Thank you for visiting Nature. The browser version you are using has limited support for CSS. For the best experience, we recommend that you use a newer version of the browser (or turn off the compatibility mode in Internet Explorer). At the same time, to ensure continued support, we will display sites without styles and JavaScript.
Perovskite photovoltaics are gaining more and more common ground and can cooperate with or compete with silicon photovoltaics to reduce solar energy costs. However, cost-effective toxic lead (Pb) waste management that may determine the fate of this technology has not yet been developed. Here, we report the end-of-life material management of perovskite solar modules to recover toxic lead and valuable transparent conductors to protect the environment and create huge economic benefits from recycled materials. Lead is separated from decommissioned components by weakly acidic cation exchange resin and can be released as soluble Pb(NO3)2, and then precipitated in the form of PbI2 for reuse. The recovery efficiency is 99.2%. Thermally delaminate packaged modules with complete transparent conductors and cover glass. Remanufacturing equipment based on the recovery of lead iodide and the recovery of transparent conductors shows performance comparable to equipment based on fresh raw materials. Cost analysis shows that this recycling technology is economically attractive.
Perovskite photovoltaic (PV) technology is revolutionizing the way electricity is generated by using a new generation of metal halide perovskite (MHP)1,2. The efficiency of the best perovskite solar cells has reached 25.5%, which is comparable to the best monocrystalline silicon photovoltaic cells, and the perovskite/silicon tandem solar cells have reached a high certified efficiency of 29.5%3. Fault-tolerant metal halide perovskites can be manufactured by low-cost solution processes, such as blade coating, slot die coating, and spraying. The capital expenditure for these processes is small4,5,6,7,8. The efficiency of perovskite mini-modules manufactured by scalable deposition methods is also close to 20%9. More than a dozen companies around the world have independently commercialized perovskite photovoltaics by combining with existing photovoltaic technologies using tandem structures, or using single junction structures10.
Most of the efforts of industry and academia are focused on upgrading perovskite photovoltaics and improving module/cell efficiency and stability. However, the most effective metal halide perovskites for this purpose contain toxic lead, such as α-FAPbI311,12, (FAPbI3)0.95(MAPbBr3)0.0513, MAxFA1−xPbI314,15, etc. Although extensive attempts have been made to replace lead in MHP, compared with lead-based batteries, all current lead-free perovskite solar cells are much less stable, such as tin-based perovskite solar cells16,17, or less efficient. It is much lower, such as double perovskite-based solar cells. 18. Assuming that the thickness of the perovskite film is 500 nm, the 1 GW solar photovoltaic capacity of a perovskite solar panel with an efficiency of 20% will contain about 3.5 tons of lead. The most famous perovskite material mentioned above. If only 20% of the estimated 8,500 GW photovoltaic market in 2050 is occupied by perovskite PV19, then perovskite solar panels will contain up to about 6000 tons of lead. Recently, it has been reported that lead adsorption materials, such as P,P’-bis(2-ethylhexyl)methanediphosphonic acid and sulfonic acid cation exchange resin, have been reported to be integrated into perovskite solar panels to prevent lead Leakage from damaged perovskite solar modules 20, 21, 22. In addition to lead management during on-site operations, lead management of scrap perovskite solar modules now needs to be prioritized to ensure the future of these technologies. Otherwise, calcium The low cost advantage promised by titanium ore solar cells will not be realized.
Proper handling and recycling of silicon solar panels at the end of their life is still a challenge, as the solar panels installed in the 2000s are approaching their useful life23,24,25, this has become an urgent task. Although silicon solar panels contain many valuable materials (such as silicon, glass, silver, aluminum, etc.), there is still a lack of cost-effective recycling technology to recycle these materials, so most decommissioned silicon panels will still enter Landfill 23, 24, 25. When it comes to perovskite solar modules containing toxic and water-soluble lead, they cannot be landfilled because they pose a threat to the ecosystem and human health. The development of a practical recycling technology, especially lead recycling technology, is essential for perovskite solar modules26,27,28,29,30. Several methods of removing lead for wastewater treatment have been reported, such as chemical precipitation, electrodeposition, ion exchange, membrane separation and adsorption 31, 32, 33, 34, 35, 36. However, they were built for water-based pollutants, and perovskite solar modules require organic solvents to achieve high lead solubility and recycling capabilities, and cost-effective technologies have not yet been developed. Recently, Park et al. It is reported that iron-doped hydroxyapatite as a new adsorbent can recover lead from organic solvents containing perovskite. However, it lacks a cost analysis for the recovery of lead through complex iron-doped hydroxyapatite hollow composite materials, and this adsorbent cannot be reused because it dissolves during the lead release process.
