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

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 × 10¹² 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.