n -Value-Tuned Quasi-2D Perovskites for Wavelength-Selective Optoelectronic Synapses

Neuromorphic vision systems demand optoelectronic synapses that combine wavelength-selective sensing with gradual and linear synaptic weight updates. In two-dimensional (2D) halide perovskites, extending visible-light absorption can be accompanied by accelerating ion migration and premature current saturation. Here, we regulate the phase composition of quasi-two-dimensional (quasi-2D) BA2MA(n–1)PbnI(3n+1) perovskites by tuning the nominal n value. Incorporation of the n = 2 phase extends the absorption edge from 525 nm (green) to approximately 600 nm (red), enabling distinguishable responses under blue, green, and red illumination. The nominal n = 1.2 composition provides sufficient higher-n phase for red-light absorption while suppressing excessive ion migration, yielding highly linear photocurrent weight updates. Using these wavelength-, intensity-, and duration-dependent responses, we construct a light-history regression model that maps accumulated exposure to electrical blue-light-hazard warning and literature-derived phototoxicity thresholds under different color temperatures. This phase-engineering strategy provides a material-level route to integrate spectral selectivity and linear signal integration in neuromorphic vision systems.