Ultrahigh Detectivity From Multi-Interfaces Engineered Near-Infrared Colloidal Quantum Dot Photodetectors

Low noise ( ${i}_{\text {noise}}$ ) and high responsivity ( ${R}$ ) are significant factors for Lead sulfide (PbS) colloidal quantum dots (CQDs) photodetectors implementing high specific detectivity ( ${D}^{\ast} $ ). However, the simultaneous achievement of the above two factors is still challenging due to the complicated roles of interfaces and the difficulties in comprehensive interface modification by individual strategy. Here, we propose a well-designed PbS CQD near-infrared (NIR) photodiode with high performance by multi-interface engineering. First, the well-passivated interface of a photo-active layer is obtained by high-quality n-type CQD inks and gentle ligands cross-linked p-type CQD solid films, which leads to low defect density and thus extremely low device dark current ( $\sim $ 70 nA $\cdot $ cm $^{-{2}}$ ). Second, the construction of LiF and MoO _x carrier-selective layers in the electrode interfaces greatly increases the photogenerated charge carrier extraction efficiency due to the enhanced built-in electric field, which promotes a high ${R}$ to 0.61 $\text{A}\cdot \text{W}^{-{1}}$ at 1100 nm. Both the two modifications enable low ${i}_{\text {noise}}$ and high ${R}$ . Hence the device exhibits an ultrahigh ${D}^{\ast} $ up to $1.42\times 10^{{12}}$ Jones. The further demonstration of high-precision biological health monitoring in both visible and infrared bands by this device illustrates its huge potential in ultra-sensitive broadband optoelectronic applications.