Suppression strategy of interfacial defects: γ-ray-induced nano structural rearrangement of NiOx sol-gel for highly sensitive organic photodetectors

This study investigated the effects of γ-ray treatment on the NiO_x (γ-Fixing NiO_x) interlayer and the consequent impact on the performance of organic photodetectors. γ-Fixing NiO_x sol-gels had reduced particle size distribution (4.26 ± 0.65 nm) and exhibit improved uniformity. The root-mean-square (RMS) roughness analysis revealed that the γ-Fixing sample exhibited 1.12 nm. It was 51.35% higher than that of the Pristine sample but 54.29% lower than that of the conventional Fixing sample. XPS analysis (Figure 3a,b) showed concurrent intensity increases in both oxidation states from pristine to γ-Fixing: Ni₂O₃ (856.5 eV, +0.89%) and NiO (854.0 eV, +1.81%). This resulted in a modified NiO/Ni₂O₃ ratio (1.003→1.013), supported by decreased Ni:O ratios (1:1.81→1:1.40) from EDS analysis (Figure 2 h), enhanced Ni-O bonding (676 cm^-1) in FT-IR spectra (Figure 3 f), and improved oxidation resistance (E_onset,ox: 0.38 V→0.41 V) as shown in cyclic voltammetry data (Figure S1a-c and Table S1). These structural changes enhanced the electrical properties of the NiO_x film, thereby significantly improving the performance of the fabricated organic photodetectors. The γ-ray-treated device exhibited a 99.29% reduction in dark current density to 8.00 × 10⁻¹¹ A/cm², an improved ideality factor of 1.38, and a 30.87% decrease in the defect state energy to 71.2 meV. Furthermore, the external quantum efficiency was >80% in the visible range and shot noise-limited detectivity was 1.00 × 10¹⁴ Jones - an 11.65-fold improvement in relation to that of the untreated sample. These findings demonstrated that γ-ray treatment effectively enhances the properties of the NiO_x interlayer and would promote developing high-performance organic photodetectors.