Principles of photovoltaics and solar energy conversion

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Principles of photovoltaics and solar energy
conversion
Juan Bisquert
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Light absorption
Juan Bisquert The Physics of Solar Energy
Conversion
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Light absorption
Juan Bisquert The Physics of Solar Energy
Conversion
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Light absorption
De Wolf, S. Holovsky, J. Moon, S.-J. Löper,
P. Niesen, B. Ledinsky, M. Haug, F.-J.
Yum,J.-H. Ballif, C. "Organometallic halide
perovskites Sharp optical absorption edge and
its relation to photovoltaic performance". The
Journal of Physical Chemistry Letters 2014, 5,
1035-1039.
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Absorptance relates to emission
Ledinsky, M. Schönfeldová, T. Holovsky, J.
Aydin, E. Hájková, Z. Landová, L. Neykova, N.
Fejfar, A. De Wolf, S. Journal of Physical
Chemistry Letters 2019, 9, 1368-1373.
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Harvesting the solar spectrum
Kiang, N. Y. Siefert, J. Govindjee
Blankenship, R. E. "Spectral signatures of
photosynthesis. I. Review of Earth organisms".
Astrobiology 2007, 7, 222-251.
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Harvesting the solar spectrum
The number of photons we can collect depends on
the incoming spectrum multiplied by the
absorptance The bandgap is transparent! More
bandgap, less photons that contribute to current
Juan Bisquert The Physics of Solar Energy
Conversion
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Fermi levels
The electrochemical potential is the free energy
per particle. It is also called the Fermi level.
Juan Bisquert The Physics of Solar Energy
Conversion
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Fermi levels
The Fermi level also indicates the population of
an energy level
Juan Bisquert The Physics of Solar Energy
Conversion
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What is a voltage
A voltage is a difference of electrochemical
potentials of electrons in the metals A
voltage in a solar cell is related to the
difference of Fermi levels at the contacts
Juan Bisquert The Physics of Solar Energy
Conversion
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Equilibration of Fermi levels
Juan Bisquert The Physics of Solar Energy
Conversion
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Fermi levels
By pumping photogenerated carriers we obtain a
separation of Fermi level, which is an internal
voltage
Juan Bisquert The Physics of Solar Energy
Conversion
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Fermi levels and recombination
The separation of Fermi levels is a
non-equilibrium situation that lives only as far
as the recombination lifetime
Juan Bisquert The Physics of Solar Energy
Conversion
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Recombination
The photogenerated carriers return to equilibrium
by recombination processes These can be either
-band-to-band radiative -non-radiative
trap-mediated (SRH) -Non-radiative Auger
Vossier, A. Gualdi, F. Dollet, A. Ares, R.
Aimez, V. "Approaching the Shockley-Queisser
limit General assessment of the main limiting
mechanisms in photovoltaic cells". Journal of
Applied Physics 2015, 117, 015102.
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Electron lifetime

• Recombination lifetime can be measured optically
  or electrically.
• The commonly used techniques are
• Optical Measurements
• Photoconductance Decay (PCD),
• Quasi-Steady-State Photoconductance (QSSPC),
• Short-Circuit Current/Open-Circuit Voltage Decay
  (SCCD/ OCVD),
• Photoluminescence Decay (PLD),
• Surface Photovoltage (SPV),
• Steady-State Short-Circuit Current (SSSCC),
• Free Carrier Absorption, Electron Beam Induced
  Current (EBIC)
• Electrical Measurements
• Diode Current-Voltage,
• Reverse Recovery (RR),
• Open-Circuit Voltage Decay (OCVD),
• Pulsed MOS Capacitor,

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Juan Bisquert The Physics of Solar Energy
Conversion
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Photovoltaics Light absorber
Bisquert, J. Cahen, D. Rühle, S. Hodes, G.
Zaban, A. "Physical chemical principles of
photovoltaic conversion with nanoparticulate,
mesoporous dye-sensitized solar cells." The
Journal of Physical Chemistry B, 108, 8106, 2004.
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Photovoltaics Charge separation
Bisquert, J. Cahen, D. Rühle, S. Hodes, G.
Zaban, A. "Physical chemical principles of
photovoltaic conversion with nanoparticulate,
mesoporous dye-sensitized solar cells." The
Journal of Physical Chemistry B, 108, 8106, 2004.
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Juan Bisquert The Physics of Solar Energy
Conversion
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Solar cell operation
Juan Bisquert The Physics of Solar Energy
Conversion
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Current voltage curves
Current-voltage characteristic I-V curve Power
delivered PI V
Juan Bisquert The Physics of Solar Energy
Conversion
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The diode equation for a solar cell
At V 0 equilibrium of generation and
recombination
Dark
Rise of the Fermi level enhances recombination
Sunlight
Equilibrium of generation and recombination
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Solar cell operation
The energy delivered is Current x Voltage The
maximum operation point
Juan Bisquert The Physics of Solar Energy
Conversion
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The fill factor
Juan Bisquert The Physics of Solar Energy
Conversion
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Energy output
The energy delivered is Current x
Voltage Less bandgap -gt less energy per
carrier
Juan Bisquert The Physics of Solar Energy
Conversion
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Shockley and Queisser (1961) efficiency limit

• SQ1. Describe a solar cell in terms of a
  semiconductor absorber material with selective
  contacts, surrounded by blackbody radiation at
  the same temperature. The solar cell can be
  operated electrically.
• SQ2. The solar cell interacts optically with an
  external radiation source. The absorber material
  is a semiconductor with optically sharp bandgap,
  characterized by a single parameter, the bandgap
  Eg that defines the onset of light absorption.
• SQ3. To obtain the minimal possible losses in
  power produced by the jV curve, assume detailed
  balance in the radiative limit, in which the only
  recombination channel is radiative emission.
• SQ4. Use the photocurrent in the radiative limit,
  
• SQ5. Use the photovoltage in the radiative limit,
  
• SQ6. Calculate the FF
• SQ7. Obtain the PCE.

Juan Bisquert The Physics of Solar Energy
Conversion
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Juan Bisquert The Physics of Solar Energy
Conversion
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2019 by Tom Veeken from AMOLF Institute
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2019 by Tom Veeken from AMOLF Institute
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2019 by Tom Veeken from AMOLF Institute