Colloidally Stable P-Type Quantum Dot Ink with an Atomic Layer Deposition Interlayer for High-Detectivity Photodetectors.

Solution-processed quantum dot (QD) photodetectors commonly rely on solid-state ligand exchange (SSLE) for the fabrication of conductive films; however, severe volume shrinkage, which induces stress throughout the QD film and generates structural defects and trap states, causes a high dark current and limited detectivity. Herein, we report a solution-processable conductive p-type PbS QD ink fabricated via solution-phase ligand exchange using 3-mercapto-1-propanol (MPOH), effectively overcoming the intrinsic limitations of SSLE. Introducing MPOH ligands results in a colloidally stable p-type QD ink that can be well-dispersed in polar solvents, enabling the formation of dense and smooth hole transport layers (HTLs) via a single coating step. QD films fabricated using the p-type ink exhibit substantially reduced surface roughness and trap density, resulting in a pronounced suppression of the dark current density in the photodetectors. Moreover, the damage-free integration of the p-type ink onto halide-passivated n-type PbS active layers is achieved by introducing an ultrathin MgO interlayer deposited using atomic layer deposition, which prevents solvent-induced interfacial degradation without compromising infrared transmission. Subsequently, a device architecture is developed by effectively increasing the HTL thickness using a p-type PbS ink, resulting in a significantly reduced dark current density and nearly 10-fold enhancement in the detectivity.