A Vertically Bandgap‐Cascaded Perovskite Single‐Crystal Film Heterojunction for On‐Chip Spectral Imaging

On‐chip spectral imaging is highly attractive for portable sensing, precision inspection, biomedical analysis, and intelligent vision systems, yet it remains challenging to simultaneously achieve fast response and accurate spectral decoding within a compact device architecture. Here, we develop a vertically bandgap‐cascaded perovskite single‐crystal film heterojunction for computational spectral imaging. The monolithic MAPbCl 3 /MAPbBr 3 /MAPbI 3 single‐crystal film heterojunction (∼200 µm), fabricated by sequential solution epitaxy, integrates wavelength‐dependent absorption depth with staircase type‐I band alignment, enabling bias‐polarity‐switchable and depth‐selective carrier collection across the device thickness. This design produces electrically programmable spectral response codes while preserving high quantum efficiency and rapid photoresponse. The device exhibits a maximum external quantum efficiency (EQE) of ∼82%, a rise time as short as 8 µs, a peak‐wavelength accuracy of ∼1.4 nm, a spectral resolution of ∼2.7 nm, and broadband operation spanning ∼400–820 nm. Integration on a thin‐film transistor substrate further enables hyperspectral imaging and accurate spectral/color reconstruction, highlighting vertically engineered perovskite heterojunctions as a promising platform for compact, high‐performance spectral imaging.