transcript
- Slide 1
- Applications of Photovoltaic Technologies
- Slide 2
- 2 Solar Cell-structure A solar cell is a P-N junction device
Light shining on the solar cell produces both a current and a
voltage to generate electric power. Busbar Fingers Emitter Base
Rear contact Antireflection coating Antireflection texturing (grid
pattern)
- Slide 3
- I-V Tester 3
- Slide 4
- Illumination Sources ClassSpectral Match Irradiance
inhomogeneity Temporal Instability Long TermShort Term A0.75 -
1.25%2%0.5%2% B0.6 - 1.4%5%2%5% C0.4-2.0%10% 4 Table: Solar
simulator classification according to IEC 60904-9 Ed. 2.0.
- Slide 5
- 5 No Resistive Losses ILIL I IDID V Solar Cell model The I-V
relation is given as: I o dark saturation current, I L light
generated current., n ideality factor.
- Slide 6
- 6 Solar Cell I-V Curve V I I (diffu.) I0I0 Effect of solar
radiation on the I-V curve Under illumination solar cell can be
operated in the fourth quadrant corresponding to delivering power
to the external circuit A P-N junction in the dark consumes power,
as it can be operated in 1 st or 3 rd quadrant Current in the
illuminated solar cell is negative, flows against the conventional
direction of a forward diode
- Slide 7
- 7 Solar Cell I-V Curve I sc I VmVm ImIm V oc PmPm V Usual I-V
plot of solar cell Current is shown on positive y - axis Solar cell
parameters V oc - open circuit voltage, I sc - short circuit
current, P m - maximum power point I m, V m current and voltage at
maximum power point FF fill factor efficiency R s series resistance
R sh shunt resistance
- Slide 8
- 8 Short-Circuit Current, I sc 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). The
short-circuit current is due to the generation and collection of
light-generated carriers. The short-circuit current is the largest
current which may be drawn from the solar cell. At V=0 I = -I L = I
sc I VmVm ImIm V oc PmPm X
- Slide 9
- 9 Open Circuit Voltage: V oc The open-circuit voltage, V oc, is
the maximum voltage available from a solar cell, and this occurs at
zero current. I sc I VmVm ImIm PmPm X V oc The open-circuit voltage
corresponds to the amount of forward bias on the solar cell
junction due to illumination. At I=0 V = V oc
- Slide 10
- 10 Maximum power: P m I sc I VmVm ImIm PmPm X V oc Power Power
out of a solar cell increases with voltage, reaches a maximum (P m
) and then decreases again. P m = I m x V m Remember we get DC
power from a solar cell
- Slide 11
- 11 Fill Factor: FF I sc I VmVm ImIm V oc Ideal diode curve PmPm
The FF is defined as the ratio of the maximum power from the actual
solar cell to the maximum power from a ideal solar cell
Graphically, the FF is a measure of the "squareness" of the solar
cell
- Slide 12
- 12 Efficiency: Efficiency is defined as the ratio of energy
output from the solar cell to input energy from the sun. The
efficiency is the most commonly used parameter to compare the
performance of one solar cell to another. I sc I VmVm ImIm PmPm X V
oc Power Efficiency of a cell also depends on the solar spectrum,
intensity of sunlight and the temperature of the solar cell.
- Slide 13
- Four Point Probe Resistivity Measurements 13
- Slide 14
- 14 Effect of R s and FF I sc V oc V I Medium Rs Large Rs
Characteristic resistance, R ch Normalized series resistance, r s
Effect of series resistance on the FF and maximum power Slope of
the I-V curve near V oc gives indication about R s
- Slide 15
- 15 Effect of R sh on FF I sc V oc V I Medium R sh Slope of the
I-V curve near I sc gives indication about R sh Normalized shunt
resistance, r sh Effect of series resistance on the FF and maximum
power
- Slide 16
- ScienceTech 150W ScienceTech 150W IV Substrate > 5.0 cm x
5.0 cm 0.1V to 1.0V I-V V oc I sc P mp (fill factor) (efficiency)
25 16
- Slide 17
- ScienceTech 17
- Slide 18
- IV measurement 18
- Slide 19
- IV Analysis 19
- Slide 20
- (IPCE) 20
- Slide 21
- Quantum Efficiency 21 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. Internal
quantum efficiency (IQE) refers to the efficiency with which
photons that are not reflected or transmitted out of the cell can
generate collectable carriers. External quantum efficiency (EQE) of
a silicon solar cell includes the effect of optical losses such as
transmission and reflection.
- Slide 22
- Quantum Efficiency 22