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Photovoltaics

Exzerpt aus:. Photovoltaics. Clemson Summer School 6.5. – 8.5.06 Dr. Karl Molter FH Trier www.fh-trier.de/~molter molter@fh-trier.de. Technology Components and Systems Applications. Zum Original : http://www0.fh-trier.de/~molter/clemson/PV-en.ppt.

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Photovoltaics

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  1. Exzerpt aus: Photovoltaics Clemson Summer School 6.5. – 8.5.06 Dr. Karl Molter FH Trier www.fh-trier.de/~molter molter@fh-trier.de Technology Components and Systems Applications Zum Original:http://www0.fh-trier.de/~molter/clemson/PV-en.ppt

  2. Zum Original:http://www0.fh-trier.de/~molter/clemson/PV-en.ppt Content • Solar Cell Physics • Solar Cell Technologies • PV Systems and Components • PV Integration into buildings Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  3. Ich benutze nur das Kaptel 1 „Solar Cells Physics“ und einige Folien aus Kapitel 2 (Materials). Ich empfehle aber den gesamten Vortrag von Dr. Molter: Zum Original:http://www0.fh-trier.de/~molter/clemson/PV-en.ppt . Clemson Summer School

  4. 1. Solar Cell Physics • Solar Cell and Photoelectric Effect • The p/n-Junction • Solar Cell Characteristics Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  5. History • 1839: Discovery of the photoelectric effect by Bequerel • 1873: Discovery of the photoelectric effect of Selen (change of electrical resistance) • 1954: First Silicon Solar Cell as a result of the upcoming semiconductor technology ( = 5 %) Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  6. h • Light absorption • Generation of „free“ charges + • effective separation of the charges - Solar Cell and Photoelectric Effect Result: wearless generation of electrical Power by light absorption Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  7. • • • • • • • • energy-states in solids:Band-Pattern Atom Molecule/Solid energy-states Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  8. energy-states in solids:Insulator electron-energy conduction-band bandgap EG (> 5 eV) Fermi- level EF valence-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  9. Terms: Fermilevel EF: limit between occupied and non occupied energy-states at T = 0 K (absolute zero) valence-band: completely occupied energy-band just be- low the Ferminiveau at T = 0 K, the electrons are „fixed“ inside the atomic structure conduction-band: energy-band just above the valence-band, the electrons can move „freely“ bandgap EG:distance between valance-band and conduction band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  10. energy-states in solids :metal / conductor electron-energy Fermi- level EF conduction-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  11. energy-states in solids:semiconductor electron-energy conduction-band bandgap EG ( 0,5 – 2 eV) Fermi- level EF valence-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  12. Electron-Energy At T=0 (absolute zero of temperature) the electrons occupy the lowest possible energy-states. They can now gain energy in two ways: • Thermal Energy: kT (k = Boltzmanns Constant, 1.381x10-23 J/K, T = absolute temperature in Kelvin) • Light quantum absorption: h (h = Plancks Constant, h = 6.626x10-34 Js,  = frequency of the light quantum in s-1). If the energy absorbed by the electron exceeds that of the bandgap, they can leave the valence-band and enter the conduction-band: Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  13. x h h x Generation Recombination + + - - energy-states in solids:energy absorption and emission electron-energy conduction-band EF valence-band Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  14. energy-states in semiconductorsphysical properties: thermal viewpoint: The larger the bandgap the lower is the conductivity. Increasing temperature reduces the electrical resistance (NTC, negative temperature coefficient resistor) optical viewpoint: the larger the bandgap the lower is the absorption of light quantums. Increasing light irradiation decreases the electrical resistance (Photoresistor) Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  15. IIIB IVB VB Si B P 14 5 15 doping of semiconductors In order to avoid recombination of photo-induced charges and to „extract“ their energy to an electric-device we need a kind of internal barrier. This can be achieved by doping of semiconductors: „Doping“ means in this case the replacement