From single molecules to dye-sensitized solar cells
This is a modal window.
The media could not be loaded, either because the server or network failed or because the format is not supported.
Formal Metadata
| Title |
| |
| Title of Series | ||
| Number of Parts | 163 | |
| Author | ||
| License | CC Attribution - NoDerivatives 4.0 International: You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/50421 (DOI) | |
| Publisher | 05jdrrw50 (ROR) | |
| Release Date | ||
| Language |
Content Metadata
| Subject Area | ||
| Genre | ||
| Abstract |
| |
| Keywords |
Beilstein TV42 / 163
16
20
31
43
44
47
51
57
67
78
102
105
112
131
135
138
139
140
144
145
146
149
150
151
154
157
159
160
161
162
163
00:00
Molecule
00:15
Atomic numberFunctional groupFrictionMoleculeAssembly (demo party)Meeting/Interview
00:59
Amorphous siliconTitandioxidSubstrat <Chemie>GlassesSetzen <Verfahrenstechnik>NanoparticleMeeting/InterviewChemical experiment
01:23
TitandioxidElectronMoleculeComputer animationChemical experiment
01:51
DyeMoleculeChemical experiment
02:06
ElectronMoleculeTitandioxidMolecular geometry
02:20
KorngrenzeMoleculeTitandioxidChemical experiment
02:34
LegierenElectronNanoparticlePanel painting
02:47
Atomic numberSurface scienceElektronentransferMoleculeChemical experiment
03:05
Surface scienceChemical experiment
03:19
Surface scienceKarstChemical experiment
03:35
ZunderbeständigkeitAtomic numberElektronentransferResonance (chemistry)Surface scienceWinnowingCryogenicsChemical experiment
04:23
WinnowingHuman body temperatureRiver sourceCryogenicsComputer animation
04:36
PorphyrinGesundheitsstörungSurface scienceCryogenicsErdrutschMolecule
04:52
PorphyrinPorphyry (geology)Surface scienceFunctional groupCopperDeposition (phase transition)MoleculeComputer animation
05:05
PorphyrinMoleculeFunctional groupComputer animation
05:21
MoleculeOptische AktivitätMoleculeComputer animation
05:38
MoleculeFunctional groupOptische AktivitätComputer animationMeeting/Interview
05:57
Chemical structureOptische AktivitätRearrangement reactionMoleculeChemical experimentMeeting/Interview
06:14
Intergranular corrosionFood additive
06:23
MoleculeAtomic numberChemical experiment
06:33
Systemic therapySurface scienceMoleculeDeposition (phase transition)Sample (material)Combustion chamberAufdampfenChemical experiment
07:06
PorphyrinChemical experiment
07:21
Functional groupMeeting/Interview
07:33
Stereoselektive SyntheseMultiprotein complexMissernteDipol <1,3->QuartzIonenbindungMoleculeFunctional groupComputer animation
07:45
MoleculeMeeting/Interview
08:05
Stereoselektive SyntheseMultiprotein complexMissernteSetzen <Verfahrenstechnik>MoleculeSodiumMeeting/InterviewComputer animation
08:20
MoleculeWalkingComputer animation
08:30
Walking
08:50
Steric effectsWalkingComputer animationMeeting/Interview
09:04
Assembly (demo party)TiermodellCell growthComputer animation
09:17
TiermodellKaliumbromidSodium chlorideMolecule
09:35
AtomclusterSurface scienceMetalElektronentransferSodium chlorideMoleculeGoldKaliumbromidMolecular geometryChemical experiment
10:14
MoleculeAssembly (demo party)GoldPermacultureMoleculeGoldAtomclusterComputer animation
10:26
Setzen <Verfahrenstechnik>Meeting/Interview
10:37
Assembly (demo party)CHARGE syndromeGoldSurface scienceSeparator (milk)PH indicatorGene clusterComputer animation
10:49
Meeting/Interview
10:58
ChemistryISO-Komplex-HeilweisePorphyrinCell growthMolekularer DrahtCrystalComputer animation
Transcript: English(auto-generated)
00:15
Hello, my name is Tilo Gladstell. I'm from University of Basel and is a group from Ernst & Meyer.
00:21
And our group is mainly focused on the development of non-contact atomic force microscopy, especially to reach ultimate resolution, atomic resolution, molecular resolution, and of course also friction force microscopy. Today I want to present you our work on molecular structures,
00:42
so analysis of molecular assemblies and single molecules at surfaces, which are related to dye-sensitized solar cells or the development of new energy-related systems, which hopefully benefit from our developments.
01:03
Dye-sensitized solar cells are quite new type of solar cells. They are based on titanium dioxide nanoparticles. In comparison with normal amorphous silicon solar cells, they are built up on a glass substrate which is covered by transparent conductive layers,
01:28
so-called TCO layer. And on top of this TCO layer, we deposit nanoparticles, which was an idea by Michael Gretzel some 20 years ago.
01:40
And these titanium dioxide nanoparticles, they have a band gap of roughly 3.5 electron volts, so in principle they are not absorbing the light. And to sensitize them, we cover them with molecules. And the nice thing is one can use a lot of different molecules, organic, natural dyes, ruthenium-based dyes.
02:00
And this dye molecule then allows to absorb the sunlight, which reaches the solar cell. So an electron is excited from the excited molecule towards the conduction band of the titanium dioxide and is then transferred to the back electrode.
02:20
And our research now is focused on the analysis of exactly this interface between the molecules and the titanium dioxide and it's interesting for non-contact AFM because the sizes, the dimensions of such a solar cell are in the range of 10 micrometer thickness of this layer. And the diameter of such a nanoparticle is 20 nanometers, which is much below the wavelength of the light.
