self-organization of polymers and applications in solar cells jung hwan woo
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Outline
Introduction Self-assembly and distinctive features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells using
self-organized polymer Bulk heterojunction solar cells
Future Improvements
Outline
Introduction Self-assembly and distinctive
features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells using
self-organized polymer Bulk heterojunction solar cells
Future Improvements
Introduction
Self-assembly Defined as spontaneous and reversible
organization of molecular units into ordered structures
Distinctive features Order
High order
Interactions Weak bonds play a role
Building blocks Nano and mesoscopic structures
http://nimet.ufl.edu/
Introduction
Types Self-ordered/assembled…
Nanocomposites Semiconductor islands Pore structures Carbon nanotubes Quantum wires and dots
www3.interscience.wiley.com
Introduction
Applications Pattern transfer Improvements in devices Optics and sensing
Applications related to the type of structures
Introduction
Different methods to template Ordered array of colloidal particles Templating using an emulsion Honeycomb structures by polymer with rod-
coil architecture Self-organized surfactants, i.e. mesoporous
silica Microphase-separated block copolymers bacteria
Templating Example
Ordered array of colloidal particles Procedure
Colloidal crystals infiltrate with a fluid which fills and solidifies in the space between the crystals
Spheres removed by thermal decomposition or solvent extraction
Solidified fluid forms 3D array of pores Main drawback
Length of pores cannot be controlled
Outline
Introduction Self-assembly and distinctive features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells using
self-organized polymer Bulk heterojunction solar cells
Future Improvements
Self-Ordered Array of Air Bubbles in a Polymer Film
Procedures include forced air flow with moist atmosphere over a volatile solvent (polystyrene)
High vapor pressure and velocity drives the temperature to 0°C
Condensed water droplets form a structured array and sinks into the solution
When new water droplets condense previous array provide a template for the next layer
Size range from 0.2 to 20 μm
Optically sectioned images
Self-Ordered Array of Air Bubbles in a Polymer Film
Srinivasarao, Science, (2001)
Hole depth profile Discontinuity of
holes seen at around 5 μm in depth
Self-Ordered Array of Air Bubbles in a Polymer Film
Srinivasarao, Science, (2001)
Parameters Solvent
2D porous films obtained when CS2 is used
whereas 3D films obtains for polystyrene Air velocity
30 m/min => 6-μm pores 300 m/min => 0.5 μm pores
Self-Ordered Array of Air Bubbles in a Polymer Film
Advantages Simple method Size of the pores controlled by air
velocity Applications
Polystyrene can be used in beam steering devices, microlens arrays or fabrication of picoliter beakers
Photonic bandgap applications Optical stop-bands
Self-Ordered Array of Air Bubbles in a Polymer Film
Why do water droplets form close packed bubbles? Liquid droplets fail to coalesce with the
same liquid in some situations This phenomenon studied by Rayleigh
in 1879 This behavior driven by
thermocapillary convection The presence of lubricating medium (air)
between two liquid droplets keeps them from coalescence.
Self-Ordered Array of Air Bubbles in a Polymer Film
Outline
Introduction Self-assembly and distinctive features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells using
self-organized polymer Bulk heterojunction solar cells
Future Improvements
Polymer PV Cells
Advantages Low cost of fabrication Ease of processing Mechanical flexibility Versatility of chemical structure
Disadvantages Low efficiency
Polymer PV Cells
Requirements for higher efficiency High fill factor
Ordered structure Efficient absorption of solar radiation
Increased thickness. However, this results in higher series resistance
Lower series resistance Ordered structure can reduce Rs
Outline
Introduction Self-assembly and distinctive features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells
using self-organized polymer Bulk heterojunction solar cells
Future Improvements
High-efficiency solution processable polymer photovoltaic cells by self-
organization of polymer blends
Gang Li, Vishal Shrotriya, Jinsong Huang, Yan Yao, Tom Moriarty, Keith Emery and Yang Yang
Introduction
Improvements in efficiency is required
Important parameters include Current-voltage behavior Fill factor (FF) Short-circuit current (JSC) Open-circuit voltage (VOC) Power conversion efficiency (PCE, η) Quantum Efficiency (EQE/IQE) e--, h+-mobility Series Resistance (RSA)
Introduction
By changing the annealing time and the growth rate of the active area, any change in these parameters are observed.
Sample Description
Active layer of poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) is sandwiched between metallic electrodes
Thickness of the active layer: 210-230 nm
Active device area: 0.11 cm2
Sample Description
Variable Active layer growth rate Annealing time
Device No. Solidification Time
Annealing Time
1 20 min 0 min
2 20 min 10 min
3 20 min 20 min
4 20 min 30 min
5 3 min 0 min
6 40 s 0 min
7 20 s 0 min
Results
Device No. S.T. A.T. JSC
(mA cm-2)
VOC
(V)PCE (%)
FF (%)
RSA (Ω cm2)
1 20 min 0 min 9.86 0.59 3.52 60.3 2.4
2 20 min 10 min 10.6 0.61 4.37 67.4 1.7
3 20 min 20 min 10.3 0.60 4.05 65.5 1.6
4 20 min 30 min 10.3 0.60 3.98 64.7 1.6
5 3 min 0 min 8.33 0.60 2.80 56.5 4.9
6 40 s 0 min 6.56 0.60 2.10 53.2 12.5
7 20 s 0 min 4.50 0.58 1.36 52.0 19.8
Results
Highly ordered structure in sample #1 results in high absorption of light in comparison to sample #7
Poorly ordered structure in sample #7 gives room for annealing to “heal” the disorder
Outline
Introduction Self-assembly and distinctive features Ordered air bubble in polymer film
example Polymer PV cells
Application Highly efficient polymer PV cells using
self-organized polymer Bulk heterojunction solar cells
Future Improvements
Bulk heterojunction solar cells with internal quantum efficiency approacing
100%
Sung Heum Park, Anshuman Roy, Serge Beaupre, Shinuk Cho, Nelson Coates, Ji Sun Moon, Daniel Moses, Mario Leclerc, Kwanghee Lee, and Alan J.
