Precisely Controlled Gradient-Bandgap Perovskite Photodiode Arrays Facilitate Accurate Reconstruction of Complex Spectra for Color Decryption Applications

Gradient bandgap perovskite photodetector arrays are a promising platform to achieve on-chip compact spectrometers, while the reported spectral resolutions are limited without a strategy to precisely control the bandgap distribution. Moreover, the effect of different photosensing structures, such as photoconductor (PC) and photodiode (PD), on the quality of spectral reconstruction is rarely discussed. In this work, we use a nonuniform stepwise ion-exchange method to generate generally distributed gradient-bandgap perovskite films and provide an accurate numerical fitting between ion-exchange time and bandgap. We further compare the PD/PC arrays and reveal that the photosensing linear dynamic range (LDR) strongly affects the accuracy of spectral reconstruction, especially for complex multipeak light sources. Benefiting from the PD arrays with precisely controlled gradient bandgap, we achieve 5 nm resolution in spectral reconstruction with only a 12-device array. In addition, an innovative application of color encryption and decryption based on this compact spectrometer is demonstrated, showing an excellent ability to discern subtle color variations in complex spectra.