(Invited) Fundamental Photophysics of Lead Halide Perovskites
Authors: Kanemitsu Yoshihiko 
Published: December 2024

Halide perovskites have been receiving significant attention as a new class of semiconductor optoelectronic materials for solar cells, displays, light-emitting diodes, and quantum light sources [1,2]. Their high-quality bulk crystal and nanocrystal samples can be fabricated by simple low-temperature solution processes, and they exhibit extremely high photoluminescence (PL) quantum yields even at room temperature. Optical spectroscopy is one of the most versatile techniques for characterizing new semiconductor materials. In this work, we discuss optical properties of ABX3 lead halide perovskites as new solar cell and light-source materials.

(1) Band-edge electronic structures: ABX3-type halide perovskites are direct-gap semiconductors with unique band structures because of strong spin-orbit couplings [3]. The electronic structures of lead halide perovskites are dominantly determined by the lead-halide octahedra. Nonlinear optical spectroscopy [4-6] and magneto-optical spectroscopy [7] revealed the Kane energy, spin-orbit splitting energy, exciton binding energy, and reduced exciton mass of lead halide perovskites.

(2) Free carrier luminescence in bulk single crystals: Strong PL with no Stokes shift is caused by the band-to-band free carrier recombination in low-bandgap iodide perovskites and the exciton recombination in wide-bandgap chloride perovskites [4,8,9]. No impurity and defect luminescence appear at room temperature. Intrinsic up-conversion PL (anti-Stokes PL) is clearly observed in perovskites, because of strong electron-phonon interactions [10,11]. In thick samples, photon recycling (photon emission and reabsorption) and carrier diffusion processes determine the PL spectra and dynamics [12,13].

(3) Exciton luminescence in nanocrystal quantum dots: Single dot PL spectroscopy revealed that the recombination dynamics of excitons, trions, and biexcitons cause unique optical responses of nanocrystal quantum dots (for example, PL blinking and spectral diffusion) [14,15]. Nonradiative Auger recombination of trions and biexcitons dominates the PL dynamics at room temperature [16,17]. At low temperatures, multipeak structures appear in the PL spectra and they originate from the exciton, trion, biexciton, and their LO-phonon assisted PL [19,20]. We determined the nanocrystal size dependence of the trion and biexciton binding energies [19,21].

Part of this work was supported by JST-CREST (Grant No. JPMJCR21B4), NEDO-GI (Grant No. JPNP21016), and JSPS KAKENHI (Grant No. JP19H05465).

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