chapter- 4 instrumentation and method characterization

chapter- 4 instrumentation and method characterization
CHAPTER- 4
INSTRUMENTATION
AND
METHOD CHARACTERIZATION
4.1. Characterization technique of ARC glass substrate
Following instruments would be require for method characterization of ARC solution and
ARC glass substrate4.1.1. pH meter
4.1.2. UV-VIS Spectrometer
4.1.3. Atomic Force Microscope (AFM)
4.1.4. Climate test chamber-WK340/40
4.1.1. pH meter:
A pH meter is an electronic device, which is used for measure the pH of a liquid. A typical PH
meter consists of a special measuring probe that is a glass electrode, connected to an
electronic meter that displays & measures the pH value. A pH meter measure a value that how
liquid is acidic or alkaline. The theory of the pH meter is to determine the conc. of H+. When
dissolved the acid in water form positively charged H+ and the higher conc of H+ ions show the
acid is stronger. In the same way when dissolved alkali in water form negative charged hydroxyl
ions and the higher conc of hydroxyl ions show the base is the stronger. The amt of hydrogen
ions present in sol is dissolved in some amt of water find out the value of pH.
A pH = 7.0, show that, solution is a neutral means pure water having a pH = 7.0. When pH
values < 7 it’s indicate solution is acidic while a pH value > 7 will indicate sol is basic. pH value
of sol is 1.0 than it’s a extremely acidic sol and a sol of pH = 14.0 is than its extremely alkaline.
Figure 41: pH meter
Probe:
Probe is a key part of a pH meter. It is a rod like structure generally made by glass. At the
bottom of the probe there is a bulb, the bulb is a very sensitive part of a probe that contains the
sensor. To determine the pH of a soln, the probe is proper dipped into the soln. Probe also
making with 02 nos. electrodes. These electrical signals go through a probe to a meter its
shows the pH value reading. Probe having 02 nos. electrodes; first one is a glass sensor
electrode and another than is a reference electrode. Both type of electrodes are hollow bulbs,
which contain a KCl sol, and also suspended AgCl wires in it. Glass sensing electrode making
with an extraordinary glass coated with metal salts & silica [101].
Figure 42: pH Electrode
Calibration and Operation of pH Meter:
pH Meter Instrument, calibration and operating procedure can be define shortly in following
simple steps:
•
First prepare buffer solution for 4.01, 9.18 and 10.01. So for dissolve one capsule of
each buffer in 100 ml distilled water or HPLC grade water.
•
Dip the electrode in PH 4.01 buffer solution and adjust display to get the reading 4.01.
•
Carried out same exercise for buffer solution of 9.18 and 10.01.
•
Display should be adjusted to specified buffer value.
•
Ensure that temperature sensor is dipped in solution while taking pH and adjust knob to
at room temperature.
•
Check the instrument twice with the above buffer solution.
•
If the value observed is with in range of ± 0.05 from specific value, then pH meter is
ready for use.
•
Wash electrode every time with distilled water or HPLC grade water, when buffer or test
solution is to be checked.
•
Keep the electrode in distilled water or HPLC grade water after used.
•
Select alkaline or acidic both buffer solution for calibration.
•
Fresh buffer solution prepared after two weeks.
Precautions of glass probes during handling:
•
All time glass probe tip kept proper wet.
•
When a glass electrode alone then stored it’s in deep in an acidic soln.
•
Distilled or DI water not used for longer-term.
•
Joint electrodes are better stored immersed in the bridge electrolyte frequently
potassium chloride 3.0 M.
4.1.2. UV-VIS Spectrometer:
UV Spectrophotometer (Perkin-Elmer Lambda 35) work on Beers & Lambert's Law, which
states that absorbance is depends on width of the absorbing layer & concentration. Here we
keep width constant. This is used for concentration determination in organic Solution [102]. In
this project we used UV-VIS spectrophotometer for treated glass substrates transmittance
analysis. The operating software of instrument is UV Winlab. UV Spectrophotometer (PerkinElmer Lambda 35) image is as follow
Figure 43: UV-VIS Spectrometer for analysis of transmittance of glass substrate
The functional part image of UV –Vis Spectrophotometer for absorbance analysis of liquid
sample are as follow
Figure 44: Functional part of UV-VIS Spectrometer
Operating procedure of UV-VIS Spectrometer:
•
Power switch on of UV VIS Spectrometer instrument and computer.
