Die Diplomarbeit wurde von mir in englischer Sprache verfaßt, da die Arbeit im Zuge eines LEONARDO DA VINCI Traineeship Programmes am CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Technológicas, Madrid, Spain) durchgeführt wurde und auch von der politechnischen Universität (Institut für Solarenergie) betreut wurde.
Diese Diplomarbeit beschreibt das Design und die Montage eines experimentellen Systems zur Charakterisierung und Strukturierung von Solarzellen und anderen Photovoltaikbauteilen.
Das designte Lasersystem kombiniert ein Werkzeug zur Strukturierung von Dünnschichtsolarzellen mit einer Charakterisierungseinheit (,,Photoresponse Mapping"-Technik)
Das Charakterisierungsteilsystem arbeitet nach dem LBIC-Prinzip (laser beam induced currents). Das System zur Strukturierung von dünnen Schichten arbeitet mit einem NdYAG Lasercutter, der gewöhnlicherweise auch zu IC-Reparaturen verwendet wird.
Ziel dieser Diplomarbeit ist der ,,Set-Up" des Doppel-Lasersystems, welches die Anstrengungen in der Forschungsarbeit der Entwicklung neuer Materialen für Solarzellen und deren Charakterisierung unterstützen soll.
Benutzt man Standardmethoden (I-V Kurven, Spektrale Empfindlichkeit), um optische-elektrische Eigenschaften einer Solarzelle zu messen, erhält man ein quantitatives Ergebnis, das einem keine Rückschlüsse auf lokale Defekte innerhalb der Probe erlaubt. Kleine Defekte innerhalb eines photovoltaischen Bauelementes können die Leistung dieses Bauteils negativ beeinflussen. Der Vorteil der ,,Photoresponse-Mapping" -Technik liegt in der Möglichkeit, lokale Messungen am Bauteil vorzunehmen.
"Laser-Scribing" ist eine Schlüsseltechnologie im Herstellungsprozess von amorphen Silizium-Solarzellen. Diese Technologie deckt bereits 50% des Fabrikationsprozesses ab und hat die konventionelle Methode mittels Photolithografie bereits komplett ersetzt. [1]
Der erste Teil dieser Arbeit soll in das Thema einführen und erläutert die vorgegebene Aufgabenstellung.
Table of Contents
1 Introduction
2 Physical principles of silicon solar cell characterization
2.1 Conventional structure of a silicon solar cell
2.2 Operating principles of silicon solar cells
2.3 Semiconductors under illumination
2.3.1 Absorption of light
2.3.2 Photoconductivity
2.3.3 Photocurrent generation in p-n junction solar cells
2.3.3 Quantum efficiency
2.4 Saturation and recombination current
2.5 Equivalent circuit of a solar cell
2.6 Fundamental parameter for solar cell characterization
3 Experimental issues - Hardware
3.1 Global system description
3.2 Laser characterization system
3.2.1 He-Ne laser
3.2.2 Beam intensity monitoring
3.2.3 Electrical measurements
3.3 Laser-scribing system
3.3.1 Nd-YAG laser
3.3.2 Optical system
3.4 Position control
4 Experimental issues - Software
4.1 Main program
4.2 Low level programming of microcontrollers
4.3 RS-232 programming of the Nd-YAG laser cutter
4.4 GPIB programming of digital multimeters
5 Cell characterization - results and discussion
5.1 Basic principles of photoresponse mapping
5.2 Calculations of expected photocurrents
5.3 I/V characteristics
5.4 Spectral response
5.5 Photoresponse mapping
6 Prospective
6.1 Optical system for improved resolution
6.2 Transmittance maps
6.3 UV laser beam for selective scribing
6.4 Selective wavelengths for photoresponse mapping
6.5 Lock-in-technique
7 Conclusions
Objectives and Topics
The primary objective of this thesis is the design and implementation of a double laser facility intended to support research in the development and characterization of photovoltaic devices. The work focuses on integrating a laser-based characterization system and a laser-scribing tool on a unified platform to enable detailed local analysis and material processing.
