Fyp slide polymer solar cells
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MEH PPV: PC60BM with Carbon as a counter electrode
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- 1. Project Title: POLYMER: FULLERENE SOLAR CELLS Name: FAIZZWAN
FAZIL (101180216) Project supervisor: DR. MUKHZEER MOHAMAD SHAHIMIN
School of Microelectronic Engineering, University Malaysia Perlis
(UniMAP) 01000, Kangar, Perlis, Malaysia Phone:+604-9798386
Fax:+6049798305
- 2. INTRODUCTION A lot of development had been made in order to
obtain high reliability, green energy source with a reasonable
capital cost. By replacing the non-renewable electrical generating
source such as fuel, charcoal and nuclear energy, photovoltaic
device also known as solar cell has been introduced which is
operating to generate and dissociate EHP by harvesting photon
shined by the sun. The organic solar cells is totally different
compared to inorganic semiconductor solar cells in terms of
structure. For the working principal, both are approximately the
same. The inorganic solar cells are using the P-N junction with the
valance and conduction band while the organic solar cells are using
Donor Acceptor with the HOMO (Highest Occupied Molecular Orbital)
and the LUMO (Lowest Unoccupied Molecular Orbital). Organic solar
cell also provide one biggest advantage which is it can be
fabricate on the flexible substrate. The capital cost also is
reasonable compare to the inorganic solar cell. founded with a
single active layer, followed by bilayer active layer, and
recently, bulk heterojunction active layer (conjugated polymer:
fullerene).
- 3. AIMS AND OBJECTIVES the absorption of photon, exciton
(electron-hole pair) diffusion, exciton (electron-hole pair)
dissociation, and the electron and hole mobility towards electrodes
are the elements that need to be put as main priority are
determined. The objectives of my project: is to relate the the
relation between the thicknesses obtained using the Atomic Force
Microscopy (AFM) after the application of those various spin speed
with the absorbance which is obtained by using the UV- Vis
Spectroscopy and the PCE obtained using the SPA which provide
several reading for PCE evaluation purpose. To study the outcomes
of using the Titanium Oxide (TiO2) as the holes blocker and the
usage of Indium Tin Oxide (ITO) coated glass as cathode by
replacing the Aluminum (Al). To review and study another parameter
of the required material has to be fixed for the
poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:
PSS) solvent deposition, the temperature with annealing duration,
and the weight ratio of polymer: fullerene with suitable dilution.
To investigate and apply proper solution is required to overcome
the failure
- 4. PROJECT CHALLENGES The active layer material itself is
highly sensitive to H20 and O2. It might degrade either during
fabrication process or inspection process where the samples are
exposed to the mentioned causes. PEDOT: PSS might be dissolved with
the H2O left on the ITO surface if the cleaned ITO coated glass is
not dried thoroughly. The holes transportation potential of its
will be degraded and will affect the performance of power
conversion to be weakened. The application of the ITO as a
substituent for Al also might result a poor result due to its
electron mobility is not as good as Als. The insufficient material
of PCBM is the biggest challenge in this experiment. The amount of
PCBM purchased is just 1g for a bottle. The price is about RM900
and the shipping of the item takes a lot of time.
- 5. The Working Principle of Polymer: Fullerene Solar Cells The
donor and acceptor material are blended together as an active layer
for this device. This morphology will enrich the generated excitons
to reach the interface of donor- acceptor if the length of the
blend is same as the diffusion length of excitons. The efficiency
of electron hole pairs (EHP) might be improved. The excitons in the
bulk which are created by the absorption of photon, are everywhere.
To observe the dissociation of exciton, we considered the exciton
placed close to the interface between Donor and Acceptor. The
absorbed exciton reaching the interface of Donor- Acceptor and the
electron is separated from the exciton due to the binding energy
broken by the electric field occurred in the interface, excited to
the LUMO of Donor. The electron transported from LUMO of Donor to
the LUMO of Acceptor then diffused and captured by the cathode. The
remaining hole will be transported towards anode and captured.
- 6. Device Structure
- 7. 1. ITO coated glass :- i) the best choice for the substrate
due to its high electrical properties and transparency ii) composed
by 90% Indium Oxide (In2O3) and 10% Tin Oxide (SnO2). iii) acts as
both electrode in this device. iv) it is providing high refractive
index which is N = 2.35046 for ITO layer which mean it could trap
incoming light besides being the electrode v) Al has been replaced
with the ITO as the anode of this device 2. PEDOT:PSS :- i) the
roughness of ITO it can has good contact with polymer in spin
coating process so it is used to overcome this problem by smoothing
the ITO surface ii) has good hole collecting (efficient electron
blocking) iii) has a good transparency to allow light to travel
into 3. Polymer: Fullerene (MEH PPV: PCBM) :- i) MEH PPV is one
type of conductive polymer ii) act as electron donor (majority
charge carrier is electron) iii) PCBM is one type of fullerene iv)
act as electron acceptor 4. CdTe (additive material in actve layer)
:- i) is in form of powder and can be diluted but it still can be
mix together in the solvent ii) providing nano-scale
interpenetrating network between the interface of Donor- Acceptor
material 5. TiO2 :- i) used as an optical spacer to gain greater
light absorption (it has high refractive index) by breaking the
symmetry and blocking hole (electron collecting) ii) It is placed
between ITO and active layer to comprise phase separated
blend.
