synthesis of semiconducting polymers for possible application in [autosaved]

Low band gap semiconducting
polymers for possible application in
organic photovoltaic cell
By: BONIFACE YEBOAH ANTWI
(PhD chemistry student)

Over view
• INTRODUCTION
• BACKGROUND
• MONOMER UNITS
• POLYMERIZATION TECHNIQUES
• CHARACTERIZATION TECHNIQUES
• SEMICONDUCTING MONOMER
UNITS OF INTEREST
• MONOMERS UNDERSTUDY
• CONCLUSION

Introduction
 Band gap and Low band gap
 Band- energy level
 Band gap – the difference between bands of energy or difference between valence band
and conduction band of atoms, molecules (HOMO-LUMO), etc.
 Measured in eV (UV-vis spectroscopy etc.)
 Low band gap polymers – band gap<2eV (absorbs light with longer wavelength, i.e. λ >
620nm) 1.
 Semiconductor
 Small band gap. And conduct only at temperatures below its melting but not at
absolute zero (−273.15°C) 2 . Eg. B, Si, Ge, As, etc.
 Polymer
 Material with repeating small molecular units that are covalently bond together. These
repeating unit is called a monomer 3. Eg. Polyethylene, polyvinylchloride,
carbohydrates etc.
 Organic photovoltaic cell
 Devices that utilize polymers and other carbon compounds in converting solar energy
to electrical energy 4.
1. Unlu H., (1992). "A Thermodynamic Model for Determining Pressure and Temperature Effects on the Bandgap Energies
and other Properties of some Semiconductors". Solid state electronics 35 (9): 1343-1352.
2. http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Electronic_Structure/Band_Theory_of_Semiconductors;
03/07/2014: 17:15.
3. Allcock, Harry R.; Lampe, Frederick W.; Mark, James E. (2003). Contemporary Polymer Chemistry (3 ed.). Pearson Education.
p. 21. ISBN 0-13-065056-0.
4. http://www.sigmaaldrich.com/content/dam/sigma-aldrich/materials-science/organic-electronics/opv-device.jpg; 03/07/2014; 18:15
Figure 1: Scheme showing
Energy levels and band gap 1
Figure 2: Polyethylene
monomer unit 2
Figure 3: Scheme of
organic photovoltaic cell 4

Figure 4: Sun
intensity
spectrum 5
Why Low band gap semiconducting polymers ?
More photons are
generated at longer
wavelength (Fig. 4).
But lower energy at
longer wavelengths.
And so, narrower band
gap for easy excitation
to conduction band.
Larger photon
absorption leads to
higher current density 5.
Figure 5: Current
density plot of
benzothiadiazole-
thiophene
copolymers 5
5. Bundgaard E., Krebs F. C., 2007. Low band gap polymers for organic photovoltaics, Journal of Solar Energy Materials & Solar Cells; 91:954–985.
CURRENT DENSITY

Why Low band gap semiconducting polymers cont.
HIGH OPEN CIRCUIT VOLTAGE VOC
The VOC – energy difference between
HOMO of a donor and LUMO of an
acceptor.
Low band gap of donor VOC(1) combined
with a higher LUMO of acceptor VOC(2)
VOC
photovoltaic of cell, hence its efficiency 5.
Figure 6: Increasing open circuit voltage by tuning the energy
levels in a bulk heterojunction OPV device.
5. Bundgaard E., Krebs F. C., 2007. Low band gap polymers for organic photovoltaics, Journal of Solar Energy Materials & Solar Cells; 91:954–985.

Factors to consider when forming low band gap
polymers
This include;
intra-chain charge transfer
substituent effect
π-conjugation length etc. 5
 To acheive this, copolymers are formed.
– polymers of two different monomer
units
Electron Donor (D)-Electron Acceptor
(A) molecules.
5. Bundgaard E., Krebs F. C., (2007). Low band gap polymers for organic photovoltaics, Journal of Solar Energy Materials & Solar Cells; 91:954–985.
Figure 7: copolymers based on thiophene and benzothiadiazole

Factors to consider when forming low band gap
polymers cont.
Copolymer
Computational studies – longer π-conjugation
length reduces band gap 6.
Reduced bond-length alternation lowers the HOMO-
LUMO gap (Aromaticity *) 6
Intra-molecular charge transfer lowers band gap
of the copolymer due to new hydride orbitals 6.
EWG (electron withdrawing groups)
EDG (electron donating groups)
EDG increases HOMO of hybrid orbital while EWG
decreases LUMO of hybrid orbital.
Figure 8: Interaction of energy level of a donor (D) and acceptor (A)
leading to a narrower HLG 6
6. Qian G. and Wang Z. Y. , (2010). Near-Infrared Organic Compounds and Emerging Applications. Chem. Asian J.;5:1006 – 1029.

