Challenges of anti-solvent method for quasi-2D perovskites: The role of steric hinderance from the Phenethylammonium (PEA⁺) spacer cation

Quasi-2D Ruddlesden-Popper organolead perovskites have emerged as promising materials due to their remarkable moisture stability and excellent optoelectronic properties, offering significant potential for advanced semiconductor applications. Maintaining device efficiency in quasi 2D perovskites without compromising efficiency is possible by the challenging synthesis of high quality quasi-2D perovskite. Herein, we utilized less explored anti-solvent method to synthesize (PEA)₂MA_n-1Pb_nI_3n+1 i.e., n = 5, 4 and 3 thin films. By employing chlorobenzene as antisolvent, PEA₂MA₄Pb₅I₁₆ obtained is randomly oriented due to its fast crystallization from the precursor solution having competing larger spacer cation phenethylammonium (PEA⁺) and smaller methylammonium (MA⁺) cation. However, by decreasing the concentration of larger spacer cation to the half of the actual molar ratios in (PEA)₂MA_n-1Pb_nI_3n+1 i.e., n = 5, 4 and 3 thin films, the crystallinity, optical absorbance and smoothness in topography is observed. However, the depletion of various phases is not possible and an undesirable PbI₂ is also formed. We incorporated an excess of MAI which decreased the PbI₂ at the cost of crystallinity for (PEA)₂MA₄Pb₅I₁₆ and (PEA)₂MA₂Pb₃I₁₀ except (PEA)₂MA₃Pb₄I₁₃ in which crystallinity enhancement is observed. Our results highlight that in chlorobenzene anti-solvent process, the structure and stability of quasi-2D perovskite thin films are governed by the competition between the spacer concentration and film crystallinity. Thus, actual quantities of PEAI in quasi-2D perovskites ( n = 5–3) are not feasible to intercalate into lower membered quasi 2D perovskites by anti-solvent method.