Ultraviolet photodetector based on PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction and preparation method thereof

Abstract

A UV photodetector based on a PVK / WO3 organic-inorganic heterojunction and its preparation method relate to an organic-inorganic hybrid photodetector, specifically a UV photodetector with a vertical ITO / PEDOT:PSS / PVK / WO3 / Al structure fabricated at low temperatures (≤150°C). The photodetector comprises, from bottom to top, a glass substrate, an ITO electrode layer, a PEDOT:PSS hole transport layer, a PVK thin film layer, a WO3 thin film layer, and an Al electrode layer. The detector preparation method includes the initial preparation of a WO3 thin film, the spin coating of PVK and PEDOT:PSS thin films, and the subsequent design and control of the device structure. The detector exhibits good selectivity for UV light and excellent device performance.

Description

Technical Field

[0001] The present invention relates to an organic-inorganic hybrid photoelectric detector, in particular to an ultraviolet photoelectric detector with an ITO / PEDOT:PSS / PVK / WO3 / Al vertical structure. Background Art

[0002] A variety of wide-bandgap metal oxide semiconductors (WBGs), such as ZnO, Ga2O3, NiO, TiO2, SnO2, and WO3, have been studied in photodetection technology to construct UV photodetectors with diverse structures. In recent years, WO3, originally used as a photocatalytic and electrochromic material, has attracted attention for its excellent optical, electrical, and nonstoichiometric properties, particularly due to the presence of numerous oxygen vacancies in its lattice. Currently, the fabrication of most oxide-based inorganic devices relies on expensive high-vacuum and high-temperature equipment operating at temperatures of 400-1400°C, which limits the large-scale production of such photodetectors. Organic-based devices, on the other hand, offer advantages such as simple fabrication, low cost, low temperature, and ease of large-area deposition. Therefore, hybrid devices based on organic-inorganic heterojunctions, such as ZnO / PVK, Ga2O3 / PEDOT:PSS, TiO2 / PANI, TiO2 / mCP, and NiO / PVK / ZnO, not only complement these shortcomings but also have the potential for industrialization. Among them, PVK is the preferred organic polymer in the field of UV detection because of its commercial availability and wide band gap (~3.6 eV), and its compatibility with various auxiliary material types as a hole layer. In addition, PEDOT:PSS is a high molecular weight polymer that usually exists in the form of aqueous solution and has high conductivity (~1.7 cm 2 V - 1 S -1 ) and tunable conductivity. Therefore, PEDOT:PSS is often used as a hole transport layer in the design and integration of organic optoelectronic devices.

[0003] Although the properties of the above materials have been reported, there is no documented technology for forming an organic-inorganic hybrid heterojunction of WO3, PVK and PEDOT:PSS to prepare ultraviolet photodetectors. Summary of the Invention

[0004] This paper proposes a low-temperature UV photodetector with an ITO / PEDOT:PSS / PVK / WO3 / Al vertical structure and its fabrication method. By using a two-step spin-coating-sputtering method to sequentially deposit the PEDOT:PSS, PVK, and WO3 thin film layers on an ITO-coated glass substrate, the device achieves high performance while maintaining low-temperature performance.

[0005] The ultraviolet photodetector based on the PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction is characterized in that the detector comprises, from bottom to top, a glass substrate, an ITO electrode layer, a PEDOT:PSS hole transport layer, a PVK thin film layer, a WO3 thin film layer, and an Al electrode layer;

[0006] The thickness of the PEDOT:PSS hole transport layer is 43 nm;

[0007] The thickness of the PVK thin film layer is 65 nm;

[0008] The thickness of the WO3 thin film layer is 120 nm.

