Michael Grätzel
2009 Balzan Prize for the Science of New Materials
Research Project

Improving the Performance of the Dye Sensitized Solar Cell (DSC)
Michael Grätzel is a Professor at the École Polytechnique Fédérale de Lausanne (EPFL) and Head of its Laboratoire de photonique et interfaces (LPI). The Balzan research project that he proposed aimed to improve the performance of the Dye Sensitized Cell (DSC), commonly known as the Grätzel Cell, by increasing the overall efficiency of this kind of photovoltaic cell from its present 12.3 to nearly 15 percent, which would strongly contribute to making the DSC a widely used method for electricity production from sunlight.
With the second half of the 2009 Balzan Prize for the Science of New Materials, the Laboratory of Photonics and Interfaces at the École Polytechnique Fédérale de Lausanne (EPFL), directed by Michael Grätzel, acquired an Atomic Layer Deposition System for the Laboratory and hired Dr. Aswani Yella as a postdoctoral fellow for two years. A sum was also set aside to support visits of students and researchers from Italian universities within a framework of collaboration on the research project.
Adopting an experimental approach to the design of the Grätzel Cell, the Balzan research project focused its attention on the interface that separates the materials used in the device for transporting the negative charge carriers (electrons) and positive charge carriers (called holes). It explored several new strategies to retard the interfacial charge carrier recombination rate. The research was conducted to improve the selfassembly of the dye molecules in order to form more compact films at the surface. Grätzel’s research group modified the chemical structure of the dye molecules to endow them with long alkyl chains enhancing their lateral attraction, which was expected to increase the packing of dye molecules retarding the unwanted interfacial recombination of negative and positive charge carriers. The group also attempted to use additives in the electrolyte that would promote the formation of dense monolayers of dye molecules. Judicious engineering of the interface retarded the interfacial charge carrier recombination, increasing the open circuit voltage and cell efficiency.
The work on introducing the ALD overlayers on the surface of the mesoscopic titania films to stop interfacial charge recombination was carried out by Aravind Kumar Chandiran. Aswani Yella tested the films prepared by Dr. Chandiran to realize gains in voltage output and overall efficiency as foreseen in the proposal.

Chandiran AK, Yella A, Mayer MT, Gao P, Nazeeruddin MdK, Grätzel M. 2014. Sub-nanometer conformal TiO2 blocking layer for high-efficiency solidstate CH3NH3PbI3 absorber solar cells. Advanced Materials. DOI: 10.1002/adma.201306271.
Chandiran AK, Abdi Jalebi M, Yella A, Ibrahim Dar M, Yi C, Shivashankar SA, Nazeeruddin MdK, Grätzel M. 2014. Analysis of electron transfer properties of ZnO and TiO2 photoanodes for dye-sensitized solar cells. ACS Nano. DOI: 10.1021/nn405535j.
Chandiran AK, Abdi Jalebi M, Nazeeruddin MdK, Grätzel M. 2014. Quantum-Confined ZnO Nanoshell Photoanodes for Mesoscopic Solar Cells. Nano Letters. DOI: 10.1021/nl4039955.
Chandiran AK, Nazeeruddin MdK, Grätzel M. 2013. The role of insulating oxides in blocking the charge carrier recombination in dye-sensitized solar cell. Advanced Functional Materials. DOI: 10.1002/adfm.201302352.
Chandiran AK, Yella A, Stefik M, Heiniger L-P, Comte P, Nazeeruddin MdK, Grätzel M. 2013. Low temperature crystalline titanium dioxide by atomic layer deposition for dye-sensitized solar cells. ACS Applied Materials and Interfaces. vol. 5, num. 8: 3487.
Chandiran AK, Comte P, Humphry-Baker R, Kessler F, Yi C, Nazeeruddin MdK, Grätzel M. 2013. Evaluating the critical thickness of TiO2 layer on insulating mesoporous templates for efficient current collection in dye-sensitized solar cells. Advanced Functional Materials. 23: 2775.
Chandiran AK, Tetreault N, Humphry-Baker R, Kessler F, Baranoff E, Yi C, Nazeeruddin MdK, Grätzel M. 2012. Sub-nanometer Ga2O3 tunneling layer by atomic layer deposition to achieve 1.1V open-circuit potential in dye-sensitized solar cells. Nano Letters. vol. 12, num. 8: 3941.
Labouchere P, Chandiran AK, Moehl T, Harms H, Chavhan S, Tena-Zaera R, Nazeeruddin MK, Graetzel M, Tetreault N. 2014. Passivation of ZnO Nanowire Guests and 3D Inverse Opal Host Photoanodes for Dye-Sensitized Solar Cells. Advanced Energy Materials. DOI: 10.1002/201400217.
Mathew S, Yella A, Gao P, Humphry-Baker R, Curchod BFE, Ashari-Astani A, Tavernelli I, Rothlisberger U, Nazeeruddin MdK, Grätzel M. 2014. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nature Chemistry. 6: 242-247.
Yum J-H, Moehl T, Yoon J, Chandiran AK, Kessler F, Gratia P, Grätzel M. 2014. Toward Higher Photovoltage: Effect of Blocking Layer on Cobalt Bipyridine Pyrazole Complexes as Redox Shuttle for Dye-Sensitized Solar Cells. The Journal of Physical Chemistry. DOI : 10.1021/jp412777n.

Excerpt from the: The Balzan Prizewinners’ Research Projects: An Overview 2016
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