Since the discovery of the photovoltaic effect by A. E. Becquerel in 1839, tremendous efforts have been made on the development of various photovoltaic (PV) technologies in order to produce electricity with the “free” sun light. Although many technologies were developed, the currently dominant one in the market is based on silicon. Silicon solar cells perform very efficiently and are quite stable under operation, but they have certain limitations. First, manufacturing PV grade silicon is costly and generates harmful wastes. Second, silicon is a very brittle material and silicon solar cells are fragile, which makes their transportation and installation inconvenient and costly. Third, silicon solar cells are heavy due to the large amount of silicon required for sufficient light absorption and for maintaining the mechanical strength of the solar module. This makes silicon solar cells inappropriate for portable power sources. The most important issue for silicon based solar cells is their high costs for both production and installation. The price of electricity generated by silicon solar cells is and will be uncompetitive to the grid electricity generated by fossil fuels. This will limit the wide spread application of silicon solar cells.
Organic solar cells emerged as a promising technology to produce electricity at much lower costs. Particularly polymer based organic solar cells have excellent mechanical properties, which are suitable as light and flexible devices for portable power sources and building integrated photovoltaics (BIPV). The manufacturing of polymer solar cells is compatible to the conventional printing technologies such as screen, gravure, and doctor blade printing, which allows for the production of polymer solar cells being at a high speed and in a roll-to-roll manner. The currently best power conversion efficiency of polymer solar cells has reached 11%, which makes this technology very promising for commercialization. On the other hand, the cost of the polymer solar cells is still too high, mainly due to the use of expensive fullerene derivatives as electron acceptors and indium-tin oxide (ITO) as the transparent electrode. In addition, the low electron mobility of fullerene derivatives limits the optimum active layer thickness to be around ~100 nm. Fabrication of polymer solar cells with such a thin active layer without defects is very challenging on an industrial scale.
This PhD project aims to develop fullerene- and ITO-free hybrid polymer solar cells to address the issues associated with the current polymer solar cells. In this study, organic and inorganic semiconductors will be used to replace fullerene derivatives to reduce the materials cost and enable high throughput manufacturing of these new hybrid polymer solar cells.
The student will first choose suitable inorganic semiconductors that have ideal energy levels to match with the electrode and semiconductor materials. Low cost and non-toxicity are also important factors to consider.
The student will then design and synthesize polymer semiconductors, which are either donors or acceptors, depending on the type of the inorganic semiconductors chosen. The energy levels, band gap, compatibility with the inorganic semiconductors and electrode materials, and solution processability are key design factors. Light absorption, photoluminescence, charge carrier mobility, and electrochemical stability will be investigated.
Finally the student will integrate the polymer materials and the chosen inorganic semiconductors into solar cell devices. Various device configurations such as mesoporous active layer structures, embedment of nanowires and nanotubes, planar bilayer junction, and bulk heterojunction will be used and studied. The solar cell performance will be characterized under simulated sun light. A newly developed transparent conductive material by us will be used as the transparent electrode to replace ITO.
The goal of this project is to understand the interplay and interactions of the polymer and inorganic semiconductors. The interfacial contact, energy matching, photon absorption, exciton generation/diffusion/dissociation will be investigated. Guidelines and approaches for matching the polymer semiconductor and inorganic semiconductors will be proposed. The target efficiency of these new hybrid polymer solar cells is about 10%, which meets the commercially viable level.
This PhD project will involve multiple disciplines including computer simulations, organic/polymer synthesis, inorganic chemistry, materials characterization, and device fabrication.
The student will have to study and conduct research between Canada and France annually. The student will have to have knowledge and, preferably experience, in one or more of the following areas: organic synthesis, polymer synthesis, inorganic materials, nanomaterials, and fabrication of organic electronics.
To be finally approved for the position, the student must be approved by all Institutions, after the initial approval by the IDS-FunMat program. More specifically, University of Waterloo requires specific English skills. More information can be found at: https://uwaterloo.ca/graduate-studies/application-admission/review-admission-requirements/english-language-proficiency-elp
University Waterloo (Canada) - Chemistry & Chemical Engineering: Synthesis of polymer and inorganic semiconductors; fabrication and testing of solar cells
Université de Bordeaux (France) – Institut des Sciences Moléculaires (ISM, CNRS UMR 5255): Photochemical properties of polymer and inorganic semiconductors; Transparent graphene conductor
MW Canada: Surface chemistry of various substrates for solar cells; Printing large scale solar cells