- 8. METHODOLOGY
- 9. Fabrication Process Cleaning and ITO etch Process a piece of
ITO coated glass is cut to 100 samples with 2cm x 2cm unit area.
all the samples are cleaned using acetone or deconex which mean
they are dipped in a beaker filled with that solutions. After 20 to
30 minutes, all the glass substrates are rinsed using DI water and
dried using an air pump 3/4 of the ITO layer which means
1.5cmx1.5cm unit area need to be etched The mixture of acid nitric
and HCL with volume ratio 1: 3 can be used for this process. The
part to be etched is partially dipped and hold in a beaker filled
with those solution for 5min to 10min. Then the glass substrate is
cleaned using DI water and dried using an air pump.
- 10. The PEDOT:PSS is coated on the substrate using a Spin
Coater with speed of 2500rpm and 20ul a drop. Before that, the 1/8
which is approximately 0.25cm of ITO layer which is located from
the right edge of the bottom glass is covered or pasted using a
sellotape. The covered area is approximately 0.5cmx0.5cm. After
depositing, the sellotape is removed. After finishing that process
for all the required sample, all the deposited substrates are baked
with 90oC for 5min PEDOT : PSS Deposition
- 11. Solvents and Paste preparation The weight ratio of MEH
PPV:PCBM:CdTe has been determined as 1:4:3 and dissolved using
chloroform or chlorobenzene which means 1mg of MEH PPV, 4mg of PCBM
and 3mg of CdTe are diluted together in 1ml of chloroform or
chlorobenzene. This weight ratio is going to be used in the
experimental and is fixed. 20ul each drop. The PEDOT:PSS is already
in the form of chemical so it doesnt require a dilution process.
The TiO2 is in form of powder so it requires to be diluted. 9ml of
acid acetic nitric is required to dissolve 6 gram of TiO2. The
process need to be done little by little which means 1ml is dropped
into beaker filled with 6g of TiO2 at the same time the mixture is
grinded slowly but heavily pressed. This process is continuously
done till the 9ml of acid acetic nitric is finished. After that,
the complete mixture need to be anneal on the hot plate with 300oC
for 10min to20min (until the colour change to brown and back to
white)
- 12. MEH PPV: PCBM Deposition The active layer solvent prepared
will be deposited at the varied spin speeds which are 1000rpm,
2000rpm, 3000rpm and 4000rpm. But before that, the area covered
with the sellotape again get covered. A drop of active layer
solvent which is 20ul is dropped on the substrate. Once it
finishes, the sellotape is removed and annealed on the hot plate
with 90oC for 5min
- 13. TiO2 Pasting The TiO2 is pasted on the etched area using a
cotton bud and rod. Then annealed with 90oC for 5min. Before
annealing process, the applied sellotape need to be removed.
- 14. Sandwiching with the top substrate the top glass is
sandwiching the bottom glass by using the epoxy as a paste
- 15. Device Characterization the Atomic Force Microscopy (AFM)
is used to obtain the thickness and surface roughness of each
device. Four pieces of 4cm x 4cm ITO coated need to be etched using
the Acid Acetic Nitric. all the substrates are deposited with the
prepared active layer solvent using 1000RPM, 2000RPM, 3000RPM and
4000RPM . Spin Speed 1000RPM 2000RPM 3000RPM 4000RPM Thickness of
MEH PPV: PCBM 40nm 30nm 20nm 10nm Surface Roughness
- 16. UV-Visible Evaluation The Lamda UV/Vis Spectrometer is used
to observe the relation of the thickness of the active layer with
the absorption to the fixed value of the wavelength which is from
250nm to 800nm. 250nm to 375nm is under UV spectrum, 375nm to 745nm
is under Visible (Vis) spectrum, and 745nm to 800nm is under Near
Infra-Red (NIR) spectrum. The figure shows the electromagnetic
spectrum as a reference to evaluate the trend of the Absorbance
versus wavelength graph.
