Highly Luminescent and Stable 2D/3D Octadecylammonium/Formamidinium Lead Bromide Perovskite Films

We developed a facile approach to fabricate highly luminescent and stable quasi-2D/3D (ODA)₂FA_n-1Pb_nBr_3n+1/FAPbBr₃ (ODA: octadecylammonium; FA: formamidinium) perovskite films. Trace amounts of octadecylamine dissolved in toluene used as an antisolvent were partially protonated by FAPbBr₃ and interacted with [PbBr₆]^4- octahedral layers, forming quasi-2D perovskites. Moreover, octadecylamine uniformly and densely covered the perovskite surface rendering it hydrophobic and prevented penetration of water, making these perovskite films stable and strongly luminescent in water for several tens of minutes without any encapsulation. Adjusting the concentration of octadecylamine, we were able to produce perovskite films with an exceptionally high photoluminescence quantum yield (PL QY) of 91%, which was ascribed to the efficient energy funneling from the 2D to the 3D perovskite phase and the passivation action of the organic additive.