Fabrication and Characterization of “persistent” Solar Cells
Supervisor: Dr. Giovanni Fanchini
Project Description (Abstract):
Solar energy requires a cost-effective mean of storage to gain competitiveness over non-renewable energy sources on the global market.The fact that solar cells only produce energy during daytime necessitates their costly integration with expensive storage components. At the present cost levels, even a solar panel operating at the theoretical maximum of 70% power conversion efficiency would not be competitive with fossil fuels due to the cost of batteries used to dispatch solar power at night. A potential, cost-effective, solution for photovoltaic operation during nighttime is offered by afterglow in materials showing persistent luminescence (PL). A breakthrough in PL was the discovery of long-living (~9-10 hours) afterglow in strontium aluminate co-doped with europium and dysprosium [SrAl2O4(Eu,Dy)].PL in this material is suspected to originate from slow photo-redox processes involving rare-earth complexes, typically (Eu2+,RE3+) → (Eu3+,RE2+), where RE = Dy or other reducing sites, for instance oxygen vacancies.
Dye-sensitized solar cells (DSSCs) are commercial-grade photovoltaics based on redox phenomena occurring between electrolytes and photo-excited dyes supported by mesoporous titania (TiO2). Due to their redox-based operation, DSSCs are uniquely positioned to integrate PL materials. One can envisage a device in which energy is accumulated as long-lived charges inside PL materials during daytime and released at night in the form of delayed photocurrents during inverse redox processes in the afterglow.
In this project, the student will work at a new family of “persistent” solar cells capable of nighttime power generation, which dramatically increase the marketability of solar energy by integrating SrAl2O4(Eu,Dy) as an afterglow redox sensitizer in a DSSC architecture. These solar cells will incorporate a composite layer of sintered indium-tin oxide nanoparticles (s-ITO) and SrAl2O4(Eu,Dy) microcrystals on top of transparent anodes, which are either fluorine-tin oxide (FTO) or indium-tin oxide (ITO) films in different sets of experiments. The electrically conducting and weakly absorbing layer of s-ITO:SrAl2O4(Eu,Dy) will form a bifunctional interface between the transparent anode below, and a TiO2 matrix sensitized with ruthenium-based dye above. This architecture will be entirely implemented by easy-to-fabricate solution processing methods. Depending on the interests of the student, the research activity will be more focussed on device fabrication or device characterization.