Perovskites, calcium titanate-based minerals with a distinctive crystal structure, have inspired the creation of synthetic materials with the same crystal lattice and endowed with photoactive properties, i.e. capable of absorbing light from the sun - which strikes them in the form of photons - and harnessing this energy to obtain the separation of electrical charges within the photoactive material. This charge separation partially reaches the respective electrodes and is transformed into electricity, thus making it possible to build a photovoltaic cell. Particularly efficient among perovskite cells are perovskites based on lead, halogens and ammonium salts.
Advanced, cost-effective and efficient solar technology
The efficiency of solar cells made from these materials has risen from 3.8% in the early prototypes to 25.7%, surpassing the efficiency not only of similar organic photovoltaic cells, but also that of the already popular silicon-based cells that we see on many roofs today. Research in this field currently offers the greatest scope for the development of photovoltaic technologies.
Together with organic photovoltaic cells, perovskite cells can be made in semi-transparent thin film with reduced material costs and production techniques, enabling applications that have hitherto been impossible for conventional solar cells, such as embedding on building facades. Among other things, this application is promoted by recent international and EU directives in the area of energy efficiency for buildings and is therefore destined to have a very wide range of use.
Another potential application is that of so-called agrivoltaics, i.e. the generation of electricity coupled with plant cultivation that exploits the semi-transparency of this new class of photovoltaic devices.
An innovative material for the window sector
To increase the transparency of perovskites, Eni researchers focused on new composite materials obtained by making perovskite precursors interact with polymers that are transparent to visible light. In particular, the inclusion of hydroxyethylcellulose in the synthetic perovskite layer (with formula CH3NH3PbI3) brought numerous advantages, such as simplifying production conditions and increasing the average transmittance in the visible - i.e. transparency - by up to 22%, while maintaining good efficiency (up to 12%).
This resulted in a light use efficiency value (the product of the previous two values, which provides a measure of the device’s performance) of around 2.4%. This ranks among the best values reported so far and is considered particularly suitable for use in the window sector.
Researchers Paolo Biagini, Riccardo Po’ and other colleagues from CNR in Lecce who collaborated on this brilliant scientific achievement received the award from the President of the Italian Republic, Sergio Mattarella, during a ceremony held on 3 October at the Quirinal Palace in Rome.
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