Study on the Ultrafast Process of Perovskite Nanoparticles Modified by Different Alkyl Chains.

Three kinds of perovskite nanoparticles encapsulated with different chain lengths of alkylammonium, (CH3NH3)x(CH3(CH2)3NH3)(1-x)PbBr3 (NP-C4), (CH3NH3)x(CH3(CH2)7NH3)(1-x)PbBr3 (NP-C8), and (CH3NH3)x(CH3(CH2)11NH3)(1-x)PbBr3 (NP-C12), are successfully prepared. X-ray powder diffraction experiments demonstrate that these three nanoparticles are all pure cubic phase. However, the compositions of these three nanoparticles are significantly different, as revealed by steady-state absorption spectra. NP-C4 mainly consists of 2D perovskite with m (number of unit cell layers) = 1 and 3D perovskite. Instead, NP-C8 and NP-C12 are mainly composed of 2D perovskite with m = 3, 4, and 5. Time-resolved fluorescence spectra and femtosecond transient absorption spectra suggest the presence of energy transfer from 2D perovskite to 3D perovskite in these three nanoparticles. More importantly, the energy-transfer rate gradually decreases from NP-C4 to NP-C12. This result suggests that the composition of perovskite nanoparticles and their corresponding photophysical properties can be controlled by the chain length of alkylammonium. This provides a new insight for preparing novel perovskite nanoparticles for special applications.