This document discusses the fabrication of organic bulk heterojunction solar cells. It begins with an introduction to organic solar cells and their advantages. It then describes the working principles of organic polymer solar cells including light absorption, exciton diffusion, charge transfer, and charge collection. The common layer stack is explained including the active layer, transport layers, electrodes, and substrates. Fabrication methods like spin coating and spray coating are outlined along with specific fabrication steps for layers. Performance parameters like open circuit voltage and power conversion efficiency are discussed. The effects of UV irradiation treatment and adding zinc oxide nanoparticles are evaluated.

1. Fabrication of Organic
bulk Heterojunction
Solar Cell
Professor: Dr.Joodaki
Presented by: Farzane Senobari
Fall 2016

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outline
I. Introduction
II. Organic Polymer solar cells
• Junction type
• Working principle
• The layer stack
III. Fabrication methods
• Spin coating
• Spray coating
• Fabrication steps
• specification
IV.Discuss the article

3. Introduction
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Organic solar cells (OSCs) have attracted strong attention in recent years
• Clean
• Renewable
• Flexibility
• Thinness
• Simple Manufacturing Process

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Introduction
Organic solar cell (OPV)
1. Dye sensitized
2. Polymer
3. Liquid crystal

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outline
I. Introduction
II. Organic Polymer solar cells
• Junction type
• Working principle
• The layer stack
III. Fabrication methods
• Spin coating
• Spray coating
• Fabrication steps
• specification
IV.Discuss the article

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Organic Polymer solar cells
Junction type
o Single layer
o Bilayer
o Bulk Heterojunction
o Graded Heterojunction
o Continues Heterojunction

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Organic Polymer solar cells
Working principle
Heterojunction
o A heterojunction is the contact of two materials with different electrical properties.
o The donor is more electron rich than the acceptor.

8. Organic Polymer solar cells
Working Principle
Light absorption (exciton formation)
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Organic Polymer solar cells
Working Principle
Exciton diffusion

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Organic Polymer solar cells
Working Principle
Charge transfer

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Organic Polymer solar cells
Working Principle
Charge collection

12. Organic Polymer solar cells
The layer stack
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 Active layer
• Absorbs light
• Consist of : donor + acceptor
 Transport layers
• based on materials which have the capability of
being able to primarily transfer either electrons or
holes
• hole transport materials : (MoOx)
• electron transport material: (LiF), (Ca) ,(ZnO)
,(TiO)

13. Organic Polymer solar cells
The layer stack
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 Electrodes
• Most common material: (ITO) due to a high optical transmission combined with a low
resistance (a transmission of >85% at <10 Ohm/sq)
• PEDOT:PSS (allow conductivities of more than 500 Scm with a transmission of >80%)
easier fabrication on flexible substrates,
better tolerance towards bending compared to
an ITO electrode
Substrates
•Glass
•plastics

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outline
I. Introduction
II. Organic Polymer solar cells
• Junction type
• Working principle
• The layer stack
III. Fabrication methods
• Spin coating
• Spray coating
• Fabrication steps
• specification
IV.Discuss the article

15. Fabrication Methods
Spin Coating
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• The deciding process parameters
involved in spin coating are:
1. Solution viscosity
2. Angular speed
3. Spin Time
• Advantage: possibility of making very well defined film thicknesses
• Disadvantage: difficulty with scaling to large area samples

16. Fabrication Methods
Spray Coating
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(Http://Www.Nanowerk.Com/Spotlight/Id17636.Jpg)

17. Fabrication Methods
Spray Coating
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Atomization
process:
1. Surface tension
viscosity
2. Fluid density
3. Gas flow
properties
4. Nozzle design
 Quality of the
coated layer
1. Wetting behavior
2. Surface properties
3. Working distance
4. Coating speed
5. Droplet sizes
6. Amount of
sprayed layers.
The Surface roughness :
spray ~tens of nanometers
spin coated ~few nanometers.

18. Fabrication Methods
ITO coating on glass substrate[7]
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𝐼𝑛𝐶𝑙3and 𝑆𝑛𝐶𝑙2 powder
Dilution with methanol
Dissolution with glaciel acetic acid
Mixing(25 ̊C,1h,air)
Glass slide substrate
rinsed in acetone
dried in air
The solutions were deposited on glass substrates by spin coating
Drying (300 ̊C,5min) heat treatment(500 ̊C,5min)
Annealing (600 ̊C,1 hr, air) ITO Film

19. Fabrication Methods
ITO−coated glass substrates cleaning[8]
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1. cleaned with detergent
2. ultrasonicated in acetone and isopropyl alcohol
for 15 min
3. dried in an oven at 120 °C
4. UV–ozone was used to treat the ITO surface
for 10 min

