ELEC 70247: Organic Solar Cell Fabrication, Characterization Report

This report details the fabrication and characterization of organic solar cells, focusing on the use of shuttlecock-type phthalocyanines. It investigates the impact of J and H aggregate transition phases on photovoltaic properties, discussing the underlying photovoltaic mechanisms, energy levels, and band gap of the active layer. The study emphasizes the advantages of organic solar cells, including lower fabrication costs and the unique properties of phthalocyanines. It covers the basic principles of organic solar cells, including organic semiconductor constituents, light absorption, diffusion, dissociation, and charge collection. The report also examines the characteristics of organic solar cells, such as short-circuit current density and open-circuit voltage, providing a comprehensive overview of the technology. Desklib provides access to this and many other solved assignments.

Fabrication and Characterization of Organic Solar Cells 1
RESEARCH PAPER ON THE FABRICATION AND CHARACTERIZATION OF ORGANIC
SOLAR CELLS
A Research Paper on Solar Cells By
Student’s Name
Name of the Professor
Institutional Affiliation
City/State
Year/Month/Day

Fabrication and Characterization of Organic Solar Cells 2
ABSTRACT
Characteristics and fabrication of the organic solar cells using the shuttle type of cock
phthalocyanines were performed. Properties of photovoltaic of the solar cells with the inverted
structures were determined using the characteristics of the current density-voltage. Effect of the
transition phase between J and H aggregates on the optical properties and photovoltaic were
investigated. The mechanism of the photovoltaic, energy levels and the band gap of the active
layer were discussed. Organic solar cells have been studied widely because of their less cost of
the process of fabrication. Phthalocyanines have the best advantage for the nobility of carrier and
properties of the photo by changing the modification of the molecular structures with many
chemical substitutions and the central metals.

Fabrication and Characterization of Organic Solar Cells 3
INTRODUCTION
Organic solar cells have been studied widely because of their less cost of the process of
fabrication. Phthalocyanines have the best advantage for the nobility of carrier and properties of
the photo by changing the modification of the molecular structures with many chemical
substitutions and the central metals. Recently, fullerene solar cells have been investigated and the
conversion efficiency was gotten to be more than 2%. The phthalocyanines have the properties
of the photovoltaic, heat resistance stability under the light and high absorption of optics in the
visible range.
They have been applied to the devices of semiconductors, solar cells and fuel cell's
catalyst. The purpose of this research is to characterize and fabricate the organic solar cells using
the shuttlecock type phthalocyanines. The effects of the transition phase of the J and H on the
properties of photovoltaic were investigated. The mechanism of the photovoltaic was discussed
for the improvement and the optimization of the photovoltaic properties in the wide optical
absorption range (Astronautics, 2016).
Basic principles of the OSCs
Organic semiconductors constituents: the field organic solar cell stated with the small
pigments of the organic compounds but actual was attained through the advance of the polymers
of semiconductors. Integrating the conjugated polymers into the organic cells resulting in the
developments for the previous years. The structure bonds between the atoms of the carbon makes
the conjugated polymers becomes attracted to the cells. Dissimilar from the best industrial plastic
where the properties of the insulation of the results from the bonds formed between the
neighboring atoms of the carbon (Duan, 2015). In the backbone of the polymers, the atom of

Fabrication and Characterization of Organic Solar Cells 4
carbon can muddle to four to three neighboring atoms meaning that one electron of every atom
of carbon is left on the Pz orbital. Meanwhile this is the trend, the electrons that are not bounded
overlap mutually between the orbitals of Pz and n bonds are formed along the backbone. In this
way, the electrons on the connections of n can be delocalizing along the path conjugated to make
the polymers conjugated an intrinsic semiconductor (Kumar, 2015).
In the system conjugated, the n-bonds are chemical covalent bonds, where the two
sections of the involved one electron orbital overlap the two lobes of another electron orbital
involved. Only one of the Nadal plane of the orbital is transferred through all of the nuclei
involved. Also, the band gap of the system conjugated depends on its size, the local LUMO and
HOMO situations can be altered by altering the polymers backbone conjugation and hence real
polymers that are conjugated are the subject to the energetic disorder (Miranda, 2014).
The figure 1 above shows the arrangements of the bonds before and after the absorption of the
photon (Parthasarathy, 2014)
The way to move the electron from the level of HOMO to the level of LUMO by the
absorption of the light if the absorbed photons' energy is greater or equals to the band or orbitals'
gap energy. Following the photon absorption with the efficient energy by the semiconductors
organic an electron is transferred to the LUMO making a hole after the HOMO. After the
separation, the pair of the electron-hole cannot be secluded because of the interactions of
electrostatic but forms the state that is bounded tightly known as the exciton. The energy binding

