Self-Organization of Polymers and Applications in Solar Cells Jung Hwan Woo.

Self-Organization of Polymersand Applications in Solar CellsJung Hwan Woo

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




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





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

Final product


Srinivasarao, Science, (2001)

Optically sectioned images



Hole depth profile Discontinuity of

holes seen at around 5 μm in depth



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


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


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.


Outline





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



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

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

Change in the carrier mobilities Electron and hole

mobilities must be well balanced.

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





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)

Questions?

G6Rebuttal: Self-ordered devices

Jung Hwan WooPlease Prepare a Rebuttal

G1Self-Organization of Polymersand Applications in Solar Cells

Review

Edson P. Bellido Sosa

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

G2Review Self-ordered devices

Alfredo Bobadilla

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

Review:Self Organization of polymersJung Hwan Woo Presentation

Mary Coan, G3Chemical Engineering

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


Diego A. Gomez Gualdron(MISSING)


Norma L. Rangel

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”

Self-Organization of Polymers and Applications in Solar Cells Jung Hwan Woo.

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