Plasmonic Au@Ag-upconversion nanoparticle hybrids for NIR photodetection via an alternating self-assembly method

Abstract

Using lanthanide doped upconversion nanoparticles (UCNPs) as absorbing photoactive materials is a feasible strategy to achieve near-infrared (NIR) photodetectors (PDs). Generally, UCNPs need to be combined with semiconductor materials for constructing UCNP-based PDs (e.g. perovskite, Si, MoS₂, graphene/GaAs); the former act as the photoabsorber, and the latter act as an efficient charge transporter. Herein, we reported UCNP-based PDs, which combine NaYF₄:20%Yb, 2%Er UCNPs with MAPbI₃ to achieve photodetection at 980 nm. In these PDs, the photodetection performance usually depends on the absolute upconversion luminescence (UCL) intensity of UCNPs, as well as the film quality of the electron transport layers. In order to obtain high performance PDs, we used different sizes of UCNPs (50, 100, 150, 220, and 400 nm) and utilized the localized surface plasmon resonance (LSPR) effect of Au@Ag nanorods (NRs) to enhance their UCL intensity. The roughness of the UCNP layers directly affects the film-formation quality of the MAPbI₃ layer, and also influences the performance of devices. Therefore, we employed a three-phase self-assembly method to fabricate large area, flat and dense monolayer Au@Ag nanorods (for short A) and 50, 100, 150, 220, and 400 nm UCNPs (for short B). Subsequently, the hybrids of AB and ABAB structures were prepared using the same strategy. Based on these structures, we prepared B/MAPbI₃ PDs, AB/MAPbI₃ PDs, and ABAB/MAPbI₃ PDs. Although the absolute intensity of UCL increases with increase of the particle size of UCNPs, the photodetection performance of PDs also relies on the quality of the electron transport layers. Finally, we obtained the optimum photodetection performance with the AB (150 nm)/MAPbI₃ structure. The optimized photoresponsivity, detectivity, and external quantum efficiency of Au@Ag NRs/UCNPs (150 nm)/MAPbI₃ PDs are respectively 0.51 A W⁻¹, 6.9 × 10⁹ Jones, and 64.9%. Compared with the PDs prepared by the spin-coating method, the responsivity has improved by two orders.