Charge Transfer Dynamics at the Interface of CsPbX₃ Perovskite Nanocrystal‐Acceptor Complexes: A Femtosecond Transient Absorption Spectroscopy Study

Abstract

CsPbX 3 (X = I -, Br -, Cl -) perovskite nanocrystals (PeNCs) are being explored extensively due to their impressive optoelectronic and photonic properties. Efficient harvest of photogenerated charge carriers from the particle is essential for photon-to-current conversion and enhancement of the performance of PeNC-based photovoltaic and optoelectronic applications. Since photoinduced charge transfer (CT) from the particle usually occurs on sub-picosecond to nanosecond timescales, time-resolved transient absorption (TA) spectroscopy is a powerful technique to investigate this transient dynamic photoinduced process. Herein reported investigations are reviewed, primarily employing femtosecond TA spectroscopy, of the CT process in CsPbX 3 PeNCs. Based on the interpretation of TA spectral features and the basic model of CT dynamics, the concerns of CT rates or efficiency characterization in TA measurements, including multiple CT pathway effects, surface ligand effects, and hot charge carrier extraction are addressed. An elucidation of plasmon-induced hot electron transfer is also provided in CsPbX 3 PeNC-noble metal heterostructures for their promising potential to contribute the development of CsPbX 3 PeNC-based hot carrier devices. It is hoped that this review can provide deeper insights into the photovoltaic conversion in order to make the most of the CT process in CsPbX 3 PeNCs.

Electron Trapping Prolongs the Lifetime of Charge-Separated States in 2D Perovskite Nanoplatelet-Hole Acceptor Complexes

“…One possible reason is the defect tolerance, especially in bromide- and iodide-based cuboidal perovskite NCs, where the defect-induced trap states locate within the conduction band (CB) and VB or near the band edges, ,− resulting in negligible changes to the electron–hole wave function overlap in the excited state. On the other hand, 2D perovskite NPLs and chloride-based cuboidal perovskite QDs may suffer from in-gap deep traps, as suggested by their low PLQY and the necessity of postsynthesis surface passivation for their blue light-emitting applications. ,,− Although charge transfer from perovskite NCs has been studied because of its importance in photovoltaics and photocatalysis applications, − how the trap states in these NCs affect the charge extraction performance remains unexplored.…”

Femtosecond transient absorption spectroscopy investigation into the electron transfer mechanism in photocatalysis

“…3(d)), which is known as simulated emission (SE). 48 In conclusion, three different DA signals can be distinguished in fs-TAS measurements, which are ascribed to the electron transition and relaxation in semiconductors (Fig. 3(e)).…”

Tailoring Interlayer Charge Transfer Dynamics in 2D Perovskites with Electroactive Spacer Molecules

“…Although it might be expected that CT would result in a faster decay of β due to the reduction of bleaching carriers, as the CT process is ultrafast (i.e., sub-ps), β does in fact not decay faster in (Cz-C 4 ) 2 PbI 4 on a ps timescale. On the contrary, we observe a significantly longer carrier lifetime (Cz-C 4 ) 2 PbI 4 (τ = 1.0 ns) compared to (PEA) 2 PbI 4 (τ = 74 ps) as indicated by the mono-exponential fits . To more accurately capture the excited state decay in (Cz-C 4 ) 2 PbI 4 , we also perform nanosecond TA spectroscopy (Figure d), revealing time constants (relative amplitudes) of τ 1 = 3 ns (90%) and τ 2 = 191 ns (10%) for the decay of β through biexponential fitting.…”

“…On the contrary, we observe a significantly longer carrier lifetime (Cz-C 4 ) 2 PbI 4 (τ = 1.0 ns) compared to (PEA) 2 PbI 4 (τ = 74 ps) as indicated by the mono-exponential fits. 82 To more accurately capture the excited state decay in (Cz-C 4 ) 2 PbI 4 , we also perform nanosecond TA spectroscopy ( Figure 3 d), revealing time constants (relative amplitudes) of τ 1 = 3 ns (90%) and τ 2 = 191 ns (10%) for the decay of β through biexponential fitting. This decay represents both the population of PbI 4 2– localized excitons, as well as, depending on the quantum yield of the CT process (vide infra), a certain population of excitons formerly localized on the PbI 4 2– layer that has been converted into a combination of Cz localized holes, which induces the absorption at 800 nm, and PbI 4 2– localized electrons.…”