Boosting Charge Transport in a 2D/3D Perovskite Heterostructure by Selecting an Ordered 2D Perovskite as the Passivator.

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA0.8Cs0.2PbI3, we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (φµ), and carrier diffusion length (LD) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of ~1.3 µs, high φµ of ~18.56 cm2V-1s-1, and long LD of ~7.85 µm is achieved in the 2D/3D films when passivated by 16.67% para-fluoro-PEA2PbI4. This carrier diffusion length is comparable to that of some perovskite single crystals (>5 µm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.