Terahertz Modulation and Ultrafast Characteristic of Two-Dimensional Lead Halide Perovskites.

In recent years, two-dimensional (2D) halide perovskites have been widely used in solar cells and photoelectric devices due to their excellent photoelectric properties and high environmental stability. However, the terahertz (THz) and ultrafast responses of the 2D halide perovskites are seldom studied, limiting the developments and applications of tunable terahertz devices based on 2D perovskites. Here, 2D R-P type (PEA)(MA)PbI perovskite films are fabricated on quartz substrates by a one-step spin-coating process to study their THz and ultrafast characteristics. Based on our homemade ultrafast optical pump-THz probe (OPTP) system, the 2D perovskite film shows an intensity modulation depth of about 10% and an ultrafast relaxation time of about 3 ps at a pump power of 100 mW due to the quantum confinement effect. To further analyze the recombination mechanisms of the photogenerated carriers, a three-exponential function is used to fit the carrier decay processes, obtaining three different decay channels, originating from free carrier recombination, exciton recombination, and trap-assisted recombination, respectively. In addition, the photoconductor changes (∆) at different pump-probe delay times are also investigated using the Drude-Smith model, and a maximum difference of 600 S/m is obtained at τ = 0 ps for a pump power of 100 mW. Therefore, these results show that the 2D (PEA)(MA)PbI film has potential applications in high-performance tunable and ultrafast THz devices.