Solar Photovoltaic Physics

Basic Physics and

Materials Science of Solar Cells

Syllabus • Chapter 1: Introduction

• Chapter 2: Solar Resource

• Chapter 3: Fundamental of Photovoltaic (Light absorption, Excitation and Transport)

• Chapter 4: PN Junctions

• Chapter 5: Solar Cells and Parameters

• Chapter 6: Design of Silicon Cells

• Chapter 7: Manufacturing Si Cells

• Chapter 8: Thin film Solar cells [CdS/CdTe, CdS/CIGS and GaAs].

• Chapter 9: Dye/Quantum dots sensitized solar cells

• Chapter 10: Modules, Arrays and Characterization

Books

http://www.pvcdrom.pveducation.org/

• Jenny Nelson: The Physics of Solar Cells:

Imperial College Press

• Peter Wurfel: Physics of Solar Cells: From Basic

Principles to Advanced Concepts: Viley -VCH

Books • Bube, R. H. Photovoltaic Materials. London, UK: Imperial College Press, 1998. ISBN:

9781860940651.

• Green, M. A. Solar Cells: Operating Principles, Technology and System Applications.

Upper Saddle River, NJ: Prentice Hall, 1981. ISBN: 9780138222703.

• Wenham, S. R., M. A. Green, M. E. Watt, R. Corkish. Applied Photovoltaics. 2nd ed.

New York, NY: Earthscan Publications Ltd., 2007. ISBN: 9781844074013.

• Green, M. A. Silicon Solar Cells: Advanced Principles and Practice. Sydney, Australia:

Centre for Photovoltaic Devices & Systems, 1995. ISBN: 9780733409943.

• Aberle, A. G. Crystalline Silicon Solar Cells - Advanced Surface Passivation &

Analysis. Sydney, Australia: University of New South Wales, 2004. ISBN:

9780733406454

• Poortmans, J., and V. Arkhipov. Thin Film Solar Cells: Fabrication, Characterization

and Applications. Hoboken, NJ: John Wiley & Sons, 2006. ISBN: 9780470091265.

• Green, M. A. Third Generation Photovoltaics: Advanced Solar Energy Conversion.

New York, NY: Springer-Verlag, 2007. ISBN: 9783540265627.

• Luque, A., and S. Hegedus. Handbook of Photovoltaic Science and Engineering.

Hoboken, NJ: John Wiley & Sons, 2003. ISBN: 9780471491965

Tests and Scores

• Mid Test : 30

• Final Test : 30

• Presentations [2] : 20

• Attendance : 20

Total : 100

A Brief History of Photovoltaic Technology

• 1839 – Photovoltaic effect discovered by Becquerel.

• 1870s – Hertz developed solid selenium PV (2%).

• 1905 – Photoelectric effect explained by A. Einstein.

• 1930s – Light meters for photography commonly employed cells of copper oxide or selenium.

• 1954 – Bell Laboratories developed the first crystalline silicon cell (4%).

• 1958 – PV cells on the space satellite U.S. Vanguard (better than expected).

Things Start To Get Interesting...

• Mid 1970s – World energy crisis started and millions of dollars spent in research and development of cheaper and more efficient solar cells.

• 1976 – First amorphous silicon cell developed by Wronski and Carlson.

• 1980’s - Steady progress towards higher efficiency and many new types introduced

• 1990’s - Large scale production of solar cells more than 10% efficient with the following materials: – Ga-As and other III-V’s – Crystalline, Polycrystalline, and Amorphous Silicon – CuInGaSe2 and CdTe – TiO2 Dye-sensitized (still under research and not yet

commercialized)

• Today prices continue to drop and new “3rd generation” solar cells are researched.

Types of Solar Photovoltaic Materials

Photovoltaic Materials

Electronic Structure of Semiconductors

• Silicon

• Group 4 elemental

semiconductor

• Silicon crystal forms the

diamond lattice

• Resulting in the use of four

valence electrons of each

silicon atom.

Crystalline

Silicon

Amorphous Silicon

Solar PV Materials: Crystalline & Polycrystalline Silicon

• Advantages:

– High Efficiency (14-22%)

– Established technology

(The leader)

– Stable

• Disadvantages:

– Expensive production

– Low absorption coefficient

– Large amount of highly

purified feedstock

Amorphous Silicon Advantages:

• High absorption (don’t need a lot of material)

• Established technology

• Ease of integration into buildings

• Excellent ecological balance sheet

• Cheaper than the glass, metal, or plastic you deposit it on

Disadvantages:

• Only moderate stabilized efficiency 7-10%

• Instability- It degrades when light hits it

– Now degraded steady state

The Sun

Solar Radiation In Space The solar irradiance on an object some distance D from the sun is found by dividing the

total power emitted from the sun by the surface area over which the sunlight falls

Solar Radiation Outside the Earth's Atmosphere

Blackbody Radiation

The total power density from a

blackbody is determined by

integrating the spectral irradiance

over all wavelengths which gives:

where is the Stefan-Boltzmann constant

and T is the temperature of the blackbody

(K).

The wavelength at which the spectral

irradiance is the highest, or, in other

words the wavelength where most of

the power is emitted.

The Solar Spectrum The spectral content of

the incident light;

• the radiant power density from the sun;

• the angle at which the incident solar radiation strikes a photovoltaic module; and

• the radiant energy from the sun throughout a year or day for a particular

surface.

The Solar Spectrum • the spectral content of

the incident light;

• the radiant power density from the sun;

• the angle at which the incident solar radiation strikes a photovoltaic module; and

• the radiant energy from the sun throughout a year or day for a particular

surface.

Atmospheric Effects

Atmospheric effects have several impacts on the solar

radiation at the Earth's surface. The major effects for

photovoltaic applications are:

• A reduction in the power of the solar radiation due to absorption, scattering and reflection in the atmosphere;

• A change in the spectral content of the solar radiation due to greater absorption or scattering of some wavelengths;

• The introduction of a diffuse or indirect component into the solar radiation; and

• Local variations in the atmosphere(such as water vapor, clouds and pollution) which have additional effects on the incident power, spectrum and directionality.

Atmospheric Effects

When dealing with "particles" such as

photons or electrons, a commonly

used unit of energy is the electron-

volt (eV) rather than the joule (J). An

electron volt is the energy required to

raise an electron through 1 volt, thus

1 eV = 1.602 x 10-19 J.

Spectral Irradiance

The spectral irradiance of xenon (green), halogen (blue) and mercury (red) light bulbs (left axis) are compared to the spectral irradiance from the sun (purple, which corresponds to the right axis).

Radiant Power Density

Quantifying Solar Power

Orbit Ellipticity

Air Mass

Standardized Solar Spectrum and Solar Irradiation

Average Monthly Solar Radiation

Attempts to Simulate Solar Spectra • Better matches: Xe lamps with air mass filters

The ideal illumination source would

have following features A spatial non uniformity of less than 1%.

A variation in total irradiance with time of

less than 1%, filtered for a given reference

spectrum to have a spectral mismatch error of

less than 1%.

These requirements are essential in obtaining

an accuracy of better than 2%

Testers are classified according to three criteria:

Spectral match

Irradiance inhomogeneity - spatial uniformity

over the illumination area

Temporal Instability - stability over time.

There are three classes within each of these

criteria where 'A' is the top rating an 'C' is the

lowest rating

Uniformity Spectral Fidelity Temporal Stability

Solar Simulator Standards

Estimating Solar Systems Outputs

Actual system outputs may be significantly lower, due to suboptimal system performance, design, installation, shading losses,

Estimating Solar Land Area Requirements

Test Case