Heeger
Introduction
The use of bulk heterojunction (BHJ) solar cells which involves the self-assembly of nanoscale heterojunction significantly improved the PCE of polymer solar cells over a single junction architecture.
Relatively high performance polymer PV cells are 4-5% (from 2005-2006)
The use of low-bandgap polymers will be able to offer a better harvest of energy
In this report, BHJ solar cell composed of PCDTBT*/[6,6]-phenyl C71 butyric acid methyl ester (PC70BM) is used to improve the IQE of the cells.* PCDTBT – poly[N-9”-hepta-decanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-
benzothiadiazole)
Description of Samples
Titanium oxide optical spacer and hole blocking layer present.
Optical spacer increases the photocurrent of the device by redistributing the maximum light intensity within the active charge separating BHJ layer.
The used spacer is TiOx
Result
Internal quantum efficiency is nearly 100%, meaning it can absorb almost all the photons
The PCE is ~6%
Future Improvements
Change of the polymer materials which could enhance PCE
Insertion of new functional layers
References
Srinivasarao, M., Collings, D., Philips, A., Patel, S., Science 292 (2001)
Li, G., Shrotriya, V., Huang, J., Yao, Y., Moriarty, T., Emery K., and Yang, Y., Nature 4 (2005)
Park, S., Roy, A., Beaupre, S., Cho, S., Coates, N., Moon, J., Moses, D., Leclerc, M., Lee, K., and Heeger A., Nature Photonics 3 (2009)
The presenter have defined self assembly and some of their distinctive features, types, applications and different methods to template. He showed one example of template using air bubbles in a polymer film. He explained the fabrication procedure, the parameters that have to be considered in the fabrication and how this affect the final result. He mentioned some applications of this templates and a hypothesis of why the air bubbles form a close packed structure.
He also explained about the use of polymer in photovoltaic cells. He describe some of the important parameters that one have to take into consideration in PV cell fabrication. In the paper he explained they have analyzed how the solidification and annealing time affects the performance of the polymer PV cell.
In other paper they have analyzed the bulk heterojunction of polymeric solar cells claiming they have obtained a quantum efficiency of 100%.
The overall presentation was good. However, there was too much text and not many figures to help in understanding the topic. The connection between self ordered materials and polymeric PV cells was not very well established. In future research would be interesting to know how the ordering of polymer and the self assembly affects the PV efficiency
Self-Organization of Polymers and Applications in Solar Cells (Lecture review)
• Essential concepts related to solar cells were not well illustrated, it should have been shown some illustrative schemes and equations.
• A comparison with Silicon solar cells was not taken into account. I think mentioning the ‘Si solar cells’ case, which is a simpler case, would have helped to illustrate the qualitative and quantitative aspect of solar cell function.
• It was not illustrated with enough detail the working principle of an organic solar cell; how or where electrons and holes are generated in the solar cell, what’s the role of each thin film layer ?
Alfredo D. Bobadilla
ReviewDefined Self-Assembly
◦Gave distinctive features◦Gave examples in the form of images
Applications
Gave examples of different templates used◦Procedure◦Draw backs
Used images to explain how a self ordered array of air bubles in a polymer film are formed and the resulting products◦Characterized parameters◦Gave advantages and Applications
Review
Spoke about polymer PV cells.◦Advantages and Disadvantages◦Efficiency issues were also discussed
Gave examples of how parameters effect the device area
Spoke about bulk Heterojunction solar cells◦Used to improve proformance
Touched on future improvements
Review
Overall the presentation was geared to a more educated audience◦Undergrads who have previous knowledge of
this topic and to the Graduate level◦Do to the shear number of undergraduates in
the audience I think it is more important to gear your presentation to the undergraduates
The presentation wasn’t too involved however more information on the solar cells may have helped the audience to understand how the polymer improves the solar cell.
ReviewThe presenter used many images
to help the audience follow the presentation and understand more complex thoughts
Overall a good presentation
Self ordered devices and applications in solar cells, Jung Hwan Woo
He covered in the introduction:• Procedures and drawbacks of the fabrication processes• Advantages and applications such as steering devices and microlens, and
also for photonic applications• Comparison air vs. water • Polymer PV Cells:
– Low efficient, but cheap to fabricate and with good mechanical properties– Efficiency can be improved ordered structures, thicker surfaces and a reduction of
the surface resistance• Solar cells paper
– Improvement of the quantum efficiency nearly 100% of photons by using polymers materials and incorporating different techniques. The PCE is ~6%
In my opinion the speaker did not show a relation between the self ordered systems and the solar cells, he was not confident explaining the operation of the solar cell, and I did not get well the importance of the “ordering”
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