors, organic thin film transistors and rectifying Schottky diodes. [1, 2, 3] In this paper we report on the manufacturing of an inkjet-printed metal-insulator-semiconductor (MIS) diode on flexible plastic substrate. The structure is comprised of an insulating and a polymeric semiconducting layer sandwiched between two silver electrodes. The current vs. voltage characteristics are rectifying with rectification ratio up to 100 at |4 V|. Furthermore, they can carry high current densities (up to mA/cm2) and have a low capacitance which makes them attractive for high frequency rectifying circuits. They are also an ideal candidate to replace conventional Schottky diodes for which the fabrication remains a challenge. This is because inkjet printing of Schottky diodes require additional processing steps such as intense pulsed light sintering (IPL sintering) [4] or post-treatments at high temperatures. The deposition of two different metal layers using inkjet printing e.g. Cu or Al with Ag is possible. However, the mentioned post treatment technologies might be incompatible with the already existing layer stack– e.g. it could degrade the organic semiconductor or can damage insulator which in this case is present in the MIS diode architecture.

Analysis of surface images indicates that GaAs(001) surfaces can be patterned directly by applying interferential irradiation of high power laser pulses on the surface. Atomic force microscopy (AFM) was used to image the patterned surfaces. The patterned surface shows strips that have the same separation as the interference period used. The direct laser patterning leaves the surface with trenches. The depth of trenches increases with the laser intensity and can be varied from few nanometers to a few hundred nanometers. At low laser intensity, strip shaped mound appears at the both edges of a trench, leaving a plateau area between them. The width of mound increases with the laser intensity, making the plateau area smaller. With a higher laser intensity, the plateau area disappear as the mounds merge together, forming a single strip between the adjacent trenches. AFM images from the patterned surface indicate that direct laser patterning can be used to fabricate nanostructures with a period smaller than that of the interference period as well as the wavelength of the laser used.

We report a low cost and high throughput electrochemical anodic oxidation method to enhance the metal-semiconductor contact between a silver electrode and an organic semiconductor in a rectifying diode application. The oxidized layer enhances the contact properties, leading to better device performance. Three different anodic oxide thicknesses were used in the study. Current-voltage and AC rectification measurements were used to characterize the printed devices. The DC output voltage of the half-wave rectifier increased consistently as a function of the oxide thickness. This procedure points toward a cost-effective way to optimize printed organic devices.

Organic thin-film transistors (OTFTs) are the most promising candidates for flexible electronics owing to their flexible structures, the simplicity of processing large-area devices, and excellent compatibility with flexible substrates. To date, many studies have been reported that have aimed at developing a wide range of plastic electronics such as flexible displays, sensors. In this paper, we discuss our recent work, focusing on OTFT arrays and their application to flexible display. An active-matrix (AM) backplane using a low-temperature cross-linkable olefin-type polymer as the gatedielectric and an air-stable DNTT as the organic semiconductor (OSC) was successfully fabricated on a plastic substrate. The short-channel TFT array exhibited a high hole mobility of over 0.5 cm2/Vs, a low subthreshold slope of 0.31, and excellent environmental and operational stability. A 5-inch flexible OLED display exhibited a high luminescence of over 300 cd/m2 by driving of the DNTT-based OTFTs. Solution-processed OTFTs are also attracting considerable attention owing to both their simple manufacturing process and excellent transistor performance. We present a simple patterning process for a solution-processable OSC that can be used to develop a high-mobility short-channel TFT array. The OSC film was directly patterned on the confined active channel region by a simple lamination coating technique and the resulting TFTs showed a high mobility of up to 1.3 cm2/Vs. In the final section, we report on eco-friendly paper-based organic TFT array. A transparent cellulose nanofibers paper was firstly applied to a flexible substrate for the TFT backplane. A solution-processed TFT on the transparent paper exhibited a high mobility exceeding 1 cm2/Vs, good air stability, and excellent mechanical stability.

Organic solar cells, comprised of P3HT-fullerene blends, have the potential for photovoltaic energy applications. However, there is limited understanding of the mechanical behavior of these devices, and how this behavior can be tailored for optimal organic solar cell performance and device reliability. Therefore, a recently developed computational approach that is based on a constitutive representation of semi-crystalline polymers and fullerenes is used to identify the dominant morphological and microstructural characteristics that would affect the mechanical behavior of the active layer. The predictions indicate that stress and dislocation-density accumulation in interfacial regions and tie molecules play a significant role on the overall behavior.

A Joule heating based self-alignment method for solution-processable insulator structures has been modeled for the passivation of metal grid lines, for example for organic light emitting diodes or photovoltaic cells. To minimize overhang of the passivation layer from line edges, we have studied the Joule heating approach using solution-processable, cross-linkable polymer insulator films. Finite element simulations were performed to investigate the heating of the sample using glass and poly(ethylene terephthalate) (PET) substrates. The sample was at room temperature and the current was selected to induce a temperature of 410 K at the conductor. It was found that the selection of substrate material is crucial for the localization of cross-linking. For a PET substrate, the temperature gradient at the edge of the conductor is approximately twice the gradient for glass. As a result, using a glass substrate demands high selectivity from the polymer cross-linking, thus making PET a more suitable substrate material for our application. A flexible PET substrate is, in addition, compatible with roll-to-roll mass-manufacturing processes.

Stretchable wires were printed on fabrics using an acrylic-based paste loaded with Ag flakes, and their fatigue properties examined. The electrical conductivity of the wires significantly decreased during a cyclic tensile test, because of a decrease in their elastic moduli (Mullins softening) as well as fatigue cracking. Because the electrical resistance and elastic moduli of the damaged samples were partially recovered by annealing at 100 °C, fatigue damage introduced to the wires was divided into reversible and irreversible components, where cracking is the irreversible damage. Although crack bridging by fibrils could occur during the fatigue test, no crack healing was observed during annealing. In contrast, fatigue damage from Mullins softening of the wires could be recovered during annealing. The recovery of electrical conductivity occurs mostly in the initial stage of rearrangement of polymer structure during annealing.