Photovoltaics Technology Components and Systems Applications Clemson Summer School 6.5. – Dr. Karl Molter FH Trier Exzerpt aus: Zum Original:

Clemson Summer School Dr. Karl Molter / FH Trier / 2 Content 1.Solar Cell Physics 2.Solar Cell Technologies 3.PV Systems and Components 4.PV Integration into buildings Zum Original:

Clemson Summer School3. 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:

Clemson Summer School Dr. Karl Molter / FH Trier / 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 / 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 / 6 Solar Cell and Photoelectric Effect 1.Light absorption h Generation of „free“ charges 3.effective separation of the charges Result: wearless generation of electrical Power by light absorption

Clemson Summer School Dr. Karl Molter / FH Trier / 7 energy-states in solids: Band-Pattern Atom Molecule/Solid energy-states

Clemson Summer School Dr. Karl Molter / FH Trier / 8 energy-states in solids: Insulator electron-energy conduction-band valence-band Fermi- level E F bandgap E G (> 5 eV)

Clemson Summer School Dr. Karl Molter / FH Trier / 9 Terms: Fermilevel E F : 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 E G :distance between valance-band and conduction band

Clemson Summer School Dr. Karl Molter / FH Trier / 10 energy-states in solids : metal / conductor electron-energy conduction-band Fermi- level E F

Clemson Summer School Dr. Karl Molter / FH Trier / 11 energy-states in solids: semiconductor electron-energy conduction-band valence-band Fermi- level E F bandgap E G (  0,5 – 2 eV)

Clemson Summer School Dr. Karl Molter / FH Trier / 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, 1.381x J/K, T = absolute temperature in Kelvin) Light quantum absorption: h (h = Plancks Constant, h = 6.626x 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 / 13 energy-states in solids: energy absorption and emission electron-energy conduction-band valence-band EFEF + - h Generation + - h Recombination x x

Clemson Summer School Dr. Karl Molter / FH Trier / 14 energy-states in semiconductors physical 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 / 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: IIIBIVBVB Si 14 B 5 P 15 „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 / 16 N - Doping Si P+P+ - n-conducting Silicon - crystal view conduction-band valence-band EFEF P+P+ P+P+ P+P+ P+P+ P+P+ majority carriers Donator level energy-band view

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

Clemson Summer School Dr. Karl Molter / FH Trier / 18 p – type region EFEF B-B- B-B- B-B- B-B- B-B n – type region ---- P+P+ P+P+ P+P+ P+P+ P+P+ p/n-junction without light Band pattern view Diffusion + internal electrical field + - EdEd UdUd depletion-zone

Clemson Summer School Dr. Karl Molter / FH Trier / 19 p–type region EFEF B-B- B-B- B-B- B-B- B-B n–type region ---- P+P+ P+P+ P+P+ P+P+ P+P+ irradiated p/n-junction band pattern view (absorption p-zone) photocurrent Internal electrical field + - EdEd UdUd depletion-zone E = h -

Clemson Summer School Dr. Karl Molter / FH Trier / 20 p/n–junction with irradiation crystal view n-Silizium p-Silizium diffusion - + electrical field E h depletion zone

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

Clemson Summer School Dr. Karl Molter / FH Trier / 22 Equivalent circuit of a solar cell RPRP U SG RSRS I SG RLRL ULUL ILIL IDID UDUD current source I PH I PH: photocurrent of the solar-cell I D /U D :current and voltage of the internal p-n diode R P :shunt resistor due to inhomogeneity of the surface and loss-current at the solar-cell edges R S :serial resistor due to resistance of the silicon-bulk and contact material I SG /U SG : Solar-cell current and voltage R L /I L /U L : Load-Resistance, current and voltage I SG = I L,U SG = U L

Clemson Summer School Dr. Karl Molter / FH Trier / 23 Solar-Cell characteristics IDID I SG RLRL U D =U SG IDID I SG / P SG U SG solar-cell characteristics I SG = I 0 = I K R L =0 R L =  Power UDUD diode- characteristic ID ID U0U0 Load resistance U MPP MPP I MPP MPP = Maximum Power Point simplified circuit

Clemson Summer School Dr. Karl Molter / FH Trier / 24 Solar-cell characteristics Short-current I SC, I 0 or I K : mostly proportional to irradiation Increases by 0,07% per Kelvin Open-voltage U 0, U OC or V OC : 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 / 25 Solar cell characteristics Power (MPP, Maximum Power Point) U MPP  (0, ,9) U OC I MPP  (0, ,95) I SC Power decreases by 0,4% per Kelvin The nominal power of a cell is measured at international defined test conditions (G 0 = 1000 W/m 2, T cell = 25°C, AM 1,5) in W P (Watt peak).

Clemson Summer School Dr. Karl Molter / FH Trier / 26 Solar cell characteristics The fillfactor (FF) of a solar-cell is the relation of electrical power generated (P MPP) and the product of short current I K and open-circuit voltage U 0 FF = P MPP / U 0  I K The solar-cell efficiency  is the relation of the electrical power generated (P MPP) and the light irradiance (AG G,g) impinging on the solar-cell :  = P MPP / AG G,g

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

Clemson Summer School Dr. Karl Molter / FH Trier / 28 Solar-cell characteristics

Clemson Summer School Dr. Karl Molter / FH Trier / 29 Zu den weiteren Folien bitte Dr. Molter‘s homepage besuchen: Zum Original:

Clemson Summer School Dr. Karl Molter / FH Trier / 30 This Powerpoint Presentation can be downloaded from: