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@PHDTHESIS{Schena:202779,
      author       = {Schena, Timo},
      title        = {{F}irst-{P}rinciples {S}tudy on {P}yrites and {M}arcasites
                      for {P}hotovoltaic {A}pplication},
      volume       = {254},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2015-04961},
      isbn         = {978-3-95806-041-8},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {206 S.},
      year         = {2015},
      note         = {RWTH Aachen, Diss., 2015},
      abstract     = {This thesis deals with first-principles calculations for
                      pyrite and marcasite compounds, with a particular focus on
                      their suitability for photovoltaic applications. Their
                      electronic structure and their optical properties are
                      thoroughly investigated within density-functional theory
                      (DFT) using various exchange-correlation functionals, among
                      them sophisticated hybrid functionals. To account for
                      electronic excitations the many-body perturbation theory in
                      the GW approximation has also been exploited. The
                      investigation of the electronic and optical properties of
                      iron pyrite (FeS$_{2}$) covers an essential part of this
                      thesis, since iron pyrite is reported to be a promising
                      material for photovoltaic applications due to its large
                      optical absorption, a suitable band gap and large
                      photocurrents. Furthermore, iron pyrite consists of abundant
                      elements, and thus would allow for a large-scale and
                      long-term utilization. However, iron pyrite solar cells
                      exhibit only an open-circuit voltage of merely 200 mV,
                      leading to a small conversion efficiency of 3\%, which
                      disqualifies iron pyrite for photovoltaic applications at
                      present. This thesis exposes that the question about the
                      size of the fundamental and optical band gap of iron pyrite,
                      both, theoretically and experimentally, might not be settled
                      yet. Low-intensity contributions in the optical absorption
                      might complicate the determination of the optical band gap,
                      and the GW results show that the fundamental band gap might
                      be much smaller than expected. Therefore, the small
                      fundamental band gap of pristine iron pyrite in the bulk
                      phase might be already responsible for the low open-circuit
                      voltage. Since interfaces and surfaces play an important
                      role for the photovoltaic performance, the electronic
                      structure of the most stable iron pyrite surfaces is also
                      discussed, revealing that surface states of Fe 3d character
                      might act as charge recombination centers. First attempts to
                      passivate these surface states indicate that heavier adatoms
                      are more suitable than light ad atoms. The application of
                      the GW approximation on iron pyrite yields an unconventional
                      reduction of the band gap compared to the “plain” DFT
                      results, whereas largely overestimated band gaps are
                      obtained using hybrid functionals. By extending the
                      calculations to other pyrite compounds (RuS$_{2}$,
                      OsS$_{2}$, NiP$_{2}$ and ZnS$_{2}$) and to the structurally
                      closely related marcasite compounds (FeS$_{2}$, FeSe$_{2}$
                      and FeTe$_{2}$), it is shown that the interplay of
                      transitions between $\textit{p}$ and $\textit{d}$ states and
                      the screening caused by the d states is responsible for this
                      peculiar behavior. Finally, a particular focus is set on
                      FeS$_{2}$ marcasite, which is reported to coexist with the
                      pyrite phase, but is presumed to degrade the photovoltaic
                      performance. However, the results in this thesis indicate
                      that iron marcasite might be better suited for photovoltaic
                      applications than iron pyrite.},
      cin          = {PGI-1 / IAS-1 / JARA-FIT},
      cid          = {I:(DE-Juel1)PGI-1-20110106 / I:(DE-Juel1)IAS-1-20090406 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {142 - Controlling Spin-Based Phenomena (POF3-142) / 143 -
                      Controlling Configuration-Based Phenomena (POF3-143)},
      pid          = {G:(DE-HGF)POF3-142 / G:(DE-HGF)POF3-143},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/202779},
}