Photoluminescence Properties of Lead Halide Perovskite Nanocrystals Revealed By Single-Dot Spectroscopy
Authors: Yamada Takumi , Cho Kenichi , Sato Ryota , Saruyama Masaki , Teranishi Toshiharu , Kanemitsu Yoshihiko 
Published: December 2024

Lead halide perovskites have attracted much attention as a new class of optoelectronic device materials because of their outstanding optical, electronic, and transport properties [1,2]. In addition, halide perovskite nanocrystals (NCs), which can be synthesized by simple chemical methods, show near unity photoluminescence (PL) quantum yields, with keeping the superior optoelectronic properties of their bulk counterparts [3,4]. Because of the small orbital degeneracy of the band edge, PL properties of halide perovskite NCs are governed by the formation and recombination dynamics of excitons, trions, and biexcitons [5,6]. Since individual NCs show narrow PL linewidths at low temperatures, multipeak PL structures appear and their origins are an exciton, a trion, and a biexciton. Single dot spectroscopy is a powerful tool to investigate the exciton–exciton, exciton–electron, and exciton–phonon interactions in perovskite NCs.
Here, we prepared three types of perovskite NC samples, CsPbBr3, CsPbI3 and FAPbBr3, and studied their PL spectra of single NCs at room temperature and low temperatures. At room temperature, all NCs show PL blinking, and nonradiative Auger recombination of trions and biexcitons determines the PL dynamics [7–10]. At low temperatures, all NC samples show strong PL, and several PL peaks originating a trion, a biexciton, and longitudinal-optical-phonon side bands of an exciton were clearly observed in the low energy side of the strong exciton peak [11–13]. The PL spectra of all samples were very similar to each other. We clarified the NC size dependence of the trion and biexciton binding energies and the Huang–Rhys (HR) factors, i.e., the strength of the exciton–phonon coupling, in three different perovskites. The positive binding energies of trions and biexcitons show the attractive exciton–exciton Coulomb interactions in the perovskite NCs, and these binding energies increase with decreasing NC size [11,13]. In addition, these size dependences follow a universal scaling curve regardless of composition when the binding energy and the NC size are normalized by the bulk exciton binding energy and the exciton Bohr radius, respectively [13]. The PL linewidths of all inorganic CsPbBr3 and CsPbI3 NCs were narrower than those of organic-inorganic hybrid FAPbBr3 NCs, suggesting the strong exciton–phonon coupling with large organic cation. In FAPbBr3 NCs, the size dependence of the HR factors is similar to that of the Urbach energy [10,11]. In all samples, the LO-phonon energies are independent of the NC size, while the HR factors increase as the NC size decreases [11,12]. Our findings provide new insights into understanding of the optical responses of halide perovskite NCs and the design of the single photon sources.
Part of this work was supported by JST-CREST (JPMJCR21B4) and JSPS KAKENHI (JP19H05465).
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