Femtosecond Upconversion Study of Interfacial Electron Transfer from Photoexcited CsPbBr₃ Perovskite Nanocrystal to Rhodamine 6G

Abstract

Photoinduced electron transfer (PET) from an excited-state CsPbBr 3 nanocrystal (NC) to rhodamine 6G (r6G) is studied in toluene using different fluorescence-based techniques. Because of weak solubility of r6G in toluene, excess r6G molecules adsorb at NC surface which result in a much slower rotational diffusion time scale of r6G in the presence of NCs. Study of intrinsic PET benefits from the soft molecular interactions leading to donor (NC)acceptor (r6G) complex formation, where solvent diffusion parameters would not play any role in the PET kinetics. Femtosecond transients of NCs are nicely fit to a Poisson expression originally proposed by Tachiya. Conclusive fittings to the temperature dependence quenching data reveal two interesting observations: (1) Even though the average number of surface trap state in a NC does not change with temperature (5−60 °C), the trap-state-induced quenching time scale is accelerated with increase in temperature, pointing toward a more efficient trapping at higher temperature. (ii) In the presence of r6G, a fast (∼150 ps per r6G molecule) interfacial PET time scale is observed, which remains unaffected by temperature (5−60 °C). Our findings demonstrate that even a simple "perovskite NC−electron acceptor" composite like that in the present study can ensure a rapid interfacial charge separation. Such information will help us to realize the actual potential of perovskites NCs in their real applications.

Dodecahedron CsPbBr3 Perovskite Nanocrystals Enable Facile Harvesting of Hot Electrons and Holes

“…FCS can record all the parameters associated with a complexation reaction, provided binding would cause PL fluctuations at a desired time scale (eq ). Association and dissociation of a quencher molecule (NMA/DNT) to the NC surface result in PL fluctuations, and the time scale of complexation reaction (τ R ) in our case was found to be slower than the average diffusion time scale (τ D ) of the NCs traversing the tiny observation volume. ,, NC + normalQ ⇄ K [ NC−Q ] , goodbreak0em1em⁣ K = k + k − k + and k – are the association and dissociation constants of the complexation reaction. , The binding of NC to a quencher (NMA/DNT) drops its PLQY to zero due to an efficient electron/hole transfer. − Since we used mM concentration NMA/DNT, with nM concentration of NCs, the concentration of quencher (NMA/DNT) at any time during the complexation reaction is approximated to its initial concentration, i.e., [Q] ≈ [Q] 0 . Thus, the binding of NMA/DNT with NC is a pseudo-first-order reaction, and the relaxation time of the reaction dynamics (τ R ) is related to the inverse sum of k + + k – (eq ).…”

Synthesis of Cs/Methylammonium/Formamidinium PbBr3 Perovskite Nanocrystals with Green Emissions: Implications for Display Applications

“…2020 standard recommendation highlighting the urgency of ultrapure green (fwhm < 25 nm)-emitting materials for tv display, green LEDs, and related technologies (Table S1). ,− …”

Facet Engineering for Decelerated Carrier Cooling in Polyhedral Perovskite Nanocrystals

“…Inspired by the recent success of facet engineering, we have studied the HC cooling dynamics in 6-, 12-, and 26-faceted polyhedral CsPbBr 3 NCs. Interestingly, our study revealed that 12-faceted dodecahedral NCs (d-CsPbBr 3 ) and 26-faceted rhombicuboctahedral NCs (r-CsPbBr 3 ) are coveted materials characterized by polaron-mediated slower cooling (up to ∼10 times) compared to that of their cubic counterpart (c-CsPbBr 3 ) of similar size. ,− Subsequently, with the help of a molecular system, we successfully harvested HCs before their thermalization, signifying the tremendous implications of surface engineering for device applications. − …”