Fabrication and Characterization of Organic Solar Cells 5
the exciton for the semiconductors organic is the one magnitude order larger than the inorganic
semiconductors like silicon where the excitations of photon results direct carrier free at the room
temperature (Parthasarathy, 2014).
Among many of the polymers, the Buckminsterfullerene C70 is very important since it
has the property of the good acceptor of electron. It's based on the practical in the heterojunction
bulk cells that when C70 is diversified with the materials of the whole conduction,
photoconductivity rises under the limitation. C70 has the tendency to crystallize in the mixture of
the polymers and lead to the PCBM development, a derivative of the C70 and the solubility of
the structure rises with the formation of the smaller structure of crystals in the blend (Poortmans,
2013).
Figure 2 above shows the chemical structure of the materials of the acceptor and the donor used
in the polymer bulk heterojunctions solar cells, (b) is the acceptor and (a) is the donor (Rand,
2017).
Absorption of light by semiconductors
When light radiates on the surface of the organic semiconductor, the photons of the light
is absorbed in the valence band by the electrons of the molecules engaged in the system of pi-
bond. This causes the excitement of the electrons and their movement to the level of LUMO
from the level of HOMO. There are two factors that affect the excitement of the photons;

Fabrication and Characterization of Organic Solar Cells 6
different in the level of the energy between the LUMO and HOMO of the molecule known as the
band gap and the content of energy of the photon. If the energy level between the LUMO and
HOMO level is high the energy for exciting an electron for the HOMO to LUMO level will be
high, hence the rate of excitement depends on the spectra part where the photon is from and the
difference in the energy level (Josphat, 2016).
The molecules having high number of the systems of conjugated Pi- bonding have the
benefit of having low energy level difference between the LUMO and HOMO because as the
molecules become big and having more system of the conjugated pi-bod, the force of the
dispersion reduces the level of the LUMO for the electrons to be excited by the longer photons
wavelength. Bigger molecules also have the disadvantage of increasing the sublimation and the
melting point which need high energy for the depositing the vacuum of the small molecules and
affects the polymer solubility for the polymers of solution deposition (Kumar, 2015).
The bands of the absorption of the materials that are used have a great impact on the
efficiency. The band of absorption of the polymers conjugated lies in the narrow range of the
spectrum solar as they are referred to intrinsic wide gap band semiconductors. The energy at the
room temperature is not suitable le to the effect produced free carrier charge into the materials of
organic by the dissociation of the exciton (Yusoff, 2016).
Diffusion
After the exciton of the neutral charge produced through the absorption of the light, they
start to transport through the diffusion. The length of the diffusion of the exciton is the important
characteristics of the polymer conjugated for the applications of the optoelectronics that ranges
from 5 to 20nm. The rise in the length of the diffusion reduced the lifetime of the exciton so that

