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BSc Thesis Jochen Wolf
- 1. Technische Universität München Realizing flexibility and artificial structures for organic solar cells Advisor: Claudia M. Palumbiny Supervisor: Peter Müller-Buschbaum Technische Universität München, Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Str.1, 85748 Garching Bachelor Thesis by Jochen Wolf
- 2. Technische Universität München 05/08/2013 Jochen Wolf 2 0. Outline 1.1 Motivation 1.2 Working principle of organic solar cells 1.3 Device architectures 1.4 Sample preparation 2.1 Current-voltage measurements 2.2 UVVis measurements 2.3 Scanning electron microscope 3. Structuring on PET 4. Conclusion and acknowledgements
- 3. Technische Universität München 05/08/2013 Jochen Wolf 3 1.1 Motivation plusplasticelectronics.com konarka.com popsci.com - transparent - potentially cheap production - flexible & light after globalwarmingart.com Sun spectrum
- 4. Technische Universität München 05/08/2013 Jochen Wolf 4 1.2 Working principle of organic solar cells Equivalent circuit of solar cells V P3HT PCBM Palumbiny MSc thesis Meier MSc thesis Meier MSc thesis
- 5. Technische Universität München 05/08/2013 Jochen Wolf 5 1.3 Device architectures substrates: glass and PET Aluminium Active Layer PEDOT:PSS ITO substrate Highly conductive PEDOT:PSS
- 6. Technische Universität München 05/08/2013 Jochen Wolf 6 1.4 Sample preparation Meier MSc thesis
- 7. Technische Universität München 05/08/2013 Jochen Wolf 7 2.1 Current-voltage measurements 𝜂 = 𝑉 𝑀𝑃𝑃 𝐼 𝑀𝑃𝑃 𝐴 𝑃𝑖𝑛 Efficiency 𝜂 𝑉 𝑀𝑃𝑃 𝐼𝑆𝐶 𝑉𝑂𝐶 𝐼 𝑀𝑃𝑃 𝑀𝑃𝑃 ITO-freeContains ITO
- 8. Technische Universität München 05/08/2013 Jochen Wolf 9 2.2 UVVis measurements Transmittance Reflectance After DOI: 10.5772/52741 Perkin Elmer Perkin Elmer
- 9. Technische Universität München 05/08/2013 Jochen Wolf 10 2.2 UVVis measurements Colour Devicearchitecture Electrode Eletrconblockinglayer Activelayer ── A ITO PEDOT:PSS ── A ITO PEDOT:PSS P3HT:PCBM ── B ITO H-PEDOT:PSS ── B ITO H-PEDOT:PSS P3HT:PCBM ── C H-PEDOT:PSS ── C H-PEDOT:PSS P3HT:PCBM ── D H-PEDOT:PSS PEDOT:PSS ── D H-PEDOT:PSS PEDOT:PSS P3HT:PCBM glass substrate PET substrate 300 400 500 600 700 800 0 20 40 60 80 100 absorption[%] wavelength [nm] 300 400 500 600 700 800 0 20 40 60 80 100 absorption[%] wavelength [nm] with active layer without active layer with active layer without active layer
- 10. Technische Universität München 05/08/2013 Jochen Wolf 11 2.3 Scanning electron microscope H-PEDOT:PSS spin coated on PET H-PEDOT:PSS spin coated on glass Edge of PET foil ITO-PET foil
- 11. Technische Universität München Lang Bachelor thesis 05/08/2013 Jochen Wolf 12 3. Structuring on PET Imprint of a CD structure in PEDOT:PSS on PET PET substrate 300 400 500 600 700 800 0 20 40 60 80 100 absorption[%] wavelength [nm] with active layer without active layer
- 12. Technische Universität München 05/08/2013 Jochen Wolf 13 3. Structuring on PET Lang Bachelor thesis Lang Bachelor thesis
