Uncovering the Electron‐Phonon Interplay and Dynamical Energy‐Dissipation Mechanisms of Hot Carriers in Hybrid Lead Halide Perovskites

Abstract

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an “S‐shaped” dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions.

Multi-Pulse Terahertz Spectroscopy: Hot Polaron Photoconductivity Dynamics in Metal-Halide Perovskites

“…𝑑𝑛 ℎ𝑙 𝑑𝑡 population density from 400 to 650 fs, as was previously observed and attributed to the hot-phonon bottleneck effect. [21][22][23][25][26][27]43 The observed timescales of both cooling processes are in excellent agreement with Bretschneider et al 58 However, the fact that a ~450 fs local lattice cooling timescale kl is observed in our experiment where polaron formation precedes (and is therefore ruled out from) the observed dynamics may point toward an alternative interpretation of their results. bonds that strongly couple to the carriers.…”

“…[21][22][23] A growing number of works implicate polarons in this aspect of the hot carrier behavior too, owing to the enhanced spatial extent, strong coupling to phonons and sharing of phonon subpopulations inherent to overlapping polarons. [24][25][26][27] The interpretation of the transient optical signals that convey the aforementioned relaxation processes in MHP-based materials must be taken with care, especially when pumping far above the bandgap and at high fluences. These conditions can favor a myriad of processes that obfuscate the intraband relaxation, including, but by no means limited to: interband transitions between distinct electronic/spin states, [28][29][30] exciton formation/dissociation, 13,[31][32][33] energy/charge migration, [34][35][36] bandgap renormalization, 21,37 refractive index changes, 21,38 Stark shifting, 39,40 and many-body (Auger) processes.…”

“…The slowing of the carrier cooling dynamics at higher push fluences (hot carrier densities) can be understood through the framework of the hot-phonon bottleneck mechanism, [21][22][23] where the energy deposited into phonons through cooling is continually re-absorbed by overlapping polarons. [24][25][26][27] Generally, the low-energy THz probe ought to be sensitive to all carriers (cold and hot), regardless of their energy within the electronic band. The push is not capable of interband excitation and therefore does not change the overall concentration of the photoexcited carriers.…”

Properties and challenges of hot-phonon physics in metals: MgB$_2$ and other compounds

“…The presence and an active role of hot phonons is also commonly revealed in the analysis of the time dependence of electronic properties upon nonequilibrium conditions. Given the plethora of ultrafast pump-probe experiments nowadays accessible, the physical properties under investigation can vary in a wide range, from optical probes (transmission [77,84,85,87,150,151], reflectivity [13,89,[110][111][112][152][153][154], absorption [91,[155][156][157][158]) to non-linear optics [86], time-resolved photoelectron spectroscopy [108,132,133,[159][160][161][162], photoluminescence [83,163], time-dependent Raman probes [164], ultrafast diffraction [6,44,109,126,[165][166][167][168][169][170][171].…”

Fingerprints of hot-phonon physics in time-resolved correlated quantum lattice dynamics

“…However, the thermalization process of some materials can be hindered by the so-called phonon bottleneck [2,3,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] that quenches the energy transfer between electron and lattice degrees of freedom. Such a physical phenomenon is usually encountered in semiconductors and semimetals where the pump-driven particle-hole excitations are restricted to few single points (valleys) in the Brillouin zone.…”