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@ARTICLE{Xiao:878470,
      author       = {Xiao, Biao and Calado, Philip and MacKenzie, Roderick C. I.
                      and Kirchartz, Thomas and Yan, Jun and Nelson, Jenny},
      title        = {{R}elationship between {F}ill {F}actor and {L}ight
                      {I}ntensity in {S}olar {C}ells {B}ased on {O}rganic
                      {D}isordered {S}emiconductors: {T}he {R}ole of {T}ail
                      {S}tates},
      journal      = {Physical review applied},
      volume       = {14},
      number       = {2},
      issn         = {2331-7019},
      address      = {College Park, Md. [u.a.]},
      publisher    = {American Physical Society},
      reportid     = {FZJ-2020-02874},
      pages        = {024034},
      year         = {2020},
      abstract     = {The origin of the relationship between fill factor (FF) and
                      light intensity (I) in organic
                      disordered-semiconductor-based solar cells is studied. An
                      analytical model describing the balance between transport
                      and recombination of charge carriers, parameterized with a
                      factor, Γm, is introduced to understand the FF-I relation,
                      where higher values of Γm correlate to larger FFs.
                      Comparing the effects of direct and tail-state-mediated
                      recombination on the FF-I plot, we find that, for
                      low-mobility systems, direct recombination with constant
                      transport mobility can deliver only a negative dependence of
                      Γm,dir on light intensity. By contrast, tail-state-mediated
                      recombination with trapping and detrapping processes can
                      produce a positive Γm,t versus sun dependency. The
                      analytical model is validated by numerical drift-diffusion
                      simulations. To further validate our model, two material
                      systems that show opposite FF-I behavior are studied:
                      poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-[4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl]}
                      (PTB7-Th):[6,6]-phenyl-C71-butyric acid methyl ester
                      (PC71BM) devices show a negative FF-I relation, while
                      PTB7-Th:(5Z,5′Z)-5,5′-{[7,7′
                      -(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl)]bis(methanylylidene)}bis(3-ethyl-2-thioxothiazolidin-4-one)
                      (O-IDTBR) devices show a positive correlation.
                      Optoelectronic measurements show that the O-IDTBR device
                      presents a higher ideality factor, stronger trapping and
                      detrapping behavior, and a higher density of trap states,
                      relative to the PC71BM device, supporting the theoretical
                      model. This work provides a comprehensive understanding of
                      the correlation between FF and light intensity for
                      disordered-semiconductor-based solar cells.},
      cin          = {IEK-5},
      ddc          = {530},
      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)16},
      UT           = {WOS:000560631000003},
      doi          = {10.1103/PhysRevApplied.14.024034},
      url          = {https://juser.fz-juelich.de/record/878470},
}