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 function 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.

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.