- 13. Technische Universität München 05/08/2013 Jochen Wolf 14 4. Conclusion and acknowledgements I would like to express my thanks the following people: My supervisor: Peter Müller-Buschbaum My advisor: Claudia M. Palumbiny And all the rest of the E13 staff that made this thesis a great experience! 300 400 500 600 700 800 0 20 40 60 80 100 absorption[%] wavelength [nm] - ITO-free organic solar cells feasible - Layer thicknesses similar on PET and glass - Need for a new supplier of PET - Structured PEDOT:PSS on PET possible
- 15. Technische Universität München 05/08/2013 Jochen Wolf 16 Worldwide radiation average
- 16. Technische Universität München 05/08/2013 Jochen Wolf 17 Solar cycle and maximum efficiency
- 17. Technische Universität München 05/08/2013 Jochen Wolf 18 Efficiencies
- 18. Technische Universität München 05/08/2013 Jochen Wolf 19 Layers of the ITO-PET foil
- 19. Technische Universität München 05/08/2013 Jochen Wolf 20 molecular orbitals
- 20. Technische Universität München 05/08/2013 Jochen Wolf 21 Molecular structures PEDOT PSS P3HTPCBM PDMS
- 21. Technische Universität München 05/08/2013 Jochen Wolf 22 atomic force microscope (AFM)
- 22. Technische Universität München 05/08/2013 Jochen Wolf 23 solar simulator
- 23. Technische Universität München 05/08/2013 Jochen Wolf 24 H-PEDOT:PSS on PET
- 24. Technische Universität München 05/08/2013 Jochen Wolf 25 PET transmittance and reflectance
- 25. Technische Universität München 05/08/2013 Jochen Wolf 26 PET reflectance and transmittance
- 26. Technische Universität München 05/08/2013 Jochen Wolf 27 Transmittance to active layer
- 27. Technische Universität München 05/08/2013 Jochen Wolf 28 Current-voltage measurement on glass
- 28. Technische Universität München 05/08/2013 Jochen Wolf 29 Current-voltage measurement on glass
- 29. Technische Universität München 05/08/2013 Jochen Wolf 30 PDMS stamp
- 30. Technische Universität München 05/08/2013 Jochen Wolf 31 Solar cell
- 31. Technische Universität München 05/08/2013 Jochen Wolf 32 Flextrode http://www.plasticphotovoltaics.org/flextrode.html Flextrode by DTU
- 32. Technische Universität München 05/08/2013 Jochen Wolf 33 structuring black silicon PDMS stamp PEDOT:PSS
Hinweis der Redaktion
- Hello and welcome to the presentation of my Bachelor thesis on realizing… Thank you for the nice introduction. As you‘ve already heard, this talk is about my Bsc thesis with the topic …
- Firstly: outline of this presentation Introductory chapter, where the foundation of my thesis is explained Followed by Measurements of device architectures Another aspect of my thesis is covered chapter 3 Lastly, I will give you a summary of the results
- To start off: present background for photovoltaics; the solar spectrum Resembles black body 5500K, (grey) spectrum at the top of the atmosphere (yellow) remainder after passing through the atmosphere (red), molecules responsible for absorption. Therefore, only the red spectrum is usable for ground based solar cells, which is about 150 to 300 W/m^2 on an annual average. Solar cells use: harvest this energy mostly silicon based Organic solar cells, however, have a number of advantages over silicon based ones: Therefore, organic solar cells have a lot of potential.
