Ultrafast terahertz probe of photoexcited free charge carriers in organometal CH3NH3PbI3 perovskite thin film

Abstract

By using optical pump-terahertz probe (OPTP) experiments, we study the free charge carrier dynamics in photoexcited drop-cast CH 3 NH 3 PbI 3 -based perovskite thin film at room temperature. Compared with the pump photon energy at 1.55 eV, the measured OPTP signal following excitation of 3.1 eV shows an additional fast decay channel of the photoconductivity. Our experimental results demonstrate that effective carrier lifetime can be strongly modulated by surface recombination. In addition, the Drude-Smith-like transient terahertz photoconductivity spectra suggest that photogenerated free carriers experience backscattering at grain boundaries in our solutionprocessed perovskite films studied here.Over the past few years, organic/inorganic hybrid perovskite absorbers have emerged as novel functional materials for thin-film solar cells reaching efficiencies of over 15 % [1,2]. Notably, owing to a combination of strong optical absorption with particularly high charge diffusion lengths, the organic-lead iodide CH 3 NH 3 PbI 3 enables devices showing strong photovoltaic performance based on simple planar heterojunction architecture [3,4].Moving forward, understanding the dynamics of nonequilibrium photoexcited carriers in CH 3 NH 3 PbI 3 is of particular interest in developing high-performance optoelectronic and photovoltaic solar cells. Past efforts are based on probing directly the parameters of charge carrier dynamics, such as carrier lifetime, mobility, and diffusion length, by using the time-resolved photoluminescence (TRPL) [5-9] and optical pump-probe spectroscopy [10][11][12][13][14]. Elucidating the role of excitons, free carriers and especially carrier trap-state in these organic/inorganic materials would provide a deeper understanding of the mechanisms that give rise to the high performance of hybrid perovskite-based devices [15,16].Ultrafast optical pump-terahertz probe (OPTP) spectroscopy as a time-resolved, contactless conductivity probe method has previously been successfully employed to investigate the dynamics of photoexcited excitons and free charge carriers with subpicosecond resolution [17]. OPTP signal can be directly converted into the time-and frequency-resolved complex-valued sheet conductivity spectrum b r s x; t p À Á ¼ b r  d, where d is the thickness of the conductive layer. Photoinduced terahertz-frequency-integrated sheet conductivity is a product of mobility and carrier concentration, r s

Hybrid Perovskite Terahertz Photoconductive Antenna

“…In Figure 4 a, one can clearly see that at zero delay, the optical pumping of the sample leads to instantaneous decrease of the sample THz transmission related to fast photoexcited carrier generation. The THz absorption for a thin film is typically proportional to the photoconductivity (Δσ), which in turn is proportional to the photogenerated carrier density (the number of excited carriers) (N) and mobility (μ) following E~Eσ~μeN [ 27 ].…”

Polaronic Charge Carrier–Lattice Interactions in Lead Halide Perovskites

“…In the context of the materials considered herein, these are ascribed to defect‐mediated (Shockley–Read–Hall (SRH), monomolecular), free‐carrier radiative (bimolecular), and three‐body (Auger) recombination, respectively. Recombination coefficients are obtained by assuming that the time‐dependent charge density n ( t ) is proportional to the optical density OD( t ) from transient absorption spectroscopy (TAS), and optical pump terahertz probe (OPTP) experiments . Table is a collection of literature values for the most prominent members of the organic–inorganic metal halide hybrid perovskites (OIHPs) and all‐inorganic metal halide perovskite (AIP) materials. …”

Photoexcited terahertz conductivity dynamics of graphene tuned by oxygen-adsorption

“…All measurements were performed at room temperature. As the monolayer graphene is thin, DT/T 0 is related to the photoinduced sheet photoconductivity, i.e., Dr 24 Therefore, the observed positive DT/T 0 indicates a suppression of the photoconductivity in the graphene sample. Figure 2(a) shows the negative photoinduced THz conductivities of our CVD graphene sample as a function of the pump-probe delay time for various gaseous atmospheres, with an optical pump fluence fixed at 50 lJ/cm 2 .…”

“…The attenuation of the terahertz waves comes for the conductivity of the intrinsic free carriers in graphene. By using the thin-film approximation (the Thinkham equation), we can obtain the intrinsic sheet complex conductivity by 23,24 E…”