Unveiling the electronic band structure and temporal dynamics of excited carriers in formamidinium lead bromide perovskite

In this study, the electronic band structure and the dynamics of the excited carriers in the formamidinium lead bromide (FAPbBr3) perovskite are investigated by combining the information obtained from steady-state absorption, photoluminescence, femtosecond transient absorption spectroscopy, photoelectron spectroscopy, and density functional theory calculations. A detailed description of the electronic transitions in the UV-vis energy range has been provided, giving an estimation of the exciton binding energy (40 +/- 5 meV), the transition energy from the first valence band (VB1) to the conduction band (CB1) (electronic bandgap at 2.37 +/- 0.01 eV) and assigning the broad peak at approximate to 3.4 eV to the transition from the second innermost valence band (VB2) to CB1. The temporal dynamics of the excited carriers involved in these transitions are investigated using different excitation energies and carrier densities. Different trends are observed in the dynamics of the transient signals associated with the VB1 -> CB1 (PB1) and VB2 -> CB1 (PB2) transitions. As the carrier density increased, PB1 exhibited a slowing down of its rise time, while PB2 showed an acceleration attributed to the thermalization of the excited holes in VB2. These valuable findings have the potential to unlock new strategies aimed at maximizing the efficiencies and performance of perovskite-based solar cell devices.With the use of a synergic and multiscale approach that brings together experiments and theory, a detailed insight into the electronic structure of FAPbBr3 along with the description of the ultrafast dynamics of photoexcited carriers is provided. The multiscale methodology allows the exploration of novel strategies for the design of perovskite-based solar cells.image