•
After initialization of instrument, open the UV Winlab software.
•
Set all instrument parameters as well as analysis parameters
•
Give command for instrument auto zero
•
After completion of auto zero, give command for blank with BaSO4 std.
•
After completion of auto zero, give command for blank with BaSO4 std.
•
After completion of blank measurement take %transmittance for substrate.
Calibration of UV-VIS Spectrometer: Calibration of UV-VIS Spectrometer can be illustrate by
following flow chart-
Figure 45: Flow chart for calibration of UV-VIS Spectrometer
External Calibration of UV-VIS Spectrometer:
•
Baseline Flatness
•
Wavelength Accuracy
•
Stray Light
•
Wavelength repeatability
•
Photometric Accuracy
•
Photometric Repeatability
Instrumental trouble during analysis:
During analysis of any solution we can be facing following problem
1) Lambda shifting.
2) Base line becomes broad.
3) Start up lambda did not show 650 nm.
4) Base line noise developing during the period of scanning.
5) Week lamp changing.
1) Lambda shifting: Following reason for lambda shifting•
In proper solution
•
Contamination in sample
•
Low lamp energy
•
Solution should be homogeneous
•
Check the contamination
•
Change the lamp.
2) Base line become broad: Following reason for base line become broad•
Filter wheel motor problem
•
Sample not proper
•
Any alignment disturb in monochromator
Solution:
•
Call to service engineer
•
Sample should be homogeneous
3) Start up lambda did not show 650 nm: It may be occurs due to D2 or Tungsten lamp is
fused or low energy.
Solution: To change the lamp. After Every change of lamp, fitment should be verified through
described method. These two are the observing points.
•
Noise observation at initializing stage.
•
Both light beam observation on the paper at single wavelength (326 nm).
4) Base line noise developing during the period of scanning: Following factor responsible
for base line noise.
•
Due to lamp
•
Due to filter wheel
•
Due to open mirror
Solution:
•
If lamp energy is low then change the lamp.
•
Do not touch the mirror or filter wheel during lamp changing.
5) Week lamp changing: If during initialization 650 nm wavelength not show, that means lamp
is fused or low energy.
Solution: Change the lamp.
Another trouble causes during analysis can be show by following flow chart-
Figure 46: Flow chart for cause of trouble in UV-VIS Spectrometer
Precautions during handling UV-VIS Spectrometer:
Figure 47: Do/Don’t Chart for UV-VIS Spectrometer
Analysis of %Transmittance of glass substrate by using Integrating Sphere in UVVIS spectrometer:
For analysis of transmittance or Reflectance by UV-VIS Spectrometer, that provides us.
Integrating Labsphere (RSA-PE-20) accessory with instrument. The Labsphere RSA-PE-20 is a
diffuse reflectance and transmittance accessory designed for a number of PerkinElmer UV-VIS
spectrometers. The list of compatible spectrometers includes the Lambda 25/35/45 series as
well as the older models Lambda 2/12/14/20/40.
Description of Integrating Sphere (RSA-PE-20):
The Integrating Sphere (RSA-PE-20) accessory is specifically designed to measure the
reflectance or transmittance of solids, liquids, powders, or other small objects that can fit in the
transmittance or reflectance ports. Basic components of the accessory include the integrating
sphere, transfer optics and detector pre amplification module. Although the RSA-PE-20 is a
single beam construction, the accessory is compatible with the double beam configuration of the
Lambda Series spectrometers and your UV Winlab software. The integrating sphere assembly,
shown in below Figure, is 50 mm in diameter and constructed of Spectralon. Spectralon is the
same material used on the reflectance standard supplied with the accessory.
Figure 48. Integrating sphere (RSA-PE-20)
The RSA-PE-20 integrating sphere features two ports: a transmittance port where the beam
enters the sphere, and a sample reflectance port. The illustration in Figure 7 shows the
accessory integrating sphere along with the transfer optics and preamplification board. The
silicon detector is mounted directly to the preamp board underneath. Two Spectralon baffles
inside the sphere shield the detector sensor from direct illumination by the ports.
