High Performance ZnO CQDs/MoSe₂ Heterojunction UV-Visible Broadband Photodetector

Abstract

This letter reports an ITO/n-ZnO CQDs/n-MoSe2/Ag structure based ultraviolet-visible (UV-Vis) broadband photodetector where the n-n heterojunction between ZnO colloidal quantum dots (CQDs) and MoSe2 thin film fabricated on an Indium tin oxide (ITO) coated glass substrate forms the active region of the device. The ZnO CQDs synthesized by hot-injection method was spin-coated on the substrate while MoSe2 nano-powder synthesized by hydrothermal method was deposited on the ZnO CQDs layer by thermal evaporation method to obtain the ZnO CQDs/MoSe2 heterojunction. The heterojunction showed a broad absorption spectrum covering the UV-Vis region. Under applied bias voltage of 2 V, the proposed photodetector showed the maximum responsivity (R) of ~282 A/W, detectivity (D) of $\sim 9\times 10 ^{12}$ Jones and external quantum efficiency (EQE) of ~90000% at 380 nm (with $47~\mu $ W/cm2 intensity) in the UV region whereas R ~16.15 A/W, D $\sim ~5.37\times 10 ^{11}$ Jones, EQE ~3660% were measured at 550 nm (with 0.22 mW/cm2 intensity) in the visible region. The transient response analysis of the device showed a rise time (fall time) as 7.25 sec (2.25 sec) at 380 nm and 1.2 sec (2.2 sec) at 550 nm.