PhD candidate: Hanbin ZHENG
Date and place of defence: November 24, 2014 - University of Bordeaux, France.
Since the breakthrough achieved by Grätzel and co-workers in 1991, it has been demonstrated that dye-sensitized solar cells (DSSCs) are a high-efficiency and low-cost alternative to conventional solar cells, the overall power conversion efficiencies reaching up to 11.2% under AM1.5 illumination.
Improvement in the field of solid-state DSSCs requires the development of routes which relies upon control of the film architectures, self-organization of the active components so as to deliver functionality beyond the properties of the individual materials and utilization of developed complex structures. The development of well-ordered mesoporous films showing high specific surface areas and with thickness above 5 microns should be a manner to improve the diffusion of the p-type conductor in the porous films when a suitable dye is employed.
The aim of the project is to develop new hybrid nanostructured architectures able to convert light into electricity by combining two expected breakthroughs: i) preparation of inverse colloidal photonic crystals (see figure) of different periodicity allowing total omnidirectional light absorption; ii) fabrication of hierarchical porous oxide networks (see figure) in order to increase the enthalpy which generates the photocurrent. This project should provide efficient and stable dye-sensitized solar cells.
The originality of the project is based on two simultaneous improvements:
1) optimization of light absorption for wide ranges of incidence angles and wavelengths, by designing inverse photonic crystal structures with a precisely controlled number of layers and periodicity;
2) optimization of the enthalpy capable to deliver the photo-induced current, through multilayered inverse metal oxide opals and meso- & macroporous oxide foams exhibiting hierarchical porous networks.
The properties of the obtained opals and foams will be investigated by both in-situ and ex-situ experiments (e. g. XRD, SEM, XPS, FTIR, UV-visible spectroscopy), while the electro-optical characterizations of the realized solar cells will be performed to evaluate recombination rate and conversion efficiency.
The research will be performed in close collaboration with two academic research groups from UB1 (Bordeaux, France) and IST (Lisboa, Portugal) having an expertise in the elaboration and characterization of opal structures and metal oxide foams. The operating scope of the industrial partner, Orange Labs (Issy les Moulineaux, France), extends from research on personal services to those intended for the largest world businesses.
Left: SEM image of a metal oxide foam
Right: SEM image of an inverse opal
UB1 - CRPP (Centre de Recherche Paul Pascal) - Preparation of colloidal crystals and metal oxide foams. Fabrication of devices and first set of characterization steps.
IST - Universidade Técnica de Lisboa - ICEMS (Institute of Materials and Surfaces Science and Engineering) - Fabrication of inverse opals - Characterization
Orange Labs - Characterization of the properties of the fabricated photovoltaic devices.