Cascade‐EDT Interface in PbS CQD/a‐IGZO Heterojunctions for Ultra‐Fast PbS QD‐Sensitized Phototransistor

High‐sensitivity near‐infrared phototransistors based on PbS quantum dots (QDs) have gained considerable attention for low‐energy optical detection. However, their response speed is often constrained by slow carrier extraction across interfaces that contain dense trap states when integrated with amorphous IGZO. In this work, we construct a Cascade‐EDT Interface (CEI) in which a solid‐state ligand‐treated PbS QDs is positioned beneath a solution‐processed iodide‐capped PbS QD film. This heterojunction interface improves interfacial band alignment and reduces trap‐related carrier loss, as confirmed by photoluminescence and picosecond transient absorption. The refined electronic landscape accelerates carrier transfer into IGZO and reduces the response time from 108 ms to 50 µs while maintaining strong photoconductive gain. The device reaches a detectivity of 2.17 × 10 13 Jones and a responsivity of 75.1 A·W −1 at 1064 nm. The upper QD layer protects the CEI from oxidation, preserving >98% of device initial performance after 720 h in air. The CEI provides an effective route toward fast and stable infrared PbS CQDs/a‐IGZO sensitized Photo‐FETs.