LAUSR

Abstract Interfacial modification is an effective strategy to suppress the dark current in photodetectors for performance improvements. Here, solution-processed conjugated polymer electrolyte poly[(9,9-bis(3’-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN), widely used for interface engineering in organic and perovskite solar cells, is introduced to the photovoltaic photodetectors based on α-phase formamidinium lead iodide (α-FAPbI3) perovskite at cathode interfaces. The PFN layer has both positive and negative impacts on the overall device performances. The steady-state device parameters including external quantum efficiency, photoresponsivity, and detectivity are enhanced because the dark current is effectively suppressed due to the hindered hole injection by the PFN layer. However, the incorporation of PFN leads to different transient photocurrent dynamics with a peak after turn-on and a long-lived tail after turn-off, increasing the fall time, although it has little impact on the rise time. The proposed mechanisms involve the trapping and detrapping effects of accumulated photogenerated electrons at the electron-transporting layer/PFN interface, which are proved by capacitance-voltage measurements and impedance spectroscopy analysis. Our results have important significance for understanding the different effects and mechanisms of conjugated polymer electrolytes for interfacial engineering in photodetectors and solar cells and selecting suitable interfacial materials for electrode modification in photodetectors.