Deciphering hot and band-edge hole transfer in CsPbBr₃ perovskite nanocrystals using ultrafast spectroscopic...

Perovskite nanomaterials have gained lots of attention in photocatalytic and photovoltaic applications due to their remarkable optoelectronic properties. However, the fundamental understanding of the charge (electron/hole) separation and transfer processes across the surface is key to projecting perovskites as efficient optoelectronic materials. Steady-state, time-resolved photoluminescence (PL) and femtosecond transient absorption spectroscopy (TAS) were used to understand the charge transfer dynamics between CsPbBr₃ perovskite nanocrystals (PNCs) and 2-hydrazinopyridine (HP). Thermodynamic consideration of the relative positions of the energy levels of PNCs and HP suggests that photogenerated hole transfer takes place from excited PNCs to HP. The observation of efficient quenching of the photoluminescence (PL) of the PNCs with appreciable changes in the PL time profile in the presence of HP indicates the dynamic nature of the interaction. The reduced growth time and the accelerated fast-decay component in the transient absorption decay kinetics of CsPbBr₃ PNCs in the presence of HP indicate an ultrafast hole transfer from CsPbBr₃ PNCs to HP. The hot hole and band edge hole transfer rates from PNCs to HP are calculated. The hot hole transfer rate is found to be ∼9 times higher than the band edge hole transfer rate and a 45% hot hole transfer efficiency was obtained upon 360 nm pump excitation in the presence of 15 µM HP. The results show that judicial selection of even a basic molecular system, like HP, can facilitate the quick transfer of photogenerated carriers to make CsPbBr₃ PNCs an efficient photovoltaic material.