Fabrication and Characterization of Organic Solar Cells 7
they either dissociate or decay through the internal mechanics and the thickness of the systems
for the polymer conjugated is determined by the length of the exciton diffusion. This is the
second process that happens during the current generation in the semiconductors. The exciton is
produced because of the absorption of the energy of the photon and after it has been created, it
has to be separated from its carrier charge. Every material has the thickness of the created
exciton that cannot reach the interface before losing their level of energy and goes back to the
ground state (Yengel, 2014).
Dissociation
The mechanism of the diffusion is then followed by the dissociation for the exciton that is
close to the interface layer, the transfer of the electron to the acceptor at the accepter donor
interface leaving behind a hole. The rest of the exciton is decaying process of recombination
hence the efficiency of the energy of the polymers of single layer device remain below
0.1percent. Then the electron-hole pair dissociation is transferred to the electrodes that are
related. The process efficiency is related to many factors like the lifetime of the exciton, length
of the carrier drift and the length of the exciton diffusion (Yengel, 2014).
Charge collection
The charge collection happens at the electrodes. Before the carrier of the charges arrives
the electrode, they should pass through the acceptors and the donors. After the carrier of the
charges is made, it is the difference between the potential electrodes and the semiconductors that
pulls them towards the electrodes. There is the extra layer known as the electrode interfacial or
buffer layer in between the anode and donor and it allows the holes flow from the donor to the
anode and hinder the electron and exciton flow in the similar direction (Yengel, 2014).

Fabrication and Characterization of Organic Solar Cells 8
These layers also contribute to the voltage of the open circuit of the solar cells. They can
also raise the serious resistance of the solar and affects the layers' transparency. After the
buffered carrier charge passes through the layer of the electrode interfacial they are efficiently
collected and the electrodes should be more conductive to electricity to prevent the dissipation or
loss of charge carrier. The morphology of every material determines the effectiveness of the
charge separation and the transport. The morphology also determines how the align materials
during the deposition. Every semiconductor has low or high spectra absorption. After the
absorption of the photons by the part of the photoactive solar cells towards the interference
between the acceptor and the donor are significant to be considered (Parthasarathy, 2014).
Figure 3 above shows two different representations (a) shows the schematic diagram for the
BHJ OSC. The layers of the photoactive are sandwiched between the electrode of collecting the
electrons AI and the hole for the extraction ITO electrode. (b) Represent the operation process
in the cells of the organic solar using the representation of the energy band diagram; (4)
changes the transport to the electrode, (3) dissociation of the exciton.(2)generation of the
exciton. (1) Absorption of the photon (Josphat, 2016).
Characteristics of the OSC

Fabrication and Characterization of Organic Solar Cells 9
Two important quantities in measuring the device efficiency are the density of short-
circuit current Jsc. and the open voltage circuit Voc. The Jsc is the generated photocurrent at 0 V
under the illumination and depends on many factors like absorption of the material, wavelength,
and the light intensity. Voc is the voltage across the device when there is no flowing of the
current. It depends mostly on the material contact with the respective functions work and
materials used within the cell for the active layer (Duan, 2015). The device power conversion
efficiency is defined as:
efficiency = P max/P light
=Jsc*Voc*FF/P light
where the FF is the fill factor and the P light is the light incident power. the fill factor is written
as FF= J max*Vmax/Jsc*Voc
Where the Vmax is the voltage at the power of maximum and J max is the density of the
current at the power of maximum. The fill factor provides good performance indication of the
device. Good verification will give a high fill factor and should be close to the unity. Vmax and
Jmax are shown below. The efficiency provides on how the cell does overall and its good to
know how the cells are efficient at the individual wavelength for the materials to be optimized
for the absorption of the light achieved by measuring the incident photon to the conducted
electron (Rand, 2017).

Fabrication and Characterization of Organic Solar Cells 10
Figure 4 above shows the current-voltage characteristics of the accepter and donor organic
solar cell (Duan, 2015)
Objectives
 The main objective of this report is to construct organic solar cells and get its electrical
characteristics like the current voltage.
 To estimate the photovoltaic factors of the devices from the characteristics of the current-
voltage measured
 To obtain the characteristics of the current voltage of the organic cells in both dark and
under the illumination is given by the simulator of the solar with the intensity of 1 sun
calibrated (100mW/cm2 (Kumar, 2015)
Note: the active area of the OSC contrived is 0.13 cm2. The basis of the light from the solar
emulator was standardized to (100mW/cm2 by the use of reference cell of the Silicon PV.
Equipment and materials
 Auto 500 system of the vacuum deposition
 Keithley 2400 meter source
 Solar simulator (LOT-LS0306)
 Spin Coater
 Aluminum wire for the deposition of the cathode
 Solvents for the substrate cleaning; isopropanol, acetone, and deionized water.
 Active solution layer- a blend donor PBDTTT-EFT, and the accepter PC17BM in the
ratio of 1; 2(25mg/mL in the dichlorobenzene co-solvent; chlorobenzene, ODCB;
CB@{3;1}
 Poly (3, 4 ethylenedioxythiophene- poly (styrene sulfonate), PEDOT: PSS {material of
the buffer layer
 Pre-patterned ITO coated glass substrate 25mm by 25mm (Rand, 2017)
Methods or the experimental procedure
All the chemicals materials for the process of fabrication of the cells of the organic solar
were used as received. The semiconductor materials of the organic and the structure of the solar
cells used in this work as stated above. Solar cells with the inverted structures were then
fabricated through the following processes. The substrate of the indium tin oxide was cleaned by

