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@PHDTHESIS{Lambertz:190115,
      author       = {Lambertz, Andreas},
      title        = {{D}evelopment of {D}oped {M}icrocrystalline {S}ilicon
                      {O}xide andits {A}pplication to {T}hin-{F}ilm {S}ilicon
                      {S}olar {C}ells},
      school       = {University Utrecht},
      type         = {Dr.},
      address      = {Utrecht},
      publisher    = {University Utrecht},
      reportid     = {FZJ-2015-03055},
      pages        = {177},
      year         = {2015},
      note         = {University Utrecht, Diss., 2015},
      abstract     = {The aim of the present study is the development of doped
                      microcrystalline silicon oxide (µc‑SiOx:H) alloys and its
                      application in thin‑film silicon solar cells. The doped
                      µc‑SiOx:H material was prepared from carbon dioxide
                      (CO2), silane (SiH4), hydrogen (H2) gas mixtures using
                      plasma enhanced chemical vapour deposition (PECVD) with
                      process conditions which are fully compatible with the
                      overall solar cell manufacturing processes. Doping was
                      achieved by adding phosphine (PH3) or trimethyl boron
                      B(CH3)3 to the process gas. Particular focus in the material
                      development is to establish the relationship between the
                      deposition process parameters and the material properties of
                      doped µc‑SiOx:H such as optical band gap, refractive
                      index, conductivity, and crystalline volume fraction. To
                      understand the individual influences of the different
                      structural phases of the composite material µc‑SiOx:H the
                      link between the optoelectronic properties and the material
                      structure as well as the material composition was
                      investigated. It is shown that doped µc‑SiOx:H material
                      is a mixture of crystalline silicon nanoparticles (highly
                      crystalline µc‑Si:H) and amorphous silicon oxide
                      (a‑SiOx:H), where the a‑SiOx:H phase itself consists of
                      a‑SiO2 and a‑Si:H. This is advantageous since an oxygen
                      rich amorphous silicon phase (a‑SiOx:H) has a wide optical
                      band gap, allowing to reduce optical losses in the device,
                      while a volume fraction of the highly crystalline µc‑Si:H
                      phase above a value as low as $30\%$ already ensures
                      sufficiently high electrical conductivity to reduce
                      electrical losses. The optical properties such as optical
                      band gap and refractive index of the doped µc‑SiOx:H
                      films can be conveniently adjusted over a wide range by the
                      CO2/SiH4 gas flow ratio. The crystalline volume fraction at
                      a given CO2/SiH4 ratio can be increased by decreasing the
                      silane concentration SC = SiH4 / (SiH4 + H2). The ideal
                      preparation conditions to obtain optimum material were
                      identified and the resulting doped µc‑SiOx:H layers were
                      evaluated in single and tandem junction solar cells. To
                      establish a link between the µc‑SiOx:H material
                      properties and the solar cell performance the research
                      addresses the parasitic absorption of the doped layers and
                      the in‑coupling of light to reduce optical losses and gain
                      more photocurrent in the device. Additionally, the device
                      stability against light exposure was investigated for a
                      variety of absorber layer thicknesses. It was shown that in
                      a‑Si:H/µc‑Si:H tandem solar cells the thickness of the
                      absorber layer of the a‑Si:H top cell can be reduced,
                      without impairing device efficiency, by incorporation of
                      µc‑SiOx:H as intermediate reflector. Most importantly,
                      such thinner cells show improved stability yielding a
                      stabilized efficiency of $10.3\%$ for single junction solar
                      cells. It is concluded that doped µc‑SiOx:H can be
                      beneficially applied to thin‑film silicon solar cells,
                      reducing the parasitic absorption, improving
                      light‑incoupling, and acting as an intermediate reflector
                      thanks to the low refractive index and the wide band gap at
                      a sufficiently high conductivity.},
      keywords     = {Dissertation (GND)},
      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},
      url          = {https://juser.fz-juelich.de/record/190115},
}