Intense focus has been placed on how the world will achieve net-zero by 2050. Perovskite solar cells have shown promise for improving the performance and efficiency of solar energy harvesting, but the environmental risks that arise from the use of toxic lead in them must be properly considered, states a paper published online in the One Earth journal.
Study: Manage the environmental risks of perovskites. Image Credit: foxbat/Shutterstock.com
The Push to Net Zero
The world is warming at an alarming rate due to human activity. Speaking in December 2020, UN Secretary-General António Guterres announced that the world must declare a climate emergency until net zero is achieved. According to the IPCC, limiting global temperature rise to 1.5oC will require drastic cuts to carbon emissions, by 45% from 2010 levels by 2030.
The fastest way is to decarbonize the energy sector, as it is responsible for 75% of all greenhouse gases. At least 40-70% of the energy mix by 2050 must come from wind and solar if targets are to be achievable. However, current technologies have problems with efficiency, facilitating the need to develop new technologies.
Perovskite Solar Cells
To overcome efficiency and performance issues in solar energy harvesting, much research has been focused on investigating the use of metal halide perovskite materials in photovoltaic solar cells. Perovskites have better power conversion efficiency than conventional silicon-based solar cells. They also have the benefit of being low-cost.
However, there is a major issue with these materials. Most perovskites contain lead, which is incredibly toxic to humans, animals, and the environment. Concerns have been raised over the widespread use of lead-based perovskite materials in photovoltaic cells, shining a light on the urgent need to investigate their potential harm to human health and the environment.
The first concerns over the health effects of lead paint were voiced in the early 20th century, but this had little international attention at the time. Since then, the harm caused by lead has been well-documented. Lead use has affected the health of many millions of people over the years, and exposure to lead contaminants is responsible for more than 1 million deaths globally per year and the loss of 24 million disability-adjusted life years.
Lead has been mined for centuries by humans, with lead water pipes used since Roman times. In the modern era, lead was added to petroleum as an anti-knocking agent until very recently and as an additive in paint. Lead is still widely used in the electronics industry and in automotive batteries.
Further Reading: Improving Solar Cells with Pristine Graphene on Lead Iodide Films
Lead poisoning can occur via various routes, including inhalation of particles emitted by industrial activities such as smelting, ingestion of contaminated water, or food grown in contaminated soil. Exposure can cause damage to vital organs such as the brain and kidneys and ultimately, death. Recent studies have shown that low-level lead poisoning is a contributing factor to cardiovascular disease.
The widespread implementation of lead-based perovskite solar cells facilitates the urgent need for research and discussions around the human and environmental risks of these materials. The research in One Earth has discussed the problem from an environmental perspective.
Considering the Problem of Lead-Based Perovskites
If the solar cell remains intact, the lead perovskite layer is not a problem as there is no exposure route. However, damaged or poorly designed solar cells can leach lead into rainwater. Over the lifetime of perovskite solar cells, 1 in 100 will break, demonstrating the potential scale of the issue. Lead from broken solar cells on domestic dwellings can leach directly into garden soil, causing health problems for residents and facilitating uptake by plant root systems.
Concerns over the harm caused by leaching increased when it was discovered that lead perovskites can release soluble forms of lead such as methyl-ammonium lead oxide. The high bioavailability of this compound is of particular concern, and studies on exposed cells have revealed massive levels of apoptosis caused by it. Plants can also absorb much higher levels of perovskite at a rate higher than common lead contaminants.
Along with evidence from other studies, these factors demonstrate the environmental risk of lead perovskite solar cells. Although it is not yet known if this will equate to large-scale human or environmental risk, the high bioavailability of lead perovskite chemicals warrants concern.
The study identified some methods that can be used to mitigate this issue. These include more durable perovskite design, better environmental risk management, and placement of perovskite solar farms away from residential areas and agricultural land. The study concluded that a precautionary approach should be taken until the true health and environmental dangers of lead-based perovskites are known.
O’Connor, D & Hou, D (2021) Manage the environmental risks of perovskites [online] One Earth 4:11 | sciencedirect.com. Available at: https://www.sciencedirect.com/science/article/abs/pii/S2590332221006126