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@PHDTHESIS{Siegloch:200910,
      author       = {Siegloch, Max},
      title        = {{F}ailure {A}nalysis of {T}hin {F}ilm {S}olar {M}odules
                      using {L}ock-in {T}hermography},
      volume       = {258},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2015-03263},
      isbn         = {978-3-95806-047-0},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {XIII, 131 S.},
      year         = {2015},
      note         = {RWTH Aachen, Diss., 2014},
      abstract     = {Lock-in thermography (LIT) is an imaging method that
                      depicts radiated heat andits diffusion in manifold samples.
                      LIT offers versatile possibilities for the characterization
                      of solar cells and modules since the radiated heat is
                      proportional to the dissipation of electrical power. Up to
                      now, the quantitative correlation of detected heat and
                      dissipated electrical power has been known for silicon solar
                      cells only. For many other types of solar cells and modules
                      – especially thin film solar cells – LIT has been used
                      as aqualitative measurement tool for depicting the location
                      of defects, for example. Thus, the potential of LIT in terms
                      of the calculation of power generation and dissipation in
                      thin film solar cells has not been exploited. This
                      visualization and calculation of power flows leads to a
                      better understanding of the influences of defects on the
                      efficiency of solar modules. Furthermore, it enables the
                      evaluation of potential improvements, which results in solar
                      modules with higher efficiencies, produced to lower costs.
                      In order to interpret LIT signals accurately, the lock-in
                      algorithm and particularly its limits have to be understood.
                      The present thesis shows the evaluation of the lock-in
                      algorithm and its algebraic complex result with simulations.
                      It is found that the weak points of the lock-in algorithm
                      lie in the sampling of the acquired heat signal. Sampling
                      moments that are not uniformly distributed in a lock-in
                      period produce unreliable results. A low sampling at high
                      measurement frequencies shows significant deviations
                      distorting the LIT result. The findings allow for the
                      development of user-friendly LIT systems that automatically
                      avoid sampling errors and produce reliable LIT results. The
                      comprehension of LIT measurements of thin film solar cells
                      needs a theoretical thermal model for the solar cells that
                      can be used to solve the differential heat diffusion
                      equation. The solution describes the surface temperature
                      distribution that is acquired in LIT measurements. By the
                      evaluation of the frequency response of a point heat source
                      in a thin film solar cell, a simple thermal model
                      representing a solid body is found to adequately reproduce
                      LIT measurements. LIT investigations in the scale of the
                      thermal diffusion length are hampered by the diffusion of
                      heat that leads to a blurring of heat sources. With the
                      description of the thermal model and a Fourier transform
                      technique, it is possible to successfully deconvolute the
                      heat generating sources from the heat diffusion, meaning the
                      removal of the thermal blurring. This leads to the unimpeded
                      visualization of the dissipated power of small heat sources
                      such as shunts or the series interconnection of cells in a
                      thin film solar module [...]},
      cin          = {IEK-5},
      cid          = {I:(DE-Juel1)IEK-5-20101013},
      pnm          = {121 - Solar cells of the next generation (POF3-121)},
      pid          = {G:(DE-HGF)POF3-121},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/200910},
}