Ligand Engineering Enables Bifacial PbS All‐QD Homojunction Photodiodes

Abstract Infrared PbS quantum dot (QD) photodiodes play a vital role in various applications, including photovoltaics, light‐emitting diodes, lasers, and photodetectors. Despite their superior potential, high‐performance all‐QD homojunction photodiodes with bifacial structures have yet to be reported. Here, post‐treatment ligand engineering is successfully employed to precisely tune the doping dipoles of PbS QDs, transitioning them from n‐type, through intrinsic, to p‐type. All‐QD homojunction photodiodes solar cells with a n‐i‐p architecture are constructed by integrating three types of PbS QD layers of 1.37 eV bandgaps with controllable doping dipoles, which delivers a power conversion efficiency of 10.0%, among the highest values reported in PbS all‐QD homojunction solar cells so far. Owing to symmetry all‐QD architecture, bifacial PbS all‐QDs photodiodes, using 1.37 eV bandgap PbS QDs as both n‐type and p‐type charge transport layers and 0.90 eV bandgap PbS QDs as intrinsic light absorber layers, achieved an almost ideal bifactor approaching 93% and decent detectivities of 1.63 × 10¹¹ Jones from ITO illumination and 1.86 × 10¹¹ Jones from silver nanowire (Ag NW) illumination at 1370 nm. Therefore, this work provides a facile approach for the design of bifacial all‐QD homojunction photodiodes, broadening their potential applications in advanced QD optoelectronic systems.