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Click one of the letters above to advance the page to terms beginning with that letter.
&
αsearch for term
alpha refers to many variables including the maximum elevation at solar noon and absorption coefficient.
Δnsearch for term
excess electron concentration.
λsearch for term
lambda is commonly used to refer to the wavelength of light in either µm or nm.
a
absorptionsearch for term
When the energy of an incident photon is large enough to excite an electron into the conduction band from the valence band (energy ≥ band gap). Depending on the wavelength of the photon, and the type of material, it will occur more readily, and a certain depth into the material.
absorption coefficientsearch for term
How far into a material light of a particular wavelength can penetrate before it is absorbed. Depends on the wavelength of the photon (light) and the type of material the light is incident on. In units of cm-1
air masssearch for term
Increase in path length of solar radiation through the atmosphere.
ARCsearch for term
anti-reflection coating
azimuth anglesearch for term
Compass direction from which the sunlight is coming. On the equinoxes, the sun rises directly east and sets directly west. All other times, the angle is off from that.
b
band gapsearch for term
Minimum change in energy required to excite an electron into the conduction band, so that it can participate in conduction
black body radiationsearch for term
A black body absorbs all radiation incident on its surface, and emits radiation based on its temperature. The sun approximates a black body. The sun emits light in the visible region, and thus can be harnessed by PV.
c
concentration gradientsearch for term
When the concentration of carriers varies from one area/region in the solar cell to another.
conductionsearch for term
Movement of the free valence electrons in a conductor material. In a conductor material, electrons are not tightly bound to the atom, and as a result, are free to participate in conduction.
conduction bandsearch for term
Energy level where excited electrons can participate in conduction. It is at a higher energy level than the valence band.
covalent bondsearch for term
Chemical bond whereby pairs of electrons are shared by two atoms
currentsearch for term
flow of electric charge carried out through the moving electrons in a conductor material
Czochralskisearch for term
A growth technique to produce a large ingot of single crystalline material such as silicon from a starting seed.
d
declination anglesearch for term
Because the earth is tilted at a 23.45 degree angle, the angle of the suns rays incident on the earth varies throughout the year. On the spring and autumnal equinoxes, the angle is 0 degrees , whereas on the winter and summer solstice, the angle is 23.45 degrees. The varying angle at which the suns rays are incident on the earth is this angle, demoted by δ.
diffusionsearch for term
Flow of free carriers from regions of high concentration to regions of low concentration, leading to a net movement of free carriers to regions of low concentration. Over time, the free carrier concentration will become uniform throughout the material.
diffusion lengthsearch for term
Average distance a carrier can move from point of generation until it recombines.
diffusivitysearch for term
Rate at which diffusion occurs. It depends on the velocity at which carriers move and on the distance between scattering events.
DLARCsearch for term
double layer anti-reflection coating
dopingsearch for term
Substituting atoms in the crystal lattice with impurity atoms to cause a change in the electron or hole concentration. In silicon, typical dopants are boron and phosphorous.
driftsearch for term
Type of transport that occurs as a result of an electric field being superimposed on the semiconductor (also occurs in metals). The result is a net movement of electrons in the direction opposite of the electric field and of holes in the direction of the electric field.
e
elevation anglesearch for term
Angular height of the sun in the sky measured from the horizontal, at 0 o at sunrise and 90 o when the sun is directly overhead.
energy of a photonsearch for term
E = hc/λ: h = Planks' constant, c = speed of light Light with high energy photons has a short wavelength, and vice-versa (low = long) Using the equation, you can determine E at a certain wavelength
equilibriumsearch for term
a system in balance with no net flow of energy. In semiconductors, equilibrium is where there is no external bias, no illumination and no transient changes.
equilibrium carrier concentrationsearch for term
Equal to the number of carriers in the conduction or the valence band. Therefore, the equilibrium concentration of minority carriers and majority carriers in each of the bands. Denoted as no for electron concentration and po for hole concentration. Typically, and because the majority carrier concentration is orders of magnitude above the intrinsic carrier concentration, the equilibrium concentration is equal to the majority carrier concentration in each band (valence (holes) or conduction (electrons)).
f
fill factorsearch for term
Maximum power from a cell divided by the ISCVOC product.
float zonesearch for term
a crystal growth process that produces high-quality ingots with few impurities. Typically abbreviated as FZ.
free carrierssearch for term
The carriers (electrons in the conduction band or the holes in the valence band) that are free move about the semiconductor lattice, and therefore participate in conduction. This can only occur when an electron in the valance band is excited into the conduction band, therefore making it free to participate in conduction.
g
generationsearch for term
When electron-hole pairs are generated due to the absorption of photons
i
ideality factorsearch for term
A measure of how closely the current voltage characteristics of a diode follow the ideal diode equation.
