With the rapid development of society, the demands for portable, lightweight, and large-area-compatible wearable electronic devices continue to grow, which drives photodetectors developing towards low-cost, high-performance, low-power, and large-scale manufacturing. One-dimensional inorganic nanomaterials facilitate the separation of electrons and holes due to their large specific surface area, high aspect ratio, abundant surface trap states, and unique electron confinement effects, thus extending the lifetime of photogenerated charge carriers. Additionally, the linear geometric structure provides sound elasticity to external stresses, making them less prone to cracking after deformation. These characteristics make one-dimensional inorganic nanomaterials an ideal choice for designing and preparing high-performance optoelectronic detection devices. In one-dimensional nanomaterial systems, nanofibers/wires have caught much attention from researchers in flexible display devices, gas sensors, and photodetectors due to their unique electrical and optical properties.

0.7993 g (0.003 mol) of acetylacetone vanadium oxide (C₁₀H₁₄O₅V) is weighed and placed in a small beaker. Then a pipette is leveraged to measure 10 mL N, N-dimethylformamide (DMF), and the solution is dropped into a small beaker. Next, the beaker is sealed with aluminum foil and is placed in a heating magnetic stirrer of collector type constant temperature, with the temperature controlled at 75 ℃. Meanwhile, heating is conducted for 10 min to ensure complete dissolution. Subsequently, 1.1500 g polyacrylonitrile (10% PAN) is added to the dissolved C₁₀H₁₄O₅V solution, placed in a heating magnetic stirrer of collector type constant temperature, and heated and stirred at 75 ℃ for 2.5 h to obtain a PAN+C₁₀H₁₄O₅V shell solution with a certain viscosity. Later, 1.0607 g (0.003 mol) pentahydrate tin tetrachloride (SnCl₄·5H₂O) is weighed and placed in a small beaker. A pipette is adopted to measure 10 mL DMF, the solution is dropped into a small beaker, and then the beaker is sealed with aluminum foil and placed in a heating magnetic stirrer of collector type constant temperature. The temperature is controlled at 55 °C and heating is carried out for 10 min to ensure complete dissolution. 1.1730 g polyacrylonitrile (10% PAN) is added to the dissolved SnCl₄·5H₂O solution, placed in a heating magnetic stirrer of collector type constant temperature, and heated at 75 ℃ for 2.5 h to obtain a uniform PAN+ SnCl₄·5H₂O core solution. This experiment employs the MSK-NFES-1U electrospinning machine of Hefei Kejing Materials Technology Co., Ltd., with a 22G+17G coaxial stainless steel electrospinning needle, to spin (PAN+C₁₀H₁₄O₅V)/(PAN+SnCl₄·5H₂O) coaxial nanofibers. Additionally, the two prepared solutions are injected into two syringes, with the shell solution connected to the outer tube of the coaxial needle and the core solution injected into the inner tube of the coaxial needle. The flow rates of the inner spinning solution and the outer spinning solution are adjusted to 0.5 mL/h and 0.8 mL/h respectively. By adopting the conditions including a voltage of 15.06 kV, a collection speed of 200.00 r/min, a moving speed of 5 mm/s, and a receiving distance of 20 cm, we successfully spin coaxial nanofibers composed of (PAN+acetophenoxy vanadium)/(PAN+stannic chloride pentahydrate). The spun original composite fibers are placed in an electric blast drying oven and dried at 90 ℃ for 8 h. Then the dried fibers are divided into two parts and placed separately in a high-temperature tubular sintering furnace. One part is annealed in an air atmosphere, and the other is annealed in an argon atmosphere. Both are kept at constant temperature for 1 h at 500 ℃, which leads to two V₂O₅/SnO₂ nanofiber heterojunctions that are thermally annealed in different atmospheres.

At room temperature, the photocurrent of V₂O₅/SnO₂ nanofiber heterojunction devices is significantly enhanced under the presence of laser irradiation. Under the ultraviolet light irradiation with a wavelength of 405 nm and a power of 48 mW at a voltage of 2.0 V, the heterojunction exhibits 1.28 μA photocurrent, significantly higher than the dark current 0.96 μA at the same bias voltage [Fig. 7(a)]. In the same conditions, the photocurrent and dark current of pure V₂O₅ nanofiber devices are 0.43 μA and 0.41 μA respectively, with a difference of 0.02 μA between the photocurrent and dark current, which indicates there is no significant change between them [Fig. 7(b)]. Figure 8 shows the I-V curves of two types of photodetectors under different laser irradiation powers, with linear relations between photocurrent and bias voltage under different laser irradiation powers. As the power density of laser irradiation increases, the device photocurrent rapidly increases. In the same laser irradiation conditions, the photocurrent of V₂O₅/SnO₂ nanofiber heterojunction photodetector is significantly higher than that of V₂O₅ nanofiber photodetector. With the periodic opening and closing of laser irradiation, the device photocurrent exhibits good repeatability corresponding to the periodic light illumination changes. During the observation period, there is almost no photocurrent attenuation, which demonstrates sound stability and photoelectric switching performance (Fig. 9). Under laser irradiation with a bias voltage of 3.0 V, a wavelength of 405 nm, and a power density of 123 mW, the optical switching ratio of the V₂O₅/SnO₂ nanofiber heterojunction photodetector is 1.9, the responsivity is 3.97 A/W, and the specific detectivity is 2.2×10⁷ Jones [Fig. 9(a)]. Under laser irradiation with a bias voltage of 3.0 V, wavelength of 405 nm, and laser power of 123 mW, the response time and decay time of the V₂O₅/SnO₂ nanofiber heterojunction photodetector are 0.556 s, while those of the V₂O₅ nanofiber photodetector are 1.39 s and 2.78 s respectively (Fig. 10). Obviously, after the combination of V₂O₅ and SnO₂, the photocurrent response time and decay time are significantly improved.

We successfully prepare a V₂O₅/SnO₂ nanofiber heterostructure using coaxial electrospinning technology. Based on this heterostructure, we design a photodetector and study the photoresponse performance of the V₂O₅/SnO₂ nanofiber heterostructure photodetector in different lighting conditions. The experimental results show that under the modulation of a periodic laser with a bias voltage of 3.0 V, the V₂O₅/SnO₂ nanofiber heterojunction photodetector exhibits fast optical response, with a response and decay time of 0.566 s, a responsivity of 3.97 A/W, and a specific detectivity of 2.2×10⁷ Jones. Meanwhile, the photodetector exhibits sound photoelectric detection performance at room temperature. The excellent performance is attributed to rapid and effective photo-generated exciton dissociation at the oxide heterojunction interface with type Ⅱ band alignment. Finally, our research can provide new ideas for the applications of oxide heterostructures in optoelectronic devices.