MgO blocking layer induced highly UV responsive TiO2 nanoparticles based self-powered photodetectors

Abstract Self-powered ultraviolet (UV) photodetector (PD) with high responsive performances are highly required. However, most reported work are focused on modifying the interface between semiconductor and electrolyte to improve separation of electrons and hole, but little work has been devoted to the interface between semiconductor and the conductive substrate, where recombinations of electrons and holes occurred, resulting in much photocurrent loss. Therefore, in this work, MgO ultra-thin layer was proposed to serve as a hole blocking layer (HBL) between TiO2 nanoparticles (NPs) layer and the FTO conductive substrate. SEM, EDX and XRD characteristics demonstrate the successful attachment of MgO nanofilm on FTO substrate. By controlling TiCl4 hydrolysis process, two layers of TiO2 NPs including the bottom compact layer and the upper multiple branches layer have grown on MgO nanofilm modified FTO substrate. The self-powered UV PDs are assembled by sandwiching TiO2 NPs with or without MgO between two FTO substrates. The MgO/TiO2 NPs based UV PD exhibits appealing performance with responsivity of 29.97 AW-1, sensitivity of 104 and rising time of 0.02 s, showing 2, 5 and 2 times higher than those of the pure-TiO2 NPs based UV PD, respectively. The obtained high response performances can be ascribed to the MgO HBL. Due to the energy band alignment between MgO and TiO2, photo-generated holes are effectively blocked to avoid their flowing back to FTO substrate to recombine with photoelectrons. While the wide band gap of MgO provides a favorable tunnel for electrons, thus resulting in less photocurrent loss between TiO2 NPs and FTO substrate. Furthermore, MgO/TiO2 NPs based UV PD shows significant UV light selectivity and stability. Consequently, the proposed holes blocking effect of MgO may pave a way to develop UV PDs with high efficiencies.