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CURRENT STATUS OF ORGANIC SOLAR CELLS

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					             3-rd International Conference




     May 22-28, 2000, Kharkiv, Ukraine

                 Wednesday, May 24, 2000
    Plenary Session 3 (Chairmen: E.Frankevich, T.Ogava)




       CURRENT STATUS
   OF ORGANIC SOLAR CELLS



                 Dieter Meissner




          AQR, Physical Chemistry
     Johannes-Kepler University, Austria
and Forschungszentrum Jülich GmbH, Germany



                                                          DM TitleKharkiv19.5.00
                             European Groups Working on
                                 Organic Solar Cells
Cell Types      Product Development      Research Institutions     Universities

Sensitization   EPF Lausanne, CH         INAP, Gelsenkirchen, D    EPF Lausanne, CH
Solar Cell      INAP, Gelsenkirchen, D   ECN, Petten, NL           Wageningen Agricult.University; NL
(SSC)           ECN, Petten, NL          ISE, Freiburg, D          University College Dublin, IRL
                Solaronix, Aubonne, CH   IMEC, Leuven, B           ETH Zürich, CH
                Leclanche, CH            DSM, Geleen, NL           University of York, GB
                                         Samsung European          Eindhoven University, NL
                                         Res.Center, Berlin, D     Univ. Louis Pasteur, Strasbourg, F
                                                                   Delft University of Technology, NL

Molecular                                CEA, Saclay, F            Wageningen Agricult. University, NL
Organic Solar                            CNR, Bologna, I           TU Dresden, D
Cell                                     CNRS, Thiais, F           University of Sheffield, GB
(MOSC)                                   Samsung European Res.     University of Cambridge, GB
                                         Center, Berlin, D         University of Bremen, D
                                                                   Limburg University. B
                                                                   RWTH Aachen, D
                                                                   TU Dresden, D
                                                                   Vilnus University, LT

Polymer         QSEL, Linz               CNRS, Gif-sur-Yvette, F   University of Linz, AU
Organic Solar                            Christian-Doppler-        University of Sheffield, GB
Cell                                     Laboratory, Linz, Au      University of Cambridge, GB
(POSC)                                   IMEC, Leuven, B           University of Eindhoven, NL
                                         CNR Bologna, I            University of Groningen, NL
                                                                   University of Oldenburg, D
                                                                   Linköping University, S
                                                                   University of Bayreuth, D
                                                                   University of Madrid, E

                                                                                           DM, EuropGroupsOnOSCs200500
                                                   Organic Solar Cells
                                                   Classification and status


        types               current status              structure               main problems               latest improvements

                           commercialization        nanoporous titan-     efficiency (voltage) > 10 %      sealing of modules
sensitization                   started            dioxide electrode,     only for platinized counter
                                                     sensitized by an     electrode and acetonitrile       stability
                 SSC   highest efficiency: 11 %                           electrolyte
  solar cell                                       organic dye in ioni-                                    first products under
                        first modules demon-                              sealing of modules
                                strated              cally conducting                                      development
                                                   electrolyte with an    replacement of liquid (ion
                       prototypes of consumer                             conductive) electrolyte by       first tests of solid state
                               products            iodidie redox cou-                                      contacts
                                                    ple and platinized    electonically conductive
                                                                          solid
                                                    counter electrode
                          laboratory scale          solid state contact efficiency (current, vol-          C60 interconnected net-
 molecular             highest solar efficien-     of crystaklline orga- tage, fill factor)                work doubled current
                                                                                                           efficiency
                                cies:              nic semiconductors understanding of basic
  organic       MOSC                                                     processes, mainly charge          new materials with hig-
                      2.4 % for single crystal
                                                                         carrier generation                her charge carrier mobi-
 solar cells            1.1 % for evaporated        C60 network forms                                      lity
                     films with C60-enlarged        solid state contact
                             interface                                                                     utilization of energy
                                                                                                           transfer
                      demonstration objects
                               (clock)                                                                     new charcterization
                                                                                                           techniques

