A new metallization technology for solar cells application

This Ph.D. thesis is focused on the development and optimization of front and rear side metallization of industrial silicon solar cells. The commonly adopted screen-printed silver metallization has several well-known issues, such as low contact resistance, moderate bulk conductivity and high cost. The approach of this work allows complete silver replacement, both on the front and the rear sides. The development of such a new technology is divided into several parts, each resulting in appropriate feedback in terms of solar cell operation parameters. A detailed investigation of the aluminum-silicon interdiffusion that occurs during the firing process of screen-printed aluminum layer usually deposited onto the rear of solar cells is reported. This process is very important because it affects solar cell operation and performance through back-surface field passivation. In this study different screen-printing aluminum pastes, differing one from each other in aluminum particle dimensions and glass frit composition, are evaluated in terms of their bulk resistivity, contact resistance to silicon, back surface field depth and solar cell performance. Finally, this study allowed to reveal certain dependences between pastes parameters and their effect on solar cells and to develop useful recommendations for better solar cell performance. In this work, a new metallization technology is based on an electroplating technique, which for a real industrial application, however, has some critical issues as throughput, floor space, quantity of liquid to manage and the necessity to use some masking technique, such as photolithography. These issues are strongly influencing the metallization technology cost, making it not economically convenient respect silver screen-printing technology. For this purpose, the proposed metallization technique is based on a novel dynamic liquid drop/meniscus (DLD/DLM) technique able to solve both issues. In this work DLD/DLM technique is studied for possible application in a new rear side metallization technology for solar cells, allowing localized formation of solder pads without any use of photolithography, limiting the cost of the process mainly to the cost of materials, such as nickel and tin, which are significantly cheaper than a silver counterpart that is currently adopted by the industry. The cost reduction is not a single advantage of the proposed technology. An efficiency improvement of up to 0.5 %abs is obtained due to a better back-surface field conditions. The development of a new front side metallization is based on a new approach which introduces a layer of mesoporous silicon helpful for further creation of nickel-copper electrical contacts to the emitter region of a solar cell. Process conditions of mesoporous silicon formation and further electroplating steps are studied and optimized in terms of contact resistance and adhesion of such a contacts, in order to guarantee a beneficial influence for solar cells fabricated with the new metallization approach. As for combination of both front and rear side metallization technologies, together, they result in complete silver removal from a metallization technology of a solar cell with a feasible efficiency enhancement of up to 1 %abs

Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets

This document is the Technical Design Report covering the two large spectrometer magnets of the PANDA detector set-up. It shows the conceptual design of the magnets and their anticipated performance. It precedes the tender and procurement of the magnets and, hence, is subject to possible modifications arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski, Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy), Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy

Device physics and failure mechanisms of deep submicron gate GaN HEMTs for microwave and millimeter-wave applications

openThis thesis presents the findings of a comprehensive characterization study on GaN-based, gate-scaled HEMTs (with Lg < 0.15 µm) for RF applications. The investigation considers performance, stability, and reliability aspects. Specifically, static and dynamic measurements were conducted for the devices under test to assess the influence of short-channel effects and deep-level traps on their characteristics. This involved double-pulse measurements both in OFF and semi-ON state stress and transient measurements. The observed results are compared with those reported in the literature to determine the nature and location of traps responsible for performance variations. In the end stress test were performed to investigate the reliability of the devices. This research contributes to a deeper understanding of the underlying mechanisms and provides valuable insights for the optimization of future GaN-based device designs.This thesis presents the findings of a comprehensive characterization study on GaN-based, gate-scaled HEMTs (with Lg < 0.15 µm) for RF applications. The investigation considers performance, stability, and reliability aspects. Specifically, static and dynamic measurements were conducted for the devices under test to assess the influence of short-channel effects and deep-level traps on their characteristics. This involved double-pulse measurements both in OFF and semi-ON state stress and transient measurements. The observed results are compared with those reported in the literature to determine the nature and location of traps responsible for performance variations. In the end stress test were performed to investigate the reliability of the devices. This research contributes to a deeper understanding of the underlying mechanisms and provides valuable insights for the optimization of future GaN-based device designs