In this slide we are going to see How Photovoltaic works and what are their parameters and factors.

1. Solar Cell
Operation
Muhammad Faizan Hassan
SP21-RPH-013
MS PHYSICS 3rd Semester
Presentation submitted to Dr. Shehzada Qamar
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Solar Energy
Solar energy in one form or another is the source of nearly all energy on the earth.
Humans, like all other animals and plants, rely on the sun for warmth and food. However,
people also harness the sun's energy in many other different ways.
Similarly, biomass converts the sun's energy into a fuel, which can then be used for heat,
transport or electricity. Wind energy, used for hundred of years to provide mechanical
energy or for transportation, uses air currents that are created by solar heated air and the
rotation of the earth. Today wind turbines convert wind power into electricity as well as its
traditional uses. Even hydroelectricity is derived from the sun. Hydropower depends on the
evaporation of water by the sun, and its subsequent return to the Earth as rain to provide
water in dams. Photovoltaic (often abbreviated as PV) is a simple and elegant method of
harnessing the sun's energy.
PV devices (solar cells) are unique in that they directly convert the incident solar radiation
into electricity, with no noise, pollution or moving parts, making them robust, reliable and
long lasting.
Solar Cell Operation

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01
Table of Content
Solar cell structure, Light generated structure, collection probability,
Quantum efficiency, Spectral response, PV effect
Ideal Solar Cells
02 IV curve, Short-circuit current, Open-circuit voltage, Fill
factor, efficiency, Detailed balance, Tandem cells.
Solar Cell Parameters
03 Characteristic resistance, Effect of parasitic resistances, series resistance,
shunt resistance, Impact of both series and shunt resistance
Resistive Effects
04 Effect of temperature, Effect of Light Intensity, Ideality
Factor.
Other Effects
Solar Cell Operation

4. Ideal Solar Cell
• Solar Cell Structure
o A solar cell is an electronic device which directly converts
sunlight into electricity.
o A material in which the absorption of light raises an
electron to a higher energy state.
o The movement of this higher energy electron from the
solar cell into an external circuit.
o Nearly all photovoltaic energy conversion uses
semiconductor materials in the form of a p-n junction.
The basic steps in the operation of a solar cell are:
• the generation of light-generated carriers;
• the collection of the light-generated carries to generate a
current;
• the generation of a large voltage across the solar cell; and
• the dissipation of power in the load and in parasitic
resistances.

5. Solaire Powered Light Generated Current
The ideal short circuit flow of electrons and holes at a p-n junction. Minority
carriers cannot cross a semiconductor-metal boundary and to prevent
recombination they must be collected by the junction if they are to contribute
to current flow.
The generation of current in a solar cell, known as the "light-generated current", involves
two key processes.
• The first process is the absorption of incident photons to create electron-hole pairs.
• A second process, the collection of these carriers by the p-n junction, prevents this
recombination by using a p-n junction to spatially separate the electron and the hole.
Solar Cell Operation

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The light-generated current depends on the generation of
carriers and the collection probability of these carriers.
Collection Probability
The "collection probability" describes the probability that a carrier
generated by light absorption in a certain region of the device will be
collected by the p-n junction and therefore contribute to the light-generated
current, but probability depends on the distance that a light-generated carrier
must travel compared to the diffusion length.
Solar Cell Operation
The impact of surface passivation and diffusion length on
collection probability is illustrated below.

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The "quantum efficiency" (Q.E.) is the ratio of the number of carriers collected by the
solar cell to the number of photons of a given energy incident on the solar cell.
Quantum Efficiency
While quantum efficiency ideally has the square shape, the quantum efficiency for most
solar cells is reduced due to recombination effects. The same mechanisms which affect
the collection probability also affect the quantum efficiency.
03
The quantum efficiency for photons with energy below the band gap is zero.
02
If all photons of a certain wavelength are absorbed and the resulting minority carriers
are collected, then the quantum efficiency at that particular wavelength is unity.
01
The quantum efficiency may be given either as a function of wavelength
or as energy.
About Quantum Efficiency
Solar Cell Operation
The quantum efficiency of a silicon solar cell. Quantum
efficiency is usually not measured much below 350 nm as
the power from the AM1.5 contained in such low
wavelengths is low.