02:47
So the idea is to really focus on the electron transfer, the photo-excited electron transfer of a single molecule in such solar cells and to improve with this the efficiency.
03:01
Atomic force microscopy relies on such a cantilever, which is in contact or non-contact on the surface. And the bending of this cantilever is detected by a laser beam, which is reflected from the back side. And then the cantilever is scanned on the surface
03:21
and the topography is imaged as a deflection of this cantilever. This still is a destructive method and to avoid this destruction of the surface and to scan molecular assemblies like on the dye-scented solar cells, we shake the cantilever, the so-called non-contact AFM mode, and measure the oscillation of the cantilever and detect the resonance frequency.
03:44
And changes in the resonance frequency, we can directly correlate with the forces, the interaction forces between our cantilever and the surface and can therefore very accurately measure molecular and atomic scale variations on the surface. Furthermore, we are able to detect electrostatic forces separately
04:03
and get additional information on the electron transfer and charging probabilities of the surface.
04:20
So this is a low temperature atomic force microscope based on a tuning fork sensor, which is shown here. Here you can see the head of the microscope, which allows to work in a low temperature environment between 5 Kelvin to 77 Kelvin. Our main experiment performed on this microscope is to study single molecules
04:43
in this low temperature conditions on different surfaces. On this slide you can see an example where we use this porphyrin molecule, which is equipped with two d-cyanophenyl groups and two terebutyl groups. Here you can see an S10 picture of the surface after deposition of this molecule on copper 111,
05:05
and you can see that each dot is a single molecule. So the study is done in the nanometer range, and here you can see a single molecule, S10 picture of a single molecule. These two dots correspond to these two groups, terebutyl groups, and these two dark dots correspond to these cyanophenyl groups.
05:24
Using the IFM ability of this microscope, we could, by using force spectroscopy, induce in a controlled way the rotation of the molecule on the surface, as shown here with these two successive STM images. The idea is that we can define carefully which target we want to use,
05:44
which cyanophenyl groups we want to use, and induce in a controlled way the rotation on the surface. The main principle is to approach the tip, which is oscillating of course, to connect the tip to one of the d-cyanophenyl groups, and while retracting we will deform locally the structure of the molecule,
06:02
which will induce a rearrangement of the molecule on the surface, and therefore its rotation. I'm Gregor Fessler, and I'm working on the development of new microscopes. This here is the newest room temperature microscope we are developing, and we try with this development to improve the sensitivity
06:22
and the stability of these microscopes to really get the best performance we can get, and to be able to perform measurements on single atoms and molecules. So this is our system with room temperature AFM. We introduce our samples to this preparation chamber,
06:41
from where we clean the surface and afterwards deposit some molecules on the surface with this evaporator here. When our surface is ready to get probed with AFM, we transfer it over to the analysis chamber here, where we have different analysis devices, but mainly our atomic force microscope.
07:05
And yeah, I can transfer now this sample to our microscope. As a first system, we used porphyrin molecule,
07:28
which is specially developed for us by a group from ETH Zurich. It has an additional cyano-phenyl group attached to it, and the cyano-phenyl group induces a very strong dipole moment in this direction of the molecule,
07:42
which allows us to stabilize this molecule on ionic crystal surfaces, which I explain in a second. This molecule is relevant also for photovoltaic dye-sensitized solar cells, Michael Gretzel in Lausanne. He developed, just recently, some months ago, a porphyrin-based solar cell.
08:02
It's green, shining, and slightly transparent, and he reached up to 13% efficiency, which is remarkable for this type of solar cells. This molecule likes to attach to step edges of this sodium crystals, and as you can see here, this is a topographic image of a non-contact AFM measurement at room temperature.
08:25
The molecules arrange a long step edges, they grow in the step edges, and in principle they stabilize themselves. So normally they are mobile on the surfaces, so they stabilize themselves by forming some pi-pi stacks, so it's like a sandwich, they stack to each other with a certain distance,
08:42
and they use their function, the Stryano-Fennel function, to attach electrostatically to the cations on the step edges. If the step edges are higher, like here, for example, three atomic layers, they have a geometrical hindrance to form these pi-pi stacks,
09:02
and they form some unordered agglomerates, or here, as you see here in the end, some self-assemblies. The self-assemblies we found are strongly dependent, the growth of the self-assemblies is strongly dependent on the substrate, so we have, for example, sodium chloride or potassium bromide substrates,
09:24
and here in this model you can see it quite nicely. In principle, the 1-1-O direction of the surface, for example here, cations, the molecules can arrange themselves, the spacing between the molecules can vary, while in the 1-O-O direction it cannot vary,
09:43
and sodium chloride exactly has the lattice spacing of the intermolecular distance of the lattice spacing of the sodium chloride. So, in sodium chloride we find both directions, and on potassium bromide only the one in the 1-O direction. These results are quite nice, but now the transfer to the more realistic application, the solar cell,
10:05
we evaporated some metal contacts to really contact those molecules on the surface, on this insulating surface. Here in this image you see some gold clusters attached to the surface, and in between the gold clusters the molecules grow themselves as a self-assembling,
10:22
and in principle this is one of the smallest solar cells in the world. In principle we have contacts, we have molecules, and now we need only to absorb photons and generate some excitons. The method we used for this type of measurements is Kelvin-Probe force microscopy.
10:41
As you can see here, this is a zoom-in of one end, the gold cluster and the molecular wires, and on the right side you see the surface potential, which is an indicator for the electrostatic charge separation or the localized charge at the surface. I hope that you enjoyed it, and if you have any further questions, please let us know.
Recommendations
Series of 34 media