Ligand engineering enables bifacial PbS all-QD homojunction photodiodes

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.