MEH PPV: PC60BM with Carbon as a counter electrode

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 Al’s.
 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 doesn’t 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 λ 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 λ Graph
 The graph is evaluated based on the changing of
the graph’s 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 λ=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
λ=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
λ=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 λ=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 can’t be achieved due to insufficient PCBM. The
application of the TiO2 also didn’t 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 weren’t 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