Research Activities

The so called 3rd generation PV, i.e. drastically reduced cost per peak W, is yet to come. Several schemes and materials have been proposed so far, and basic studies are being developed by several groups (Nozik at NREL in primis).

Hot carrier cells, multicolour cells, quantum dots with multicarrier generation and several other have been proposed, but only the QD type has recently been demonstrated based on a multilayer approach (i.e. recent publications from M. A. Green’s group).

We already developed the capability to realize complex multilayered or graded nanostructures using metals, oxides and semiconductors. Hence, our mid term goal is to realize a mixed QD-oxide structure or a multilayer QD architecture developing means of producing and assembling the different components in a controlled manner. The QD’s to be used to sensitize our hierarchical photoanode nanostructures will also be produced by the IIT GE-Facilities and Nanochemistry.

In the long term we aim at developing and investigating other QD-based structures interesting for PV applications.

Novel mesostructured TCO for photovoltaics

The terrific increment in efficiency of crystalline Si solar cells (cSi) (from ≈15% up to ≈26%) is mainly due to optimized light trapping and carrier diffusion schemes. Unfortunately, the texturing strategies used for cSi are not replicable on policrytalline and amorphous materials, but are still urgently required in order to increase efficiency. Thus, novel approaches are needed.

Among the different possibilities an interesting approach is the three dimensional patterning of the Transparent Conducting Oxide (TCO). This approach has been little explored in the literature but holds promises for those PV technologies where the main limitation arises from the compromise between optical absorption and carriers transport, being both parallel in the typical flat architecture. On the contrary, by realizing optical micro-cavities with integrated photonic crystals it would be possible, in principle, to separate the two paths, yielding large absorption volumes with reduced absorber thickness, that means shorter diffusion length.

The activity, requiring an established experience on nanostructured surfaces and interfaces, is focused on photoanodes for Dye Sensitized Solar Cells (DSC or Graetzel Cells) and hybrid organic-inorganic solar cells. In fact, the photoanode is one of the key components of these emerging PV technologies. Constituted essentially by nanostructured transition metal oxides (i.e. TiO2) the photoanode has to satisfy several requirements, much more demanding than for photocatalysis: thickness in the order of 10 μm, porosity higher than 50%, high surface area available for dye chemisorption, low defect density, high electron mobility.