New Insights into Hot-Charge Relaxation in Lead Halide Perovskite: Dynamical Bandgap Change, Hot-Biexciton Effect, and Photo-Bleaching Shift

Abstract

Harnessing hot-charge relaxation in lead halide perovskites (LHPs) is the key to developing next-generation high-performance concentrator solar cells that break the Shockley–Queisser limit. Though the physical origins of the slow hot-carrier cooling and their interplays have been unveiled, consensus is still lacking concerning the mechanisms of many-body interactions during hot-charge relaxation. Here, we propose a unified theory to explain the spectral and temporal evolution of the band edge in LHPs at the early time-scale following femtosecond laser excitation. We demonstrate that at early times, the hot-biexciton effect imposes a transient bandgap shrinkage decaying rapidly with exciton dissociation. Subsequently, bandgap renormalization (BGR) effect dominates the bandgap change, with a partial compensation by the free-carrier Stark (FCS) effect. Additionally, we confirmed that the shift in the photo-bleaching (PB) peak in the transient absorption (TA) spectra is modulated by carrier temperature rather than the bandgap change, which has negligible influence on the bleaching position, contrary to previous studies. Importantly, this work demonstrates the significant role played by the hot-biexciton interaction to the exciton generation-dissociation and carrier relaxation dynamics in perovskite solar cell materials at early times. Our insights resolve the existing contradictions on the nature of early-time photo-induced absorption and PB shift via reliable quantifications. By unraveling the role of hot-charge cooling and the intricate many-body interactions among the hot-biexciton interplay, BGR and FCS effects, our study contributes to a deeper comprehension of the fundamental photo-physics in LHPs.

Giant Band-Gap Renormalization and Morphology-Tunable Defect-Assisted Carrier Recombination in CsPbBr3 Microstructures

“…At short time scales (before 2 ps), the competition between BGR (causing a red shift) and BM effects (causing a blue shift) yield a red shift of the PB peak (insets of Figure c) . The nonlinear increased red shift with increasing pump fluence shown in the inset of Figure d further demonstrated this competitive relationship because the BM effect would be more dominant for higher pump fluence and thus gradually diminish the influence of the BGR effect . These results were similar to those of CsPbBr 3 microrods (see Supporting Information (3)).…”

Spatial Heterogeneity of Biexcitons in Two-Dimensional Ruddlesden–Popper Lead Iodide Perovskites

“…No spectral evolution was observed within our 10 ps time window. The few picosecond lifetime of the ESA peak in all three n phases confirms the biexciton assignment to this feature as opposed to bandgap renormalization, which would be expected to have a lifetime of <1 ps. − …”

Additive-Stabilized Emission Centers for Blue Perovskite Light-Emitting Diodes

“…EL spectra of devices were recorded by a luminance meter (Konica Minolta, CS-200) and a flame spectrometer (Ocean Optics). The transient absorption (TA) test referred to previous reports …”