Lead-Free Perovskite Solar Cells: Why Efficiency and Stability Lag Behind Lead

… more less Lead-free perovskite solar cells try to remove lead, which is toxic and dissolves in water. The idea is sound, but so far no swap works as well as lead. Tin is the closest match. Pure tin cells absorb well, but tin oxidises from Sn2+ to Sn4+ in air. That self-dopes the film and drops the voltage. Bismuth and antimony carry a 3+ charge, not 2+, so they cannot sit in the same cage. They form other structures with wider gaps and poorer charge flow. Double perovskites pair one 1+ metal and one 3+ metal, such as silver and bismuth. They are very stable, but their gap is wide and often indirect, so they absorb sunlight weakly. Many also hold deep traps. Lead is special because of how its outer electrons are arranged. That layout is what makes its common defects shallow, which gives lead its defect tolerance. Remove lead and you often lose that gift. The honest state is that tin-based cells reach roughly half the efficiency of the best lead cells, and the others lag further. Lead cells hold only a small amount of lead per panel, and capture layers can trap it if a panel breaks. When you read a lead-free claim, check the efficiency, the band gap, and how long the cell lasted in air. After this Concept you can name the main lead-free options and say what each one gives up compared with lead.