Graphene-Coated Substrate-Mediated Photoresponse from MoS₂/UCNP Nanohybrid-Based Photodetectors

Hybrids of two-dimensional (2D) and 0D nanomaterials offer a wider spectrum of properties than their counterparts. Here, we choose a molybdenum disulfide and NaGdF₄:Yb³⁺, Er³⁺upconversion nanoparticle (MoS₂-UCNP) nanocomposite (NC) on graphene (G)-coated polydimethylsiloxane (PDMS) and silica/silicon (SiO₂/Si) substrates as broadband photodetectors (PDs). The band gap (∼680 nm) limited response of pure MoS₂is broadened by the infrared (980 nm) absorbing UCNPs. Identically fabricated PDs on PDMS and SiO₂/Si showed the highest photoresponsivity of 26.18 and 84.52 AW^-1, respectively, under 661 nm laser illumination at a density of 1 mW/cm²at 1 V bias. The MoS₂-UCNPs/Graphene/SiO₂/Si PD (SiO₂/Si PD) showed a response time of ∼100 ms compared to ∼3 s for the PDMS-based PD. The PDMS-based PD showed a reasonably stable photocurrent, decaying by ∼39%, under 250 repetitive cycles of 6.25% bending strain; a maximum decrease of ∼40% of the photocurrent was observed under the 11.11% bending strain compared to the as-prepared flat PD. Both devices could detect signals from domestic appliances such as air conditioner remotes, laser pointers, and cellphone flashlights. The flexible PD based on a hybrid of two nanomaterials having complementary ranges of absorption offers the possibility for better wearable sensors.