A method for recycling selenium from waste selenium photovoltaic cells in near space

Abstract

The present invention relates to a method for recycling selenium from waste selenium photovoltaic cells, comprising the following steps: (S1) performing oxidation treatment on waste selenium photovoltaic cell devices; (S2) performing surface passivation treatment on substrates; (S3) placing the waste selenium photovoltaic cell devices after oxidation treatment in step (S1) in a vacuum heating furnace, placing the substrate after passivation treatment in step (S2) above the waste selenium photovoltaic cell devices, heating under vacuum conditions, condensing selenium on the substrate surface after sublimation, taking out selenium deposited on the substrate after cooling, and completing the recycling of selenium. The method of the present invention has the advantages of simple equipment, fast recycling speed, high recovery rate, low production cost, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling thin-film photovoltaic cells, and in particular relates to a method for recycling selenium from waste selenium photovoltaic cells in near space. Background Art

[0002] Solar energy is favored by people because of its abundant total amount, wide distribution, safety and pollution-free. Photovoltaic power generation is the most direct and effective way to utilize solar energy. As of the end of March 2022, the total installed capacity of photovoltaic power generation in the world has reached 1TW, of which crystalline silicon solar cells account for more than 90% of the market. Selenium solar cells are the earliest solar cells in the world. However, due to their wide band gap (~1.9eV), they are not completely suitable for use under sunlight, so they have developed slowly.

[0003] With the rapid development of the Internet of Things (IoT), the demand for indoor photovoltaic devices has increased dramatically. These products are usually used in indoor environments and have the characteristics of low power consumption, large number of uses, and wide distribution. The spectral range of common artificial lighting (fluorescent lamps, etc.) is concentrated between 400-700nm, which requires suitable indoor photovoltaic device absorption layer materials to have a wide band gap. Selenium has a high absorption coefficient (10 5 cm -1 ), non-toxic, low-cost, wide band gap (1.8-1.9eV), etc., making it very suitable as an absorber material for indoor photovoltaic devices. According to previous reports and experimental results, its performance in indoor light tests is higher than that of commercial amorphous silicon solar cells. It can be predicted that selenium photovoltaic cells may have a greater demand in the future.

[0004] The content of selenium in the earth's crust is 0.05ppm, which is relatively low, with limited production and reserves; and its distribution is extremely uneven. China is a country with a shortage of selenium. The development of recycling and utilization of waste selenium photovoltaic cells can not only efficiently utilize selenium resources, but also reduce the manufacturing cost of devices, which has good economic value.

[0005] CN110607513A discloses a selenium recovery method, and its device includes a selenium evaporator, a selenium deposition chamber, and a selenium condensation recovery device. However, the space of the selenium recovery device of the patent method is relatively large, and compared with the near-space recovery of this patent, the recovery rate is relatively low, and the recovery time is relatively long. CN106319222A discloses a method for recovering copper indium gallium selenide photovoltaic modules, wherein the broken copper indium gallium selenide thin-film photovoltaic module fragments are immersed in alkali solution, and the concentration and temperature of the alkali solution are controlled so that the alkali solution reacts with the molybdenum layer but not with indium and gallium. After the molybdenum layer is corroded, the copper indium gallium selenide layer is separated from the substrate. The patent method has a slow recovery speed, and the purity of the recovered selenium is not high, and the photovoltaic performance cannot meet the actual requirements. Summary of the invention

[0006] There is still a lack of an effective and industrially suitable method for recovering selenium from waste selenium photovoltaic cells. The present invention proposes a method for recovering selenium from waste selenium photovoltaic cells, comprising the following steps:

[0007] (S1) oxidation treatment of waste selenium photovoltaic cell devices;

[0008] (S2) the substrate is subjected to surface passivation treatment;

[0009] (S3) placing the waste selenium photovoltaic cell device after oxidation treatment in step (S1) in a vacuum heating furnace, placing the substrate after passivation treatment in step (S2) on top of the waste selenium photovoltaic cell device, heating under vacuum conditions, allowing selenium to sublime and then condense on the surface of the substrate, and taking out the selenium deposited on the substrate after cooling, thereby completing the recycling of selenium.

