Research areas in Experimental Physics
High pressure spectroscopy
- Fullerenes and materials derived from fullerenes (polymers of fullerenes, phase transitions at high pressure and temperature)
- spectroscopy of carbon nanotubes (CNTs) (individual, functionalized SWCNTs, DWNTs)
- CNT stability under extreme conditions: high pressure, high temperature, laser heating
- Graphene at high pressure
- Materials of CNTs and fullerenes
- High temperature superconductors (systems based on MgB2)
Charge/energy transfer in composite nanosystems
The efficiency of solar cells relies on the ability of the active material to exploit incoming photons for generating electrical charges that are thereof transported and collected. This may be done by using different nanocomposite materials p-n junctions, organic dyes, quantum and carbon dots and other optically active nanosystems. We are strongly interested in understanding the basic principles of the charge transfer process, to maximize the efficiency of the solar cell through careful optimization of the different cell’s components. The interaction of the light with the absorbing element and the efficiency of the electron injection to the conductive layer of the cell are investigated by photoluminescence intensity and lifetime measurements.
Furthermore, a parallel research activity for improving the efficiency of the solar cells is based on the spectral modification of the incoming light to match the absorption of the active material by proper downconverting and upconverting layers. In particular, we are studying Ag-sensitized Tb-Yb sol-gel glasses and glass-ceramics for quantum-cutting and hybrid downshifting Eu-complexes for broadband enhancement of the cell’s efficiency. In this field we are focused on the investigation of the energy-transfer mechanism between the sensitizer and/or the involved rare earths by PL intensity and time-resolved measurements.
All-oxide solar cells
Metal oxides (MOx) are suitable candidates for photovoltaics (PV) applications. Due to their chemical stability, non-toxicity, abundance, low-cost production and theoretical high efficiency, a new field in PV has emerged, focusing on solar cells entirely based on MOx semiconductors (from thin films to nanostructured architectures).
At Experimental Physics at LTU we synthesize nanostructured all-oxide solar cells, based on n-type nanowires (mainly ZnO, TiO2 NW) with p-type layer on top of them (mainly Cu2O, Co3O4, deposited by ALD or by sputtering technique) in a conformal core-shell structure.
Investigation on the macro- and nano-electronic properties of the all-oxide device is carried out by standard macro IV measurements under solar simulator, by photoluminescence (PL) and time-resolved PL spectroscopy, and with advanced AFM techniques such as c-AFM and KPFM.
Photo-electrodes for organic catalysis
The synthesis of organic species is typically performed by using either hazardous reactants or high temperatures. These might be replaced upon using light as energy source in presence of proper photo-catalyst. Solution-phase photo-catalysts typically suffer from relatively low photo-stability, high cost, and they rely on time-consuming purification techniques. Metal-oxides nanostructured electrodes might represent a viable alternative to conventional solution-phase photo-catalysts due to the low-cost, tunable absorption contribution and elevated stability in oxidizing environment. In addition, by growing these semiconducting nanostructures on conductive substrates, they allow for easy purification of the reaction product and re-utilization of the photo-catalyst, as well as the possibility to couple the photo-redox reaction with complementary useful reaction in a photo-electrochemical configuration.
Our current activity is focused on the growth and characterization of nanostructured oxides for photo-induced oxidation (Fe2O3, TiO2, Co3O4) and reduction reactions (Cu2O), as well as hetero-junctions able to enhance charge separation and catalytic activity. These structures are fully characterized by means of optical spectroscopy (UV/Vis/NIR abs and PL), electron microscopy (HR-SEM, EDS, HR-TEM) and electrochemical investigation (CV and impedance). Functional properties towards specific organic reaction are currently under investigation and further collaboration with organic chemistry groups are foreseen to enlarge the reactions portfolio.
Photocatalysis and photoelectrochemical water splitting
We work on the design and development of semiconducting metal oxides (MOx) nanostructures capable of exploiting solar light to enhance chemical reactions in liquid environment.
We design hybrid materials where graphene derivatives are carefully incorporated in the MOx scaffold as storing and shuttling agents for charge transport management.
Promotion of useful chemical reactions (degradation/requisition of organic and inorganic water pollutants, generation of oxygen and hydrogen from water splitting) at the interface catalyst||environment requires for a careful materials design, especially devoted to promote photogenerated charge transport towards the surface, where the redox exchanges take place. Increasing photogenerated charge lifetime and minority carriers diffusion length, as well as modulating light management inside these hybrid architectures are our most important focus in this research line.
Our attention is especially paid to unveil basic physical and chemical processes on materials surfaces, which are behind the success of photo(electro)catalytic systems.
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