Charge Carrier Dynamics in Thallium Halide ...

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Avinash Warankar, Wasim J. Mir, Angshuman Nag,Pankaj Mandal*. Department of Chemistry, Indian Institute of Science Education and Research. (IISER), Pune ...
Charge Carrier Dynamics in Thallium Halide Nanocrystals by Terahertz Spectroscopy Avinash Warankar, Wasim J. Mir, Angshuman Nag, Pankaj Mandal* Department of Chemistry, Indian Institute of Science Education and Research (IISER), Pune, 411008, India. *Corresponding author: [email protected] ABSTRACT: Thallium halides (TlX) are a new class of semiconductor nanocrystals with band gap close to ultraviolet (UV) range. Usually, in semiconductors, the traprelated defects start dominating as band gap increases towards UV range. Defect tolerance is one of the main reasons behind the high performance of the metal halide perovskites in various optoelectronic properties, which originates from their unique electronic band structure.1 Due to the compositional similarity between the metal halide perovskite and the TlX, they have similar electronic band structure. Timeresolved terahertz (THz) spectroscopy (TRTS) is a contactless technique to measure electronic properties of the material.2 In TRTS, the sample is excited with femtosecond pulses of optical light and dynamics of photoexcited species are probed by THz pulses. We have applied optical pump (with wavelength of 400 nm) and THz probe (OPTP) on the TlX (X= Br, I) NCs films on polystyrene substrate.3 The distinct charge carrier dynamics have been observed in the TlBr and TlI NCs films under the fluence ranging from 4 to 29 µJ cm-2. Carrier decay dynamics become slower with increase in the fluence in the TlBr NCs and remain the same in the TlI NCs for all fluences. The shortest and the longest time scales are assigned to the fast charge trapping and the electron-hole (bimolecular) recombination processes respectively. The process with intermediate time scale in the TlBr NCs can possibly be the different type of trapping or Auger recombination that lead to the slowing down the dynamics with an increase in fluence. In the TlBr NCs, we have obtained high values of effective mobility and diffusion length, around 300 cm2V-1s-1 and 1 µm respectively with the average lifetime close to 1 ns. References: 1. 2. 3.

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