Our colleague Dino Novko, in collaboration with Ivor Lončarić from Ruđer Bošković Institute and with scientists based in Hong Kong and Guangzhou (China), has published a paper in the prestigious journal Advanced Energy Materials. The authors investigate the role of electron-phonon interactions in ultrafast hot‐carrier cooling processes for several hybrid lead halide perovskites by employing transient absorption spectroscopy and density functional perturbation theory.

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

Christopher C. S. Chan, Kezhou Fan, Han Wang, Zhanfeng Huang, Dino Novko, Keyou Yan, Jianbin Xu, Wallace C. H. Choy, Ivor Lončarić, and Kam Sing Wong, Advanced Energy Materials (2021).

DOI: 10.1002/aenm.202003071

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 functional 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.

Fig. 1 Dominant cooling mechanisms and microscopic physical processes involved at different carrier density in a prototypical hybrid organic–inorganic lead halide perovskite. i.) Isolated large polaron screening effect at low carrier concentration; ii.) large polaron destabilization induced by overlapping effect at medium density, where the Mott nonmetal-metal transition from insulating exciton gas to the metal-like electron-hole plasma takes place; iii.) hot-phonon bottleneck effect pumped at high fluence, where materials show metal-like properties induced by electron-hole plasma. The findings will help shed light on hot‐carrier harvesting in high‐performance photovoltaic applications.