Figure 49: Constructions of Integrating Sphere
The sample holders, mounted either at the transmittance or sample reflectance port, clamp the
Sample Reflectance standard or sample against the respective port. Three sample holders are
provided with the accessory for mounting a sample either at 0° or 8° angles of incidence. The
sample holders mount directly to the port frame at each end of the sphere. The sphere detector
is a silicon photodiode installed at the detector port at the bottom of the integrating sphere. The
photodiode operates in photovoltaic mode; the preamplifier board for compatibility with the
instrument electronics conditions the detector output.
Integrating sphere accessory alignment: Proper alignment of integrating sphere is requiring
during installation of instrument. The Optical setup of the RSA-PE-20 accessory can be show
as in following figure-
Figure 50: Optical setup of the RSA-PE-20 accessory
Sample Beam Energy Scan: Before analysis the sample we require sample beam energy scan
of instrument for that setup the following instrument parameter according to below tableInstrument Parameters
Setting
Lamps
UV/Vis ON
Beam
Single Beam
Method
Scan
Data Interval
1 nm
Abscissa Start
250
Abscissa End
1100
Slit Mode
Fix
Slit
2 nm
Integration Time
0.08 s
Ordinate Mode
E1
Sample Beam
Front
Attenuator
100%
Table 2: Instrument setup for sample beam energy scan
100% Baseline Scan: After sample beam energy scan we require 100% Baseline
Scanning of instrument. For that purpose, setup the following instrument
parameter according to below table-
Instrument Parameters
Setting
Lamps
UV/Vis ON
Beam
Double Beam
Method
Scan
Data Interval
1 nm
Abscissa Start
250
Abscissa End
1100
Slit Mode
Fix
Slit
2 nm
Integration Time
0.08 s
Ordinate Mode
%T
Sample Beam
Front
Attenuator
100% /100%
Table 3: Instrument setup for 100% Baseline Scane
Loading the Sample Holders:
Both transmittance and sample reflectance ports are 5/8-inch holes at either end of the
accessory sphere. The transmittance port is closest to mirror M3. A sample holder clamp fits
over a dovetail extension located underneath each port, securing the reflectance standard or
sample tightly against the port opening.
The sample holder with the 8ーwedge should be installed at the sample reflectance port when
taking 8ーhemispherical measurements. The 0ーsample holder should be installed at the sample
reflectance port when taking diffuse measurements with the specular component excluded.
Figure 8 describes the proper way to load the sample holder. When mounting a sample or
reflectance standard at any port, you should make sure the
reflecting surface lies flat against the wedge and completely fills the port surface area. To
remove the sample holder at the sample reflectance port, loosen the setscrews along the side of
the respective wedge and remove the entire sample holder assembly.
Figure 51: Loading a standard or sample in to sample holder
In some instances, you may need to load a light trap at the sample reflectance port. The light
trap can be loaded using either wedge or fits into the sample holder in the same manner as a
reflectance standard.
Theory of Operation:
During the traditional measurement of sample absorption by a spectrometer, the relationship
between absorptance and transmittance of the sample beam is described by the Kirchoff
equation:
A+T=1
Where: A = absorbance & T = transmittance.
When measuring the absorbance of a sample in the sample compartment, the detector signal of
the spectrometer represents the portion of the sample beam i.e. not absorbed or scattered by
sample.
When using the RSA-PE-20 accessory, it is convenient to use the Kirchoff relationship:
A+T+R=1
where R = reflectance of the sample beam at the sample surface.
During reflectance analysis, the reflected component of the sample beam is collected by the
integrating sphere and detected by sphere detector.
Zero line Correction:
An integrating sphere is sensitive to small-angle scatter from the sample beam coupling optics.
The scattered radiation strikes the wall of the integrating sphere near the sample reflectance
port, creating a "halo" surrounding the port. This "halo-effect" gives rise to a small error in
measurement of reflectance factor which is most significant when measuring samples of very
low reflectance.
Fortunately, this error is relatively easy to characterize and correct. The following procedure
may be used to correct reflectance factor measurements of diffuse or specular samples, in
either the 8°/Hemispherical or 0°/Diffuse geometries:
1. Perform a reflectance factor measurement of a given sample as described in the operating
procedures.
2. Replace the sample with a light trap. The reflectance of the light trap is approximately
0%.