insolationsearch for term
INcidnet SOLar radiATION. The amount of energy from the sun over a given time period. Typical units are MJ/m2/day. Solar insolation is often used interchangeably with irradiance since both can be expressed in kW/m2.
insulatorsearch for term
description of a class of materials that do not participate in conduction because the valence electrons are tightly bonded to their atoms
intrinsic carrier concentrationsearch for term
Concentration of carriers in undoped material. This concentration is typically significantly lower than the concentration of the majority carrier concentration in doped materials. In intrinsic material, the concentration of electrons in the conduction band is equal to the concentration of holes in the valence band.
irradiancesearch for term
Solar radiation falling on a surface per unit area usually expressed in W/m2. It provides the power density at specific wavelengths. See also (solar) insolation.
l
lifetimesearch for term
Lifetime has two meanings on this website. It has the tradition definition of operational lifetime of the device. In photovoltaics the system lifetime may be 30 years or more. Lifetime also frequently refers to the minority carrier lifetime.
m
majority carriersearch for term
In doped material, the carrier with the higher concentration. Electrons are the majority carrier in n-type material. Holes are the majority carrier in p-type material.
minority carriersearch for term
In doped material, the carrier with the lower concentration. Electrons are the minority carrier in p-type material. Holes are the minority carrier in n-type material.
n
nisearch for term
intrinsic carrier concentration
o
open-circuit voltagesearch for term
The maximum cell voltage at zero current. VOC increases logarithmically with increased sunlight. Units of volts or millivolts.
optical path length search for term
The distance that an unabsorbed photon may travel within the device before it escapes out of the device.
p
PERLsearch for term
Passivated Emitter Rear Locally diffused
phononsearch for term
At a given temperature the crystal lattice vibrates. Vibrations in the crystal lattice are described by phonons the same way that electromagnetic vibrations are described by photons. While phonons are not covered in these pages they modify the way that electrons and photons interact and explain absorption and emission in greater detail.
photonsearch for term
A quantum of electromagnetic energy, regarded as a discrete particle having zero mass and no electric charge. Can be pictured as a wave packet
photon fluxsearch for term
Used in determining the number of electrons which are generated, and hence the current produced from a solar cell. Defined as the number of photons per second per unit area.
photovoltaicssearch for term
Abbreviated as PV, is a method of harnessing the sun's energy. PV devices (solar cells) convert incident solar radiation into electricity.
power densitysearch for term
Amount of power per unit area. It is calculated by multiplying photon flux by the photon energy. The photon flux of high energy (short wavelength)photons needed to give a certain power density is less than that photon flux for low energy (long wavelength)photons. Total power density (radiant power density) can be calculated by integrating the spectral irradiance over all wavelengths and energy of interest.
r
recombinationsearch for term
The process whereby an electron decays from its meta-stable state in the conduction band, into the valence band, and thus removes a hole.
s
semiconductorsearch for term
Material having unique properties such that it can act as both a conductor and an insulator.
short-circuit Currentsearch for term
The maximum current, at zero voltage. Ideally, ISC = IL so at zero voltage Isc is directly proportional to the incident sunlight.
shunt resistancesearch for term
A parasitic resistance in parallel with the solar cell. A high efficiency solar cell requires a high shunt resistance.
solar cellsearch for term
PV device that converts sunlight directly into electricity
solar radiancesearch for term
Instantaneous power density in units of KW/m2. It varies throughout the day from 0 (at night) to 1 (max during the day). It can be measured either globally, or directly. This is also known as solar radiation. It can go over 1 KW/m2.
solar timesearch for term
local solar time (LST) = when the sun is the highest in the sky, local time (LT)= varies from LST because of time zones, eccentricity of earth's orbit, etc.
surface recombinationsearch for term
Area of high recombination rates because the lattice structure is disrupted, leaving dangling bonds.
t
texturingsearch for term
A process, usually an etch, to structure the surface of a solar cell to reduce reflectivity.
TMYsearch for term
Typical Meteorological Year
v
valence bandsearch for term
Energy level holding bound electrons. It is at a lower energy level than the conduction band. Electrons become unbound when they become excited and have enough energy to be in the conduction band. The spot where these electrons were in this band becomes holes when they are excited into the conduction band.
valence electronssearch for term
Electrons that can participate in the formation of bonds with other atoms
Vocsearch for term
VOC open-circuit voltage
w
wave packetsearch for term
Collection of waves which may interact in such a way that the wave-packet may either appear spatially localised (act as a particle) or a wave. This concept is known as "wave-particle duality."
what have you learned?search for term
Provides the user with a question that checks their knowledge on the material covered in the section. The user will be asked to type a response to the question. After submitting the response, the correct answer to the question will be displayed. All submitted responses will be used to develop better questions for future users to check their knowledge of the content covered.
p
PVsearch for term
photovoltaics