Combining two-photon photoemission and transient absorption spectroscopy to resolve hot carrier cooling in 2D perovskite single crystals: the effect of surface layer

Abstract

We investigate hot carrier (HC) cooling in two-dimensional (2D) perovskite single crystals by applying two complementary ultrafast spectroscopy techniques – transient absorption (TA) and time-resolved two-photon photoemission (TR-2PPE) spectroscopies. TR-2PPE...

Probing the Multiexcitonic Dynamics in CsPbI3 Nanocrystals across the Temperature‐Induced Reversible Phase Transitions

“…The buildup of the GSB signal grows with the decay of PIA1 and carries information about the HC cooling process. [ 48–50 ] Note that the GSB signal takes a longer time to reach the maximum with a lowering temperature (see Figure 4b), indicating a longer HCs relaxation time. Figure 4d–f depict the line shapes of three time components (extracted from the exponential decay‐associated spectral (DAS) through the global fitting analysis on the fs‐TA results) at 78 K ( γ phase), 178 K ( β phase), and 298 K ( α phase), respectively.…”

“…Despite some recognized limitations, it remains a common method for extracting the temperature of the HCs. [48,50,51] The HCs cooling dynamics of the three phases are shown in Figure S16a-c (Supporting Information). Two time constants were extracted by fitting the curves to the bi-exponential function, indicating different cooling stages (Figure S16d, Supporting Information).…”

Carrier Cooling in Lead Halide Perovskites: A Perspective on Hot Carrier Solar Cells

“…Regardless of the signal source and setup configuration, the measurements listed in Figure have been used to understand the HC cooling dynamics in perovskites directly or indirectly. Since analyses of the experimental results and interpretations typically involve approximations and assumptions, combining information from multiple techniques can provide a more complete picture of the HC cooling dynamics in LHPs . The reported time scales of HC cooling cover a broad range depending on the material and the measurement.…”

“…Since analyses of the experimental results and interpretations typically involve approximations and assumptions, combining information from multiple techniques can provide a more complete picture of the HC cooling dynamics in LHPs. 46 The reported time scales of HC cooling cover a broad range depending on the material and the measurement. In Table 1 we summarize the typical times for carrier cooling to 600 K in the perovskite materials under different excitation conditions.…”

“…Even though two-dimensional electronic spectroscopy (2DES) is not free from such difficulties, it allows superb simultaneous time and energy resolution . As a powerful alternative, in time-resolved two-photon photoemission (TR-2PPE) spectroscopy, the system is excited by a short pump pulse and the hot electrons are ionized by a delayed probe pulse. , In this way, the emitted photoelectrons directly map out the energy distribution of hot electrons in the conduction band as a function of delay time, although the energy resolution of the method is currently not very high. Extra caution should be exercised regarding sample degradation, e.g., conduct measurements at low environmental temperatures, especially when mapping the hot electrons with high excitation fluence for a better signal-to-noise ratio.…”