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TY  - THES
AU  - Misic, Boris
TI  - Analysis and simulation of macroscopic defects in Cu(In,Ga)Se<sub>2</sub> photovoltaic thin film modules
PB  - RWTH Aachen
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2016-01132
SP  - 1 Online-Ressource (iv, 147 Seiten) : Illustrationen, Diagramme
PY  - 2015
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2016
N1  - Dissertation, RWTH Aachen, 2015
AB  - The present work deals with production induced defects in CIGS thin film modules which can deteriorate the electrical performance of the module. The motivation of this work is to both find ways how these defects can be diagnosed, e.g. in a quality control in the production site, and to gain a better understanding of the actual defect influence on the voltage and current in the surrounding of the defect. Thus, I investigate the use of electroluminescence and thermography as diagnostic tools to detect and identify common defects occurring in CIGS production. I begin this work with a study of the CIGS production process and list potential defect origins for relevant production steps. In order to allow an experimental investigation of defects, I intentionally implement them into CIGS photovoltaic modules in a real CIGS production site environment. The defect implementation includes e.g. interrupted P1, P2, and P3 scribing lines for the monolithic series connection, as they can be caused by faulty scribing tools, and changes in the normal CIGS layer structure, as they can be caused by local contamination. Furthermore, I vary the geometry of the implemented defects. I characterise the implemented defects with microscope, electroluminescence (EL), and dark lock-in thermography (DLIT) measurements. EL and DLIT are chosen as they are spatially resolved measurements and therefore allow a comparatively fast investigation of a complete module. In addition to the defect measurements, I implement a software that is based on the principle of network simulation model and allows to model and simulate the implemented defect types in a CIGS module. The software models the CIGS module with a network, that consists of equivalent circuits of a solar cell and resistances, and translates the network into a non-linear system of equations that are solved. Finally, I investigate methods to repair an incomplete insulation of the Mo back contacts of two neighbouring cells. The measurements on defects yield that P1, P2, and P3 scribing defects have characteristic EL and DLIT patterns. I show that the scribing defects can be reliably identified by these patterns if the length of the scribing line interruptions is sufficiently resolved in the EL and DLIT images. The explanation of the characteristic El and DLIT patterns of scribing defects is facilitated by the simulation software that yields the voltage distribution, which can explain the El images, and the current flow, which can explain the DLIT images. With regard to the simulation software itself, I present an alternative solving approach for the non-linear system of equations, that differs from the standard Newton-Raphson procedure and allows a scaling behaviour of the simulation duration with the number of equations close to the linear optimum. Moreover, EL measurements of point defects with implemented abnormal layer sequences show that the i-ZnO/CdS buffer layer combination has a shunt mitigating effect. From comparison of various point defect types I conclude that the CdS has during chemical bath deposition a surface smoothing effect and fills up cavities and holes in the CIGS absorber. I suggest that this surface smoothing allows the sputtered i-ZnO to form a uniform and unbroken layer, and thus prevent shunting contact between the front and back electrode. In contrast, when I remove the CdS layer locally, the point defects show strong shunting in EL and DLIT measurements if the defect implementation has caused sharp edges or flakes at the Mo or CIGS layer. Furthermore, Cu-rich debris is a potential contamination during CIGS co-evaporation, where it can fall down from the Cu evaporation source onto the module. For Cu-rich debris I find that its position within the cell determines whether it can be reliably identified by EL and DLIT measurements. Cu-rich debris on the P1 line evokes among all defects a unique EL brightness pattern, which I explain by the simulation software as an overlay of a P1 defect with two shunting defects, one located in each of the neighbouring cells. Eventually, I develop two repair processes for defective Mo back contact insulation (P1 line). The first process is a thermal repair which uses thermally induced mechanical stress to create insulating fractures at the defect position. The second process is an electrical repair, where an applied current melts and evaporates remaining conductive Mo at the defect position, which finally results in an insulation, too. To draw a conclusion, the present work contributes to the understanding and diagnostics of production induced defects in Cu(In,Ga)Se<sub>2</sub> photovoltaic thin film modules, and in case of the P1 scribing defects even shows ways how they can be repaired.
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/568190
ER  -