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Self-Organization of Polymers and Applications in Solar Cells

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Presentation on theme: "Self-Organization of Polymers and Applications in Solar Cells"— Presentation transcript:

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

2 Outline Introduction Application Future Improvements
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

3 Outline Introduction Application Future Improvements
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

4 Introduction Self-assembly Distinctive features
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

5 Introduction Types Self-ordered/assembled… Nanocomposites
Semiconductor islands Pore structures Carbon nanotubes Quantum wires and dots www3.interscience.wiley.com

6 Introduction Applications
Pattern transfer Improvements in devices Optics and sensing Applications related to the type of structures

7 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

8 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

9 Outline Introduction Application Future Improvements
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

10 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

11 Self-Ordered Array of Air Bubbles in a Polymer Film
Final product Srinivasarao, Science, (2001)

12 Self-Ordered Array of Air Bubbles in a Polymer Film
Optically sectioned images Srinivasarao, Science, (2001)

13 Self-Ordered Array of Air Bubbles in a Polymer Film
Hole depth profile Discontinuity of holes seen at around 5 μm in depth Srinivasarao, Science, (2001)

14 Self-Ordered Array of Air Bubbles in a Polymer Film
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

15 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

16 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.

17 Outline Introduction Application Future Improvements
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

18 Polymer PV Cells Advantages Disadvantages Low cost of fabrication
Ease of processing Mechanical flexibility Versatility of chemical structure Disadvantages Low efficiency

19 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

20 Outline Introduction Application Future Improvements
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

21 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

22 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)

23 Introduction By changing the annealing time and the growth rate of the active area, any change in these parameters are observed.

24 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: nm Active device area: 0.11 cm2

25 Sample Description Variable Active layer growth rate Annealing time
Device No. Solidification Time Annealing Time 1 20 min 0 min 2 10 min 3 4 30 min 5 3 min 6 40 s 7 20 s

26 Results

27 Results Device No. S.T. A.T. JSC VOC (V) PCE (%) FF (%) RSA 1 20 min
(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 10 min 10.6 0.61 4.37 67.4 1.7 3 10.3 0.60 4.05 65.5 1.6 4 30 min 3.98 64.7 5 3 min 8.33 2.80 56.5 4.9 6 40 s 6.56 2.10 53.2 12.5 7 20 s 4.50 0.58 1.36 52.0 19.8

28 Results Change in the carrier mobilities
Electron and hole mobilities must be well balanced.

29 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

30 Outline Introduction Application Future Improvements
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

31 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

32 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 ) 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)

33 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

34 Result Internal quantum efficiency is nearly 100%, meaning it can absorb almost all the photons The PCE is ~6%

35 Future Improvements Change of the polymer materials which could enhance PCE Insertion of new functional layers

36 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)

37 Questions?

38 G6 Rebuttal: Self-ordered devices
Jung Hwan Woo Please Prepare a Rebuttal

39 G1 Self-Organization of Polymers and Applications in Solar Cells Review
Edson P. Bellido Sosa

40 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

41 G2 Review Self-ordered devices
Alfredo Bobadilla

42 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

43 Review: Self Organization of polymers Jung Hwan Woo Presentation
Mary Coan, G3 Chemical Engineering Review: Self Organization of polymers Jung Hwan Woo Presentation

44 Review Defined Self-Assembly Gave examples of different templates used
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

45 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

46 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.

47 Review The presenter used many images to help the audience follow the presentation and understand more complex thoughts Overall a good presentation

48 G4 Review Self-ordered devices
Diego A. Gomez Gualdron (MISSING)

49 G5 Review Self-ordered devices
Norma L. Rangel

50 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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