In this research, we propose a low-cost recovery technology for perovskite solar modules that uses carboxylic acid cation exchange resin as a lead adsorbent and uses thermal stratification to expose the perovskite film. Carboxylic acid cation exchange resin can effectively adsorb lead ions in organic solvents, and effectively release the adsorbed lead ions into the cleaning solution through the ion exchange process between Pb2+ ions and H+ ions. Different from previous studies on the capture of lead by strong acid cation exchange resins 21, 22, weak acid cation exchange resins show better lead recovery efficiency because Pb2+ ions are more easily released from carboxylic acid functional groups than sulfonic acids. Lead is precipitated from the aqueous solution as recrystallized PbI2, and is reused after reacting with sodium iodide. We have also developed a thermal layering method to disassemble the packaged perovskite solar module with a complete glass substrate, which recovers the front transparent conductor and the back cover glass with high reuse value. Finally, estimate the cost of recycling to evaluate the economic incentives of this recycling technology.
The proposed road map for the recovery of toxic lead and valuable glass substrates from perovskite solar modules is shown in Figure 1. After the encapsulated perovskite solar module is layered, the lead in the perovskite layer is dissolved by an organic solvent, such as dimethylformamide (DMF). The lead ions are first adsorbed by the lead adsorbent to completely remove the lead in the organic solvent, then released into the cleaning solvent, and then precipitated as PbI2 for repeated use. In this study, we chose carboxylic acid cation exchange resin as the adsorbent to recover lead from decommissioned perovskite solar modules. The lead adsorption process and lead release process on the resin are based on ion exchange between H+ ions and Pb2+ ions:
a The encapsulated perovskite solar module is layered, and MHP is dissolved by DMF. b Lead ions in DMF are removed by carboxylic acid cation exchange resin. c The lead ions adsorbed on the resin are released into the aqueous solution through HNO3 through the resin regeneration process. d Precipitate PbI2 by pouring NaI into a solution containing Pb(NO3)2. e Module remanufacturing based on recycled materials.
It is worth noting that the ion exchange process is a reversible reaction. The high concentration of H+ ions in the solution can reverse the equilibrium in equation (1), which is a resin regeneration process, so it can be used for lead release. The typical regenerant of cation exchange resin is high concentration HCl or H2SO4 acid solution. Taking into account the low solubility of PbCl2 and PbSO4 in aqueous solutions, regeneration with HCl and H2SO4 can directly precipitate the released Pb2+ ions into PbCl2 and PbSO4, respectively, resulting in difficulty in separating lead from resin. Here, we choose HNO3 aqueous solution as the regenerant to release the adsorbed lead ions into water-soluble Pb(NO3)2. Since PbI2 is the main lead source for most high-efficiency perovskite solar cells, the best form of lead recovery for reuse is PbI2. Therefore, by adding low-cost NaI, lead is converted from Pb(NO3)2 to PbI2 for precipitation. Differences in solubility in aqueous solutions.