Fabrication and Characterization of Organic Solar Cells 11
the bath of ultrasonic with the methanol and acetone for around 5 minutes and dried using the
nitrogen gas, and then the electrodes of the indium tin oxide were cleaned in an atmosphere of
the ozone using the cleaner of the ultraviolet ozone for around 15 minutes.
The precursor solution for the TiOx was made from the titanium isopropoxide, 2-
methoxyethanol, and acetylacetone as reported above. The speed of the spin coater was
programmed according to the thickness desired. The thickness of the spin-coated film is the
function of the speed spun. The concentration of the solution is another important factor that
affects the thickness of the film. The precursor solution for the TiOx was then spin coated on the
substrate of the ITO at the 2000 revolutions per minute, known as ITO/TiOx. After annealing for
around 60 minutes at 150 degrees Celsius in the atmosphere (Yengel, 2014).
The C60 thin film was evaporated on the ITO/TiOx at the rate of deposition of 0.1 nm-1
under the condition of the vacuum of 1.2*10-3 Pa to get the semiconductor layer of the n-type,
denoted as the ITO/TiOx/60. The thin film of the PbPc was evaporated on the ITO/TiOx/60 at
the rate of deposition of 10nms-1 under the pressure vacuum of 1.2*10-3 Pa to get the layer of
semiconductor denoted as ITO/TiOx/C60/PbPc. A thin layer of the PEDOT; PSS a layer of the
transport hole was pin coated at the 2000 revolutions per minute for around 30 seconds onto the
ITO/TiOx/ C60/PbPc, denoted as ITO/TiOx/C60/PbPc/PEDOT: PSS (Astronautics, 2016).
The density of the current-voltage characteristics of the photovoltaic cells of the solar
was measured both under the illumination and in the dark at 100m Wcm2 using the simulator of
the solar and the systems of polarization. The absorption properties of the optics were evaluated
by the means of the visible ultraviolet near the spectroscopy infrared. The photovoltaic
conversion efficiency of the power was gotten by the following formulae;

Fabrication and Characterization of Organic Solar Cells 12
efficiency = P max/P light
=Jsc*Voc*FF/P light
where the FF is the fill factor and the P light is the light incident power. the fill factor is written
as FF= J max*Vmax/Jsc*Voc
Where the Vmax is the voltage at the power of maximum and J max is the density of the current
at the power of maximum (Parthasarathy, 2014)
The open circuit voltage
This is the maximum gotten from the terminals of the cells of solar when the circuit is
open and no flowing of the current. The voltage is somehow related to the offset energy between
the materials of the photoactive portion of the solar cells more the difference of their levels of
energy between the LUMO of the donor and the HOMO of the acceptor. When the I-V is
measured with the simulators with light, it enables one to predict the factors of the solar cells
when illuminated (Poortmans, 2013).
Short circuit density currents
This is the maximum level of the current gotten from the solar cells that occur when there
is no resistance in the similar circuit of the solar cells. This is the correct that flows through the
outward circuit to the loads located externally when the carrier charges created in the cells of
solar arrives at the electrode with ease (Miranda, 2014).
The maximum power
Power is the product of the voltage and current of the device of electronic. The maximum
power can be removed from the cells of solar hence is the reduction of the maximum current as
gotten from the solar. The maximum current and voltage of the solar of the current of short