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@INPROCEEDINGS{Hoffmann:172731,
      author       = {Hoffmann, Andre and Bittkau, Karsten and Zhang, Chao and
                      Merdzhanova, Tsvetelina and Rau, Uwe},
      title        = {{C}oupling {I}ncident {L}ight to {G}uided {M}odes in
                      {T}hin-{F}ilm {T}andem {S}olar {C}ells with {I}ntermediate
                      {R}eflector},
      reportid     = {FZJ-2014-06175},
      year         = {2014},
      abstract     = {In thin-film silicon tandem solar cells, hydrogenated
                      amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon
                      solar cells are connected in series. Due to inherent
                      material properties, the thickness of the a-Si:H top cell
                      has to be small. Different light management concepts are
                      applied to increase the top cell photocurrent generation.
                      Typically, textured interfaces as well as intermediate
                      reflectors (IRs) between top and bottom cell are
                      incorporated into the device structure. The design and
                      optimization of the device structure with IR on textured
                      substrates is often done by rigorous optical simulations
                      assuming large calculation domains.We will show in our
                      contribution that such optical simulations provide much more
                      information about the physical mechanism of light trapping
                      inside the tandem solar cells. In particular, we investigate
                      the light coupling to guided optical modes in the a-Si:H top
                      cell by the interplay between the textured interfaces and
                      the chosen type of IR. This study is done by Fourier
                      analysis of the local light intensity distribution inside
                      the absorber layers. This analysis provides information
                      about light intensity as a function of planar wave vector.
                      Guided modes are characterized by their large planar wave
                      vector which forbids light propagation in air.The amount of
                      light intensity in guided modes inside the a-Si:H absorber
                      layer is correlated to the experimentally determined
                      external quantum efficiency in the top cell for different
                      types of IR and different front side textures. Those results
                      show the importance of an efficient light coupling to guided
                      modes in order to achieve high efficiency thin-film solar
                      cells.},
      month         = {Jun},
      date          = {2014-06-08},
      organization  = {40th IEEE Photovoltaic Specialist
                       Conference, Denver, CO (USA), 8 Jun
                       2014 - 13 Jun 2014},
      subtyp        = {Invited},
      cin          = {IEK-5},
      cid          = {I:(DE-Juel1)IEK-5-20101013},
      pnm          = {111 - Thin Film Photovoltaics (POF2-111) / HITEC -
                      Helmholtz Interdisciplinary Doctoral Training in Energy and
                      Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF2-111 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/172731},
}