In order to recycle scrapped perovskite solar modules, the first step is to develop a layering technique to disassemble the packaged modules to expose the perovskite layer. Here, we consider a perovskite module structure manufactured on indium tin oxide (ITO) glass and encapsulated with another piece of glass and sealant. Existing packaging materials for perovskite solar cells include epoxy resin, polyolefin, Surlyn, polyisobutylene, polyurethane, etc. The back cover glass can effectively prevent the penetration of moisture, oxygen and other hazards 38, 39, 40, 41. This is the structure most likely to provide the best stability among commercial perovskite solar modules and was therefore selected for this study. We found that a short heat treatment at high temperature can effectively disassemble the packaged perovskite solar module and obtain a complete ITO glass and back cover glass. After 2 minutes of thermal stress at 250 °C, the polymer sealant melts and strains, causing the perovskite solar module to delaminate at the interface between the electron transport layer (ETL) and the metal electrode. For example, epoxy resin is used as a sealant. As shown in Figure 2, the lead halide perovskite film and ETL stay on the ITO/glass side, then the ETL is cleaned with 1,2-dichlorobenzene (DCB), and the lead halide perovskite is dissolved in DMF for subsequent lead recovery (Figure 2b) ). After washing away the hole transport layer and other residues, ITO/glass can be reused for module remanufacturing. We found that the conductivity of the ITO/glass substrate did not change significantly after the recycling process. Even after annealing at 250°C for 1 hour, the conductivity of ITO/glass only slightly increased from 14.6 Ω/sq to 15.2 Ω/sq (Figure 2c). The Cr and Cu electrodes with sealant stay on the back cover glass side, where the 30 nm Cr layer on the top surface causes black, and the electrode/sealant film forms wrinkles after thermal stress (Figure 2b). When the potting glue is still soft, scrape the potting glue and the metal electrode with a knife, and then clean the back cover glass for reuse.
a Schematic diagram of the delamination of the interface between the electron transport layer and the metal electrode. b Photos of encapsulated perovskite solar modules, layered modules on the ITO/glass side and back cover glass side, and the ITO/glass and cover glass recovered after cleaning. The size of the front glass is 8.5 cm × 6.5 cm. c After thermal annealing at 250°C in an ambient atmosphere for 1 hour, the sheet resistance of the ITO/glass substrate changes.
In order to effectively recover lead, it is very important to find a material that can absorb lead from waste liquid with high efficiency and release rate. We have previously proved that integrating the cation exchange resin layer on the perovskite layer and the electrode can effectively avoid lead leakage when the module is broken. The strong acid cation exchange resin with strong bonding between sulfonic acid and lead shows excellent lead Capture effect 21,22. We want to start with a proven lead adsorbent that can retain lead in the perovskite module during its lifetime. However, we found that the choice of lead absorber for lead recycling is different from previous lead capture studies because lead ions need to be released in this case. In this case, lead absorber with appropriate bonding strength with lead may be preferred Agent. Figure 3a-b compares the lead recovery performance of a weakly acidic cation (WAC) exchange resin with carboxylic acid functional groups based on gel and macroporous (MP) matrix structures and a strong acid cation (SAC) exchange resin with functional groups for lead recovery. And the sulfonic acid of the MP matrix. For 4 mM PbI2 in 10 mL DMF (lead concentration of 830 parts per million (ppm)), all four types of cation exchange resins were stirred with 1 g of resin for 20 h (Figure 3a). When the initial lead concentration was increased to 40 mM, WAC-gel maintained a high lead adsorption rate of 95%, while the lead adsorption rate of the other three cation exchange resins dropped below 80% (Figure 3a). For the lead release process using HNO3 regenerant, Figure 3b shows that when the concentration of HNO3 regenerant is higher than 0.16, the carboxylic acid cation exchange resins WAC-gel and WAC-MP release most of the adsorbed Pb2+ after 30 minutes of regeneration. Ion M. However, both the sulfonic acid cation exchange resins SAC-gel and SAC-MP showed lower lead release rates, even though the concentration of HNO3 regenerant was as high as 2M (Figure 3b).
a After stirring with 1 g of cation exchange resin for 20 hours, the lead adsorption rate of 10 mL of PbI2 solution of different concentrations in DMF. b Lead release rate of 1 g cation exchange resin under different concentrations of HNO3 in 30 minutes. c Adsorption kinetics and (d) second-order kinetics fitting of lead adsorption to WAC-gel resin under different initial Pb concentrations. e After three days of adsorption, the relationship between the amount of lead adsorbed in the DMF solution and the equilibrium Pb2+ ion concentration. f WAC-gel single treatment and three treatments can adsorb 10 mL of 40 mM lead in DMF. Use 1 gram of WAC gel for a single treatment for 20 hours. Use 1 g WAC-gel for 3 treatments for 1 hour, then transfer the remaining PbI2 solution to 1 g of fresh resin for the second and third treatments. g The lead concentration in the solution after mixing 0.04 M Pb(NO3)2 and 1.5 M NaI in different volume ratios. The illustration is a photo of 1.5 M NaI solution dripped into a solution containing Pb(NO3)2. h The lead recovery rate of 10 mL 40 mM PbI2 in DMF through the three WAC-gel treatments, the release of lead through HNO3 solution for 30 minutes, and the lead conversion through reaction with NaI solution. The error bars in (a), (b), (c), (f), and (g) represent the standard deviation of the three samples.