[0010] Furthermore, in step (S1), the oxidant is selected from oxygen, ozone, and hydrogen peroxide. Oxygen is preferred, which can facilitate the control of the degree of oxidation. When the oxidant is oxygen, the waste selenium photovoltaic cell device is placed in a tubular furnace and heated at a temperature of 200° C. and an oxygen flow rate of 10-20 mL / min.

[0011] The general structure of waste selenium photovoltaic cells is glass, transparent conductive oxide (ICO), electron transport layer, selenium, and electrode. Figure 1 The vapor pressure of common functional layer materials and selenium is compared. At 300-600°C, the vapor pressure of these functional layers is much smaller than that of selenium. Therefore, the vacuum method can be used to utilize the large vapor pressure difference between selenium and other functional layer materials to achieve the purpose of recovering selenium. However, since a certain amount of tellurium (Te) is contained in waste selenium photovoltaic cell devices, the relatively similar vapor pressure and azeotropic phenomenon in the binary system of selenium and tellurium make it difficult to separate Se and Te by vacuum evaporation in the prior art. Moreover, the thermal weight loss (TGA) of Se and Te powders shows that there is no significant difference in their weight loss temperatures. Therefore, Te is the main impurity that is inevitable for recovering selenium by traditional vacuum evaporation, which will affect the photoelectric performance of recovered selenium as a photovoltaic device. The present invention selectively oxidizes, for example, by using oxygen to heat the waste selenium photovoltaic cell device, Te is oxidized to TeO2, while Se is not oxidized. The vapor pressure of TeO2 is extremely low, which provides a theoretical method of separating Se and Te by selective oxidation, followed by heating and evaporation, so that Se is evaporated and TeO2 is not evaporated. In order to verify the feasibility of the theory, we calculated the separation coefficient of Se and TeO2. The calculation formula is as follows:

[0012]

[0013] is the separation coefficient of Se and TeO2, γSe and γTe are the activity coefficients of Se and Te respectively; P*Se and P* TeO2 are the saturated vapor pressures of Se and TeO2 respectively. According to theoretical calculations, Se and TeO2 can be effectively separated above 200°C.

[0014] Furthermore, in step (S2), the substrate is any high temperature resistant (resistant to 700-1000°C) substrate in the prior art, such as a glass substrate or a quartz substrate; the surface passivation treatment is to immerse the substrate in a dilute alkali solution, the purpose of which is to increase the roughness of the substrate and prevent the crystallized Se film on the substrate from falling off during the recycling process. The dilute alkali solution is selected from at least one of NaOH and KOH, the concentration of the dilute alkali solution is 0.1-0.5 mol / L, and the immersion time is 10-30 min.

[0015] Furthermore, in step (S3), the vacuum heating furnace is not particularly limited, and any device that can control program heating, control heating rate, and adjust furnace pressure is sufficient, such as a rapid annealing furnace.

[0016] Furthermore, in step (S3), the distance between the substrate after passivation treatment and the waste selenium photovoltaic cell device is 1-3 cm, preferably 1-2 cm. In order to realize the comprehensive utilization of waste selenium photovoltaic cells, the present invention proposes a method for recovering selenium using a rapid annealing furnace. The distance between the glass substrate and the recovery device is very important for the recovery rate. The formula for the mean free path of gas molecules is as follows:

[0017]

[0018] Where K is the Boltzmann constant, T is the temperature, d is the molecular diameter, and P is the pressure. After calculation, the mean free path is 3 cm; when the distance is too close, back evaporation will occur and the recovery rate will be greatly reduced; when the distance is too far, the recovery rate will decrease. Taking into account the comprehensive consideration, we choose the distance from the waste device to the substrate to be 1-3 cm, preferably 1-2 cm. This is much smaller than the distance between the photovoltaic device and the substrate in the traditional vacuum evaporation method, so the selenium recovery method of the present invention is called the close space evaporation method.

