Unraveling the Radiative Pathways of Hot Carriers upon Intense Photoexcitation of Lead Halide Perovskite Nanocrystals

Abstract

The slowdown of carrier cooling in lead halide perovskites (LHP) may allow the realization of efficient hot carrier solar cells. Much of the current effort focuses on the understanding of the mechanisms that retard the carrier relaxation, while proof-of-principle demonstrations of hot carrier harvesting have started to emerge. Less attention has been placed on the impact that the energy and momentum relaxation slowdown imparts on the spontaneous and stimulated light-emission process. LHP nanocrystals (NCs) provide an ideal testing ground for such studies as they exhibit bright emission and high optical gain, while the carrier cooling bottleneck is further pronounced compared to their bulk analogues due to confinement. Herein, the luminescent properties of CsPbBr3, FAPbBr3, and FAPbI3 NCs in the strong photoexcitation regime are investigated. In the former two NC systems, amplified spontaneous emission is found to dominate over the radiative recombination at average carrier occupancy per nanocrystal larger than 5–10. On the other hand, under the same photoexcitation conditions in the FAPbI3 NCs, a longer lived population of hot carriers results in a competition between hot luminescence, stimulated emission, and defect recombination. The dynamic interplay between the aforementioned three emissive channels appears to be influenced by various experimental and material parameters that include temperature, material purity, film morphology, and excitation pulse width and wavelength.

Exciton and Carrier Dynamics in Two-Dimensional Perovskites

“…This is not the case, and the reason may lie in the impossibility of hot exciton formation. In fact, we do not observe hot exciton emission in the way that it was observed for nanoplatelets and nanoparticles. , This initial decay may therefore be limited by cooling, which can be lengthened at higher fluences due to phonon bottleneck effects, Auger heating, , and polaron screening. ,, Afterward, a carrier–exciton equilibrium is formed, and the decay dynamics are dominated by exciton recombination. At higher fluences, bimolecular exciton–exciton annihilation becomes increasingly important, shortening the decay of both carriers and excitons.…”

“…In fact, we do not observe hot exciton emission in the way that it was observed for nanoplatelets and nanoparticles. 43,44 This initial decay may therefore be limited by cooling, which can be lengthened at higher fluences due to phonon bottleneck effects, 45 Auger heating, 46,47 and polaron screening. 26,48,49 Afterward, a carrier−exciton equilibrium is formed, and the decay dynamics are dominated by exciton recombination.…”

Spectral Dynamics and Multiphoton Absorption Properties of All-Inorganic Perovskite Nanorods

“…An in-depth understanding of the origin, influencing factors, and lifetime of typical carrier dynamic processes in semiconductors, including radiative and nonradiative transitions, is essential to broaden their relevant applications. − For solar cell applications, we must maximize the hot-carrier cooling time . However, for the manufacture of micro-nanolasers, a large biexciton binding energy, high optical gain, long biexciton lifetime, and short hot-carrier cooling time are preferable. , Although the ultrafast dynamics of cubic NCs has been intensively studied, − less attention has been devoted to the relevant studies on perovskite NRs.…”

Solvent Recrystallization‐Enabled Green Amplified Spontaneous Emissions with an Ultra‐Low Threshold from Pinhole‐Free Perovskite Films

“…This value is the lowest reported threshold for solution-processed perovskite films with green emissions and is comparable to the state-of-art performance of ASEs from CsPbBr 3 nanocrystals (Table 1). [10,18,19,[35][36][37][38][39][40][41][42][43][44][45][46] The net optical modal gain (G) was then studied by using the variable stripe length (VSL) technique. [10] ASE peaks were obtained above the stripe length threshold, resulting in a super-linear rise in the emission intensity (Figure 2d, Figure S6, and Note S1, Supporting Information).…”