Dr. Elisa Sani | January 21, 2:30 PM | Novel materials for sunlight absorption and energy transfer

On January 21, 2026, at 2:30 PM, Dr. Elisa Sani, Senior Researcher at National Institute of Optics, National Research Council of Italy (INO-CNR), will present a seminar entitled "Novel materials for sunlight absorption and energy transfer". The event will take place in Manuel Laranjeira Room, Physics Department (Building I).

Abstract:

Materials science can provide a dramatic contribution for solar energy exploitation. We will discuss three case-studies chosen in different solar energy technology fields, with the common focus on materials for effective sunlight capture and energy transfer.

Conventional solar collectors operating at low-mid temperatures consist of a sunlight absorbing coating deposed on a solid surface exchanging heat with a working fluid. This scheme can be significantly simplified by the use of a dark fluid working at the same time both as volumetric light absorber and heat exchanger. The first idea of a direct-absorption solar collector (DASC) dated back to 1975 [1], but the approach was practically disregarded until the development of nanotechnology allowed the creation of new nanoparticles and their stable suspension in fluids. In this presentation, as a first case-study, I will summarize our several-year investigations about black colloids based on different carbon nanoparticles (nanohorns, nanodiamonds, graphene nanoplatelets).

Again in the field of Solar Thermal, but focusing to a different temperature range and system architecture, I will consider, as a second case-study, solar absorbers for high-temperature CSP plants. The increase of the operating temperature is particularly important for this application and the receiver is the most critical element.  Ultra-High-Temperature Ceramics (UHTCs), aerospace materials characterized by the highest melting points of any known compound and by a number of favourable characteristics [2], have the potential to be suited for application in high temperature solar receivers, once their optical properties have been properly investigated, correlated to the bulk and surface characteristics, and optimized.

Finally, the third case-study will be concerned with photovoltaics (PV). Conventional single-junction semiconductor solar cells effectively convert photons of energy only close to the semiconductor band gap (Eg). A conceptually simple approach to increase the efficiency is the spectral modification of incident solar radiation. Two types of spectral modifications are possible: downconversion (DC), where photons with energy more than twice Eg are converted into a doubled (ideally) number of photons with energy ≈Eg, and upconversion (UC), where two or more sub-bandgap photons produce at least one photon with energy matched to Eg. These concepts show significant promise [3,4]. In this presentation the wavelength conversion idea will be focused on the study of DC materials to be coupled to crystalline silicon (c-Si) solar cells. With its single excited state radiatively emitting at around 1 µm wavelength, where the spectral responsivity of c-Si is the highest, the trivalent Ytterbium ion (Yb3+) is the ideal candidate for DC, once coupled to proper donor centers.

References:

[1] J. E. Minardi et al, Solar Energy 17, 179, 1975

[2] E.J. Fahrenholtz et al (Eds.), Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications, (John Wiley & Sons, Hoboken, NJ, 2014)

[3] T. Trupke et al, J. Appl. Phys. 92, 1668, 2002

[4] T. Trupke et al, J. Appl. Phys. 92, 4117, 2002

Brief Biography:

Elisa Sani, PhD. (ORCID ID: 0000-0001-9854-2892), is Senior Researcher at National Institute of Optics, National Research Council of Italy (INO-CNR), where is Principal Investigator of the Smart & Solar Energy Materials Laboratory in Florence.

Her main research interests span from solids for high-temperature solar thermodynamic plants, colloidal suspensions for mid-temperature solar thermal plants, optical property tailoring of surfaces, fundamental optical constants of liquids, as well as nonlinear optical phenomena in liquids and colloids and solar-enabled hybrid power generation in different materials and by different effects.

Elisa is co-author of 129 papers in peer-reviewed international journals, 2 book chapters and holds 3 patents.