- 17. UV-Visible Graph The graph is evaluated based on the
changing of the graphs trend and the value of absorbance (A) and
wavelength are obtained via the median position of each trend
changing. maximum A is obtained, A=2.35 =300nm (boundary between UV
and Vis region) by all devices. 330nm to 530nm, the trend of graph
drops (concave-curve-shaped). 4000rpm shows A=0.4 =380nm, 3000rpm
shows A=0.35, 2000rpm shows A=0.25, and 1000rpm shows A=0.23. (in
visible region) 530nm to 570nm, the trend of graph drops
(convex-curve-shaped). 4000rpm shows A=0.3 =550nm, 3000rpm shows
A=0.27, 2000rpm shows A=0.24, and 1000rpm shows A=0.22. (in the
middle of visible region) 570nm to 800nm, the trend of graph drops
slightly. 4000rpm shows A=0.25 =685nm, 3000rpm shows A=0.22,
2000rpm shows A=0.18, and 1000rpm shows A=0.1. (Near Infra Red
region) This evaluation shows the 1000rpm device is the best device
at trapping the EM wave/ light due to its lowest absorbance
- 18. I-V Curve Evaluation The Semiconductor Parametric Analyzer
(SPA) is used to obtain the electrical characteristic (I-V curve
graph) and record the Isc (short cicuit current), Voc (open circuit
voltage), Vmax (maximum voltage), Imax (maximum current) and FF
(Fill Factor) for PCE (power conversion efficiency) evaluation
purpose. the graph cross at the 0 of x-axis which is Voltage axis,
the Isc value could be obtained. (refer to figure) the graph cross
at the 0 of y-axis which is current axis, the Voc value could be
obtained. (refer to figure) The Voc supposedly occur at the
positive voltage region of the graph and the Isc supposedly occur
at the negative current region of the graph. FF also supposedly
obtained as a positive value because the FF indicates the ratio of
the maximum power from the solar cells to the product of Voc and
Isc.
- 19. Fill Factor (FF) evaluation: Power Conversion
Efficiency:
- 20. I-V Curve of each device
- 21. The Recorded and Evaluated results Refer to the graph
obtained, obviously the huge error could be observed. The trend of
the graph is absolutely different compared to the typical one All
the Vocs occur at negative voltage region (left side of the graph)
All the Iscs occur at positive current region (upper side of the
graph) This is because the solar cells operate in reverse bias The
best power conversion efficiency is obtained by 1000rpm device (PCE
percentage = 1.2484488 x 10-5) Others sample show worse performance
especially the 4000rpm sample. attenuated by the reduced of Donor-
Acceptor interface number (thin active layer obtained). The
degradation could occur during illumination and in the dark, also
could happen during fabrication process. the exposure of the active
layer material towards the oxygen and water (H2O) PEDOT: PSS also
can be dissolved with water The problem occur during pasting the
TiO2 process (easily dry and hard to adhere to the substrate) Spin
Speed (RPM) Voc (V) Isc (A/cm2) FF Plight (mW) PCE (%) 1000 (40nm)
-32.0000E-3 80.1478E-9 -48.6776E+0 1000 1.2484488 x 10-5 2000
(30nm) -10.0000E-3 48.9684E-9 -251.0371E+0 1000 1.2293 x 10-5 3000
(20nm) -48.0000E-3 135.4012E-9 -14.6055E+0 1000 1.075441 x 10-5
4000 (10nm) -26.0000E-3 19.4816E-12 -121.8237E+0 1000 6.17063 x10
-11
- 22. Introduction of Carbon as counter electrode (cathode)
Carbon was introduced to replace the TiO2 (idea obtained by viewing
the application of carbon as counter electrode in dye sensitize
solar cells structure)
- 23. I-V Curve of applied Carbon device (1000rpm)
- 24. The comparison of upgraded device with the previous devices
Higher Voc is obtained Higher Isc is obtained Higher PCE is
obtained The graph similar to the typical one The mobility of the
electrons toward cathode have been enhanced The potential of the
electrons to be captured by cathode also have been improved as well
Spin Speed (RPM) Voc (V) Isc (A/cm2) FF Plight (mW) PCE (%) 1000
(40nm) -32.0000E-3 80.1478E-9 -48.6776E+0 1000 1.2484488 x 10-5
2000 (30nm) -10.0000E-3 48.9684E-9 -251.0371E+0 1000 1.2293 x 10-5
3000 (20nm) -48.0000E-3 135.4012E-9 -14.6055E+0 1000 1.075441 x
10-5 4000 (10nm) -26.0000E-3 19.4816E-12 -121.8237E+0 1000 6.17063
x10 -11 1000 (40nm) Carbon 2.2000E-3 180.1765E-6 173.0310E+0 1000
6.8588 x10-3
- 25. CONCLUSION The target to fabricate the device using CdTe as
additive in active layer cant be achieved due to insufficient PCBM.
The application of the TiO2 also didnt achieve the target. All the
devices applied with the TiO2 degraded. But by using the Carbon as
a counter electrode, the mobility and the power conversion
efficiency are enhanced. Eventhough the results obtained werent
good enough, but still the idea of applying ITO substrate glass as
a replacement for Al is worthwhile because of the ability of
absorbing the photon from both side of the device. (top and
bottom)
- 26. THANK YOU