AbstractThe ongoing Internet of Things revolution has led to strong demand for low‐cost, ubiquitous light sensing based on easy‐to‐fabricate, self‐powered photodetectors. While solution‐processable lead‐halide perovskites have raised significant hopes in this regard, toxicity concerns have prompted the search for safer, lead‐free perovskite‐inspired materials (PIMs) with similar optoelectronic potential. Antimony‐ and bismuth‐based PIMs are found particularly promising; however, their self‐powered photodetector performance to date has lagged behind the lead‐based counterparts. Aiming to realize the full potential of antimony‐based PIMs, this study examines, for the first time, the impact of their structural dimensionality on their self‐powered photodetection capabilities, with a focus on 2D Cs3Sb2I9−xClx and Rb3Sb2I9 and 0D Cs3Sb2I9. The 2D absorbers deliver cutting‐edge self‐powered photodetector performance, with a more‐than‐tenfold increase in external quantum efficiency (up to 55%), speed of response (>5 kHz), and linear dynamic range (>four orders of magnitude) compared to prior self‐powered A3M2X9 implementations (A+: monovalent cation; M3+: Sb3+/Bi3+; X−: halide anion). Detailed characterization reveals that such a performance boost originates from the superior carrier lifetimes and reduced exciton self‐trapping enabled by the 2D structure. By delivering cutting‐edge performance and mechanistic insight, this study represents an important step in lead‐free perovskite‐inspired optoelectronics toward self‐powered, ubiquitous light sensing.