Revealing the Crystallization and Thermal-Induced Phase Evolution in Aromatic-Based Quasi-2D Perovskites Using a Robot-Based Platform

Introducing large organic cations to form reduced-dimensional(quasi-2D)perovskites has proven to be effective in stabilizing three-dimensionalperovskites. In this study, we synthesized 28 Ruddlesden-Popper-typequasi-2D perovskites using four aromatic-based cations (phenylmethylammonium(PMA), phenethylammonium (PEA), phenylpropylammonium (PPA), and phenylbutanammonium(PBA)) and systematically investigated their optoelectronic and structuralproperties and thermal stability. A counterintuitive finding thatlonger-chain PPA-based films exhibited relatively poorer stabilitycompared to films with shorter-chain cations has been found. Thisinstability in PPA-based samples is attributed to significant latticedistortion and a mismatched phase between face-sharing trimers, causingintense configurational strain. On the other hand, PBA-containingfilms maintained robust structural stability due to distinctive crystallizationkinetics and a gradual phase-transformation process (from larger-n to lower-n phases) induced by a strongersteric-hindrance effect. Our study sheds light on the complex impactof aromatic-based cations on optoelectronic properties and stabilityof perovskites, providing guidelines for the rational compositionaldesign engineering of highly stable perovskite materials.