P3HT:PCBM

1
P3HTPCBM
Possible way to home-use solar cell foliage
Ge, Weihao
2
Major steps of the working process of all solar
cells

• Absorb photon
• Create charge
• Collect charge

Efficiency - Stability - Synthesis
3
Step1 Absorption

• Factors
• Intensity at the active layer
• concentrating devices
• decreasing surface reflection
• Band structure of the material

Efficiency - Stability - Synthesis
4
Step1 Absorption

• Absorption Spectrum
• Photoelectric effect
• for ? gt ?max, photon passes through
• for ? lt ?max, Excessive energy is wasted in the
  form of heat.
• Absorption spectrum of P3HTPCBM blends

Cook et al. J. Phys. Chem. C, Vol. 113, No. 6,
2009
Efficiency - Stability - Synthesis
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Step1 Absorption

• Spectrum
• Difference from inorganic solar cell materials
• Band gap width
• Si
• organics higher absorption at UV
• Adjustable

Chapin et al. J.Appl.Phys.25 (1954) pp. 676 Cook
et al. J. Phys. Chem. C, Vol. 113, No. 6, 2009
Efficiency - Stability - Synthesis
6
Step2 Charge generation

• Exciton creation
• Electron and hole are paired via (screened)
  Coulomb interaction
• Binding energy of excitons

• A very high separation rate which is not good.

Ashcroft et al. Solid State Physics ISBN
7-5062-6631-8/O482 pp.626-628 Cook et al. J.
Phys. Chem. C, Vol. 113, No. 6, 2009
Efficiency - Stability - Synthesis
7
Step2 Charge generation

• Exciton separation
• Diffusion, -gt recombination / separation
• Difference from inorganic ones
• higher binding energy
• lower diffusion range

Efficiency - Stability - Synthesis
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Step2 Charge generation

• Exciton separation
• Internal field at junctions
• how is an internal field built up?
• Fermi energy must be matched when in
  equilibrium
• Some properties of heterojunction
• Window effect
• superinjection
• Bulk heterojunction in organic materials
• Enlarge D-A interface
• Excitons meet field within diffusion range

Alferov, Nobel Lecture, Dec. 8, (2000) Hoppe, et,
al. J.Mater.Res., Vol.19, No.7, Jul (2004)
Efficiency - Stability - Synthesis
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Step 3 Charge Collection

• Challenges poor charge mobility
• High surface resistivity
• Diffused metal particles from the cathode
  impairs acceptors strength
• Bulk heterojunction

Hoppe, et, al. J.Mater.Res., Vol.19, No.7, Jul
(2004) Christoph, et, al. Adv. Funct. Mater.
2001, 11, No. 5, October Mayer, et,al. Materials
today, Vol.10, No.11, Nov. (2007) pp.28-33
Efficiency - Stability - Synthesis
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Methods to improve efficiency

• Additional layers
• Optical spacer
• Buffer layer

P.D. Andersen et al., Opt. Mater. (2008),
doi10.1016/j.optmat.2008.11.014 Y.Zhao,etal.,Sol.
EnergyMater.Sol.Cells(2009),doi10.1016/j.solmat.2
008.12.007
Efficiency - Stability - Synthesis
11
Methods to improve efficiency

• Morphology
• Experiment results
• Enhanced absorption
• Enhanced charge mobility

P. Vanlaeke et al. Solar Energy Materials Solar
Cells 90 (2006) 21502158 F. Padinger, et al.
Adv. Func. Mat. 13 (2003) 85.
Efficiency - Stability - Synthesis
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Methods to improve efficiency

• Thermal annealing
• Nanocrystal of PCBM
• P3HT rod-like crystalline

X.Yang, et al. Nano Lett., Vol. 5, No. 4,
2005 P.Vanlaeke et al. Solar Energy Materials
Solar Cells 90 (2006) 21502158
Efficiency - Stability - Synthesis
13
Methods to improve efficiency

• Thermal annealing
• In blends, crystallization inhibited
• by annealing, resumed

P.Vanlaeke et al. Solar Energy Materials Solar
Cells 90 (2006) 21502158 J.Zhao, et al. J. Phys.
Chem. B 2009, 113, 15871591
Efficiency - Stability - Synthesis
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Methods to improve efficiency

• Supplements
• Dye
• Enhance IR absorption
• Lower exciton separation percentage

