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@PHDTHESIS{Michard:202665,
      author       = {Michard, Stephan},
      title        = {{R}elation between growth rate, material quality, and
                      device grade condition for intrinsic microcrystalline
                      silicon: {F}rom layer investigation to the application to
                      thin-film tandem solar cells},
      volume       = {259},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2015-04855},
      isbn         = {978-3-95806-048-7},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {vi, 184 S.},
      year         = {2015},
      note         = {RWTH Aachen, Diss., 2015},
      abstract     = {Investigations on the relation between the growth rate,
                      material quality, and device grade condition for intrinsic
                      microcrystalline silicon is presented in this thesis.
                      Hydrogenated microcrystalline silicon deposited by plasma
                      enhanced chemical vapor deposition is a widely used material
                      for the absorber layer of the bottom solar cell in silicon
                      thin-film tandem solar cells. Microcrystalline silicon is a
                      mixed phase material consisting of crystal grains, amorphous
                      phase, grain boundaries, and voids. To guarantee sufficient
                      light absorption absorber layer thicknesses of more than 1
                      μm to 3 μm are required for the absorber layer of the
                      bottom solar cell. The increase of the deposition rate for
                      intrinsic microcrystalline silicon is one essential point
                      for cost reduction in the mass production of thin-film solar
                      cells. The combination of excitation frequencies in the very
                      high frequency range altogether with the application of the
                      high pressure depletion regime enabled to reach deposition
                      rates up to 2.8 nm/s for optimal phase mixture material,
                      which is until today considered to be of device grade
                      quality. According to conductivity, electron spin resonance,
                      and Raman measurements the quality properties of the
                      material deposited at high deposition rates is similar to
                      reference material deposited at low deposition rates.
                      Nevertheless this material showed to be susceptible to
                      oxygen uptake, which was shown to occur along the grain
                      boundaries. Furthermore a decrease in crystal grain size
                      with a simultaneous increase in tensile stress was observed
                      by X-ray diffraction and Raman measurements, respectively.
                      Thickness dependent Raman measurements showed a decrease in
                      incubation layer thickness with increasing deposition rate.
                      The investigations performed by X-ray diffraction and
                      thickness dependent Raman measurements were supported by
                      investigations performed with transmission electron
                      microscopy. With this work it was found that the present
                      criteria to classify microcrystalline silicon being of
                      device grade quality should be extended for deposition rates
                      beyond 1nm/s. In addition to the measures describing the
                      optimal phase mixture quantities describing the materials
                      microstructure, the tendency for oxygen uptake, and the
                      mechanical stress should be taken into account. The device
                      performance of microcrystalline thin-film single junction as
                      well as of amorphous / microcrystalline thin-film tandem
                      solar was observed to decrease with increasing deposition
                      rate. The decrease in device performance was shown to be
                      either related to inferior material quality of the
                      microcrystalline absorber layer with increasing deposition
                      rate and to an impairment of the pi-interface of the
                      microcrystalline (sub) solar cell. Simulations on the impact
                      of ions in matter showed that a damage of the pi-interface
                      by ion bombardment is unlikely. As possible sources for the
                      impairment ofthe pi-interface a variation of the nucleation
                      conditions and structural inhomogeneities at the
                      substrate/film interface are discussed. Despite the decrease
                      in device performance of the amorphous / microcrystalline
                      thin-film tandem solar cells calculations showed that the
                      output of deposition systems in produced Watt per hour can
                      be increased by more than a factor of two. An increase in
                      system output leads to a decrease in costs per produced unit
                      and can lead to a decrease in initial investment costs.},
      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/202665},
}