Light harvesting to increase the efficiency of silicon solar cells (S. Binetti, M. Acciarri)

First generation solar devices suffer from high cost of manufacturing and installation. New initiatives to harvest incident photons with greater efficiency could therefore be considered to improve the energy conversion features of silicon based devices, which presently cover almost 90% of the photovoltaic market, as monocrystalline, multicrystalline, amorphous or thin film based material.
As reported in literature, an increase of the energy conversion efficiency of commercially available silicon solar cells could be obtained exploiting the solar spectrum component below 450 nm, this high energy tail being not efficiently converted from silicon. Molecular systems strongly absorbing in this spectral range and showing a consistent Stokes shift of their emission towards the region of the maximum conversion efficiency of the photovoltaic device are good candidates for down-shifting of the absorbed light. In particular, rare earth organic complexes present the separation between the absorption and the emission bands required to obtain large Stokes shift and to avoid self-absorption losses.

Our research activity in this field is devoted to the optical and electrical characterization of commercial c-Si solar cells coated with layers doped with different Eu3+ organic complexes, which are able to realize down-shifting of photons with wavelength lower than 400 nm. We have tested different commercial crystalline silicon solar cells encapsulated with Ethylene-Vinyl-Acetate layers (that is the encapsulating matrix used nowadays by the photovoltaic industry) doped with different europium complexes absorbing between 260 and 380 nm and emitting at 612 nm. In particular, crystalline silicon  test modules have been realized using as encapsulating matrix EVA doped with Eu(tfc)3-EABP in order to enhance their performances by down-shifting of the absorbed light. Doping of PV module encapsulating matrix with such a complex allow the exploitation of a wide portion of the solar spectrum since the sensitized region of Eu(tfc)3 is broadened due to the presence of the co-ligand EABP. Such a procedure allows an improvement of the PV conversion efficiency without modification of the industrial process leading to the fabrication of the solar modules. A significant increase of the total power delivered by such test modules has been obtained under Air Mass 1.5 conditions (simulating terrestrial applications), allowing a reduction in the WP price.

Post-doctoral fellow: Alessia Le Donne