Ultrafast carrier thermalization in lead iodide perovskite probed with two-dimensional electronic spectroscopy

Abstract

In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid perovskites, the cooling of such thermal carrier distributions occurs on timescales of about 300 fs via carrier-phonon scattering. However, the initial build-up of the thermal distribution proved difficult to resolve with pump–probe techniques due to the requirement of high resolution, both in time and pump energy. Here, we use two-dimensional electronic spectroscopy with sub-10 fs resolution to directly observe the carrier interactions that lead to a thermal carrier distribution. We find that thermalization occurs dominantly via carrier-carrier scattering under the investigated fluences and report the dependence of carrier scattering rates on excess energy and carrier density. We extract characteristic carrier thermalization times from below 10 to 85 fs. These values allow for mobilities of 500 cm2 V−1 s−1 at carrier densities lower than 2 × 1019 cm−3 and limit the time for carrier extraction in hot carrier solar cells.

Slow Hot‐Carrier Cooling in Halide Perovskites: Prospects for Hot‐Carrier Solar Cells

“…Lastly, the cooled carriers will recombine (usually in nanosecond timescale -process 6). [22,[28][29][30][31][37][38][39][40][41][42][43][44][45] These studies include the 3) carrier-optical phonon interactions; 4) decay of optical phonons into acoustic phonons; 5) further phonon emission to thermal equilibrium; (6) onset of carrier recombination. Next, we trace the milestones of slow HC cooling phenomena in halide perovskites.…”

“…Attempts to leverage the hot phonon bottleneck effect observed in InN for photovoltaics have been unsuccessful due to various reasons such as challenging fabrication processes, poor material quality, and low abundance of In, etc. [22,[26][27][28][29][30][31] We shall next review the dynamics of HC cooling in semiconductors, followed by a discussion on the findings of slow HC cooling dynamics in halide perovskites; and subsequently a review of its origins and mechanisms. [22,[26][27][28][29][30][31] We shall next review the dynamics of HC cooling in semiconductors, followed by a discussion on the findings of slow HC cooling dynamics in halide perovskites; and subsequently a review of its origins and mechanisms.…”

“…Figure 2 shows the basic photophysical processes of HC cooling in semiconductors and a schematic evolution of the electron and hole distributions with time following above bandgap pulsed laser excitation. [28] Following carrier thermalization, the thermalized HCs will start to equilibrate with the lattice mainly through inelastic carrierphonon interactions. The energetic carriers will first thermalize among themselves through carrier-carrier interactions and scattering.…”

Direct Observation of Charge Injection From CH3NH3PbI3−xClx to Organic Semiconductors Monitored With sub‐ps Transient Absorption Spectroscopy

“…The knowledge of injection times can be a key factor in further improving perovskite solar cells due to the reduced probability of charge carrier recombination inside the perovskite layer in case of ultrafast injection . The method of ultrafast pump probe TAS has been used extensively in hybrid perovskite research during the last years leading to a better understanding of the general charge dynamics after photoexcitation, charge carrier cooling, population of trap states, and recombination dynamics . Ultrafast electron injection from the perovskite into inorganic n‐TiO 2 , and hole injection into the p‐type organic hole conductor spiro‐OMeTAD was reported earlier.…”

Carrier-Specific Femtosecond XUV Transient Absorption of PbI2 Reveals Ultrafast Nonradiative Recombination

“…Carriers (electrons and holes) were assumed to have reached a thermal distribution from electron-electron and hole-hole interactions within our instrument response (95 fs). 7 Thus, a Fermi distribution with carrier temperature T c and quasi-Fermi levels of E q fe and E q fh was used to represent the band-filling (hole burning). With our experimental broadening (Voigt with Gaussian FWHM of 0.4 eV and Lorentzian FWHM of 0.5 eV), the impact of T c will be difficult to observe so modeling was done using 300K.…”