A team of researchers has successfully tested modules in perovskite with the aim of creating self-sufficient greenhouses thanks tosolar energy. Perovskite, in fact, allows you to build semi-transparent photovoltaic panelswhile in traditional photovoltaics silicon cells are used which produce a lot of energy but, being opaque, can penalize the growth of crops.
The results of this experiment are promising and have highlighted a faster growth for radicchio seedlings: however, as underlined by the authors themselves, the study was carried out on a small scale for a period of 15 dayswithout testing large-area semitransparent perovskite modules installed on operational greenhouses. Also for this reason, it is a “proof-of-concept”, which indicates the need for further studies before large-scale application.
We interviewed Dr. Carlo Spampinato – researcher at the National Research Council, Institute of Microsystems and Microelectronics of Catania – main author of the study, to tell us how the experiment was carried out and what the possible future developments are.
Dr. Spampinato, what are the technical characteristics of perovskite and why was this material used?
The experiment shows that the semi-transparent perovskite modules let a controlled part of the light through light and, above all, they modify the spectrum in a favorable way for radicchio: less blue and UV, more red and infrared. This leads, surprisingly, to seedlings with more leaves, larger leaves and more biomass, while receiving less light overall than plain glass. The material used is a completely inorganic perovskite based on cesium, lead and iodine, with a small addition of europium iodide: in compact form it can be indicated as CsPbI3:EuI2.
The active layer on the “cover” of the mini-greenhouse has a thickness of approximately 130 nm. From an optical point of view, in the visible (400–700 nm) the average transmittance is ~32%: it therefore means that about 32% of visible light passes through, while the rest is absorbed to make electricity. In the far red/infrared (700–1100 nm) the transmittance rises to approximately 70–80%; in the UV band (360–400 nm) only ~15.8% of the light passes, the rest is shielded.
Were different types of perovskite tested during the experiment?
Yes, we compare different types of perovskite for have a “right mix” between energy production and semi-transparency: the narrowest bandgap perovskite (which determines which energetic particles (photons) of sunlight the solar cell can absorb) – such as FAPbI3 and MAPbI3 – they absorb more in the visible, therefore they are less transparent. Those with wider bandgap (like CsPbIBr2) are more transparent, but have lower record photovoltaic efficiencies.
The composition of CsPbI3 doped with europium (Eu) is in the middle: quite absorbent to guarantee good photovoltaic efficiency in a semi-transparent configuration, but “open” enough in the visible and near infrared to let useful light pass to plants. Furthermore, being inorganic, it is more thermally stable than hybrid perovskites and europium helps reduce defects and improve phase stability.
What are the characteristics of this experimental “greenhouse”?
In the experimental work the “greenhouse” is laboratory scale, not a commercial greenhouse. In practice, the roof of the micro-greenhouse is made up of 4 slides side by sideeach measuring 2.5 × 2.5 cm²: in one case they are just glass, in the other they are coated with the perovskite layer, so that we can have a comparison. Inside every box there are 4 radicchio plantsfor a total of 10 boxes (5 with glass roof, 5 with perovskite roof), repeated in several experimental cycles. Finally, above the roofs there is a 12 LED tower that simulates the Sun, with a 16h/8h light/dark cycle.
In this experimental part there is not a complete photovoltaic module (with contacts, encapsulation, connection to the grid), but there is only the perovskite film that filters the light. For energy production, a simulation was made of a greenhouse roof covered with real semi-transparent modules based on the same material: the simulated photovoltaic efficiency of the device is around 12.7%, the estimated annual production is around 220–243 kWh per square meter of roof, while in the same 15 days of the seedling experiment, the simulated roof would produce around 16 kWh/m².
This is the first systematic study on the use of perovskite in agrovoltaics: what have you managed to demonstrate?
For the first time it is shown that a semi-transparent perovskite can simultaneously improve the initial growth of radicchio and, in theory, make the greenhouse energetically self-sufficient. Furthermore, the work shows that under a semi-transparent perovskite roof, radicchio seedlings, despite receiving approximately half the total radiation compared to glass, developed more leaves (3–4 versus 2) and with ~25% greater average area, and more fresh and dry biomass.
Energy simulations indicated that a real greenhouse roof covered by these modules could cover the annual energy requirement of a greenhouse intensive for lettuce/radicchio (lighting, air conditioning, irrigation).
What were the difficulties encountered during the experiment and what were the problems to be solved?
The article highlights some critical issues, first of all stability: the Perovskites are sensitive to moistureheat and light. In the laboratory the roof was kept under a flow of dry nitrogen, but in a real greenhouse very effective encapsulations would be needed.
Secondly, there is the fact that perovskite contains lead: this requires attention to the environmental impact and the development of lead “capture” strategies in the event of breakage. The experiment, then, is on a small scale, lasts only 15 days and concerns only the seedling phase: there is still no data on final yield, commercial quality, metabolite content in the mature plant. The “real” photovoltaic part is only simulated: large-area semi-transparent perovskite modules installed on operational greenhouses have not yet been tested in this work.
At this point, what are the next developments given the promising results?
In the study we indicated several future directions, including:
- extension to real-sized systemsi.e. real greenhouses with roofs completely covered by semi-transparent perovskite modules, exposed to real atmospheric conditions;
- longer studies over the entire crop cycle, to understand if the initial advantage of the seedlings translates into more yield or better quality of the harvest;
- test complete semi-transparent perovskite modulesencapsulated, on the roofs of real greenhouses, therefore on larger surfaces;
- verify the behavior of the modules even in indoor environments at different lighting levels: we have already shown that, under low intensity white LEDs, these devices could reach efficiencies of 21–22% and power, for example, environmental sensors for continuous monitoring.