- Setup and automation of a multi-laser experimental facility.
- Implementation of photoresponse mapping (LBIC) for local characterization.
- Development of software interfaces (GPIB, RS-232) for hardware control.
- Experimental validation using monocrystalline silicon solar cells.
- Exploration of advanced techniques including laser scribing and lock-in amplification.
Excerpt from the Book
2.1 Conventional structure of a silicon solar cell [19]
Solar cells require a particular p-n junction design, which is depicted in figure 2.1 as a schematic representation of a conventional silicon solar cell. It consists of a shallow junction built near the front surface, a front ohmic contact, usually in the form of stripes and fingers, and a back ohmic contact that covers the entire back surface. Usually, an antireflective coating is applied to the illuminated side to increase the fraction of incident light not reflected.
An electrical field is created between two regions of a crystalline semiconductor having opposed types of conductivity. One of these regions (n-type) is doped with phosphorus, which has five valence electrons. This region has a much higher concentration of electrons than holes. The other region (p-type) is doped with boron, having three valence electrons. Here the concentration of holes is greater.
Chapter Summaries
1 Introduction: Provides an overview of the global energy landscape and establishes the motivation for developing specialized laser-based characterization tools for thin-film photovoltaic devices.
2 Physical principles of silicon solar cell characterization: Details the theoretical foundations of photovoltaic energy conversion, including carrier generation, current-voltage characteristics, and the physical parameters governing solar cell performance.
3 Experimental issues - Hardware: Describes the design and construction of the experimental facility, focusing on the mechanical structure, the dual-laser setup, and the monitoring instrumentation.
4 Experimental issues - Software: Explains the software architecture used to control the hardware components, including low-level programming for microcontrollers and interface communication.
5 Cell characterization - results and discussion: Presents the experimental data obtained, including I/V curves, spectral response measurements, and photoresponse maps of monocrystalline silicon cells.
6 Prospective: Discusses potential future enhancements to the system, such as improved resolution for thin-film analysis and additional characterization techniques.
7 Conclusions: Summarizes the achievements of the diploma thesis, confirming the reliability of the system and its potential for ongoing research at CIEMAT.
Keywords
Photovoltaics, Solar Cells, Laser Characterization, Photoresponse Mapping, LBIC, Laser Scribing, Silicon, Electrical Measurement, GPIB, TurboBasic, Spectral Response, Semiconductor, Thin-film, Nd-YAG Laser, He-Ne Laser.
Frequently Asked Questions
What is the core purpose of this thesis?
The thesis describes the design, construction, and automation of a dual-laser laboratory facility used for both characterizing photovoltaic devices and performing thin-film laser scribing.
What research field is the work associated with?
The work is situated in the field of photovoltaic device development, specifically focusing on the preparation and characterization of solar cell materials at the CIEMAT research center.
What is the primary scientific method employed?
The work utilizes the LBIC (Laser Beam Induced Current) principle to create photoresponse maps, allowing for the detection of local defects and surface heterogeneity in solar cells.
Which interfaces are used for system automation?
The system uses GPIB for digital multimeter data acquisition, RS-232 for remote laser control, and a custom I/O-PC-card for controlling the micropositioning system.
How is the spectral response calculated?
The author relates relative spectral response measurements to absolute values by using calibrated standards and integrating current-voltage data obtained under standard test conditions.
What are the major hardware components of the setup?
The setup consists of an He-Ne laser for characterization, an Nd-YAG laser for scribing, a precision x-y micropositioning stage, and various electrical measurement instruments like digital multimeters.
What is the significance of the "Laser Scribing" technology mentioned?
It is a key manufacturing process for amorphous silicon integrated modules that has replaced conventional photolithography methods in roughly 50% of production steps.
How does the system handle signal noise during measurements?
The author discusses the implementation of lock-in-amplifying techniques using chopper wheels to isolate photocurrents from background noise.
- Quote paper
- Günther Krauß (Author), 1998, Setup of a laser facility for characterization and treatment of photovoltaic devices, Munich, GRIN Verlag, https://www.grin.com/document/78
