Ionic Density‐Controlled Conjugated Polyelectrolytes for Interface Engineering in Inverted Colloidal PbS Quantum‐Dots Infrared Photodetector

Abstract PbS colloidal quantum dots (CQDs) have attracted significant attention as next‐generation infrared absorbers, offering a cost‐effective alternative to conventional III–V compound semiconductors. Despite extensive efforts devoted to enhancing electron extraction, strategies for improving hole extraction at the metal‐oxide/PbS CQD interface, particularly in inverted architectures, remain limited. Here, an effective interface engineering approach is reported using conjugated polyelectrolytes (CPEs) bearing ionic sidechains at the indium‐tin oxide (ITO)/PbS CQD interface. By systematically increasing the ionic density within the CPEs, dark current and enhance photocurrent is simultaneously reduced, resulting in high near‐infrared detectivity of 5.4 × 10 12 Jones at 900 nm. These enhancements are attributed to favorable dipole orientation of the CPE at the interface, facilitating efficient hole extraction. Additionally, Br − ion functionalities in CPE sidechains provide effective surface passivation of PbS CQDs, increasing the device's built‐in potential. This work highlights the importance of tailored CPE interlayers in achieving high‐performance inverted PbS CQD photodiodes.