[0019] Further, in step (S3), in the vacuum heating furnace, the pressure in the furnace is 10-80mTorr, and the heating temperature is 300-700°C. Preferably, the pressure in the furnace is 15-30mTorr, and the heating temperature is 400-600°C; more preferably, the heating temperature in the furnace is 450-550°C, such as 470°C, 500°C, 520°C.

[0020] Furthermore, the heating of step (S3) is followed by rapid heating, temperature maintenance, and cooling. The rapid heating is to heat up to 300-700°C at a heating rate of 20-40°C / s, preferably to 400-600°C at a heating rate of 25-35°C / s; the temperature maintenance time is 10-120s, preferably 20-70s, and more preferably 40-50s. The cooling process is to stop heating immediately, and when the temperature drops below 300°C, open the furnace cover and continue cooling. When the temperature drops to room temperature, release the gas and take out the substrate; if the heating temperature is less than 300°C, cooling is to directly open the furnace cover for cooling.

[0021] Schematically, the vacuum heating furnace used in the present invention is as follows Figure 1 As shown, 1-quartz cavity; 2-thermocouple; 3-quartz bracket; 4-waste selenium photovoltaic cell; 5-glass substrate; 6-graphite plate. It is heated by infrared lamps on both sides of the upper and lower outer walls of the cavity; it includes a closed quartz cavity 1; one side of the cavity has an air outlet for air extraction by a mechanical pump, and the other side has an air inlet for air or nitrogen; the lower part of the cavity has a support rod, on which a quartz bracket 3 is placed, the inner bottom of the bracket contains an aluminum nitride sheet, and under the sheet is a thermocouple 2 for measuring the temperature in the furnace; the waste selenium photovoltaic cell 4 is placed on the aluminum nitride sheet, a clean glass substrate 5 is buckled on the quartz bracket, and a graphite block 6 is covered on the glass substrate. The graphite block has a large specific heat capacity, which can keep the temperature of the glass substrate within a certain range in a short time.

[0022] Preferably, after recovering selenium in step (S3), the method of the present invention further comprises the following steps:

[0023] (S4) recycling the glass ICO / electron transport layer substrate using adhesive tape;

[0024] More preferably, after the electrode is recovered in step (S4), the method of the present invention further comprises the following steps:

[0025] (S5) Re-preparing a selenium photovoltaic device using the glass ICO / electron transport layer substrate recovered in step (S4) and the selenium recovered in step (S3).

[0026] After the selenium is recovered, the electrode and the glass ICO / electron transport layer substrate can also be recovered. The device is re-prepared using the recovered glass ICO / electron transport layer substrate and selenium, and its performance is close to that of the device prepared by fresh commercial materials. This provides a beneficial solution for the sustainable management of waste selenium photovoltaic cells.

[0027] The present invention provides a method for recovering selenium from waste selenium photovoltaic cells. First, the waste devices are selectively oxidized to oxidize Te to TeO2, while Se is not oxidized. Then, the different evaporation properties of TeO2 and Se are utilized. Se in the waste photovoltaic devices is effectively recovered by a close space method in a rapid annealing furnace in combination with specific temperature and pressure. The recovery rate is high, and the recovered Se has high purity and good quality. The method of the present invention has the advantages of simple equipment, fast recovery speed, high recovery rate, low production cost, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the waste selenium photovoltaic cell recovery device (rapid annealing furnace) of the present invention.

[0029] Figure 2 This is a physical picture of the waste selenium photovoltaic cell recycling device of the present invention.

[0030] Figure 3 is the recovery rate of selenium at different temperatures.

[0031] Figure 4 It is the photovoltaic conversion efficiency diagram of the device. DETAILED DESCRIPTION

[0032] To make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified.

[0033] The source of waste devices is waste selenium solar cells and indoor photovoltaic devices, including electron transport layers (TiO2 or ZnO, etc.), absorption layers (Se), and electrodes (Ag or Au). Before using thermal evaporation to prepare Se thin films, a thin layer of Te is usually required to be evaporated to avoid film stripping during annealing. The saturated vapor pressures of Se and Te are relatively close, and it is difficult to separate them using the vacuum method. Se recycled from untreated devices often contains impurities Te (about 0.1%).