The large total capacity of WAC resin and its high affinity for hydrogen ions are essential for achieving high delead rate during the adsorption process and high delead rate during the regeneration process. The reversible ion exchange between H+ and Pb2+ is shown in equation (1), the equilibrium constant \({K}_{{\rm {H}}^{+}}^{{{{{{\rm{ } Pb}}}}}}^{2+}}\) can be defined as:
Where \({\left[{{{{{{{\rm{Pb}}}}}}}^{2+}\right]}_{{{{{{\rm{r}}}}}} }\) and \({\left[{{{{{{\rm{H}}}}}}}^{+}\right]}_{{{{{{\rm{r}}}} }}}\) are the concentrations of Pb2+ and H+ ions on the resin, and \({\left[{{{{{{{{\rm{Pb}}}}}}}^{2+}\right]} _{{{{{{\rm{s}}}}}}}}\) and \({\left[{{{{{{{\rm{H}}}}}}}}^{+}\ right ]}_{{{{{{\rm{s}}}}}}\) are the concentrations of Pb2+ and H+ ions in the solution, respectively. The ratio of the Pb2+ concentration on the resin to the Pb2+ concentration in the solution is expressed by the distribution coefficient D:
The lead adsorption process requires a larger D value, and a smaller D value is preferred during the regeneration process. The difference in the concentration of H+ in the resin and the solution is also important, except for \({K}_{{{{{{{\ rm{ H}}}}}}^{+}}^{{{{{{\rm{Pb}}}}}}^{2+}}\) value. During the lead adsorption process, the concentration of H+ ions on the resin varies greatly.\({\left[{{{{{{\rm{H}}}}}}}}^{+}\right]}_{{{ {{{\rm{r}}}}}}}\) and solutions\({\left[{{{{{{\rm{H}}}}}}}}^{+}\right]} _{{{{{{\rm{r}}}}}}}\) Produce a larger D value to effectively adsorb Pb2+ ions. The WAC-gel and WAC-MP resins in this study have a high total capacity (total active H+ sites on the resin) of 4 eq/L (resin equivalent per liter), and a total capacity greater than 1.9 eq/L is very important for SAC-coagulation. Glue resin and 1.7 eq/L for SAC-MP resin. This big \({\left[{{{{{{{\rm{H}}}}}}}^{+}\right]}_{{{{{{\rm{r}}}}}} }\) Explained its excellent lead adsorption performance on WAC resin. During the resin regeneration process, the high H+ ion concentration in the HNO3 solution\({\left[{{{{{{\rm{H}}}}}}}}}^{+}\right]}_{{{ {{{\rm{s}}}}}}\) Reduce the value of D to release Pb2+ ions. The main difference between WAC resin and SAC resin is their affinity for Pb2+ ions and H+ ions. Due to different acid decomposition constants, \({K}_{{{{{{\rm{H}}}}}}^{+}}^{{{{{{\rm{Pb}}} }}} ^{2+}}\) For WAC resins based on carboxylic acid functional groups, it is less than 1, while \({K}_{{{{{\rm{H}}}}}}^ {+}}^{{{ {{{\rm{Pb}}}}}}^{2+}}\) For SAC resin based on sulfonic acid functional group, it is greater than 142. Therefore, WAC resin can be regenerated to its maximum capacity with a lead desorption rate close to 100% by using a low-concentration HNO3 solution. However, even in a high concentration of HNO3 solution, SAC resin is difficult to completely release the adsorbed Pb2+ ions. Therefore, we chose WAC resin for lead recycling.
In order to better understand the lead adsorption process on WAC-gel resin, the characteristics of adsorption kinetics are shown in Figure 3c. In the rate limiting step, if the adsorbed ion interacts with a single unoccupied site on the adsorbent, the curve can be fitted to a pseudo first-order kinetic model 43, 44:
Where qe and qt are the adsorption capacity (mg/g) at equilibrium and time t, respectively, and k1 is the rate constant (min−1). The quasi-two-stage kinetic model is based on the adsorption equilibrium, that is, in the rate-limiting step, the adsorbed ion interacts with the pair of independent unoccupied sites on the adsorbent, and the kinetic rate is 43,44:
Where k2 is the rate constant (min-1). Figure 3d and Supplementary Figure 1 show that the pseudo-second-order kinetic model of WAC-gel resin adsorption of lead is more matched than the pseudo-first-order kinetic model. This indicates that the chemical adsorption of Pb2+ ions involves ion exchange with two H+ sites on the WAC-gel resin in the rate-limiting step.
