Surface engineering of CsPbBr3 perovskite nanocrystals: hole transfer dynamics and enhanced photocurrent response using a novel organic molecule

Abstract

In the last few years, cesium lead bromide (CsPbBr₃) perovskite nanocrystals (PNCs) have achieved tremendous recognition due to their state-of-the-art photophysical properties. A hybrid combination of perovskite nanocrystals with organic molecules could be a viable option for efficient charge separation at the interface. However, the surface chemistry of PNCs plays a pivotal role, which determines the excited state of these PNCs and interactions with charge shuttle redox-active molecules. Efforts are being made to find suitable organic molecules that can efficiently extract charges from these nanocrystals. But the choices of organic molecules are limited. Herein, we have reported a novel organic hole acceptor, i.e. fluorene derivative 7,7-diethyl-5,7-dihydroindeno[2,1-b]carbazole (SPS-Cbz), and investigated the effect of nanocrystal surface chemistries for surface-bound charge transfer. We evaluated the photoinduced hole transfer (PHT) using the time-resolved PL lifetime decay curves and steady-state PL. We interestingly found that amine-free CsPbBr₃ PNCs have five times higher PHT compared with conventional amine-based CsPbBr₃ PNCs. The hole transfer rate constant (K_ht) is 6.96 × 10⁸ S⁻¹, calculated using lifetime fast component rate constants (τ₁) from the lifetime decay curves, which is three times higher than that of amine-based ligand CsPbBr₃ PNCs. Furthermore, photocurrent density studies were carried out and it was found that amine-free nanocrystals with SPS-Cbz were two times higher than bare amine-free CsPbBr₃ PNCs. This work envisioned a judicious selection of organic acceptors that can make an efficient hybrid combination with perovskite nanocrystals for efficient charge separation, which implies various photonic applications.