- Working principle of OSCs somewhat different to silicon: Optically active layer OSCs built in this work consist of: Polymer P3HT, an electron donor, small molecule PCBM, an electron acceptor. If a photon is absorbed in the P3HT, an exciton is generated. Due to a limited lifetime, the exciton can only travel about 10 nm. Within this distance an interface between the acceptor and the donor has to be located, otherwise the exciton will dissapate. At the interface, the exciton can be separated, generating a current. Most commonly used bulk hetero junction Due to the exciton limited structure size, the overall thickness of the active layer is only a few hundred nm. The current modelled by equivalent circuit of SCs An actual device that uses this active layer is shown
- In This schematic of a reference organic solar cell: LAYERS PEDOT PSS electron blocking layer However ITO is expensive, and brittle. An alternative is post treated PEDOT:PSS, which shows conductivities 2-3 orders of magnitude higher than pristine PEDOT:PSS Same order of magnitude as ITO To investigate the possibility of ITO free organic solar cells, four device architectures are built: B-D All of device arch. Built on two substrates, namely glass and PET foil to realize flexibility advantage of OSC
- To achieve the homogeneous and thin films Required OSC and the production of device architectures Solved Polymers dropped on substrate Substrate spun, solved polymers spilled off Solvent evaporates, creating the thin and homogeneous films The produced OSCs are then measured by a I-V measurement
- For which the Equivalent circuit model explained before is used Characteristic points: V_OC I_SC MPP, associated V and I Efficiency calculated via output at MPP and the incoming radiation Two samples of each device architecture are built on glass, then measured with a solar simulator. The measurements are plotted and evaluated using a self made program, which can be found in the appendix of my thesis. Applied external voltage sweeps from -1V to 1V, out of which this section is shown. The different colours represent different samples, multiple lines of one sample represent different pixels. A and B contain ITO, C and D ITO free The evaluated characteristica shown region The white circle represents the average of all pixels of one sample. Highest efficiency of OSC: 2.77 percent, Best ITO-free efficiency with 1.71 percent. Therefore ITO free organic solar cells are feasible All of the device architectures are also prepared on PET, however, failed to show efficiencies comparable to glass, despite five prepared batches. Reasons investigated with UV/VIS
- Equivalent circuit model explained before used for I-V measurement Characteristic points: V_OC I_SC MPP, associated V and I Two samples of each device architecture are built on glass, then measured with a solar simulator. The measurements are plotted and evaluated using a self made program, which can be found in the appendix of my thesis. Applied external voltage sweeps from -1V to 1V, out of which this section is shown. The different colors represent different samples, multiple lines of one sample represent different pixels. The evaluated efficiencies are shown region – five other characteristic are also evaluated The white circle represents the average of all pixels of one sample. Highest efficiency of OSC: 2.77 percent, Best ITO-free efficiency with 1.71 percent. Therefore ITO free organic solar cells are feasible All of the device architectures are also prepared on PET, however, failed to show efficiencies comparable to glass, despite five prepared batches. Reasons investigated with UV/VIS
- For UV\Vis measurements, the sample is illuminated with monochromatic light, sweeping from a wavelength of 800nm to 260nm. This figure shows the model used in the evaluation of the data. Incoming radiation can either be reflected, absorbed or transmitted. If absorbed, it can be emitted with lower energy, which is called photoluminescence. The measurement is done with an integrating sphere, which also detects diffusely reflected light. The transmittance is measured with the sample at the front of the integrating sphere, reflectance at the back
- The calculated absorption on glass can be seen in this figure. Two colors represent the same device architecture, but with the active layer(upper graphs) and without the active layer. Photoluminesence neglected, detector not differentiate Crystallinity Peaks The wavelength at which the samples with the active layer start absorbing more light shows the band gap of P3HT. It can be seen at 650nm, which corresponds to an energy of 1.9eV, in accordance with values found in literature. 10 to 20% of light lost before reaching active layer Absorbed in active layer: difference between the corresponding samples with and without active layer 40 to 50% light absorbed in active layer Comparison PET: Higher absorption Similar layer thicknesses
- Puzzled why PET not working + light microscope inconcusive: SEM H-PEDOT:PSS on PET, DEFECTS, holes, inhomogeneous – could be dewetting Comparison to GLASS: homogeneous PET foil shows defects, ITO-PET foil shows defects same length scale, Do note the different scales These defects in PET might cause short circuits in the PET OSCs Different supplier used in future
- As a reminder: 10-20% light not reaching active layer: Structuring can improve that light PEDOT:PSS with CD structure leads to Light diffraction Light trapping Improves efficiency Imprint of CD structure in PEDOT:PSS on PET works Measure Structure depth by AFM
- This picture shows the same structure as light microscope Profile cut: 8 nm structure depth Earlier work by Felix Lang: 20 nm on glass with same pressure => Higher pressure on PET?
- Feasible but room for improvement; e.g. different post treatment (sulphuric acid), optimized layer thicknesses And thank you for listening!
- Carbon grey Hydrogen black Sulfur yellow Nitrogen blue Oxygen red Hydrogen on oxygen light red highly polar