Mike Hambsch

Complementary Ring Oscillator Exclusively Prepared by Means of Gravure and Flexographic Printing

A complementary ring oscillator has been prepared using exclusively fast and continuous rotary printing methods, namely, gravure and flexographic printing, so that all layers were additively deposited and no additional patterning nor interconnecting step whatsoever was involved. This became possible due to the availability of a printable air-stable n-type organic semiconductor, i.e., a small molecule perylene derivative. Using the same dielectric for both types of transistors, the characteristics of the n-type transistors are reasonably similar to the ones of the p-type transistors, which are based on the previously used organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene. The printed circuits are robust against variations of individual transistor parameters and significantly outperform comparable unipolar circuits in terms of all relevant properties. The superior performance can be attributed to complementary circuitry, the advantage of which is thereby demonstrated for the case of printed circuits.

Spectral Dependence of the Internal Quantum Efficiency of Organic Solar Cells: Effect of Charge Generation Pathways

The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:PC70BM and PCPDTBT:PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes.

Efficient, monolithic large area organohalide perovskite solar cells

Solar cells based on organohalide perovskites (PSCs) have made rapid progress in recent years and are a promising emerging technology. An important next evolutionary step for PSCs is their up-scaling to commercially relevant dimensions. The main challenges in scaling PSCs to be compatible with current c-Si cells are related to the limited conductivity of the transparent electrode, and the processing of a uniform and defect-free organohalide perovskite layer over large areas. In this work we present a generic and simple approach to realizing efficient solution-processed, monolithic solar cells based on methylammonium lead iodide (CH3NH3PbI3). Our devices have an aperture area of 25 cm2 without relying on an interconnected strip design, therefore reducing the complexity of the fabrication process and enhancing compatibility with the c-Si cell geometry. We utilize simple aluminum grid lines to increase the conductivity of the transparent electrode. These grid lines were exposed to an UV-ozone plasma to grow a thin aluminum oxide layer. This dramatically improves the wetting and film forming of the organohalide perovskite junction on top of the lines, reducing the probability of short circuits between the grid and the top electrode. The best devices employing these modified grids achieved power conversion efficiencies of up to 6.8%.

Labeling the World: Tagging Mass Products with Printing Processes

There are many motivations for labeling items to link the real and the virtual world, including supply chain management; fabrication control process efficiency improvement; complete product traceability; product liability; quality guarantees; and recycling products correctly. The article discusses some of the automatic identification (auto-id) technologies that includes printed ID codes, 1D/2D bar codes, RFID, magnetic stripe and smart card(chip) to label various products. Labeling technologies for industrial applications must meet several demands, requiring highly efficient mass production processes for tagging technologies and readers.

Design of Printed Circuits – New Requirements and New Opportunities (Entwurf gedruckter Schaltungen – Neue Anforderungen und neue Möglichkeiten)

Summary Design of printed circuits becomes an increasingly important research field as applications of this emerging technology come into sight. However, significant demand of research and development exists because new technology-related requirements apply as well as new opportunities evolve. We illustrate recent progress and future developments in terms of device modelling, circuit design and simulation as well as circuitry concepts using practical examples. Zusammenfassung Das Design gedruckter Schaltungen wird zu einem zunehmend wichtigen Forschungsfeld in dem Maße, in dem Anwendungen der gedruckten Elektronik entstehen. Jedoch besteht noch erheblicher Forschungs- und Entwicklungsbedarf, da sich sowohl neue Anforderungen als auch neue Möglichkeiten aus der neuen Technologie ergeben. Wir illustrieren jüngste Fortschritte und zukünftige Entwicklungen anhand praktischer Beispiele.

Large area monolithic organic solar cells

Although efficiencies of > 10% have recently been achieved in laboratory-scale organic solar cells, these competitive performance figures are yet to be translated to large active areas and geometries relevant for viable manufacturing. One of the factors hindering scale-up is a lack of knowledge of device physics at the sub-module level, particularly cell architecture, electrode geometry and current collection pathways. A more in depth understanding of how photocurrent and photovoltage extraction can be optimised over large active areas is urgently needed. Another key factor suppressing conversion efficiencies in large area cells is the relatively high sheet resistance of the transparent conducting anode - typically indium tin oxide. Hence, to replace ITO with alternative transparent conducting anodes is also a high priority on the pathway to viable module-level organic solar cells. In our paper we will focus on large area devices relevant to sub-module scales – 5 cm × 5 cm monolithic geometry. We have applied a range of experimental techniques to create a more comprehensive understanding of the true device physics that could help make large area, monolithic organic solar cells more viable. By employing this knowledge, a novel transparent anode consisting of molybdenum oxide (MoOx) and silver (Ag) is developed to replace ITO and PEDOT-free large area solar cell sub-modules, acting as both a transparent window and hole-collecting electrode. The proposed architecture and anode materials are well suited to high throughput, low cost all-solution processing.