OligoANT b P3HT Jacob Strain Hemali Rathnayake Jinjun Liu 20170621 The 72 nd International Symposium on Molecular Spectroscopy Outline Background Introduction to Poly3hexylthiopheneblockoligoanthracene910diyl ID: 632013
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Slide1
Ultrafast Transient Absorption Spectroscopy Investigation of Photoinduced Dynamics in Poly(3-hexylthiophene)-block-oligo(anthracene-9,10-diyl)(Oligo-ANT-b-P3HT)
Jacob Strain*,
Hemali
Rathnayake
,
Jinjun
Liu
2017-06-21
The 72
nd
International Symposium on Molecular Spectroscopy Slide2
OutlineBackgroundIntroduction to Poly(3-hexylthiophene)-block-oligo(anthracene-9,10-diyl)
--Will be referred to as “Oligo-ANT-
b
-P3HT or block polymer” for the remainder of the presentation--Experimental SetupOligo-ANT-b-P3HT:PCBM Blend Transient Absorption SpectraControl: P3HT:PCBM BlendDiscussion Concluding Remarks
PCBM: 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61
P3HT: Poly-3-hexylthiopheneSlide3NREL chartSlide4Why Organic Solar Cells?
Advantages:
Low cost
Lightweight
Large Area
Flexible
Simple Solution Processing:
Printing
Spray
CoatingSlide5
Bulk Heterojunction Cell Schematic
Glass Substrate
ITO
PEDOT:PSS
Active Layer
Al
+
-
Light
Donor Phase
Acceptor Phase
OR
+
+
-
-
+
-
Cathode
Anode
h
n
h
n
ET
HT
Guo, J.; Ohkita, H.; Benten, H.; Ito, S.
Journal of the American Chemical Society
2010
,
132
, 6154.
Processes Involved in Photovoltaic
Conversion
:
Light absorption
Monomolecular deactivations of singlet excitons
Singlet exciton diffusion to the interface
Charge transfer
Geminate recombination of bound radical pair
Charge dissociation from bound radical pair
Charge collection of free carriers
+
-
h
nSlide6What is an Exciton?
Coulombically bound electron and hole pair
Chunk of Energy
Quasi-particle
L
D
: distance exciton can physically travelSlide7
The Active Layer: Processes Involved in Photovoltaic Conversion:
Light absorption (
h
n
)
Monomolecular deactivations of singlet excitons (
kF)
Singlet exciton diffusion to the interface (
k
ED
)
Charge transfer (
k
CT
)
Geminate recombination of bound radical pair (
k
GCR
)
Charge dissociation from bound radical pair (
kCD
)Charge collection of free carriers (kCC
)
Guo, J.; Ohkita, H.; Benten, H.; Ito, S.
Journal of the American Chemical Society
2010, 132, 6154.Slide8
Internal Quantum Efficiency (IQE): numbers of charge carriers formed
CT
= ~100%: Charge Transfer
CD: Charge Dissociation
CC:
Charge Collection
ED
:
Exciton Diffusion
, can be estimated from pristine polymer and polymer:fullerene time constant (
t
ED
= 6-16
ps
);
where
ED ̴
kED higher
kED -> higher ED
->higher IQE ->higher PCE!Slide9
Visual for Exciton Diffusion’s Impact on PCE
PCBM
Phase
PCBM
Phase
Polymer
Phase
+
-
~20 nm
Excitons
able to reach interface
Excitons
unable to reach interfaceSlide10
Visual for Exciton Diffusion’s Impact on PCE
PCBM
Phase
PCBM
Phase
Excitons
able to reach interface
Excitons
unable to reach interface
+
-
Polymer
Phase
~10 nmSlide11
Oligo-ANT-b-P3HT
Ananthakrishnan
, S. J.; Strain, J.;
Neerudu
Sreeramulu, N.; Mitul, A.; McNamara, L. E.;
Iefanova, A.; Hammer, N. I.;
Qiao
, Q.;
Rathnayake
, H.
Journal of Polymer Science Part A: Polymer Chemistry
2016
,
54
, 3032.
50 nm
P3HT
Oligo-ANT
Twisted Geometry:Slide12Steady State Spectra
The 0-0 peak is due to interchain interactions
between polymersSlide13
t1 = 0.603 ps
t
2
= 8.93 pst3 = 110 pst4 = longSlide14
t1 = 0.834 ps
t
2
= 12.75 pst3 = 160 pst4 = longSlide15
What are these peaks in polymer:fullerene films?
Polymer GSB
Polymer Polarons
Delocalized
Localized
The GSB
peak around 610 nm generated from interchain interactions in the polymer is almost absent in Oligo(ANT-b-P3HT) at 1 ps.Slide16What does the time constants mean?
t
P3HT:PCBM (
ps
)Oligo(ANT-b-P3HT):PCBM (ps
)Assignmentt1
0.8340.603polaron generation at the polymer:fullerene interface
t
212.75
8.93
polaron generation
in the polymer
t
3
160
110
hole
transfer from crystalline polymer to amorphous
t
4
longlongcharge carriers
25% decrease in lifetime or
25% increase in rates
Guo, J.; Ohkita, H.; Benten, H.; Ito, S.
Journal of the American Chemical Society
2010, 132, 6154.
Paraecattil, A. A.; Banerji, N. Journal of the American Chemical Society 2014
, 136, 1472..Slide17
Discussion: Marcus Theory, a Decrease in Reorganization Energy
Higher crystalline order (and slightly
smaller domains)
caused by the Oligo-Ant moieties
decrease the reorganization energy (l) thus increasing
k
Gibbs
Energy
Reaction Coordinate
~50% less
D
G
ǂ
D
G
ǂ
D
G
°
D
G
°
l
l
Brédas
, J.-L.;
Beljonne
, D.;
Coropceanu, V.; Cornil, J. Chemical Reviews 2004, 104, 4971.DA
D+A-DAD+A-P3HT:PCBMBlock:PCBMSlide18Conclusions
The presence of Oligo-ANT in the P3HT polymer causes higher crystalline order.
Because of the higher crystalline order the rates of charge separation increases.
Furthermore, because of the smaller phase domains in the Oligo(ANT-b-P3HT):PCBM blend a higher amount of surface area present between the donor and acceptor domains allowing more possible sites for charge dissociation.Slide19Acknowledgements
University of Louisville Lab Group:
Advisors
Dr.
Jinjun
Liu
Dr.
Hemali Rathnayake
Funding:NSF MRI CHE 1338072KCF-KSEF-144-401-13-062Department of Energy