3. Execute a sample scan to record the measurement data on the light trap
4. Compute the corrected reflectance factor for the sample, Ps, as follows:
Ps = (R – Z) Pr / (100 – Z)
where:
Pr = the reflectance value of the reference standard,
R = the sample data displayed on the instrument expressed in percent, and
Z = the data from the light trap measurement, expressed in percent.
Operating Procedures for the RSA-PE-20 Accessory:
The RSA-PE-20 accessory can measure transmittance factors at either 0° or 8° angles
of incidence. The angle of incidence is controlled by the sample holder configuration at
the sample reflectance port. You should keep in mind, however, that 8° hemispherical
measurements will include the specular component reflecting off the sample surface.
Although calibrations using the 0° geometry are available on a custom basis, the
standard calibrations at Labsphere are performed at 8° If your application requires NIST
traceability, you should use a calibrated reflectance standard and the 8° reflectance
geometry.
Since any integrating sphere accessory acts as a signal attenuator, you should run scans at a
slower scan speed than in ordinary transmittance work without the accessory, or increase the
integration time if collecting data at a fixed wavelength.
Transmittance Measurements:
ASTM E 179-91a describes three categories of transmittance measurement: regular
transmittance, diffuse transmittance, and total transmittance. These three terms relate to each
other in the same fashion as regular or specular, diffuse and total reflectance. Regular
transmittance is the ratio of the undiffused transmitted flux to the incident flux. Diffuse
transmittance is the ratio of transmitted flux measured at all forward angles except the regular
transmittance angle, to the incident flux. Total transmittance is the ratio of flux transmittance at
all forward angles to the incident flux. The following procedure can be used to measure total
transmittance of a sample•
Load a diffuse reflectance standard at the sample reflectance port.
•
If you are scanning a liquid sample, load an empty cuvette into the cuvette holder, and
load the entire cuvette holder assembly at the transmittance port. Otherwise, leave the
transmittance port empty.
•
Choose your transmittance sample method from the UV Winlab software or manually set
all instrument parameters as desired.
•
Perform a background correction scan.
•
Load your sample at the transmittance port. If you are measuring a liquid, replace the
empty cuvette with your sample cuvette.
•
Execute a sample scan and save the scan data.
•
The value displayed by the instrument is the sample transmittance.
The procedure here for total transmittance measurement will produce accurate results for nonscattering samples. For transmittance samples exhibiting high degree of scattering, the scan
results will be instrument-specific.
We can measure the diffuse transmittance of a test sample using the following procedure:
•
Perform a background correction scan on the accessory with a diffuse reflectance
standard loaded at the sample reflectance port, and an empty cuvette, if used, fitted in
front of the transmittance port.
•
Replace the reflectance standard at the sample reflectance port with a light-trap. This
light trap will capture and exclude from measurement the undiffused portion of the flux
transmitted by the sample.
•
Load the test sample or sample cuvette at the transmittance port and execute a sample
scan.
•
Measuring the total and diffuse transmittance, as described above, and subtracting the
diffuse component from the total transmittance can determine an approximate regular
transmittance of a sample [103].
4.1.3. Atomic Force Microscope (AFM):
After chemical treatment of glass substrate we require analysis of surface roughnes because
due to that type of data or image show the effect of chemical tretment or chemical etching on
glass surface, so for AFM is a most suitable instrument for that purpose. The surface
morphology of the glass substrate was examined by AFM.
AFM is a very high-resolution type of scanning probe microscopy, with demonstrated resolution
on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction
limit. In some variations, electric potentials can also be scanned by using conducting cantilevers
[104].
Figure 52: Atomic Force Microscope (AFM)
AFM provides a 3D profile of the surface on a nano scale, by measuring forces b/w a sharp
probe (<10 nm) and surface. The probe is supported on a flexible cantilever. The AFM tip
“gently” touches the surface and records the small force b/w the probe and the surface. The amt
of force b/w the probe & sample is dependent on the spring constant of the cantilever & the
distance b/w the probe and sample surface. This force could be described using Hooke’s law:
F=-K.X
F= Force
K= Spring constant
X= Cantilever deflection
Probes are typically made from Si3N4 or Si. Different cantilever lengths, materials, and shapes
allow for varied spring constants and resonant frequencies. Probes may be coated with other
materials for addition SPM applications such as chemical force microscopy (CFM) and magnetic
force microscopy (MFM).
