Stabilizing perovskite solar cells

If solar cells based on metal halide perovskites have grown tired of all the attention they’ve grabbed recently, they’re not showing it. The efficiency with which these soon-to-be-commercialized low-cost devices convert sunlight to electricity continues to grow quickly and now sits around 23%, comparable to more expensive commercial silicon cells. But perovskite cells, especially ones based on record-holding methylammonium (MA) lead trihalides, are known to be unstable. The MA moiety can decompose on prolonged exposure to sunlight and moisture, leading to poor performance. To combat the instability, researchers have tried numerous strategies. Some of them—for example, replacing the commonly used iodide with bromide—blueshift the absorption spectrum, lowering efficiency. Other approaches require treatments above 100 °C, limiting compatibility with flexible substrates. Silver-Hamill Turren-Cruz and Anders Hagfeldt of the Swiss Federal Institute of Technology, Lausanne (EPFL), and Michael Saliba of Adolphe Merkle Institute in Fribourg may have come up with a way around those shortcomings. The team avoided high temperatures and the bromide component, and they replaced the MA cation with combinations of formamidinium (FA), rubidium, and cesium ions. Cells made with one of the top performers, Rb₅Cs₁₀FAPbI₃, exhibited just over 20% efficiency and remained relatively stable for 1,000 hours (Science 2018, DOI: 10.1126/science.aat3583).