Let the sun shine in

Ensuring sustainability of new photovoltaic materials

Net zero by 2050 – this goal is at the heart of the EU’s Green Deal. To achieve it, the deployment of solar photovoltaic technologies must be scaled up exponentially. New materials offer a leap forward in the capacity of solar panels to absorb and convert energy, but it’s important not to lose sight of sustainability considerations relating to their production, use and end of life.

Dr. Markus Lenz and his team at the Institute for Ecopreneurship are leading the charge in investigating the sustainability of new photovoltaic materials. Specializing in the circular economy of metals and minerals, they are participating in two EU Horizon projects, namely Nexus and Pearl, to examine if perovskites can be safely used in the next generation of solar panels. In parallel, they are working on recycling perovskites so that they will not become a waste problem in the future.

Perovskite cells contain minimal amounts of lead, with a protective layer of glass or plastic designed to contain it. Lenz’s team is conducting outdoor leaching tests to determine if the cells are hermetic. To do this, they installed several perovskite panels on the roof of the FHNW School of Life Sciences in Muttenz that are exposed to real-life weather conditions. Temperature, light, moisture and wind vary throughout the year, and the panels are subject to more extreme weather events such as hail. Metal quantification tests performed on rainwater samples collected from the panels have shown very low predicted environmental concentrations, comparable to those permitted in drinking water.

Within the Nexus project, further facilities are now being installed in Bolzano and Valencia to ensure that perovskites can be safely operated under different climate conditions. “We currently see little reason to be concerned about the possible environmental impacts of lead during the use phase” says Lenz.

But what if the cell were to be damaged? To find out, Lenz’s team simulates more extreme weather events in a controlled environment. In the Pearl project, they expose perovskite modules to higher UV radiation, create defects (holes) using a laser, and look at whether bacteria could damage protective plastic layers.

And when the modules reach their end of life? Recovery and recycling of critical minerals is key to solidifying an independent European supply chain and ensuring sustainability of solar and battery power. Using their expertise in hydrometallic recovery, Lenz’s team has demon­strated for the first time how water alone is sufficient to recover pure lead iodide (PbI2) from perovskites. The recovered lead iodide can be used to produce new perovskite materials, while the old cells are no longer considered hazardous waste, a win-win situation.

Innovative solar firms participating in the Nexus and Pearl projects are grateful for the environmental fate testing and material recycling done by Lenz’s team. Oxford PV, who set a world record in energy conversion of 28.6% for their commercial-sized perovskite-on-silicon tandem solar cell in January 2024, is working toward a target of >30% for module power conversion efficiency in the Nexus project. Saule Technologies, who is participating in the Pearl project, specialises in printing perovskite solar cells on thin, flexible substrates at low temperatures.

“In the past decade, perovskite PV has gone from a lab curiosity to a powerhouse with the potential to democratise clean energy. At Saule Technologies, we recognise the urgency of the climate crisis and are committed to harnessing this technology responsibly, minimising environmental impacts at every stage of development and production. Through the PEARL project, we are gaining crucial insights, ensuring a sustainable future for the clean energy coming from our perovskite PV technology ” says Konrad Wojciechowski, Chief Science Officer at Saule.

“Our role is neither to engage in greenwashing, nor to generate alarmism” says Lenz. “In these projects, we’re providing scientific facts that can help manage possible risks of perovskites, determine their environmental and social acceptability and facilitate their adoption. We also hope our methods contribute to scaling-up and broadly deploying recycling processes for critical minerals.”

Perovskites - Did you know?

Perovskite is a mineral composed of calcium titanium oxide. Its crystal structure has inspired the development of a class of materials, also called perovskites, which feature two positively charged ions and three negatively charged ions. Perovskite solar cells (PSCs) contain compounds with the perovskite structure, most often methyl- ammonium lead halides.

They offer a high absorption coefficient coupled with simplicity and low production cost. Incorporation of carbon elec­trodes in PSCs can further improve their sustainability, using fewer critical raw materials. However, there are also voices expressing concerns about environmental compatibility due to their lead content, which is low but present.

Perovskite solar cells can be printed as thin, flexible films for applications in buildings, vehicles and electronic devices. In tandem perovskite cells, a perovskite cell is layered on top of a traditional silicon cell, which significantly boosts its energy conversion. PSCs can also be used alone to power small vehicles such as drones. As solar panel size, location and energy needs vary, PSCs can provide new options to help diversify the solar market and meet clean energy targets.