In order to better characterize the adsorption performance, we analyzed the adsorption capacity of WAC-gel resin under different Pb2+ ion concentrations. Dissolve 2 mmol PbI2 powder in different amounts of DMF solvents to prepare PbI2 solutions with different initial concentrations, then add 1 g of WAC-gel resin to these PbI2 solutions, and stir at 400-rpm at room temperature for 3 days. Figure 3e shows the measured relationship between the amount of lead adsorbed on the WAC-gel resin and the equilibrium Pb2+ ion concentration in the solution. For 1 g of WAC-gel resin, when the equilibrium Pb2+ concentration in the solution is greater than 200 ppm and 6000 ppm, respectively, it can adsorb more than 100 mg and about 150 mg of lead.
The lead recovery speed and efficiency of carboxylic acid cation exchange resin for high-concentration PbI2 solution were analyzed. Since the lead adsorption rate depends on the number of active sites available on the resin, when there are fewer active sites, the adsorption rate will slow down. In order to increase the lead removal speed of the high-concentration PbI2 solution, we adopted three treatment methods, instead of using WAC-gel resin for a single treatment, the remaining PbI2 solution was transferred to fresh resin for the second and third treatments. Therefore, after the 40 mM lead solution is treated with WAC gel for 3 times, the lead removal rate can reach 99.6% for 1 hour each time (Figure 3f). This greatly reduces the time required to effectively remove lead. It is worth noting that the previously reported lead adsorption study using iron-doped hydroxyapatite as an adsorbent was carried out at an initial PbI2 concentration of 2 mM37. The initial PbI2 concentration in this study was 20 times higher, which resulted in a 20-fold decrease -Solvents required for the recovery process. This can greatly reduce the cost of recycling. DMF will be discussed later as one of the main recycling costs.
The NaI solution was added to the solution containing Pb(NO3)2 to convert soluble Pb(NO3)2 into insoluble PbI2 as a precipitate. The low solubility of PbI2 in aqueous solutions, especially solutions containing additional I- ions, is the key to the high conversion rate of lead from Pb(NO3)2 to PbI2. Supplementary Figure 2 shows the measured lead concentration of PbI2 in water as a function of the added iodide concentration. The Pb2+ ion concentration in the saturated PbI2 aqueous solution is 261.7 ppm. With the addition of NaI, the concentration of I- ions in the solution increases. As a result, the concentration of Pb2+ ions in the solution decreases to maintain the solubility product constant Ksp=[Pb2+][I-]2. However, when the I- ion concentration is too high , It will promote the formation of other types of soluble lead, such as \({{{{{{{\rm{PbI}}}}}}}}_{3}^ {-}\) and \({{{{ {{\rm{PbI}}}}}}}_{4}^{2-}\) (Supplementary Figure 2b). For 0.04 M Pb(NO3)2 solution, Figure 3g shows that after mixing Pb(NO3)2 solution and 1.5 M NaI solution in a volume ratio of 14:1 to 1:1, more than 99.6% of Pb(NO3) can be mixed )2 and PbI2, the volume ratio of 5:1 results in a reduction of the lead concentration to ~1 ppm, which corresponds to a theoretical maximum PbI2 precipitation yield of 99.98%. The yield of PbI2 precipitation in the Pb(NO3)2 solution was calculated by the amount of Pb2+ ions in the solution before and after the NaI solution was added. Taking into account the lead adsorption rate of 99.6% and the lead release rate of 99.7%, after the process of lead adsorption, lead release and lead conversion, the total lead recovery rate is 99.2% (Figure 3h).