20. Fabrication Methods
PEDOT:PSS layer formation[8]
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PEDOT:PSS solution
irradiated with UV light
(emission centered at 365 nm and power density of 300 µW 𝑐𝑚−2)
in a dark glove box for 15, 30, 45, or 60 min.
sprayed (by handheld airbrush
,0.1 Mpa, distance 30cm,20s)
spin-coated(5000 rpm ,30 s)
Annealing (150 °C, hot plate ,10 min)
The thickness of the PEDOT:PSS film was well controlled in the range of 30–40 nm

21. Fabrication Methods
active layer formation (bulk heterojunction film )[8]
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mixing in chlorobenzene solution
different blend ratios(1:1; 1:1.5, 1:2, 1:3, and 1:4 (w/w))
sprayed (0.1 Mpa, distance 20 cm, 30 s)
spin-coated(1500 rpm, 30 s)
Polymer and PC70BM
The thickness of active ~ 120 nm

22. Fabrication Methods
AL Deposition[8]
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The active surface area of the device was 0.12 cm2 .
samples
transferred into a vacuum chamber
deposit Al (100 nm, pressure 2.0 * 10-6 Torr.)

23. Specification
Spin coating Spray coating
• Max Temperature: 150 ̊C
• No need to clean room
• Needs vacuum for AL dep
• Thickness≅260nm
• Weight: light weight
• Material: no rare, not toxic
• PCE=4.94%
• Short life time
• Can’t be used in R2R process
• flexible
• Max Temperature: 150 ̊C
• No need to clean room
• Need vacuum for AL dep
• Thickness≅260nm
• Weight: light weight
• Material: no rare, not toxic
• PCE=4.94%
• Short life time
• Can be used in R2R process
• flexible
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outline
I. Introduction
II. Organic Polymer solar cells
• Junction type
• Working principle
• The layer stack
III. Fabrication methods
• Spin coating
• Spray coating
• Fabrication steps
• specification
IV.Discuss the article

25. Discuss the article
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• Open Circuit Voltage (𝑉𝑜𝑐)
• Short Circuit Current (𝐼𝑆𝐶)
• Fill Factor(FF)
• Power Conversion Energy(PCE)

26. Discuss the article
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• UV irradiated PEDOT:PSS films were qualitatively similar to annealed films
• The UV-irradiated solvent-modified PEDOT:PSS films have a high dipole moment. The PEDOT:PSS segments
are evenly distributed throughout the entire thin film and this could effectively reduce light scattering
• Enlargement of the PEDOT grains and the reduction in the density of pores
improvement of conductivity by increasing the number of conducting pathways for carriers.
Discuss the article
UV irradiation
time
15 min 30 min 45 min 60 min
RMS roughness 1.33 nm 1.24 nm 1.20 nm 1.17 nm

28. Discuss the article
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• Low performance + Low life time need a solution!
Nanoparticle
The size of metal nanoparticles is one of
key factors to strong light trapping

29. Discuss the article
nanoparticle[9]
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0.5 ml PEDOT:PSS solution+ 0.1 mg ZnO powder (size of nanoparticles smaller than 100 nm)
LiF thin layer
deposited by thermal vacuum evaporation
ultrasonicated (2 hours and 30 minutes,
room temperature)
spin-coating

30. Discuss the article
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31. Discuss the article
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life time decreased due to:
• The diffusion of PCBM molecules between the P3HT chains leading to a low
crystalinity

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33. References
[1] http://energy.dtu.dk/
[2] http://plasticphotovoltaics.org/lc/lc-solarcells.html /
[3] https://en.wikipedia.org/wiki/Organic_solar_cell
[4] http://depts.washington.edu/cmditr/modules/opv/index.html
[5] http://edu.nano.ir/paper/68
[6] V.Doojin,” Fabrication of organic bulk heterojunction solar cells by a spray deposition method for low-cost power
generation”, Appl. Phys. Lett,vol.91,Aug,2007.
[7] E. Celik,U. Aybarc,” ITO films on glass substrate by sol–gel technique: synthesis, characterization and optical
properties”, JSST,vol.50,pp.337-347,June,2009.
[8] P.Kumar,” Comparison of properties of polymer organic solar cells prepared using highly conductive modified
PEDOT:PSS films by spin- and spray-coating methods”, JJAP, vol.53,no.1s, Dec,2013.
[9] A. Radu,” The Influence of LiF layer and ZnO nanoparticles adding on the performances of flexible photovoltaic
cells based on polymer blends”, DIG J NANOMATER BIOS,Vol. 6,no.3, pp.1141-1148, Sep, 2011.