of original atoms of the semiconductor by different ones (with slightly different electron configuration). Semiconductors like Silicon have four covalent electrons, doping is done e.g. with Boron or Phosphorus: Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  16. energy-band view conduction-band majority carriers P+ P+ P+ P+ P+ P+ EF Si Si Si Si Si Si Si Si Si Donator level valence-band - - - - - - - N - Doping crystal view n-conducting Silicon Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  17. energy-band view conduction band B- Si Si Si Si Si Si Si Si Si EF Acceptor level B- B- B- B- B- majority carriers + + + + + + + valence-band P - Doping crystal p-conducting Silicon Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  18. depletion-zone Diffusion Ud EF P+ P+ P+ P+ P+ B- B- B- B- B- + + + + + + Diffusion p – type region Ed - + n – type region internal electrical field - - - - - - p/n-junction without light Band pattern view Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  19. E = h photocurrent + + + + + + - irradiated p/n-junction band pattern view (absorption p-zone) depletion-zone - - - - - Ud EF P+ P+ P+ P+ P+ B- B- B- B- B- Ed p–type region - + n–type region Internal electrical field Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  20. h + + + + + + + + + + + + + p-Silizium + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - diffusion E electrical field + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - n-Silizium - - - - - - - - - - - - depletion zone - - - - - - - - - - - - - - - - - - - - - - - - - p/n–junction with irradiationcrystal view Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  21. Front-contact - hn Antireflection- coating n-region p-region ~0,2µm + + + + + + + + + + + - - - - - - - - - - ~300µm depletion zone Backside contact The real Silicon Solar-cell Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  22. ISG IL IPH RS ID current source RP RL USG UL UD Equivalent circuit of a solar cell IPH: photocurrent of the solar-cell ID /UD: current and voltage of the internal p-n diode RP: shunt resistor due to inhomogeneityof the surface and loss-current at the solar-cell edges RS: serial resistor due to resistance of the silicon-bulk and contact material ISG/USG: Solar-cell current and voltage RL/IL/UL: Load-Resistance, current and voltage ISG = IL, USG = UL Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  23. ID diode- characteristic ID ISG UD=USG UD RL RL=  RL=0 MPP ISG / PSG Load resistance ISG = I0 = IK solar-cell characteristics ID IMPP Power MPP = Maximum Power Point USG UMPP U0 Solar-Cell characteristics simplified circuit Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  24. Solar-cell characteristics • Short-current ISC, I0 or IK: • mostly proportional to irradiation • Increases by 0,07% per Kelvin • Open-voltage U0, UOC or VOC: • This is the voltage along the internal diode • Increases rapidly with initial irradiation • Typical for Silicon: 0,5...0,9V • decreases by 0,4% per Kelvin Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  25. Solar cell characteristics • Power (MPP, Maximum Power Point) • UMPP» (0,75 ... 0,9) UOC • IMPP» (0,85 ... 0,95) ISC • Power decreases by 0,4% per Kelvin • The nominal power of a cell is measured at international defined test conditions(G0 = 1000 W/m2, Tcell = 25°C, AM 1,5) in WP (Watt peak). Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  26. Solar cell characteristics • The fillfactor (FF) of a solar-cell is the relation of electrical power generated (PMPP) and the product of short current IK and open-circuit voltage U0 • FF = PMPP / U0 IK • The solar-cell efficiencyis the relation of the electrical power generated (PMPP) and the light irradiance (AGG,g) impinging on the solar-cell : •  = PMPP / AGG,g Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  27. P = 0,88W, (0,18) P = 1,05W, (0,26) P = 0,98W, (0,29) Solar-cell characteristics (cSi) Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  28. Solar-cell characteristics Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  29. Zu den weiteren Folien bitte Dr. Molter‘s homepage besuchen: Zum Original:http://www0.fh-trier.de/~molter/clemson/PV-en.ppt Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

  30. This Powerpoint Presentation can be downloaded from: www.fh-trier.de/~molter www.fh-trier.de/~molter Clemson Summer School Dr. Karl Molter / FH Trier / molter@fh-trier.de

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