Manipulation of hot carrier cooling dynamics in two-dimensional Dion-Jacobson hybrid perovskites via Rashba band splitting

Abstract

Hot-carrier cooling processes of perovskite materials are typically described by a single parabolic band model that includes the effects of carrier-phonon scattering, hot phonon bottleneck, and Auger heating. However, little is known (if anything) about the cooling processes in which the spin-degenerate parabolic band splits into two spin-polarized bands, i.e., the Rashba band splitting effect. Here, we investigated the hot-carrier cooling processes for two slightly different compositions of two-dimensional Dion-Jacobson hybrid perovskites, namely, (3AMP)PbI₄ and (4AMP)PbI₄ (3AMP = 3-(aminomethyl)piperidinium; 4AMP = 4-(aminomethyl)piperidinium), using a combination of ultrafast transient absorption spectroscopy and first-principles calculations. In (4AMP)PbI₄, upon Rashba band splitting, the spin-dependent scattering of hot electrons is responsible for accelerating hot-carrier cooling at longer delays. Importantly, the hot-carrier cooling of (4AMP)PbI₄ can be extended by manipulating the spin state of the hot carriers. Our findings suggest a new approach for prolonging hot-carrier cooling in hybrid perovskites, which is conducive to further improving the performance of hot-carrier-based optoelectronic and spintronic devices.

Fig. 1. Crystal structure, electronic bands, and PL spectra of 2D Dion–Jacobson perovskites.

a, b Crystal structures of 2D Dion–Jacobson perovskites, (3AMP)PbI₄ and (4AMP)PbI₄, together with the chemical structures of the organic cations. c, d Electronic bands and total and projected density of states (PDOS) of (3AMP)PbI₄ and (4AMP)PbI₄ calculated at the DFT HSE06 level with spin-orbit coupling (SOC). Enlarged electronic bands near the valence band maximum and conduction band minimum are shown in the insets. e, f Temperature-dependent PL spectra of the (3AMP)PbI₄ and (4AMP)PbI₄ films, together with the time-resolved PL decays for the emission from the (3AMP)PbI₄ film at 565 nm and the emission from the (4AMP)PbI₄ film measured at 560 nm and room temperature. The solid lines represent fits to a biexponential decay function. Note that the observed spikes in (e) could be due to the presence of film irregularities that lead to small reflections inside the film.

Fig. 2. Hot carrier cooling dynamics of 2D Dion–Jacobson perovskites.

Normalized transient absorption spectra measured at an excitation wavelength of (a, c) 330 nm for the (3AMP)PbI₄ film and (b, d) 316 nm for the (4AMP)PbI₄ film with a pump fluence of 2.0 μJ/cm² and 4.0 μJ/cm². Extracted hot-carrier temperatures as a function of delay time for (e) (3AMP)PbI₄ and (f) (4AMP)PbI₄ at different pump fluences (2.0 μJ/cm² and 4.0 μJ/cm²). The hot carrier temperatures of (PMA)₂PbI₄ and (PEA)₂PbI₄ are shown with gray and purple circles for comparison. The solid lines represent fits to a biexponential decay function.

Fig. 3. Kinetics and intraband relaxation in 2D Dion–Jacobson perovskites.

Normalized transient absorption kinetics (a) probed at a wavelength of 554 nm for the (3AMP)PbI₄ film (excitation at 330 nm) and (b) probed at a wavelength of 518 nm for the (4AMP)PbI₄ film (excitation at 316 nm), with different pump fluences of 0.8 μJ/cm², 2.0 μJ/cm², and 4.0 μJ/cm². The solid lines show best fits to the experimental data with an exponential function. Time evolution of hot electron relaxation (c) starting from CBM + 7 for (3AMP)PbI₄ (excess energy = 1.52 eV) and (d) starting from CBM + 4 for (4AMP)PbI₄ (excess energy = 1.38 eV). Inserts show the electronic energy levels of (3AMP)PbI₄ and (4AMP)PbI₄ at the high-symmetry Γ-point and B-point, respectively, involved in the nonadiabatic molecular dynamics calculations (NAMD). Vibrational modes responsible for the intraband relaxation in (e) (3AMP)PbI₄ and (f) (4AMP)PbI₄ (the vibrational motions of the organic cations are omitted). The DFT and NAMD calculations were performed at the GGA/PBE level with SOC.

Fig. 4. Spin-selective hot carrier relaxation of 2D Dion–Jacobson perovskites.

a Scheme for the optical selection for the circular polarized TA measurements of 2D DJ perovskite films. Right (left) circular polarized light σ⁺ (σ⁻) couples to the electronic transition from the valence bands to high-level conduction bands. Extracted hot-carrier temperature as a function of delay time of (b) (3AMP)PbI₄ and (c) (4AMP)PbI₄ obtained from cocircular (σ⁺σ⁺ and σ⁻σ⁻) and counter circular (σ⁺σ⁻ and σ⁻σ⁺) polarized pump-probe TA spectra. d Time evolution of hot-electron relaxation starting from the two split bands for (3AMP)PbI₄ calculated with consideration of spin-orbit coupling and decoherence effects. e Schematic illustration of the hot-electron relaxation processes in 2D DJ perovskites without and with band splitting and of the spin-flip/precession and scattering processes in (4AMP)PbI₄.