pv solar cells i-v characteristic
TRANSCRIPT
8/11/2019 Pv Solar Cells I-V Characteristic.
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1
University of Technology
Laser and Optoelectronics Engineering Department
Optoelectronics Engineering Branch
Detector Lab 2010-2011
7Exp
Solar Cells I-V characteristic.
فخري عد د وتنفيذ لمدرس مكرم عبد لمطل
Object.
Find the current and voltage response under illumination depending on the magnitude of the
variable resistance.
Tools1- Source
2- Variable resistance
3- Slid board
4- Voltmeters
How a Solar Cell Works?
A solar photovoltaic (PV) cell converts sunlight to electricity. In the photoelectric effect at a
metal surface, electrons are freed once the
energy exceeds the bond energy. In a solar cell, an asymmetry is established by contacting twosemiconductors of opposite polarity which drives electrons that are freed by the incident light in
a circuitsolar cell consists of two layers of semiconductor, one positive (p-type) and the other negative(n-type), sandwiched together to form a p/n junction.
When the semiconductor is exposed to light, the energy hµ of incident photons exceeding the
threshold band gap is absorbed by the semiconductors electrons that access the conduction bandstarting to conduct electricity. Electrons in semiconductors, in fact, are weakly bonded to the
atomic nucleus and occupy the valence energy band.
for each negatively charged electron, a corresponding mobile positive charge, a hole, is created.The electrons and holes near the p/n junction are swept across in opposite directions by the
action of the electric field, where a contact drives such electrons to an external circuit where they
lose energy doing work such as powering a
light source and then return to the materials valence band through a second selective contactclosing the circuit .
Only photons whose energy is greater than the energy band gap (EG) are able to create an
electron–hole pair and thus contribute to the energy conversion process. Therefore, the spectralnature of sunlight is a fundamental aspect affecting the design of efficient solar cells.
The solar cell is the photovoltaic’s building block. Usually, it is made of a 100 cm2 silicon wafer
whose surface has been treated to maximize light absorption and thus appears dark blue or black.
Such a cell hit by radiation from the sun generates tens of milliamps per cm2 current caused by a
0.5–1 V potential, which is too low for most applications.
EXP.NO. (7)
Solar Cells I-V characteristic
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University of Technology
Laser and Optoelectronics Engineering Department
Optoelectronics Engineering Branch
Detector Lab 2010-2011
The Solar Cell: A Current Generator.
In practice, when a load is present a potential difference develops between the terminals of the
cell. This potential generates a current which acts in the opposite direction to the photocurrent,and the net current is reduced from its short circuit value. This reverse current is called the dark
current, in analogy with the current I dark (V) which flows across the device under an applied
voltage, or bias, V, in the dark.
Most solar cells behave as a diode in the dark, admitting a much larger current under forward bias (V > 0) than under reverse bias (V < 0). For an ideal diode, the dark current density varies
like
Jdark = Jo(eqV/kBT
_1)
Where kB is Boltzmann.s constant, T is the temperature and Jo is a constant. Thusthe net current
flowing in a circuit powered by a solar cell is
J(V) = Jsc _Jdark
J(V) = Jsc _Jo(eqV/kBT
_1)
.
Current–voltage curve for an ideal diode in the dark
and under light.
J–V curve for solar cell shows a strongly
field-dependent photocurrent
EXP.NO. (7)
Solar Cells I-V characteristic
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University of Technology
Laser and Optoelectronics Engineering Department
Optoelectronics Engineering Branch
Detector Lab 2010-2011
Procedure.In this measurement we want to record with high accuracy the voltage versus current
dependence on our device. While the previous measurement allowed us to see the response of the
device to different colors of light we did not get any accurate information as to the magnitude ofthe response. It’s important when reporting the performance of a solar cell to report the
efficiency of the response to a solar light source we will now allow bright white light to excite
the solar cell .we will record the current and voltage response under this illumination depending
on the magnitude of variable resistance.
To determine the Ideality factor of the Solar cell. (Optional)
Fig. 1: Experimental set-up for determining characteristic curves.
Fig. 2: Circuit for measuring the current-voltage characteristic.
EXP.NO. (7)
Solar Cells I-V characteristic
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University of Technology
Laser and Optoelectronics Engineering Department
Optoelectronics Engineering Branch
Detector Lab 2010-2011
typical I-V curve plot.
On an I-V plot, the ordinate refers to current, and the abscissa to voltage. The I-V
curve passes through two significant points, the short-circuit current (Isc
) and the open-circuit
voltage (Voc
). The Isc
refers to the current when the output terminals of the cell are short-circuited.
In the plot this point is the intercept of the
curve with vertical axis. The Voc
is the voltage measured at open circuit conditions and is represented
as the intercept of the curve with the horizontal axis in the plot
.
Figure 3: Typical I-V Curve
Maximum Power (Pmp
)
The solar cell may be operated over a wide range of voltages and currents by varyingthe load resistance from zero to infinity. The Maximum Power (P
mp) point occurs when the
product of the current and voltage is maximum. The current and voltage at the maximum power
point are denoted by Imp
and Vmp
, respectively. (See Figure 3).
The maximum power that a cell can deliver to a load is obtained when . VI =VmIm
Fill Factor (FF)
The fill factor (FF) percentage measures the "squareness" of the I-V curve. It statesthe degree to which the voltage at the maximum power point (V
mp) matches the open-circuit
voltage (Voc
) and that the current at the maximum power point (Imp
) matches the short-circuit
Imax
Voc
Voc
EXP.NO. (7)
Solar Cells I-V characteristic
8/11/2019 Pv Solar Cells I-V Characteristic.
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University of Technology
Laser and Optoelectronics Engineering Department
Optoelectronics Engineering Branch
Detector Lab 2010-2011
current (Isc
). Therefore, a more “squared” I-V curve will have a higher fill factor.
This relation is given by.
The fill factor (FF) is defined by the ratio
FF =VscIsc
Vm Im
Quantum Efficiency (QE)
Quantum efficiency (QE) is the ratio of the number of charge carriers collected by
the solar cell to the number of photons of a given energy incident on the PV device. QE thereforeis related to the response of a solar cell to the various wavelengths in the spectrum of incident
light on the cell. The QE is given as a function of either wavelength or energy.
QE = pin
pout =
Ps
Pm
Where Pm = VmImPs is incident light power
Variable ResistanceΩ Voltage Vvolt Current I m amp Power Pwatt = V.I0
1050
100
500
1000100000
15000
25000
50000
100000500000
1000000
Discussion.
1-Describe the J-V plot that you made and tell me what the physical effect is responsible for each
of the features that you observe.
2-what is different between photoelectric properties of any type and iso type of heterojunctions
EXP.NO. (7)
Solar Cells I-V characteristic