[0034] Example 1

[0035] A method for recycling waste selenium photovoltaic cells, specifically including the steps of pre-processing the device, recovering selenium, and re-preparing the photovoltaic device using the recovered selenium and glass FTO / TiO2 substrate:

[0036] (S1) placing the waste components in a tube furnace, then introducing oxygen, raising the temperature to 200° C., keeping the temperature for 12 hours, then slowly cooling to room temperature, and taking them out for use;

[0037] (S2) soaking the glass substrate in a dilute sodium hydroxide solution for 10 minutes, and then ultrasonically cleaning the glass substrate in deionized water three times;

[0038] (S3) A rapid annealing furnace is used to recover Se from waste selenium photovoltaic cells. The schematic diagram of the device is as follows Figure 1 As shown, adjust the distance between the waste selenium photovoltaic cell and the glass substrate to 1 cm, weigh the mass of the waste selenium photovoltaic cell and the glass substrate, place the waste selenium photovoltaic cell on the aluminum nitride sheet on the quartz support, buckle the glass substrate on the quartz support, cover it with a graphite plate, and start vacuuming until the pressure in the furnace is 15mTorr. Raise the rapid annealing furnace from room temperature to 500°C at 30°C / s, and end the temperature operation program after keeping warm for 30 seconds. When the temperature drops below 400°C, open the lid of the rapid annealing furnace to continue cooling. When the temperature drops to room temperature, vent and take out the sample. Weigh the mass of the waste selenium photovoltaic cell and the glass substrate, calculate the recovery rate, which is 77%, and the purity of the recovered selenium is 99.999% (electron probe microanalysis method). Scrape the selenium deposited on the glass substrate and use it as a selenium source for re-preparing the device.

[0039] Example 2

[0040] The temperature of heating and holding in step (S3) of Example 1 was changed from 500°C to 300°C, 400°C, 600°C, and 700°C, respectively. The results are as follows: Figure 3 As shown. The recovery rate is the highest at 500℃, reaching 77%. The recovery rate is only 11% at 300℃ and only 1% at 700℃. Since the substrate is close to the evaporation source, when the temperature is too high, the selenium on the substrate will evaporate back, and the recovery rate is low; since the evaporation time of the whole process is short and the temperature is too low, the selenium on the waste device cannot be completely evaporated, and the recovery rate is low.

[0041] The temperature of heating and keeping in step (S3) was changed from 500°C to 450°C and 550°C, and the recovery rates were 71.8% and 63.6% respectively.

[0042] Example 3

[0043] We select 500° C. as the heating temperature in step (S3). The distances between different waste selenium photovoltaic cells and the glass substrate are adjusted, and the results are shown in Table 1 below.

[0044] Table 1 Effect of the distance between waste selenium photovoltaic cells and glass substrate on Se recovery rate

[0045]

[0046]

[0047] Example 4

[0048] We selected a heating temperature of 500°C, a distance of 1 cm between the waste selenium photovoltaic cell and the glass substrate, and adjusted the pressure in the vacuum heating furnace. The results are shown in Table 2 below:

[0049] Table 2 Effect of furnace pressure on Se recovery rate

[0050] pressure Se recovery 10mTorr 77％ 15mTorr 77％ 30mTorr 76％ 50mTorr 71％

[0051] Example 5

[0052] The other steps are the same as those in Example 1, except that there are steps (S4) and (S5) after step (S3):

[0053] (S4) The gold of the waste device after the selenium is recovered will adhere to the glass FTO / TiO2 substrate, and the gold attached to the substrate is recovered with tape;