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The spectral response uses the power of the light at each wavelength whereas the
quantum efficiency uses the photon flux. Converting QE to SR is done with the following
formula:
Spectral Response
• The ideal spectral response is limited at long wavelengths by the
inability of the semiconductor to absorb photons with energies
below the band gap.
• Unlike the square shape of QE curves, the spectral response
decreases at small photon wavelengths.
• The inability to fully utilize the incident energy at high energies, and
the inability to absorb low energies of light represents a significant
power loss in solar cells consisting of a single p-n junction.
Properties/Dependence
The quantum efficiency gives the number of electrons output by the solar
cell compared to the number of photons incident on the device, while the
spectral response is the ratio of the current generated by the solar cell to
the power incident on the solar
Solar Cell Operation

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Voltage is generated in a solar cell by a process known as the "photovoltaic effect“.
The collection of light-generated carriers by the p-n junction causes a movement of electrons to the n-type
side and holes to the p-type side of the junction. Under short circuit conditions, there is no build up of
charge, as the carriers exit the device as light-generated current.
The photovoltaic effect
• This separation of charge creates an electric field at the junction which is in opposition to that already existing at the junction, there
by reducing the net electric field.
• The electric field represents a barrier to the flow of the forward bias diffusion current, the reduction of the electric field increases the
diffusion current. A new equilibrium is reached in which a voltage exists across the p-n junction.
Process of PV
Solar Cell Operation

10. Solar Cell Parameters
 IV Curve
 Short-Circuit Current
 Open-Circuit Voltage
 Fill Factor
 Efficiency
 Tandem Cells

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Solar Cell I-V Characteristics Curves are basically a graphical representation of the
operation of a solar cell or module summarizing the relationship between the current
and voltage at the existing conditions of irradiance and temperature.
I-V Curve
The light has the effect of shifting the IV
curve down into the fourth quadrant where
power can be extracted from the diode.
Illuminating a cell adds to the normal "dark"
currents in the diode so that the diode law
becomes:
About I-V Curve:
Andreas
Current voltage (IV) cure of a solar cell. To get the maximum
power output of a solar cell it needs to operate at the
maximum power point, PMP.
Solar Cell Operation
The equation for the IV curve in the first
quadrant is:

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The short-circuit current is the current through the solar cell when the voltage across the
solar cell is zero (i.e., when the solar cell is short circuited). Usually written as ISC, the
short-circuit current is shown on the IV curve below.
Short-Circuit Current
The short-circuit current is due to the
generation and collection of light-
generated carriers. For an ideal solar
cell at most moderate resistive loss
mechanisms, the short-circuit current
and the light-generated current are
identical. Therefore, the short-circuit
current is the largest current which may
be drawn from the solar cell.
About Short-Circuit Current:
Andreas
IV curve of a solar cell showing the short-circuit current.
Solar Cell Operation
Dependence of Short-Circuit Current:
• The area of the solar cell.
• The number of photons
• The spectrum of the incident light.
• The optical properties
• The collection probability
In a cell with perfectly passivized
surface and uniform generation, the
equation for the short-circuit current
density can be approximated as:
The short circuit current, ISC, is the short circuit current density, JSC,
times the cell area:

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The open-circuit voltage, VOC, is the maximum voltage available from a solar cell, and this occurs at
zero current. The open-circuit voltage corresponds to the amount of forward bias on the solar cell due to
the bias of the solar cell junction with the light-generated current. The open-circuit voltage is shown on
the IV curve below.
Open-Circuit Voltage
An equation for Voc is found by setting the net
current equal to zero in the solar cell
equation to give:
About Open-Circuit Voltage:
Andreas
IV curve of a solar cell showing the open-circuit voltage.
Solar Cell Operation
A casual inspection of the above equation might indicate that VOC goes
up linearly with temperature. However, this is not the case as
I0 increases rapidly with temperature primarily due to changes in
the intrinsic carrier concentration ni. The effect of temperature is
complicated and varies with cell technology.
VOC decreases with temperature. If temperature changes, I0 also
changes.
The VOC can also be determined from the carrier concentration:

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The short-circuit current and the open-circuit voltage are the maximum current and voltage respectively from
a solar cell. However, at both of these operating points, the power from the solar cell is zero. The "fill factor",
more commonly known by its abbreviation "FF", is a parameter which, in conjunction with Voc and Isc,
determines the maximum power from a solar cell. The FF is defined as the ratio of the maximum power from
the solar cell to the product of Voc and Isc so that:
Fill Factor
As FF is a measure of the "squareness" of the IV curve, a solar cell with a
higher voltage has a larger possible FF since the "rounded" portion of the IV
curve takes up less area. The maximum theoretical FF from a solar cell can
be determined by differentiating the power from a solar cell with respect to
voltage and finding where this is equal to zero. Hence:
About Fill Factor:
Andreas Graph of cell output current (red line) and power (blue line) as a
function of voltage. Also shown are the cell short-circuit current
(Isc) and open-circuit voltage (VOC) points, as well as the
maximum power point (Vmp, Imp).
Solar Cell Operation
Substituting the value of VMP back into the diode equation gives IMP and
then FF. A more commonly used empirical expression for the FF is

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The efficiency is the most commonly used parameter to compare the performance of one
solar cell to another.
“Efficiency is defined as the ratio of energy output from the solar cell to input energy from
the sun”.
Solar Cell Efficiency
Andreas
Solar Cell Operation
Dependence of Solar Cell Efficiency:
• Spectrum
• Intensity of incident sunlight
• Temperature of Solar Cell
Conditions:
Conditions under which efficiency is measured must be carefully controlled
in order to compare the performance of one device to another.
Terrestrial solar cells are measured under AM1.5 conditions and at a
temperature of 25°C.
Solar cells intended for space use are measured under AM0 conditions
The efficiency of a solar cell is determined as the fraction of incident
power which is converted to electricity and is defined as:

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One method to increase the efficiency of a solar cell is to split the spectrum and use a solar cell that
is optimized to each section of the spectrum..
Tandem Cells
About Tandem Cells:
Andreas
Solar Cell Operation
Tandem solar cells can either be individual cells or connected in series. Series connected cells are simpler to fabricate but the current is
the same though each cell so this contains the band gaps that can be used. The most common arrangement for tandem cells is to grow
them monolithically so that all the cells are grown as layers on the on substrate and tunnel junctions connect the individual cells.

17. Resistive Effects
I. Characteristic Resistance
II. Effect of Parasitic Resistances
III. Series Resistance
IV. Shunt Resistance
V. Impact of Both Series and Shunt Resistance

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The characteristic resistance of a solar cell is the cell's output resistance at its maximum power point. If the resistance of the load is equal to the
characteristic resistance of the solar cell, then the maximum power is transferred to the load, and the solar cell operates at its maximum power
point. It is a useful parameter in solar cell analysis, particularly when examining the impact of parasitic loss mechanisms. The characteristic
resistance is shown in the figure below.
Characteristic Resistance
The characteristic resistance of a solar cell is the
inverse of the slope of the line, shown in the figure as
VMP divided by IMP. For most cells, RCH can be
approximated by VOC divided by ISC:
About Characteristic Resistance:
Andreas
Solar Cell Operation
The equation for The characteristic resistance is
useful because it puts series and shunt resistance in
context.
Series Resistance and Power Loss:
As long as the power loss is reasonable (< 20%), the
characteristic resistance also allows for a conversion
between the fractional power loss and series
resistance in Ω or Ω cm².
Shunt Resistance and Power Loss:
Similarly, the shunt resistance is related to the power loss by