2-(2,5-di(pyrrol-2-yl)thiophen-3-yl)ethyl 2-
bromopropanoate)
(PyThon)
Known Monomers 7-10
(Electron rich monomers)
7. Xu T. and Yu L., (2014). How to design low band gap polymers for highly efficient organic solar cells. Materials Today; 17:1:1-5.
8. Dai Liming, (1999). Advanced Syntheses and Microfabrications of Conjugated Polymers, C60-containing Polymers and Carbon Nanotubes for Optoelectronic Application. Polym. Adv. Technol. 10, 357-420.
9. Strover L. T., Malmström J. , Laita O., Reynisson J., Aydemir N., Nieuwoudt M. K., Williams D. E., Dunbar R. P., Brimble M. A., Travas-Sejdic J., (2013). A new precursor for conducting polymer-based brush interfaces with
electroactivity in aqueous solution. J. Polymer, 54; 1305-1317.
3,4-dihydro-3,3-dialkyl-6,8-
bis(trimethylstannyl)-2H-
thieno[3,4-b][1,4]dioxepines
10. Mishra S. P., Palai A. K., Patri, (2010). Synthesis and characterization of soluble narrow band gap conducting polymers based on diketopyrrolopyrrole and propylenedioxythiophenes. J. Synthetic Metals, 160, 2422–2429.
poly(styrenesulfonate) anion (PSS−) bis-thienylpyrrole

Known Monomers 7-10
(Electron deficient monomers)

Known Low Band gap Polymers 7-10

synthesis of semiconducting polymers for possible application in [autosaved]

Types
1. Oxidative preparative routes
I. Electrochemical polymerization
II. Chemical oxidative polymerization
2. Metal-Catalysed routes
I. Kumada cross coupling
II. Suzuki cross coupling
III. Stille coupling
IV. Yamamoto cross coupling

Oxidative Preparative routes
Electrochemical Polymerization (EP)
Electrochemical cell utilised
Monomer is oxidized by electrolyte
Polymer deposited on anode
Eg. Pyrrole11, thiophene12, etc.
Similar to EP
But utilizes chemical oxidant, such as
FeCl3 for polyaniline 13.
(Regioselectivity, intractability problems)
Chemical oxidative polymerization
11. A. F. Diaz and K. Keiji Kanazawj, (1979). Electrochemical Polymerization of Pyrrole. J.C.S. Chem. Comm.; 1-2
12. Albery W.J., Li F., Mount A.R., (1991). Electrochemical polymerization of poly(thiophene-3-acetic acid),
poly(thiophene-co-thiophene-3-acetic acid) and determination of their molar mass. Prog. Polym. Sci.; 301: 1-2:
239–253.
13. Gospodinova N. , Terlemezyan l., (1998). Conducting polymers prepared by Oxidative polymerization: polyaniline. Polym. Sci.; 23, 1443–1484.
Figure 9: Electrochemical cell for
polymerization

Types and differences
Cross coupling Methods Reacting species Catalyst Comments
Kumada
Nickel
or
Palladium
• Limited functional group tolerant
(Grignard reagent-high reactivity)
Negishi Zinc
• Cross coupling at lower
temperatures
• Tolerant of other functional
groups
• Toxic catalyst
Suzuki Palladium
• Mild reaction conditions
• availability of boric acid
• Less toxic
Stille Tin
• Polymerize at higher
temperatures
• Difficulties in purification
• Toxic catalyst

• 1H and 13C NMR were
• Infrared spectrometry
• Cyclic voltammety
• Gel Permeation Chromatography (GPC)
• Thermal gravimetric analyses
(TGA).
• UV-visible
• And many more

SEMICONDUCTING MONOMER
UNITS OF INTEREST

Band gap
(1.46 eV to 1.60 eV)
• Mimic

SELECTED SEMICONDUCTING MONOMER (2.80 eV)

Synthesis of N-tosyl pyrrole
Synthesis of 3-hexyl pyrrole
by Friedel-Craft acylation

Together we shall obtain a Low band gap semiconducting
polymers for solar cell application

synthesis of semiconducting polymers for possible application in [autosaved]

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to synthesis of semiconducting polymers for possible application in [autosaved] (20)

Recently uploaded (20)

synthesis of semiconducting polymers for possible application in [autosaved]