Performance Optimization of ZnO/TiO2/NPB Heterojunction for Visible-Blind UV Photodetectors via SCAPS-1D Simulation

Abstract

This work presents a detailed numerical optimization of an ITO/ZnO/TiO₂/NPB heterostructure for visible-blind ultraviolet (UV) photodetection. The device incorporates a thin TiO₂ interfacial layer between the inorganic ZnO electron transport layer and the organic NPB hole transport/absorbing layer. We systematically investigate the influence of layer thickness and doping and their corresponding dependency on the essential device performance characteristics in SCAPS-1D simulation tool, which is validated with available experimental data. The best performance of the photodetector occurs with a 110 nm NPB layer thickness among the tested thicknesses and an acceptor concentration of 10¹⁶ cm³ among the tested doping concentrations, yielding a photocurrent density of 0.440 mA cm⁻², a responsivity of 0.070 A W-1, and a QE of 23.47%. Following the 150 nm thickness of ZnO layer and donor concentration of 1020 cm-3, the figures now show increased Jsc to 0.4414 mA cm⁻², QE to 29.5%, and responsivity to 0.088 A W-1. The total device then exhibits a peak responsivity value of 0.088 A W-1 at -5 V bias, peaking near 370 nm and decreasing sharply toward the 410-420 nm cutoff. A key finding is that low NPB doping is important for reducing recombination losses. The optimized structure also has a high UV-to-visible rejection ratio.