Enhancing the Hot-Phonon Bottleneck Effect in a Metal Halide Perovskite by Terahertz Phonon Excitation

We investigate the impact of phonon excitations on the photoexcited carrier dynamics in a lead-halide perovskite ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$, which hosts unique low-energy phonons that can be directly excited by terahertz pulses. Our time-resolved photoluminescence measurements reveal that strong terahertz excitation prolongs the cooling time of hot carriers, providing direct evidence for the hot-phonon bottleneck effect. In contrast to the previous studies where phonons are treated as a passive heat bath, our results demonstrate that phonon excitation can significantly perturb the carrier relaxation dynamics in halide perovskites through the coupling between transverse- and longitudinal-optical phonons.

Figure 1

THz excitation of phonon modes and time-resolved PL measurement. (a) Schematic diagram of the THz excitation-PL probe experiment. (b) The electric field (upper panel) and intensity (lower panel) of the THz pulse. (c) Power spectrum of the THz pulse (black solid line) and absorption spectrum of the ${\mathrm{MAPbI}}_3$ thin film in the THz frequency range (red dots). The blue dashed curves are fits obtained using a Lorentz model. (d) Spectrally integrated total PL intensity $I_{\mathrm{total}}$ dynamics with and without THz excitation, for a THz-excitation delay time of $t_D=50\mathrm{ps}$. The vertical solid line and arrow indicate the time of the optical excitation and THz excitation, respectively. Dashed line: simulated $I_{\mathrm{total}}$ dynamics for an instantaneous PL quench and recovery time of 15 ps.

Figure 2

Time evolutions of PL spectra and carrier temperature at the THz-excitation delay time of $t_D=50\mathrm{ps}$. (a) PL spectra before (blue) and immediately after the THz excitation (red), i.e., at $t=40$, 55 ps. For each spectrum, the PL counts of the streak data were integrated over a time period of 10 ps. (b) PL spectra at various times, i.e., at $t=0$, 40, 55, and 90 ps normalized to their peak intensities. (c) Carrier temperatures as a function of time with and without THz excitation. (d) $I_{\mathrm{HE}}$ dynamics; PL intensity dynamics in the high (1.8 eV)-photon energy region. To obtain time traces with sufficient intensity, the PL counts were integrated over a spectral width of 0.1 eV.

Figure 3

PL recovery time prolonged by the THz excitation. THz-excitation intensity dependence of (a) $I_{\mathrm{total}}$ dynamics for $t_D=50\mathrm{ps}$ with $E_0=530\mathrm{kV}/\mathrm{cm}$ and (b) the PL recovery time constant, where the dashed line around 6 ps indicates the time resolution of the streak camera.

Figure 4

PL modulation induced by THz excitations at negative delay times. (a) $I_{\mathrm{total}}$ for negative delay times ($t_D=-3$ and $-23\mathrm{ps}$) and without the THz excitation. Each time trace is normalized to the value at $t=70\mathrm{ps}$. The vertical purple solid line and red (blue) arrow indicate the time of the optical excitation and THz excitation at $t_D=-3\mathrm{ps}$ ($-23\mathrm{ps}$), respectively. (b) The corresponding carrier-temperature dynamics. (c) $I_{\mathrm{HE}}$ dynamics; PL intensity dynamics in the high (1.8 eV)-photon energy region. (d) Delay time $t_D$ dependence of $I_{\mathrm{total}}$ reduction at negative delay times. The values were obtained by integrating the data within the time range $t=0–20\mathrm{ps}$. The reduction is measured relative to the data without THz excitation. (e) Phenomenological model of the thermal couplings between the subsystems: photoexcited carriers, LO phonons, TO phonons, and acoustic phonons.