                            laboratory scale         interconnected       efficiency (current, fill fac-   new improved polmers
  polymer                highest solar efficien-    polymer / C60 net-    tor)
                               cies: 3 %             work forms solid     absorption coefficient of        derivatized C60 impro-
  organic       POSC                                                      polymers                         ves solubility in polmer
                        demonstration objects         state contact
                                                                          stability of polymer             and
 solar cells             (compare exhibition)
                                                                          understanding of basic           new startegies for better
                                                                          processes, mainly charge         ordered systems
                                                                          carrier transport

                                                                                                                        DM, TypesOfOSCs200500
                    Single Crystalline
               Molecular Organic Solar Cell
J. H. Schön, Ch. Kloc, E. Bucher, B. Batlogg, Nature 403 (2000), 408


                                       Single crystalline Pentacene,
                                       about 7 mm2, halogen doped
                                           AM 1.5, 100 mA/cm2,
                                             η = 1.9 and 2.4 %




           mobility, internal efficiency
           and photovoltaic efficiency
 as a fuction of doping concentration


                             Model:
                             a: light absorption leads to
                                exciton formation
                             b: diffusion to dopant site
                             c: complex of exciton, dopant and neigh-
                                bouring pentacene molecule
                             d: charge transfer to dopant and separation
                                in built-in electric field of the device


                                                        DM, SchönNature200500, 20.5.2000
                            Strategies
                  to Improve Organic Solar Cells

Main problem:
                                                           A
  extremely thin "active layer" (red)
                                                           B
Solution 1: increasing the thickness of the active layer
                                                           A
a) Improving the materials:
   new, better materials                                   B
   pureness of materials, morphology, doping

b) new Strategies:- p/i/n-Junction,     - Mixed Layers
                  - Gradient Films,     - Doping Profiles

Solution 2:       new cell structures,                   A
                  utilizing extremely thin active layers B
                                                            A
                                                            B
a) Multiple-Tandems:                                        A
                                                            B
   problem:
   non absorbing ohmic contacts between cells


b) active layers perpendicular to incoming light            A BA BA BA BA BA BA B
   LIGA-technique?
                                                                            B
c) active layers between inorganic and
   organic semiconductors oriented perpendicular
                                                                                       TiO 2
   to the incoming light (comp. Sensitization)
                                                                molecules
                                                                 Antenna




d) Improvement of the active layer by
   antenna molecules (comp. photosynthesis)
                                                       AB                   AB        AB

e) The Jülich/Osaka-Approach: C60-Interlayer


                                                                            DM, Strategies, 20.5.2000
 Molecular structures of the Materials Used for TiO2 DSCs


                                       S               2-
              C8H17
                                       C
                          OOC                   COOH
                                       N
                                   N        N
                                       Ru                   .              +
        S      n                                                 2 (C4H7)N
                                   N        N
                                       N
                          HOOC                  COO
                                       C

                                       S
Poly(3-octylthiophene),        cis-bis(isothiocyanato)bis(2,2′-
        (P3OT)                   bipyridyl-4,4′dicarboxylato)-
                             ruthenium(II), RuL2(NCS)2 : 2TBA
                                        L =2,2′-bipyridyl-4,4′-
                                  dicarboxylic acid
                                     TBA = tetrabutylammonium

                                                                D. Gebeyehu
                 Solid-State nanoporous TiO2 Dye-Sensitization Solar Cells
             Polymer/Dye/nanoporous TiO2 :                                                              Polymer/nanoporousTiO2 :
                                  Iinc = 80 mW/cm2 (AM 1.5)                                             Iinc = 80 mW/cm2 (AM 1.5)
                                          Voc = 550 mV                                                          Voc = 660 mV
                                        Isc = 450 µΑ/cm2                                                      Isc = 225 µA/cm2
                                             FF = 0.3                                                              FF = 0.4
                                        ηeff ~ 0.1%                                                              ηeff. = 0.07%