Figure 53: Tip of AFM
Scanning probe microscopes (SPM) describe a broad group of instruments used to image &
determine properties of material, chemical, and biological surfaces. SPM images are find out by
scanning a sharp probe across a surface while monitoring & compiling tip–sample interactions
to provide an image. The 02 primary forms of SPM are scanning tunneling microscopy (STM)
and AFM. The functional schematic flow diagram of atomic force microscope (AFM) is show as
like
Figure 54: Schematic diagram of AFM
Systematic operating procedure (SOP) of AFM:
•
AFM Instrument operating procedure can be define in following simple steps:
•
Switch on the main power supply.
•
Ensure air pressure must be open.
•
Switch on the AFM control P.C. or monitor.
•
Switch on the nano scope scanning probe controller.
•
Switch on the nano scope dimension controller.
•
Now open nano scope SPM icon than open real time mode icon.
•
Now select profile and load tapping AFM and go for initialization.
•
Change the stage chuck as per sample requirement. During changing of chuck,
switch off the vacuum.
•
Now put the sample on stage chuck.
•
Move the table under scanner head and then focus the surface.
•
Set the tip and adjust cantilever in central during surface examine or sampling
focusing.
•
Care must be taken during focusing the sample that tip does not hit the sample
surface.
•
Move the start of groove area measurement point under the cross hair.
•
Adjust scan parameters, adjust groove by X, Y offset in scan control.
•
If image is comfortable than capture it and save data or images in 2D or 3 D mode.
4.1.4. Climate test chamber-WK340/40 (Environment Chamber):
So many chemical treated methods are available for increasing transmittance on glass
substrate for application in solar module but environmental stability is crucial factor for this layer.
Solar modules are make use in all our world for exclusion power crisis so keep this mind many
environment factor which will be directly effect anti reflection coating of solar module glass. The
above observations point to the fact that environmental test is must for solar module glass which
treated by any chemical process for improving transmittance. During this test we observe the
effect of different environment conditions like temperature, humidity on anti reflective coated
glass substrate and analyze visual defects, peak wavelength shifting of transmittance and the
reduction of transmittance with respect to chemical treated anti reflected coated glass.
It is the main focus area of our research that treated substrate layer will be environment stable.
It characteristics will isolate this process to other exist developing process. Due to analysis of
process stability we would be require following environment test i.e. (a) Thermal cycle test (b)
Damp heat test (c) Humidity freeze test. For those entire environment tests we require climatic
chamber or Environment chamber. Environmental chamber is a system of sufficient thermal and
humidification capacity shall be used to change ambient conditions to meet test necessities and
to reach specified temp. conditions. The temp. change test shall be executed in accordance IEC
61646 standard.
The International Electro technical Commission (IEC) is a worldwide organization for
standardization comprising all national electro technical committees (IEC National Committees).
IEC technical committee 82 has prepared International Standard IEC 61646: Solar photovoltaic
energy systems [105].
We have carried out all environment tests in Climate test chamber-WK340/40 (Weiss Technik).
Performance for temperature tests of Climate test chamber-WK340/40 are as
Maximum temperature (°C): +180
Minimum temperature (°C): -45
Temperature changing rate cooling (K/min): 2.0
Temperature changing rate heating (K/min): 3.0
Temperature changing rate linear (K/min): 1.0
Humidity range (% r.h.): 10 to 98
Calibration values (°C): +23°C / 50% r.h. and +95°C/ 50 % r.h.
Figure 55: Climate test chamber
chamber-WK340/40
WK340/40 (Environment Chamber)
Transmittance would be measure before and after taken environment test. We mention
conditions for different environment test i.e.
Thermal cycle test: This environment test consist 50,100 & 150 thermal cycle and each cycle
consist - 40* to 85* C temperature for 6.0 Hrs.
Damp heat test: During this environment test substrate putting for 1000Hrs.at temperature 85*
C and 85%RH.
Humidity freeze test: 85*C to – 40*C @ 85%RH 10Cycle each cycle=24Hrs [106].
