Takumi Yamada1,Kenichi Cho1,Hirokazu Tahara1,Terumasa Tadano2,Hidekatsu Suzuura3,Ryota Sato1,Masaki Saruyama1,Toshiharu Teranishi1,Yoshihiko Kanemitsu1
Kyoto University1,National Institute for Materials Science2,Hokkaido University3
Takumi Yamada1,Kenichi Cho1,Hirokazu Tahara1,Terumasa Tadano2,Hidekatsu Suzuura3,Ryota Sato1,Masaki Saruyama1,Toshiharu Teranishi1,Yoshihiko Kanemitsu1
Kyoto University1,National Institute for Materials Science2,Hokkaido University3
Lead halide perovskite semiconductors are recently attracting much attention as a new class of optoelectronic device materials, because of their outstanding optical and electronic properties at room temperature. It is considered that strong electron–phonon interactions play a key role in unique optical and transport responses of halide perovskites [1]. They determine the effective carrier mass, the carrier mobility, the photoluminescence (PL) linewidth, the Urbach tail of optical absorption, and so on. The efficient anti-Stokes PL and the slow hot-carrier cooling are also closely related to strong electron–phonon interactions [2–5]. Since individual nanocrystals (NCs) show extremely high PL quantum yields and narrow PL linewidths, longitudinal-optical (LO) phonon replicas reflecting electron–phonon interactions can be observed in the PL spectra at cryogenic temperatures. Therefore, single dot spectroscopy is a powerful tool to investigate the exciton–phonon interactions of perovskite NCs.<br/>Here, we prepared CsPbBr<sub>3</sub>, FAPbBr<sub>3</sub>, and MAPbBr<sub>3</sub> perovskite NC samples and measured their PL spectra of single NCs [6–8]. At low temperatures, CsPbBr<sub>3</sub> NCs show very sharp PL lines including fine-structure splitting in the PL peaks of excitons, biexcitons, and the LO-phonon replicas of excitons. We discuss the exciton–phonon and trion–phonon interactions in perovskites from the PL fine structures in CsPbBr<sub>3</sub> NCs. We found that the LO-phonon energies are independent of the NC size. However, the Huang–Rhys (HR) factors of excitons, i.e., the strength of the exciton–phonon coupling, depend on the LO-phonon energy. Both HR factors for excitons and trions increase as the NC size decreases. The HR factors of trions are larger than those of excitons in larger NCs. We conclude that the size-dependent HR factors for excitons and trions are closely related to the spatial distributions of the electron and hole wavefunctions in the NC.<br/>Part of this work was supported by JST-CREST (JPMJCR21B4) and JSPS KAKENHI (JP19H05465, JP20K03798, JP21K03424, and JP22H01990).<br/><br/>[1] Y. Yamada and Y. Kanemitsu, <i>NPG Asia Materials</i> <b>14</b>, 48 (2022).<br/>[2] T. Yamada <i>et al</i>., <i>Phys. Rev. Materials</i> <b>3</b>, 024601 (2019).<br/>[3] Y. Yamada <i>et al</i>., <i>Phys. Rev. Lett.</i> <b>126</b>, 237401 (2021).<br/>[4] F. Sekiguchi <i>et al</i>., <i>Phys. Rev. Lett.</i> <b>126</b>, 077401 (2021).<br/>[5] Y. Kajino <i>et al</i>., <i>Phys. Rev. Materials</i> <b>6</b>, L043001 (2022).<br/>[6] S. Masada <i>et al</i>., <i>Nano Lett.</i> <b>20</b>, 4022–4028 (2020).<br/>[7] K. Cho <i>et al</i>., <i>Nano Lett.</i> <b>21</b>, 7206–7212 (2021).<br/>[8] K. Cho <i>et al</i>., <i>Nano Lett</i>. <b>22</b>, 7674–7681 (2022).