[0054] (S5) Using glass FTO / TiO2 liner and recovered selenium as raw materials, re-preparing selenium photovoltaic cells. Figure 4 As shown. The devices were prepared by using fresh commercial materials and recycled materials. The FTO glass was ultrasonically cleaned with deionized water, acetone and isopropanol for 10 minutes, blown dry with a nitrogen gun, and the cleaned glass was treated with ultraviolet sampling. Bis(acetylacetonato)diisopropoxytitanium (75% isopropanol solution) was prepared into a 10% ethanol solution. The FTO glass was preheated on a 400℃ hot plate, and titanium dioxide film was sprayed and then kept at 500℃ for 30 minutes. Tellurium film was evaporated by thermal evaporation, and the vacuum degree of thermal evaporation was controlled at 9×10 －4 Pa; thickness is 0.5nm, thermal evaporation rate is 0.05nm s-1, substrate temperature is room temperature. Selenium thin film is evaporated by thermal evaporation, the vacuum of thermal evaporation is controlled below 9×10-4Pa; thickness is 1000nm, thermal evaporation rate is 0.1nm s －1 The temperature of the substrate is room temperature. The gold electrode is deposited by thermal evaporation, and the vacuum degree of thermal evaporation is controlled at 5×10 －4 Pa or less; thickness is 70nm, electrode area is 0.09cm2, thermal evaporation rate is 0.1nm s -1 The substrate temperature is room temperature. The device is annealed on a hot stage at 200°C for 2 min.

[0055] Test conditions: The device was tested for performance under simulated sunlight. Test conditions: The JV test of the solar cell used a Newport AM 1.5G solar simulator (model: 94023A, Sol3A Class AAA, 450W) as the light source, and was equipped with a Keithley 2420 digital source meter to collect the signal. Before use, a standard silicon cell purchased and certified by NREL (VLSI Standards, model SRC-1000-TC-QZ, area 4cm2) was used for light intensity calibration. The measurement was performed at room temperature in air. During the test, the scanning range was -1 to 1V, and the scanning speed was 100mV / s (step length 20mV, interval time 200ms).

[0056] Its photovoltaic conversion efficiency is Figure 4 As shown, it can be found that the performance of the device prepared by the recycled material of the present invention is very close to that of the device using fresh commercial Se material, which illustrates the reliability and industrial feasibility of the method of the present invention.

Claims

1. A method for recycling selenium from waste selenium photovoltaic cells, characterized in that: The following steps are involved: (S1) The waste selenium photovoltaic cell device is subjected to oxidation treatment; the oxidant is oxygen, the temperature is 200°C, and the oxygen flow rate is 10-20 mL / min; (S2) the substrate is subjected to surface passivation treatment; (S3) placing the waste selenium photovoltaic cell device after oxidation treatment in step (S1) in a vacuum heating furnace, placing the substrate after passivation treatment in step (S2) above the waste selenium photovoltaic cell device, and the distance between the passivated substrate and the waste selenium photovoltaic cell device is 1-3 cm; heating under vacuum conditions, the pressure in the furnace is 10-80 mTorr, the heating temperature is 500°C, selenium sublimates and condenses on the surface of the substrate, and the selenium deposited on the substrate is taken out after cooling, thereby completing the recycling of selenium; heating is sequentially rapid heating, temperature maintenance, and cooling; the rapid heating is heating to 500°C at a heating rate of 20-40°C / s; the temperature maintenance time is maintained for 20-70s.

2. The method according to claim 1, characterized in that In step (S2), the substrate is a glass substrate or a quartz substrate; and the surface passivation treatment is performed by immersing the substrate in a dilute alkaline solution.

3. The method according to claim 2, characterized in that The dilute alkali solution is selected from at least one of NaOH and KOH, the concentration of the dilute alkali solution is 0.1-0.5 mol / L, and the soaking time is 10-30 min.

4. The method according to claim 1, characterized in that: In step (S3), the distance between the passivated substrate and the waste selenium photovoltaic cell device is 1-2 cm.

5. The method according to claim 4, characterized in that In step (S3), the pressure in the furnace is 15-30 mTorr.

6. The method according to claim 1, characterized in that The rapid heating is to heat the temperature to 500° C. at a heating rate of 25-35° C. / s.

7. The method according to claim 1, characterized in that After the selenium is recovered in step (S3), the following steps are also included: (S4) Recovering the glass ICO / electron transport layer substrate using adhesive tape.

8. The method according to claim 7, characterized in that After the electrode is recovered in step (S4), the following steps are also included: (S5) Re-preparing a selenium photovoltaic device using the glass ICO / electron transport layer substrate recovered in step (S4) and the selenium recovered in step (S3).

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