E.Johansson, et.al. J. Phys. Chem. C, 2009, 113
(7), 3014-3020
Efficiency - Stability - Synthesis
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Methods to improve efficiency

• Supplements
• Hole-extraction layer, increasing surface
  conductivity
• ITO anode
• PEDOTPSS, as modifier and as anode
• Carbon nanotube

J.Kang, et.al Electrochemical and Solid-State
Letters, 12 3 H64-H66 2009 A. Colsmann et al.
Thin Solid Films 517 (2009) 17501752 R.A. Hatton
et al., Org. Electron. (2009), doi10.1016/j.orgel
.2008.12.013
Efficiency - Stability - Synthesis
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Stability test, experimental results

• P3HTPCBM 1 year lifetime out-door

J.A. Hauch et al. Solar Energy Materials Solar
Cells 92 (2008) 727731
Efficiency - Stability - Synthesis
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Methods to enhance stability

• Protection from electrodes slow down phase
  transition
• Selection of Cathod material
• An outlook self-repair and defect-tolerating
  material

J.Zhao, et al. J. Phys. Chem. B 2009, 113,
15871591 De Bettingnies, et.al. Synthetic
Metals, 156 (2006) pp.510-513 DOE office of
Science. Basic Research Needs for Solar Energy
Utilization, Apr. (2005)
Efficiency - Stability - Synthesis
18
Synthesis methods

• Wet processing
• spin coating
• repeatable
• Screening printing
• easy to define pattern
• Good choice of solvent also increases efficiency

www.brewerscience.com F.Krebs, Solar Energy
Materials Solar Cells 93 (2009) 465475 S.E.
Shaheen, et.al. Appl. Phys. Lett. 79, 2996
(2001) Maher Al-Ibrahim,et.al. Appl. Phys. Lett.
86,201120 (2005)
Efficiency - Stability - Synthesis
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Summary

• Main challenge to organic solar cells
  efficiency
• Morphology plays an important role.
• Possible for low-cost mass-production
• Additionally, therere other advantages.

20
References
1 Cook et al. J. Phys. Chem. C, Vol. 113, No.
6, 2009 2 Chapin et al. J.Appl.Phys.25
(1954) pp. 676 3 Ashcroft et al. Solid
State Physics ISBN 7-5062-6631-8/O482
pp.626-628 4 Alferov, Nobel Lecture, Dec. 8,
(2000) 5 Hoppe, et, al. J.Mater.Res.,
Vol.19, No.7, Jul (2004) 6 Christoph, et, al.
Adv. Funct. Mater. 2001, 11, No. 5, October 7
Mayer, et,al. Materials today, Vol.10, No.11,
Nov. (2007) pp.28-33 8 P.D. Andersen et al.,
Opt. Mater. (2008), doi10.1016/j.optmat.2008.11.0
14 9 Y.Zhao,etal.,Sol.EnergyMater.Sol.Cells(20
09),doi10.1016/j.solmat.2008.12.007 10 P.
Vanlaeke et al. Solar Energy Materials Solar
Cells 90 (2006) 21502158 11 F. Padinger, et
al. Adv. Func. Mat. 13 (2003) 85. 12 X.Yang,
et al. Nano Lett., Vol. 5, No. 4, 2005 13
J.Zhao, et al. J. Phys. Chem. B 2009, 113,
15871591 14 E.Johansson, et.al. J. Phys. Chem.
C, 2009, 113 (7), 3014-3020 15 J.Kang, et.al
Electrochemical and Solid-State Letters, 12 3
H64-H66 2009 16 A. Colsmann et al. Thin Solid
Films 517 (2009) 17501752 17 R.A. Hatton et
al., Org. Electron. (2009), doi10.1016/j.orgel.20
08.12.013 18 J.A. Hauch et al. Solar Energy
Materials Solar Cells 92 (2008) 727731 19 De
Bettingnies, et.al. Synthetic Metals, 156 (2006)
pp.510-513 20 DOE office of Science. Basic
Research Needs for Solar Energy Utilization,
Apr. (2005) 21 www.brewerscience.com 22
F.Krebs, Solar Energy Materials Solar Cells 93
(2009) 465475 23 S.E. Shaheen, et.al. Appl.
Phys. Lett. 79, 2996 (2001) 24 Maher
Al-Ibrahim,et.al. Appl. Phys. Lett. 86,201120
(2005)