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Resistive effects in solar cells reduce the efficiency of the solar cell by dissipating power in the
resistances. The most common parasitic resistances are series resistance and shunt resistance.
The inclusion of the series and shunt resistance on the solar cell model is shown in the figure
below.
Effect of Parasitic Resistances
About Parasitic Resistances:
Andreas
Solar Cell Operation
Parasitic series and shunt resistances in a solar cell circuit.
The key impact of parasitic resistance is to
reduce the fill factor. Both the magnitude and
impact of series and shunt resistance depend
on the geometry of the solar cell, at the
operating point of the solar cell.
Series Resistance
Series resistance in a solar cell has three causes: firstly, the movement of current through
the emitter and base of the solar cell; secondly, the contact resistance between the metal
contact and the silicon; and finally the resistance of the top and rear metal contacts. The
main impact of series resistance is to reduce the fill factor, although excessively high
values may also reduce the short-circuit current.
Schematic of a solar cell with series resistance.

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Significant power losses caused by the presence of a shunt resistance, RSH, are typically due to manufacturing defects, rather than poor solar cell
design. Low shunt resistance causes power losses in solar cells by providing an alternate current path for the light-generated current. The effect of a
shunt resistance is particularly severe at low light levels, since there will be less light-generated current. The loss of this current to the shunt
therefore has a larger impact. In addition, at lower voltages where the effective resistance of the solar cell is high, the impact of a resistance in
parallel is large.
Shunt Resistance
About Shunt Resistance:
Solar Cell Operation
Circuit diagram of a solar cell including the shunt resistance.
The equation for a solar cell in presence of a shunt resistance is:
where: I is the cell output current, IL is the light generated current, V is the
voltage across the cell terminals, T is the temperature, q and k
are constants, n is the ideality factor, and RSH is the cell shunt resistance.
Impact of Both Series and Shunt Resistance

21. Other Effects
 Effect of Temperature
 Effect of Light Intensity
 Ideality Factor

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Like all other semiconductor devices, solar cells are sensitive to temperature. Increases in temperature reduce the band gap of a
semiconductor, thereby effecting most of the semiconductor material parameters. The decrease in the band gap of a semiconductor
with increasing temperature can be viewed as increasing the energy of the electrons in the material. Lower energy is therefore
needed to break the bond. In the bond model of a semiconductor band gap, a reduction in the bond energy also reduces the band
gap. Therefore increasing the temperature reduces the band gap.
In a solar cell, the parameter most affected by an increase in temperature is the open-circuit voltage. The impact of increasing
temperature is shown in the figure below.
Effect of Temperature
Andreas
Solar Cell Operation
Change in Voc with temperature as reported in the CEC module database
compared with the prediction from ni change with temperature.
The effect of temperature on the IV characteristics of a
solar cell.

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Andreas
Solar Cell Operation
Changing the light intensity incident on a solar cell changes all solar cell parameters, including the short-circuit current, the
open-circuit voltage, the FF, the efficiency and the impact of series and shunt resistances. The light intensity on a solar cell is
called the number of suns, where 1 sun corresponds to standard illumination at AM1.5, or 1 kW/m2
The experimental results show that the open circuit voltage, short-
circuit current, and maximum output power of solar cells increase
with the increase of light intensity. Therefore, it can be known that
the greater the light intensity, the better the power generation
performance of the solar cell.

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Ideality Factor
Andreas
Solar Cell Operation
The ideality factor of a diode is a measure of how closely the diode follows the ideal diode equation. The derivation of the
simple diode equation uses certain assumption about the cell. In practice, there are second order effects so that the diode
does not follow the simple diode equation and the ideality factor provides a way of describing them.

25. Thank You