Hot Carrier Cooling and Biexciton Dynamics of Anisotropic-Shaped CsPbBr3 Perovskite Nanocrystals

Fast hot-carrier (HC) cooling and the Auger recombination (AR) rate in solar absorbers act as a fundamental barrier toward the harvest of improved solar-energy efficiency. The recent emergence of lead halide perovskite (LHP) has shown enormous potential in high-performance solar cells; however, they are primarily limited to isotropic cubic shapes. It is thus essential to assess whether other anisotropic shapes can be utilized for improving the device's functionality. Herein, we have studied HC relaxation and AR rates in hexapod CsPbBr3 NCs using ultrafast transient absorption (TA) spectroscopy. Our results indicate a prolonged HC cooling time and bi-exciton lifetime in a hexapod nanostructure compared to cubic CsPbBr3. In coordination with the HC temperature, we further confirm the slower HC relaxation rate in hexapod CsPbBr3 NCs by employing the electron-phonon coupling model, suggesting a retarded decay of longitudinal optical (LO) phonons. We demonstrate that the delocalization of charge carriers in the shallow trap states leads to a reduced overlap of electron and hole wave functions that is responsible for suppressing the bi-exciton AR rate.

Automated summary

We investigate the fast hot-carrier (HC) relaxation and Auger recombination (AR) rates in hexapod CsPbBr3 NCs using ultrafast transient absorption (TA) spectroscopy. Our results show that hexapod CsPbBr3 has a prolonged HC cooling time and bi-exciton lifetime compared to cubic CsPbBr3. By employing the electron-phonon coupling model, we confirm the slower HC relaxation rate in hexapod CsPbBr3, suggesting a delayed decay of longitudinal optical (LO) phonons. We demonstrate that delocalization of charge carriers in shallow trap states leads to reduced overlap of electron and hole wave functions and suppresses the bi-exciton AR rate.