Construction of V2O5/SnO2 Nanofiber Heterojunctions and Their Optoelectronic Properties
Objective 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.As a transition metal oxide,V2O5 has a moderate direct bandgap(2.2-2.8 eV),significant optical absorption characteristics in the visible light region,and excellent physical and chemical properties.It is considered a candidate material for excellent optoelectronic devices.Meanwhile,SnO2 is a common n-type semiconductor material with high electron mobility(240 cm2·V-1.s-1),which makes it a good electron transfer material with a low hole electron recombination rate and the ability to generate stable photocurrent.The nanofiber system exhibits sound crystallization,and the construction of specific functional heterojunctions can significantly enhance its performance,leading to its applicability in preparing high-performance optoelectronic detection devices.Therefore,photodetectors based on V2O5/SnO2 nanofiber heterostructures should theoretically have a faster light response speed than single component materials.To further investigate the optoelectronic properties of V2O5/SnO2 nanofiber heterostructures,we employ coaxial electrospinning technology to prepare V2O5/SnO2 nanofiber heterostructures with good crystallinity by adopting different vanadium and tin sources as precursors.Heat annealing treatment is carried out in different atmospheres to construct V2O5/SnO2 nanofiber heterojunctions with various morphology and sizes.By utilizing V2O5/SnO2 nanofiber heterostructures with varying morphology and sizes as a foundation,a high-speed optoelectronic detection device is constructed to assess its responsiveness to visible light in various laser irradiation conditions.We also elucidate the specific physical mechanism behind the rapid response to further expand the potential applications of V2O5/SnO2 nanofiber heterostructures.Methods 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 ℃ 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.Results and Discussions 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.Conclusions 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.
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