## 1 Introduction  
Recently, 3D layered topological insulators (TIs) materials, such as Bi\({}_{2}\)Se\({}_{3}\), Bi\({}_{2}\)Te\({}_{3}\), and Sb\({}_{2}\)Te\({}_{3}\), have attracted extensive attention due to their unique surface state properties, which are topologically protected against back-scattering and immune to defect-driven localization [1; 2; 3]. These materials also are fascinating materials conventionally used in thermoelectricity [4; 5]. Thermoelectric materials can be used to directly convert waste heat into electrical power, which is a potential technology for clean and reliable energy harvesting [6]. Improving the energy conversion efficiency is the ultimate goal of global researchers. The record of conversion efficiency was refurbished continuously in the past decade [7; 8]. The thermoelectric efficiency is governed by the dimensionless thermoelectric figure of merit ZT (ZT = S\({}^{2}\sigma\)T/K, where S, \(\sigma\), T, and K denote the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively) [9]. Nanostructuring to minimize the thermal conductivity is one of the most common approaches to obtain high ZT [10; 11]. For example, nanostructured lead chalcogenides PbQ (Q = Te, Se, S) have demonstrated high thermoelectric ZT [12]. However, Pb-free materials are more desirable to replace the toxic PbQ, which may be unfriendly to the environment and human health. Raman spectroscopy is a conventional and non-destructive technique for crystal structure characterization [13], which can provide important information on lattice vibration, doping, strain engineering, and crystal phases [14; 15]. Insight into the lattice dynamics property is essential to understand the thermal/transport properties, thermal expansion and diffusion, entropy, specific heat, and electron-phonon interaction, all of which have great impact on the thermoelectric performance [16]. Furthermore, it is well known that change of temperature can vary inter-atomic distances and vary the overlap among adjacent electronic orbitals. Therefore, temperature-dependent Raman spectra are well suitable to obtain information on the thermal conductivity of materials, as well as isotopic effects and phonon lifetimes [17; 18; 19]. With a band gap of 0.3 eV, Bi\({}_{2}\)Se\({}_{3}\) is the most important V-VI semiconductor [20; 21; 22; 23]. Bi\({}_{2}\)Se\({}_{3}\) has an extensive application as thermoelectric and photoelectric materials near the room temperature [24; 25]. Raman spectroscopy was an important tool to characterize the physical properties of various nanostructures, such as: 1T-TaS\({}_{2}\)[26], TiS\({}_{3}\)[27], MoS\({}_{2}\)[28], CoFe\({}_{2}\)O\({}_{4}\)[29], CuGaO\({}_{2}\)[30], Bi\({}_{3.25}\)La\({}_{0.75}\)Ti\({}_{3}\)O\({}_{12}\)[31], ZnSe [18; 32], ZnO [33], etc. Recently, there are some reports about the Raman-active optical phonon of Bi\({}_{2}\)Se\({}_{3}\) micro/nanostructures [34; 35; 36]. For example, [PERSON] et al. reported the synthesis and Raman spectra investigation of few-quintuple layer Bi\({}_{2}\)Se\({}_{3}\) nanoplates [37]. However, the size of their Bi\({}_{2}\)Se\({}_{3}\) nanoplates was only 0.7-1.6 \(\upmu\)m, which makes it hard to obtain the Raman spectra of a single nanoplate under optical microscopy. Therefore, it is highly desired to synthesize large Bi\({}_{2}\)Se\({}_{3}\) nanoplates with only a few layers in thickness. As far as we know, there is not yet any report on the Raman spectra of the single solution process Bi\({}_{2}\)Se\({}_{3}\) nanoplate. Herein, we synthesized large (7.50-10.0 \(\upmu\)m) Bi\({}_{2}\)Se\({}_{3}\) hexagonal single-crystal nanoplates by hydrothermal method and investigated their Raman spectra over a wide temperature range of 83-603 K. The variation of Raman peak position and full wave at half maximum (FWHM) with temperature were discussed in detail.