4.2. Characterization Technique of Solar Modules:
Following instruments would be require during fabrication of Solar module and their
characterization4.2.1.Differential Scanning Calorimeter (DSC)
4.2.2. Sun simulator machine for I – V Characterization
4.2.1. Differential Scanning Calorimeter (DSC):
In our experiment Differential Scanning Calorimeter (DSC) is used for thermal analysis of tedlar
and EVA materials, which materials used in fabrication of solar modules. Typical applications of
this instrument like reaction kinetics, purity analysis, polymer cures through heats and
temperatures of transitions and reactions. A Differential Scanning Calorimeter (DSC) image is
show as follow
Figure 56: Differential Scanning Calorimeter instrument
A typical DSC cell uses a Cu-Ni disk for transferring heat to the sample and reference. The
differential heat flow to the sample and the reference is monitoring by the constantan/chromel
thermocouples formed by the junction of the constantan plate and the chromel wafer covering
the underside of each pan. DSC provides max calorimetric accuracy from -170°C to 750°C and
sample size from 0.10 mg to 40 mg. A typical DSC Machine flow diagram can be show as follow
Figure 57: A typical DSC Machine flow diagram
Analysis Procedure of DSC:
DSC instrument operating procedure can be define in following steps
steps•
•
Clean sample pan and cover by means of slow pressure nitrogen gas.
Then tare weight pan and cover, weigh accurately (1.0mg to 9.0 mg) by a presicion
balance.
•
Now pan and cover crimped by crmping machine to sealed pan.
•
Then this kept in left side of the furnace and reference was placed in right hand positions
during the experimentations.
•
Sample and reference lid handled with the help of tweezers only to minimize
interference.
•
Keep nitrogen gas flow 20 ml/min, heating rrate
ate 10°C/minute from ambient to 500°C.
•
After analysis, furnace cooled to at ambient conditions before next experiment.
•
After reaching the furnace temperature at room temperature swith off the instrument and
now close the software.
Thermal Analysis of polymer by DSC:
Thermal analysis includes a group of technique in which specific physical properties of a
material are measured as a function of temperature. Different of thermal analysis techniques are
Differential
Scanning
Calorimetry
(DSC),
Differential
Thermal
Analysis
(DTA),
Thermogravimetric Analysis (TGA), Thermomechanical Analysis (TMA), Dynamic Mechanical
Analysis(DMA), Evolved Gas Analysis (EGA).
In this technique, the sample and reference materials are subjected to a precisely programmed
temperature changed. Thermal energy is added to either the reference or the sample chambers
in order to maintain both reference and sample at same temp since the energy transferred is
exactly equivalent in magnitude to energy evolved or absorbed in the transition, the balancing
energy yields a direct calorimetric measurement of the transition energy. A polymer DSC curves
shown below in figure [102].
Figure 58: Example of a polymer curve in DSC Machine
Also show another curve in figure 59, which shows the temperature curve and indicates
exothermic and endothermic process.
Figure 59: DSC Thermo gram different temperature points
The heat flow into the sample holder can be calculated by using the following equation:
dQ
= K (Tb − T )
dT
Where,
T: Sample temp.
Tb: Programs block temp.
K: Thermal conductivity
Tb = T0 + qt ---------- [1]
Where,
T0 : Initial temp.
q : Programs heating rate.
Heat capacity expressed, as the amt of heat energy required for raise the temp of a body by 1K.
For a substance with a constant heat capacity, defined by the following eq;
Q = C P (T − T0 ) --------- [2]
To derive an eq. from eq. [1] & [2], that express for the DSC as follows:
∆T = q
CP
------------ [3]
K
Where,
∆T: Diff. in temp b/w the reference mat. & sample.
The heat capacity show as:
C P = mcP ---------- [4]
Where,
c: The specific heat
For a given phase transition the enthalpy change may found by integrating over the area where
the transition is seen to arise on the DSC curve. This change show with following integral eq:
Tf
Tf
 K∆T
∆H = ∫ C P dt = ∫ 
q
Ti
Ti 

dT ----------- [5]

Where,
Tf and Ti are the final and initial temperatures of integration limits for graph integration. So, it
indicates enthalpy changes involved in the various transition phases. Different transition
temperatures describe in footnotes as follows:
Glass Transition Temperature-Tg:
It is a temp at which, on heating, an amorphous polymer changes from being hard, brittle and
glass like to transformed a soft rubber like substance. The factors with relating to polymers and
their effect on Tg are show in following table:
Table - 4: Effect of Glass Transition Temperature (Tg)
Crystallization Temperatures- Tc:
It is the temp at which molecules gained sufficient freedom to move into a stable phase that is in
crystalline phase and a transition occurs.
