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, ie, 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) PbI 4 and (4AMP) PbI 4 (3AMP= 3-(aminomethyl) piperidinium; 4AMP= 4-(aminomethyl) piperidinium), using a combination of ultrafast transient absorption spectroscopy and first-principles calculations. In (4AMP) PbI 4, upon Rashba band splitting, the spin-dependent scattering of hot electrons is responsible for accelerating hot-carrier cooling at longer delays …