Research Of Transition And Charge Carrier Dynamics In Two Dimensional And Three Dimensional Perovskites

Organic-inorganic perovskite has been gradually applied to some optical appliances because of its excellent performance.Such as adjustable bandgap,long carrier lifetime and so on.Two-dimensional(2D)layered perovskites have emerged as promising materials for optoelectronic application owing to their tunable bandgap and improved stability.Herein,we studied in depth the transition and carrier transfer of perovskite phase from small n to large n(i.e.,so-called“low energy state”)in 2D perovskite(BA)₂(FA)Pb₂Br₇(BA=CH₃(CH₂)₃NH₃⁺,FA=CH(NH₂)₂⁺)single crystals(SCs),and the carrier diffusion in FAPbBr₃3D perovskite.The main research contents are as follows:(1)The large-n phase in 2D perovskites was found to play an important role in device performance and can be formed via the transition from small-n phase triggered by moisture.Herein,we studied in depth the effect of laser irradiation in the transition of perovskite phase from small n to large n in 2D perovskite(BA)₂(FA)Pb₂Br₇SCs.We demonstrated that laser irradiation can significantly accelerate the phase transition from small n to large n under normal atmosphere.This finding might provide new insight into the formation of large-n phase in 2D perovskites,which is helpful to better regulate their optical properties for applications in 2D perovskite devices.(2)Because the 2D perovskite exhibited a certain band alignment,we reported on the carrier transfer from small-n phase to large-n phase of(BA)₂(FA)Pb₂Br₇SCs by transient absorption(TA)spectroscopy.The small n excitons dissociated into electrons and holes,and transferred to the large-n phase rapidly in(BA)₂(FA)Pb₂Br₇SCs.(3)FAPbBr₃3D perovskite formed by the loss of long-chain ligands of(BA)₂(FA)Pb₂Br₇2D perovskite.Compared with 2D perovskite,its electrons and holes exist in the form of carriers,and it also showed high stability in water and oxygen environment.Time-resolved PL-scanned imaging microscopy system built in the laboratory was used to research the diffusion process of photogenerated carriers in FAPbBr₃under laser excitation.By using spot expansion method,the carrier distribution can be clearly seen at decay times,and the carrier diffusion distance can be obtained.Mechanism analysis was conducive to better regulation of the role of 3D perovskite in optoelectronic devices.In this paper,we studied in depth the transition,carrier transfer and diffusion of2D/3D perovskite.Meanwhile,the use of time-correlated single photon counting(TCSPC),time-resolved and PL-scanned imaging microscopy and TA system were systematically explained,which provides new methods and ideas for the future research of some perovskite materials.