Melting Temperatures- Tm:
It is temp at which the crystalline molecules turns liquid from solid state that have gained
enough vibrational freedom. For the increased freedom of these molecules, the thermo gram of
DSC shows sudden dip at this temp. M.P. of any materials could be show by following
equations:
Tm =
∆H m
----------- [6]
∆S m
Where,
∆Hm: Melting temperature
∆Sm: Entropy change.
Degradation Temperature- Td:
It is the temperature, at which the molecules decompose; atoms start to break as vibrational
energy more in this stage. This temperature may be exothermic or endothermic depending upon
the nature of samples.
4.2.2. Sun Simulator Machine (Spectranova) for I – V Characterization: Sun simulator
machine
(Spectranova)
is
used
for
analyze
electric
parameters
(current-voltage
characterization) of solar module. The image of Spectranova Sun simulator machine is as follow
Figure 60: Sun Simulator (Spectranova) Machine
The inside image of Spectranova Sun simulator, where we put the solar module or solar cell for
electric parameter analysis can be show as following
Figure 61: Insight image of Sun Simulator (Spectranova) Machine
For different electrical parameters like current, voltage, fill factor etc measured by Sun simulator
machine which having a light source and their filtering unit. When filtered light flashed on solar
module, measuring system of sun simulator machine analyze the electrical parameters due to
the variable change and their correction in temperature.
We can show the sun simulator
machine process flow diagram is as follow in figure –
Figure 62: Schematic process flow diagram of Sun Simulator machine
Current-Voltage Characterization:
Photovoltaic cells modeled as a current source in parallel with a diode. When there is no light to
produce any current, then PV cell worked as a diode. When intensity of incident light raises, the
PV cell, as illustrated in Figure, generates current like
Figure 63: Current generation in PV cell
The current-voltage graph of a PV cell has illustrated in Fig as the V across the measuring load
is swept from zero to VOC and different electric parameters for the cell could be resolute from
this data
Figure 64: I-V curve of PV cell
1) Open circuit voltage-Voc
2) Short circuit current-Isc
3) Max power (Pmax), Current @ Pmax (Imax), Voltage @ Pmax (Vmax)
4) %Fill Factor-FF
5) %Efficiency
1) Voc:
The VOC found when there is no any current passing through the cell like
V (at I=0) = VOC
2) Isc:
The ISC corresponds to the short circuit condition when the impedance is low and is calculated
when the voltage equals 0.
I (at V=0) = ISC
3) Max. Power (Pmax), Current at Pmax (Imax), Voltage at Pmax (Vmax):
Power generated by the cell in watts could be calculated along the current-voltage sweep with
the equ. P=IV. At ISC and VOC points, the power would be zero (0) & the max value for power
will occur b/w the two. The voltage (V) and current (I) at this max power point are denote
as VMP and IMP correspondingly.
Figure 65: Maximum power (Pmax), Maximum Current (Imax) and Maximum Voltage
(Vmax)
4) %FF:
It is finding out by compare the max power to the hypothetical power (PT) that would be output
at both the Voc & Isc together. Fill factor could also be interpreted graphically as in Fig.
Figure 66: Fill factor calculated by II-V curve
5) %Efficiency:
Efficiency is the ratio of electrical power output Pout, with compare to the solar power input, Pin,
into the photovoltaic cell. Pout can be taken to be PMAX since the solar cell could be operated up
to its max power output to obtain the max efficiency.
I-V Test system:
First a light source providing incident radiation to excite the PV cell or module. After that, an
SMU like “PXI-4130”
4130” is used to sweep the voltage (V) & determine the current (I) from the photo
voltaic cell. In addition, several sensors are used to find out the ambient conditions of
atmosphere.
Figure 67: Test arrangement for Current-Voltage Characterization
Software like “LabVIEW, Kiethley” is used to obtain measure & display the value of currentvoltage characterization tests and evaluate the main performance parameters for solar panel.
Generally this instrument is used for small solar module current voltage characterization
purpose. To uphold the ambient temp and the temp of the photovoltaic cell, a cooling system
also be used to counter balance the heat from the source of light [107]. A Keithley (2400- A
source meter) instrument figure can be show as following
Figure 68: Keithley (2400- A source meter)
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