Perovskite Additive Engineering: Methylammonium Chloride and Excess Lead Iodide

… more less Perovskite additive engineering means adding a small amount of an extra chemical to the ink to steer how the film grows or to heal defects. Two common ones show the idea. Methylammonium chloride, MACl, helps FAPbI3 form its black phase instead of the yellow one. It widens the range of bake times and heats that work. Most of it leaves the film during the bake, so little stays in the final layer. A slight excess of PbI2, a few percent more than the recipe needs, tends to sit at grain edges and reduce charge loss there. That can raise the voltage. But that leftover PbI2 can break down under light and start damage, so the gain at day one can cost you lifetime. Other additives are Lewis bases that bind lead and slow crystal growth, giving larger grains. The rule is that an additive is a trade, not a free gain. It can change the band gap, leave residue, or speed up decay. So when you compare cells, check the stability plot, not only the efficiency. Also check how much of the additive is still in the film after the bake. After this Concept you can read an additive list in a recipe, say what each one is for, and name the trade-off to test for.