[0009] The method for preparing the ultraviolet photodetector based on the PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction comprises the following steps:

[0010] Step 1, substrate cleaning: the ITO-coated glass substrate is wet cleaned in a mixed solution of ammonia, hydrogen peroxide and deionized water;

[0011] Step 2, spin coating of a PEDOT:PSS hole transport layer: an ultrasonically homogenized PEDOT:PSS aqueous solution was spin-coated on a cleaned ITO substrate and then dried to a thickness of 43 nm;

[0012] Step 3, spin coating PVK thin film layer: the pre-formulated PVK solution is prepared on the PEDOT:PSS hole transport layer by spin coating, and then dried to a thickness of 65 nm;

[0013] Step 4, sputtering WO3 thin film layer: depositing WO3 on the PVK thin film layer by radio frequency magnetron sputtering with a thickness of 120 nm;

[0014] Step 5, evaporating Al electrode layer: evaporating metal Al on the surface of WO3 film.

[0015] This invention fabricates a UV photodetector based on a PEDOT:PSS / PVK / WO3 organic-inorganic hybrid heterojunction on an ITO-coated glass substrate using a two-step spin-coating-sputtering method. The three thin film layers of PEDOT:PSS, PVK, and WO3 are sequentially deposited at temperatures below 150°C. The resulting device exhibits high performance, such as a high on / off ratio, high response rate, and high detectivity, while maintaining low-temperature fabrication. The device is also simple to fabricate, low-cost, and easily deposited over large areas, suggesting potential for the development of UV focal plane imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the structure of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device.

[0017] Figure 2 This is the current-voltage test result of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device.

[0018] Figure 3 This is the current-time test result diagram of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device.

[0019] Figure 4 This is a graph showing the relationship between the response rate of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device and the bias voltage.

[0020] Figure 5 This is a graph showing the relationship between the detection rate of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device and the bias voltage.

[0021] Figure 6 This is a performance comparison chart of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device and other ultraviolet photodetectors. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below through specific embodiments, but this should not be construed as limiting the scope of the present invention to the following examples. Various substitutions or modifications made according to common technical knowledge and customary means in the art without departing from the above-mentioned method concept of the present invention are intended to be included within the scope of the present invention.

[0023] Example 1: An organic-inorganic hybrid ultraviolet photodetector based on a PEDOT:PSS / PVK / WO3 vertical structure, comprising, from bottom to top, a glass substrate 1, an ITO electrode layer 2, a PEDOT:PSS hole transport layer 3, a PVK thin film layer 4, a WO3 thin film layer 5, and an Al electrode layer 6.

[0024] The preparation method of the ultraviolet photodetector based on the PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction includes the following steps:

[0025] Step 1, substrate cleaning: The ITO-coated glass substrate is wet-cleaned in a mixed solution of ammonia, hydrogen peroxide, and deionized water. The solution is heated to 80°C and maintained for 30-50 minutes. The substrate is then repeatedly rinsed with deionized water and blown dry with a nitrogen spray gun for later use.

[0026] Step 2, spin coating of a PEDOT:PSS hole transport layer: an ultrasonically homogenized PEDOT:PSS aqueous solution was spin coated on a cleaned ITO substrate at 3000 rpm and then dried at 120°C to a thickness of 43 nm.

[0027] Step 3, spin coating of PVK thin film: a pre-prepared PVK solution with a concentration of 5-20 mg / mL was spin-coated on the PEDOT:PSS hole transport layer at a speed of 2500 rpm, and then dried at 60 °C to a thickness of 65 nm;

[0028] Step 4: Sputtering WO3 thin film layer: WO3 is deposited on the PVK thin film layer by radio frequency magnetron sputtering. The vacuum degree of the equipment is pumped to 6.9×10 -4 Pa below, the sputtering pressure is 3 Pa, the sputtering power is 100 W, the sputtering time is 22 min, and the thickness is 120 nm;

[0029] Step 5, evaporation of Al electrode layer: Prepare Al electrode on the surface of WO3 film by vacuum evaporation method, using a mask for shielding during the process. ITO and Al serve as bottom and top electrodes respectively for testing.

