Multilayer Chlorophyll-Based Unidirectional Bias-Switchable Photodetector with Dual-Mode Operation in Narrowband and Broadband

Photodetectors (PDs) generally operate in either broadband (BB) or narrowband (NB) mode. However, single-mode PDs can no longer meet the diverse and complex demands of contemporary applications. In this study, an NB/BB dual-mode PD is fabricated by sensitizing mesoporous TiO₂ (m-TiO₂) with methyl trans-3²-carboxy-pyropheophorbide-a (H₂Chl-1) and spin-coating films of 13¹-deoxo-13¹-dicyanomethylene-pyropheophorbide-a (H₂Chl-2) and zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (ZnChl). As the external electric field increases from −2 to −3 V, the operating mode of the PD shifts from NB to BB mode. This transition is attributed to the recombination of electrons and holes at the interface between m-TiO₂ and H₂Chl-1, as well as the regulation by the external electric field. The PD demonstrates an NB photoresponse in the near-ultraviolet region, with a full width at half maximum of 45 nm at −2 V. As the bias voltage increases, the PDs transition to a BB photoresponse mode, achieving a responsivity of 8.07 × 10⁴ A W⁻¹ and a specific detectivity of 5.82 × 10¹² Jones at −6 V. NB-PD arrays are constructed for image sensing. BB-PD arrays enable image random encryption and decryption functions by implementing “OR” logic gate. Furthermore, the integration of NB-PD and BB-PD modes enhances the security of information transmission.