Gentle, Versatile, Environment friendly Perovskite-Primarily based Tandem Solar Cells

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All-perovskite tandem photo voltaic cells might quickly take over the place silicon photo voltaic cells attain their limits. These extremely environment friendly, light-weight, and renewable cells have already confirmed themselves within the laboratory – now, Empa researchers are engaged on scaling them up and making them prepared for the true world.

Roof tiles have gotten a factor of the previous: Today, increasingly more rooftops in Switzerland boast giant black and blue rectangles that convert daylight into electrical energy. The blue colour comes from silicon crystals, as most photo voltaic cells obtainable immediately are based mostly on this semiconductor materials. But silicon shouldn’t be the one option to make a photo voltaic cell – and perhaps not even the very best.

Silicon-based photovoltaic cells have been perfected till they attain the boundaries of their effectivity. Although a number of proportion factors of enchancment can nonetheless be obtained, the theoretical higher restrict for the effectivity of a silicon cell is 33 p.c. In apply, it’s comparatively low, as a result of a small lack of vitality inevitably happens in the course of the building and operation of the cells.

The purpose for this tough effectivity restrict lies within the materials properties of silicon. The so-called band hole of the fabric signifies that solely photons with a sure vitality will be transformed into electrical energy. If the photon vitality is just too excessive, it can’t be absolutely “used” by the photo voltaic cell.

Two layers are higher than one

Solar cells constructed from different supplies supply a option to overcome this limitation, says Empa researcher Fan Fu. The group chief of the Laboratory for Thin Films and Photovoltaics researches extremely environment friendly photo voltaic cells fabricated from perovskite. A perovskite cell alone can not obtain a better effectivity, as a result of perovskite as a semiconductor has a restricted band hole. The actual power of this new materials lies in the truth that, in contrast to silicon, this band hole will be simply adjusted by altering the precise composition of the perovskite materials.

When two perovskites with totally different band gaps are processed into skinny movie photo voltaic cells and “stacked” on prime of one another, the result’s a so-called tandem photo voltaic cell. One layer of perovskite “captures” photons with excessive vitality, the opposite with low vitality. In idea, this enables efficiencies of as much as 45% – a lot larger than the 33% of single-junction cells. Alternatively, a perovskite layer will also be added to a silicon cell to create a extremely environment friendly tandem cell.

However, Fu and his staff are actually specializing in all perovskite tandem cells, particularly as a part of the EU analysis undertaking SuPerTandem, the place a complete of 15 main analysis establishments in Europe and firm are concerned. The objective of the undertaking is to develop versatile perovskite tandem modules with an effectivity of greater than 30 p.c, which will also be produced utilizing scalable and cost-effective processes. This is one other power of perovskite photo voltaic cells: “Silicon photo voltaic cells often require high-purity silicon monocrystals produced at excessive temperatures,” explains Fu. “Perovskite skinny movies, however, will be printed, resolution processed or produced by vapor deposition with a really low CO2 footprint. Small defects that happen within the course of have little impact on their optoelectronic properties. .”

The potential advantages of initiatives like SuPerTandem are vital, as a result of the upper the effectivity, the cheaper solar energy shall be on the finish of the day. “The cell itself prices lower than 20 p.c of the price of a PV system,” stated Fu. “The remaining 80 p.c is accounted for by cables, inverters, junction bins and, in fact, the labor concerned within the set up.” If the effectivity of the person cells is elevated, a smaller – and due to this fact cheaper – PV system shall be ample for a similar energy output. Thin cells fabricated from perovskite will also be produced in mild versatile movies as a substitute of heavy, inflexible glass plates like silicon cells. This signifies that it will also be utilized in many areas, for instance on automotive roofs or in buildings with a small load-bearing capability.

From the lab to the roof

This potential of perovskite photo voltaic cells ought to now be exploited. In addition to SuPerTandem, Fan Fu’s staff can also be engaged on two initiatives in Switzerland. In a undertaking funded by the Swiss National Science Foundation (SNSF), Empa researchers are working to raised perceive the basic properties and challenges of perovskite photo voltaic cells that contribute to their effectivity and sturdiness. And in a undertaking with the Swiss Federal Office of Energy (SFOE), they put their current data into apply by scaling up the tandem cells already developed at Empa.

What else do we have to do to make sure that the black and blue rectangles on our roofs are joined by pink perovskite movies? “First of all, we have to scale the perovskite cells from current prototypes of some centimeters to industrial sizes,” stated Fu. The cells, that are comparatively fragile, should even be successfully protected against the climate. Fan Fu is optimistic that each shall be achieved within the subsequent 5 to 10 years. “We are making good progress, and there’s a lot of curiosity from business,” stated the scientist. “Researchers have solely been engaged on perovskite-based photo voltaic cells for under 15 years. For comparability, analysis on silicon cells has been occurring for nearly 70 years.

By Anna Ettlin, by Empa, Swiss Federal Laboratories for Materials Science and Technology