Thin Film Photovoltaics by pzk16293

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									Thin Film Photovoltaics

     By Justin Hibbard
       Thin Film Photovoltaics
• What is a thin film photovoltaic?
• Thin film voltaics are materials that have a light
  absorbing thickness that is less than 10 μm.
• The thin film material can converting sunlight to
  electricity.
• Thin films are predicted to be as efficient as
  monocrystalline Si wafer cells with more R & D.
• Need more R & D to evolve from the laboratory
  to the marketplace.
• Two competing materials are
  (CIGS):Cu(In,Ga)Se2 and CdTe.
           Thin Film Photovoltaics
Thin film photovoltaic devices take advantage of absorption of ir-vis-ir light by
   semiconductors and converts the light to power.
What is a semiconductor?
Semiconductors are materials that require a “turn on” energy to conduct energy
   ≈ current.
Semiconductors share the electrons respectively with the individual atomic
   nuclei and require a minimum voltage to make the electrons mobile.
   Whereas metals are materials that are referred to as conductors and have
   “free” electrons that respond to a small voltage.
Semiconductors are materials that prefer a Lewis/closed shell structure.
This rule may be deviated with the addition of element(s) that differ by group
   number ±1,0. Which may give the material an extra or a missing (hole)
   valence electron. This atomic substitution allows the material scientist to
   “tune” the material by manipulation of the conduction properties of the
   material.
Semiconductors are preferable because of the ability to tune the eV with the
   right elemental mixture and the small amount of material needed.
            Thin Film Photovoltaics
Thin films technologies have a common device/module structure: substrate, base
 electrode, absorber, junction layer, top electrode, patterning steps for monolithic
               integration and encapsulation but in a reverse order.
Thin film photovoltaics are cheap if the elements are not rare. They are becoming
         cheaper to produce and will become cheaper with time be R & D.
  Monocrystalline Si is expensive to grow. Amorphous and polycrystalline silicon
    are not very efficient. Thin film CIGS cell and modules are 19.5% and 13%
 efficient and CdTe cells and modules are 16.5% and 10.2% efficient. CdTe and
    CIGS PV modules have the potential to reach cost effective PV-generated
                                       electricity.
                 They have transitioned from the laboratory to the
   market place. Pilot production/first-time manufacturing (US) ~ 25 MW. CdTe
          technology ramping to 75 MW. Enjoying a flux of venture capital
funding.Transitioning from the lab to manufacturing has been much more difficult
                                    than anticipated.
              CIGS and CdTe Device Structure


                                       CdTe
                                                           Glass
                                                           CTO/ZTO,SnO2
 ZnO, ITO                                                  0.2-0.5 µm
   2500 Å
     CdS
                                                           CdS
    700 Å
                                                           600-2000 Å



    CIGS
 1-2.5 µm
                                                           CdTe
                                                           2-8 µm



       Mo
 0.5-1 µm
   Glass,                                                  C-Paste
Metal Foil,                                                with Cu,
  Plastics                                                 or Metals
                CIGS
                                CTO/ZTO = Cd2SnO4/ZnSnOx
CIGS Deposition System
   Thin Film Photovoltaics
          Thin films challenges:
1)Science and Engineering support.
2)Long Term Stability.
3)In-Situ Process Diagnostics and
  control.
4)Thinner CIGS and CdTe Abosrbers.
5)Need for High-Throughput , Low-Cost
  Processes.
6)Inproved Voc in CdTe devices.
                Thin Film CIGS Solar Cells
                        Efficiency
 Area    Area     VOC      JSC       FF     Efficiency
 (cm2)   (cm2)    (V)    (mA/cm2)    (%)        (%)            Comments
                                                           CIGSe/CdS/Cell
CIGSe 0.410 0.697         35.1      79.52     19.5       NREL, 3-stage process
                                                          CIGSe/ZnS (O,OH)
CIGSe 0.402 0.67          35.1      78.78     18.5        NREL, Nakada et al
                                                           Cu(In,Ga)S2/CdS
CIGS     0.409 0.83       20.9      69.13     12.0          Dhere, FSEC
                                                           Cu(In,Al)Se2/CdS
CIAS       –     0.621    36.0      75.50     16.9
                                                           IEC, Eg = 1.15eV
                                                          CTO/ZTO/CdS/CdTe
CdTe     1.03    0.845    25.9      75.51     16.5
                                                             NREL, CSS
CdTe       –     0.840    24.4      65.00     13.3       SnO2/Ga2O3/CdS/CdTe
                                                               IEC, VTD
CdTe     0.16    0.814    23.56 73.25         14.0       ZnO/CdS/CdTe/Metal
                                                         U. of Toledo, sputtered
Thin Film Photovoltaics




Justin Hibbard thanks the nrel.gov
    webpage for pictures and
           information.

								
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