Hot carrier relaxation in CsPbBr₃ nanocrystals: electron-hole asymmetry and shape effects

Optimization of the optoelectronic performance of lead halide perovskite (LHP) nanocrystals calls for understanding and manipulation of their hot carrier relaxation processes. In this work, the hot carrier relaxation in a nanocube (NC) and a nanoplate (NPL) of CsPbBr₃ is studied using non-adiabatic molecular dynamics based on first-principles calculations. Strong electron-hole asymmetry in the relaxation processes is observed. Regardless of the nanocrystal shape, the hot hole cooling rate is much faster than that of hot electrons. Moreover, while the hot-hole relaxation is insensitive to the excitation energy, faster relaxation of hot electrons is observed with a lower excitation energy. The origin of the asymmetry is associated with the orbital characters and density of states at the band edges. The hot-hole relaxation is strongly affected by the shape of the nanocrystal. It is faster in the NPL than in the NC. This is attributed to the larger atomic displacements in the NPL due to its higher surface/volume ratio. These results provide theoretical insights for fundamental understanding of excited-state dynamics in LHPs and may help the development of hot-carrier optoelectronic devices.