[0030] like Figure 2 This is the current-voltage test result of the PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device prepared in Example 1. When the device is irradiated with 365 nm ultraviolet light, the reverse current increases sharply compared to the dark condition. The light-to-dark current ratio at a bias voltage of -2 V is about 10 2 , the light-to-dark current ratio at -1 V bias is about 10 3 .

[0031] Figure 3 This graph shows the current-time test results for the PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device prepared in Example 1. During device testing, the applied bias voltage was 0 V and the frequency was 0.1 Hz. When the light source was turned on or off, the current rapidly increased or decreased to varying degrees, demonstrating good repeatability and self-powered characteristics, enabling the device to operate in an unpowered environment.

[0032] Figure 4 The following is a graph showing the relationship between the responsivity of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device and the bias voltage. Under negative bias, the responsivity increases with increasing voltage, and the responsivity value increases with higher optical power density. When the voltage is -1.96 V, the responsivity reaches a maximum of ~12.4 AW -1 .

[0033] Figure 5 The relationship between the detectivity of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device and the bias voltage is shown in the figure. The detectivity value under negative bias is significantly higher than that under positive bias. When the voltage is -0.6 V, the detectivity reaches a maximum value of ~1.8×10 13 cmHz 1 / 2 W -1 , its average value remains at 10 12 Magnitude.

[0034] Figure 6 This figure compares the performance of the prepared PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction device with other tungsten oxide-based and other classic oxide-based UV photodetectors. The horizontal axis represents the responsivity, and the vertical axis represents the detectivity. The comparison results demonstrate that the device of the present invention exhibits both high responsivity and detectivity, outperforming the vast majority of similar UV photodetectors.

[0035] The high performance of the PEDOT:PSS / PVK / WO3 device is directly related to the photoelectric conversion mechanism of the organic-inorganic heterojunction. The photoresponse of semiconductor heterojunctions, particularly organic-inorganic heterojunctions, is a complex process. Before contact, the energy levels of each material are independent. After contact, PEDOT:PSS, PVK, and WO3 have a unified Fermi level, with the PVK band bending downward at the interface and the WO3 band bending upward. Due to carrier diffusion, a space charge region, or barrier region, forms at the interface, with the band bending primarily occurring on the WO3 side. When the device is illuminated, valence electrons gain energy and transition to the conduction band, generating photogenerated electron-hole pairs. Driven by the internal electric field, electrons migrate toward the WO3, while holes migrate toward the PVK, where they are collected by the electrodes. This is the primary reason the device can operate at a 0 V bias.

Claims

1. Ultraviolet photodetector based on PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction, characterized by The detector consists of glass substrate, ITO electrode layer, PEDOT:PSS hole transport layer, PVK thin film layer, WO3 thin film layer and Al electrode layer from bottom to top; The thickness of the PEDOT:PSS hole transport layer is 43 nm; The thickness of the PVK thin film layer is 65 nm; The thickness of the WO3 thin film layer is 120 nm.

2. A method for preparing a UV photodetector based on a PEDOT:PSS / PVK / WO3 organic-inorganic heterojunction, comprising the following steps: Step 1, substrate cleaning: the ITO-coated glass substrate is wet cleaned in a mixed solution of ammonia, hydrogen peroxide and deionized water; Step 2, spin coating of a PEDOT:PSS hole transport layer: an ultrasonically homogenized PEDOT:PSS aqueous solution was spin-coated on a cleaned ITO substrate and then dried to a thickness of 43 nm; Step 3, spin coating PVK thin film layer: the pre-formulated PVK solution is prepared on the PEDOT:PSS hole transport layer by spin coating, and then dried to a thickness of 65 nm; Step 4, sputtering WO3 thin film layer: depositing WO3 on the PVK thin film layer by radio frequency magnetron sputtering with a thickness of 120 nm; Step 5, evaporating Al electrode layer: evaporating metal Al on the surface of WO3 film.

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