From Composition to Composite Design—Chemical Tricks that Stabilize Halide Perovskites

Despite the outstanding optoelectronic properties of hybrid organic-inorganic perovskites (HOIPs), prototypical halide perovskites, such as methylammonium lead iodide (MAPbI₃, MA = CH₃NH₃), suffer from poor environmental stability. From ionic substitutions at an atomic level to post-synthesis treatment at a microscopic level, there has been intensive research in the community of materials chemistry to increase the structural and chemical stability of MAPbI₃. However, obstacles exist efficiently navigating this large and complex materials design space. A question that often gets asked is: how far can we extend the stability lifetime of a perovskite photoactive material, without lowering its optoelectronic performance?<br/><br/>In this talk, I will demonstrate three distinct approaches to delay the onset of HOIP degradation and discuss their relative advantages and disadvantages in perovskite electronics applications. I will start by discussing how stability changes non-linearly as a result of composition engineering in a combinatorial space, where the MA ions in MAPbI₃ are partially replaced by less volatile cations such as Cs and formamidinium.[1] Without modifications on the MAPbI₃ lattice, I will then move to capping methods, where a capping layer serves the dual function of forming a protective layer against oxygen and water, as well as improving the interface passivation.[2] I will then share our most recent findings in additive engineering, where porous organic cage molecules were introduced for the first time in perovskite films, forming perovskite-cage composites that show remarkable resistances to high humidity and temperature.[3] I will end my talk by briefly mentioning the role of machine learning in helping guide the experimental exploration of materials design and optimization in our projects.<br/><br/>[1] Sun et al., Matter, 2021, 4, 1305-1322<br/>[2] Hartono et al., J. Mater. Chem. A, 2022, 6, 2957-2965<br/>[3] Sun et al., Chem. Mater. 2022, accepted manuscript<b> </b>