                                                                          Current density [mA/cm
    Current density [mA/cm




                                                                                              ]
                        ]




            40                                                                      2.5




                                                                      2
2




                                                                                    2.0
            30
                                             light                                  1.5                                           dark
            20                               dark                                                                                 light
                                                                                    1.0

            10                                                                      0.5
                                                                                    0.0
                    0
                                                                               -0.5
                             -2         -1           0        1   2
                                                Voltage [V]                                        -2         -1      0           1       2
                                                                                                                   Voltage [V]



                                                                                                                                 D. Gebeyehu
                                    Solid- State Flat TiO2 Dye-Sensitization Solar Cells
                 Polymer/dye/flat TiO 2 :                                                           Polymer/flat TiO2 :
              TiO /Dye (N3)/ P3OT/
SnO2 :F/flatIinc =264 mW/cm2 (AM 1.5) Graphite powder:                                            Iinc = 64 mW/cm2 (AM 1.5)
                    Voc = 460 mV                                                                           Voc ~ 550 mV
                   Isc = 26 µA/cm2                                                                        Isc = 9 µA/cm2
                       FF = 0.5                                                                              FF = 0.45
                                    ηeff. = 9.3 x 10-3%                                                 ηeff. = 3.5 x 10-3%
                                                                                            10




                                                                      A/cm ]
  Current density A/cm ]




                                                                          2
                      30
                µ [ 2




                                      light
                                      dark




                                                                      µ
                      20                                                                    5




                                                                        Current density [
                      10
                                                                                            0
                           0
                                                                                                                   light
                                                                                            -5
                  -10                                                                                              dark

                           -0 . 6    -0.5 -0.4 -0.3 -0.2    -0 . 1   0.0                         -0.6       -0.4      -0.2        0.0
                                              Voltage [V]                                                Voltage [V ]
                                                                                                                           D. Gebeyehu
      Spectral Resolution of Solid-State Flat TiO2 DSCs

Incident photon to current conversion efficiencies, IPCE:

                    Polymer/Dye/flat TiO2 ~ 1%

                    Polymer/flat TiO2          ~ 0.5%
                   2.0
                                      Polymer/Dye/flat TiO2
                                      Polymer/flat TiO2
        IPCE [%]



                   1.5


                   1.0


                   0.5


                   0.0
                         400    500      600      700         800
                                 Wavelength [nm]

                                                                    D. Gebeyehu
                 The Solid-State
                 The Solid-State
   Photo-electrochemical Solar Cells Based on
   Photo-electrochemical Solar Cells Based on
   Polymers & Dye-Sensitized TiO22 Electrodes
   Polymers & Dye-Sensitized TiO Electrodes
                 will be appear
                 will be appear
--as full paper in Journal of Solar Energy Materials and Solar Cells
  as full paper in Journal of Solar Energy Materials and Solar Cells
                  & as Proceedings in ICSM 2000.
                   & as Proceedings in ICSM 2000.
                                  Dieter Meissner

                                THE STATUS
                          OF ORGANIC SOLAR CELLS


                                     Summary

All three types of Organic Solar Cells, i.e.
    - Sensitization (SSC),

    - Molecular (MOSC)and
    - Polymer (POSC) based cells,
are becoming real competitors for classical cells based the

    possibility to utilize extremely rough

    (nanoporous interconnected network) interfaces
allowing for very thin charge generation layers.



As for sensitization solar cells achieved already, solar efficiencies in the range of
10 % will be achieved within the next year also for the other types of solar cells, for

which todays state of the art is between 1 and 3 %. It will basically depend on the

available support, where this will be: in Europe, the USA, or Japan.




Which of the three types will finally succeed will finally depend on the possibility to
overcome the specific problem being
    the module manufacturing for SSCs (sealing of every cell)
    the cell production for MOSCs, and

    the stability (sealing) for POSCs



with the long time stability being still a key issue.



                                                                         DM SummaryKharkiv19.05.00

				
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