Post on 07-Apr-2018
8/4/2019 Towards thermally stable poly (3-hexylthiophene) based photovoltaic devices
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TOWARDS THERMALLY STABLE POLY (3-HEXYLTHIOPHENE)
BASED PHOTOVOLTAIC DEVICES
NAUMAN MITHANI
CHEM 481
Supervisor: DR. STEVEN HOLDCROFT
Term 1104
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INTRO: need for alternative/renewable energy
2
eventuality
economics
smoggreenhouse extreme weather
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INTRO: energy consumption forecast
3Source: Arvizu, D; National Renewable Energy Laboratory: Milken/Sandia workshop for financial & capital market leaders, 2007/10/23.
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INTRO: photovoltaic materials - organic vs.inorganic
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lightness of weight
flexibility
large scale
low cost
printability / substrate
flexibility
molecular engineering
band gap control
lower
efficiency
poorer
stability
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INTRO: choice oforganic materialsefficiency & promise
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organic photovoltaic materials
-conjugated polymers
P3HT & PCBM *
poly (3-hexylthiophene)(P3HT)
donor (D)/hole carrier
[6,6]-phenyl C61 butyric acid methyl ester(PCBM)
acceptor (A)/electron transporter
* Yao, Y.; Hou, J.; Xu, Z.; Li, G.; Yang, Y. Advanced Functional Materials2008, 18, 1783.
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INTRO: mechanism ofphoto (photon)voltaic(charge)
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diffusion to interface2 exciton dissociation3exciton generation1
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INTRO: mechanism ofphoto (photon)voltaic(charge) {contd.}
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charge transport photocurrent5free electron/hole pairs4
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INTRO: the mish-mash ORbulk heterojunction (BHJ)
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scale of exciton diffusion is (tens of)
nanometres
exciton must reach interface in
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INTRO: prelude to project
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P3HT & PCBM are ultimately immiscible
eventual microscopicscalephase segregation (103 over limit)
interruption of bi-continuity (discrete aggregates)
P3HT & PCBM blend
Thermal annealing: somePCBMpost-functionalisedonto P3HT
serves to tethersome PCBM to P3HT
serves asaccelerated lifetime evaluation of (thermal) stability
P3HT-(graft-PCBM)& PCBM blend
Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
excess post-functionalisation
interruption of P3HT chains self-organisation & semi-crystallinity
decrease in electronhole mobility
performance & stabilitybi-continuity& semi-crystallinity
annealing duration/temp. must be optimised to avoidphase segregation
100 m
10 m
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EXPT.: synthesis ofpoly 2%(3-bromo-4-hexylthiophene), 1
10Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
where extent ofpost-functionalisation,
n = 0.02
P3HT98% regioregular (H-T)
1
NBS (2% by mole)
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EXPT.: P3HT-2%(TEMPO-styrene) macroinitiator, 2
Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708. 11
n = 0.02
1 2
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EXPT.: synthesis ofP3HT-2%(graft-(ST-stat-CMS)), 3
Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708. 12
n = 0.02
2 3
x:y = 1:1
nitroxide-mediated living
radical polymerisation
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RESULTS & CHARACTERISATION: 1H-NMR ofP3HT-2%(graft-(ST-stat-CMS)), 3
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CMS:ST provided by
m:k
1:12
93.1:99.0
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RESULTS & CHARACTERISATION:aggregation ofP3HT-2%(graft-(ST-stat-CMS)), 3
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UV-Vis spectra of3 in CHCl3
Polymer aggregation
induced by MeOH
max of P3HT backbone
shifts from 452 nm to
530/570 nm -* stacking of the
P3HT chains
semi-crystalline
arrangement of chains
occurrence of vibrionic
side bands
2% graftdensity is acceptable towards P3HT self-organisation
long-range -conjugation (hole mobility) is NOT hampered
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EXPT.: synthesis ofP3HT-2%(graft-(ST-stat-N3MS)), 4
Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708. 15
n = 0.02
3 4
x:y = 1:1
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EXPT.: blendofP3HT-2%(graft-(ST-stat-N3MS)) + PCBM (1:1)
16Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
Step 2: spin-coat on quartz substrate
slow evaporation
bulk
heterojunction
&Step 1:
freePCBM
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EXPT.: 1:1 blendofP3HT-2%(graft-(ST-stat-(NMS-graft-PCBM))) + PCBM
17Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
in excess relative
to number of
reaction sites on 4
blend of
4
5
freePCBM
graftedPCBM
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pre-annealed graftcopolymer blend post-annealed graftcopolymer blend
RESULTS & CHARACTERISATION: optical microscope photographs ofblend, pre- & post-annealed
18Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
100 m
10 m1:1
P3HT+PCBM
system
microscopic
phase
separation
discrete PCBM aggregates
semi-crystalline P3HT domain
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P3HT abs.PCBM abs.
RESULTS & CHARACTERISATION: UV-Vis spectra ofblend, pre- & post-annealed
19Gholamkhass, B.; Peckham, T. J.; Holdcroft, S. Polymer Chemistry2010, 1, 708.
pre-anneal: P3HT max blue-shifts
from 525 nm to 500 nm
-* stacking of the P3HT chains
is hindered
post-anneal: P3HT max appears to
be less blue-shifted
-* stacking of the P3HT chains
is lesshindered
same relative intensity of vibrionic side-bands to abs. maximum suggests semi-crystalline
arrangement stilloccurs
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CONCLUSION
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1:1 P3HT(copolymer) + PCBM blends do NOT suffer microscopic phase separation
Thermal annealing was successful: greater degree of self-organisation of P3HT
as shown by red-shifting in UV-Vis spectra relative to pre-annealed blends
temperature of 150 oC and duration of 1 hr. are acceptable
P3HT(copolymer)+PCBM blends exhibit thermal stability
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FUTUREWORK
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Photoluminescence spectroscopy: better understanding of SPR such as electron hole formation
efficiency by PL quenching
Detailed morphology study by Transmission Electron Microscopy: determination of P3HT(copolymer)
and PCBM domains, and changes after annealing
Addition ofhigh boiling point additive e.g. 1,8-octanedithiol*to solution in film-casting: selective
dissolution of PCBM
enhanced solubility of PCBM uniform film formation, no spots of insolubility
Photovoltaic performance parameters: hole mobility, current densityvs.potential, external quantum
efficiency(EQE) and overallpower conversion efficiency(PCE)
Optimisation ofblend ratio
quantitative analysis by Thermo-gravimetric analysis (TGA) & NMR
*Lee, J. K.; Ma, W. L.; Brabec, C. J.; Yuen, J.; Moon, J. S.; Kim, J. Y.; Lee, K.; Bazan, G. C.; Heeger, A. J. Journal of the American Chemical
Society2008, 130, 3619.
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ACKNOWLEDGEMENTS
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Bobak Gholamkhass
Dr. Steven Holdcroft
Dr. Timothy Peckham
Dr. Mahesh Kulkarni
Dr. Jaclyn Brusso
Kristen Soo
Graeme Suppes
Owen Thomas
Martyn Stocker
Jessica Luo
Emily Tsang
Ami Yang
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Fin
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