Ion-exchange-induced MAPbI3 thin-film 3D–2D and 3D–1D conversions: unveiling structural transformations in films via synergistic and competitive approaches

The gas-induced transformation of organic–inorganic halide perovskites shows unprecedented phenomena and applications in the area of optoelectronics. In this study, the chemical origins of the gas-induced dimensional transformation (GIDT) of MAPbI3 have been investigated within CH3NH2 (MA), CH3(CH2)5NH2 (C6) and (CH3CH2)3N (C6′) atmospheres. With the exposure of the as-synthesized MAPbI3 perovskite thin film to the C6 gas, the rapid displacement of the MA+ cations by the C6+ cations is achieved, thus inducing the MAPbI3 thin film structure to turn from a three-dimensional motif to two-dimensional (CH3(CH2)5NH3)2PbI4. By comparison, no response is observed when the same process is carried out in the presence of the tertiary amine C6′ gas. With MA acting as a coinduction conversion agent, the MAPbI3 film transfers to a quasi-2D perovskite structure within MA and C6 mixture atmosphere, while it changes to a one-dimensional (C6H15NH)PbI3 chain as MA combines with the C6′ gas, showing an effective mixed amine strategy for GIDT. Interestingly, the obtained quasi-2D perovskite films display tuneable absorption and emission luminescent characters associated with the volume ratios of MA/C6-mixed amines.