The lead recovery performance of carboxylic acid cation exchange resin for mixed cation solution was studied. It is important to selectively recover PbI2 from a perovskite solution with mixed cations. We compared the lead adsorption rate of the PbI2 solution and the mixed cation Cs0.1FA0.9PbI3 perovskite solution through the WAC-gel in Figure 4a, and they showed similar rates. This shows that Cs+ ions and FA+ ions did not reduce the lead adsorption rate. This is because the combination of Pb2+ ions with the cation exchange resin is stronger than other cations in the perovskite solution. For 10 layered perovskite solar modules composed of Cs0.1FA0.9PbI3 directly dissolved in 20 mL DMF, the initial lead concentration is 1955 ppm, and after three WAC-gels, the lead adsorption rate is 99.97% and then drops to 0.5 ppm treatment. For the mixed cation Cs0.1FA0.9PbI3 perovskite solution, after ion exchange adsorption and desorption and subsequent reaction with NaI solution, the precipitate is pure PbI2 without CsI or FAI, as confirmed by the XRD pattern (Figure 4c). This is because CsI and FAI have greater solubility in aqueous solutions and will not form precipitates, even if Cs+ ions and FA+ ions are absorbed and released by the cation exchange resin.
a The lead adsorption kinetics of WAC-gel resin to 10 mL 40 mM PbI2 and 40 mM Cs0.1FA0.9PbI3 solutions. b Adsorption of lead to the perovskite solution through three WAC gel treatments, each treatment for 1 hour. The perovskite solution is prepared by dissolving 10 layered perovskite solar modules in 20 mL DMF, and the active area of ​​the modules is approximately 25.0 cm2. c XRD patterns of recovered PbI2 from Cs0.1FA0.9PbI3 solution, compared with XRD patterns of commercial PbI2, FAI and CsI. d Relative lead concentration and (e) Relative lead concentration in DMF solution and the same amount of commercial 99.99% PbI2, recovered PbI2 and commercial 99% PbI2, of which commercial 99.99% PbI2 is used as a reference, and the concentration is measured by ICP-MS. f The ratio of Cs and Na to Pb in PbI2 recovered in DMF solution was measured by ICP-MS. g The PCE of the perovskite solar cell is made of commercial 99.99% PbI2, recycled PbI2 and commercial 99% PbI2, and the device size is 8 mm2. The e PCE of perovskite solar modules manufactured on fresh ITO/glass and recycled ITO/glass has an effective area of ​​approximately 25.0 cm2. f Compared with fresh WAC gel, regenerated WAC gel has lead adsorption. The error bars in (a), (d), (e), (f), and (i) represent the standard deviation of the three samples. The box range in (g) and (h) is the standard deviation, and the center line is the median.
We compared the purity of the recovered PbI2 powder with the commercial PbI2 powder-the purity of TCI is 99.99%, and the purity of Sigma-Aldrich is 99%. For lead in the form of PbI2 recovered from perovskite photovoltaic cells, we will denote it as recovered PbI2. For 184 mg of different types of PbI2 powder dissolved in 2 mL of DMF solvent, Figures 4d and e show that compared with commercial 99.99% PbI2, the recovered PbI2 has a relative lead concentration of 99.9% and a relative iodine concentration of 100%, and it It has a purity higher than commercial 99% PbI2. For the recovered PbI2 dissolved in DMF, the ratio of Cs and Na to Pb is less than 0.1% (Figure 4f). For the Cs0.1FA0.9PbI3 perovskite solar cells based on different types of PbI2, the median PCE of 99.99% PbI2, recycled PbI2, and 99% PbI2 are 21.0%, 20.4%, and 19.4%, respectively (Figure 4g). The results show that the purity of PbI2 powder affects the photovoltaic performance of perovskite solar cells. Perovskite solar cells based on recycled PbI2 show efficiency comparable to devices made with commercial high-purity (99.99%) PbI2.
Throughout the recycling process, lead, front ITO/glass and back cover glass can be recycled from degraded perovskite solar modules. Perovskite solar cells based on recycled PbI2 and perovskite solar modules based on recycled ITO/glass show PCE close to equipment manufactured on fresh commercial raw materials (Figure 4g, h and Supplementary Figure 3). Supplementary Figure 4 shows that recycled PbI2 and recycled ITO/glass substrates will not compromise the photovoltaic stability of perovskite solar devices. In addition, DMF organic solvent and regenerated cation exchange resin can be reused to reduce the cost of the recycling process. The regenerated WAC-gel resin showed similar lead adsorption performance to the fresh resin (Figure 4i). Supplementary Figure 5 shows that WAC-gel resin has excellent lead adsorption performance in different organic solvents, aqueous solutions, and solvents with a wide range of pH values. This allows fresh and recycled resins to easily recover lead from different types of lead-containing solutions.
