Page 25

EETE JAN 2016

photovoltaics Nanostructured germanium for custom photovoltaics By Paul Buckley Researchers at the Technical University of Munich (TUM) and the Ludwig Maximillians University of Munich (LMU) have discovered a procedure using nanostructured germanium to produce thin robust and porous semiconductor layers for portable photovoltaics and battery electrodes. The material is ideal for use in small, light-weight, flexible solar cells or electrodes that improve the performance of rechargeable batteries. By integrating suitable organic polymers into the pores of the material, the scientists can custom tailor the electrical properties of the ensuing hybrid material. The design not only saves space, it also creates large interface surfaces that improve overall effectiveness. “You can imagine our raw material as a porous scaffold with a structure akin to a honeycomb. The walls comprise inorganic, semiconducting germanium, which can produce and store electric charges. Since the honeycomb walls are extremely thin, charges can flow along short paths,” explained Professor Thomas Fässler, chair of Inorganic Chemistry with a Focus on Novel Materials at TU Munich. To transform brittle, hard germanium into a flexible and porous layer the researchers had to apply a few tricks. Traditionally, etching processes are used to structure the surface of germanium. However, the top-down approach is difficult to control on an atomic level. The new procedure solves the problem. Together with his team, Fässler established a synthesis methodology to fabricate the desired structures very precisely and reproducibly. The raw material is germanium with atoms arranged in clusters of nine. Since these clusters are electrically charged, they repel each other as long as they are dissolved. Netting only takes place when the solvent is evaporated. Netting can be easily achieved by applying heat of 500°C or it can be chemically induced, by adding germanium chloride, for example. By using other chlorides like phosphorous chloride the germanium structures can be easily doped. This allows the researchers to directly adjust the properties of the resulting nanomaterials in a targeted manner. To give the germanium clusters the desired porous structure, the LMU researcher Dr. Dina Fattakhova-Rohlfing has developed a methodology to enable nanostructuring: tiny polymer beads form three-dimensional templates in an initial step. In the next step, the germanium-cluster solution fills the gaps between the beads. As soon as stable germanium networks have formed on the surface of the tiny beads, the templates are removed by applying heat. What remains is the highly porous nanofilm. The deployed polymer beads have a diameter of 50 to 200 nanometers and form an opal structure. The germanium scaffold that emerges on the surface acts as a negative mold – an inverse opal structure is formed which is why the nanolayers shimmer like an opal. “The porous germanium alone has unique optical and electrical properties that many energy relevant applications can profit from,” said LMU researcher Dr. Dina Fattakhova-Rohlfing, who, in collaboration with Fässler, developed the material. “Beyond that, we can fill the pores with a wide variety of functional materials, thereby creating a broad range of novel hybrid materials.” “When combined with polymers, porous germanium structures are suitable for the development of a new generation of stable, extremely light-weight and flexible solar cells that can charge mobile phones, cameras and laptops while on the road,” explained the physicist Peter Müller-Buschbaum, professor of functional materials at TU Munich. Flexible Bluetooth LE beacon sticker operates on photovoltaics By Julien Happich Fujitsu has unveiled a battery-less flexible Bluetooth LE-enabled geolocation beacon, measuring 108x26mm and only 3mm thick. The ready-to-stick beacon features a flexible photovoltaic panel that can generate power from sunlight, fluorescent light, and LED light. Fujitsu claims the prototype beacon has obtained the world’s first ucode tag certification for a beacon from the TRON Forum. It can be easily mass produced and is capable of transmitting a globally unique ID for more reliable location information services. Location codes are sent inside packets. Bluetooth-enabled devices receiving the code send enquiries to a server that manages the location codes thus allowing them to receive locational information. Thanks to this certification, the beacons can be linked with all types of map data that form the foundation for delivering services. The beacon was produced printing a circuit wiring pattern (with a conductive paste) to which electric components were mounted and connected with conductive adhesive. The paste and adhesive materials were selected to enable mass-production with existing production facilities. Some application scenarios for these low-cost battery-less Bluetooth LE beacons include location information services such as guidance support for the visually impaired within stations or around town, or efficient seat management for stadiums. The conformable nature of the tags makes them suitable to be affixed to clothes and shoes, extending use cases to usercentric applications. www.electronics-eetimes.com Electronic Engineering Times Europe January 2016 25


EETE JAN 2016
To see the actual publication please follow the link above