Due to oxidation, a small amount of PbO may be formed in the end-of-life perovskite solar module. Although PbO is insoluble in DMF, after ultrasonic cleaning the degraded perovskite film in DMF, PbO particles can be filtered and dissolved by HNO3 solution for recycling. Supplementary Figure 6 shows that for PbO dissolved in an HNO3 solution with an initial lead concentration of 40 mM and a pH of 2.4, the WAC-gel resin can achieve a lead adsorption rate of 99.9%. The excellent lead adsorption performance of WAC-gel resin in acidic aqueous and organic solvents enables us to recover lead from perovskite solar modules, even if lead is present in different compounds such as perovskite, PbI2 and PbO. In addition, most of the lead ions in scrapped perovskite solar modules should still remain in the perovskite phase or PbI2. When perovskite photovoltaic cells are well encapsulated to prevent oxygen penetration, other degradation channels should dominate, such as the formation of defects, the formation of non-perovskite phases, or the decomposition of perovskite into PbI2. For the Cs0.1FA0.9PbI3 solar cell after 2000 hours of exposure, its PCE fell below 80% of the initial PCE value, and we did not find significant PbO formation, although the perovskite film has become yellow due to the formation of δ (Supplementary Figure 7).
A techno-economic assessment was conducted to understand the potential cost savings of perovskite solar module recycling technology. Here we mainly consider material costs. As shown in Table 1, the total material cost of the perovskite solar module calculated based on the structure in Figure 2a is approximately US$24.8/m2, similar to the cost model of Li et al. And Cai et al. 45,46. The total value of recycled components including front ITO/glass, PbI2 and back cover glass is approximately US$12/m2. Since the perovskite raw material itself only accounts for a small part of the material cost of the perovskite solar module, the material cost saved by recycling lead as PbI2 is not large. Most of the material cost savings come from expensive ITO glass and cover glass 45, 46, 47, 48, 49, 50, 51. The recycling process does consume materials, including DMF, cation exchange resin, DCB, HNO3, and NaI, and some of them can be reused for multiple cycles. For a 1 square meter perovskite solar module with a 1 micron thick lead halide perovskite layer, it takes approximately 63 grams of DMF to dissolve them into a 0.1 M perovskite solution, 20 grams of resin for three WAC gel adsorption treatments, 4 Grams of DCB is used to remove C6052, 2.5 grams of nitric acid is used for lead release, and 2.7 grams of NaI is used for lead conversion. According to this recycling process, if these materials are used only once, the material consumption for recycling perovskite solar modules is 4.24 USD/m2. If DMF and resin are reused five times, the material cost can be further reduced to $1.35 per square meter, which is about an order of magnitude lower than the total value of recycled components. In addition to removing toxic lead from scrapped perovskite solar modules to avoid environmental pollution, this recycling technology can also bring considerable revenue, making recycling attractive. Compared with the production of new materials, recycled components can save energy, and they provide another source of raw materials that do not rely on primary mining, and can alleviate some supply chain constraints.
In short, we have developed a recycling technology for scrapped perovskite solar modules. This technology can not only recover toxic lead to avoid environmental pollution, but also recover valuable glass components as a cost-effective method. The recycling process includes thermal stratification to disassemble modules with intact glass substrates and effective ion exchange to separate and recover lead from organic solvents. Carboxylic acid cation exchange resin shows high lead adsorption rate when separating lead from lead-containing solution. During resin regeneration, lead ions are recovered with high lead release rate as soluble Pb(NO3)2, and then converted to PbI2. Precipitation can be reused . This method can recover toxic lead and valuable ITO/glass and back cover glass substrates from decommissioned perovskite solar modules for equipment remanufacturing. Compared with fresh counterparts, the photovoltaic performance of perovskite solar devices based on recycled PbI2 or recycled ITO/glass has not significantly decreased. This provides a cost-effective recycling method for the closed-loop lead management of perovskite solar modules to avoid environmental pollution, which can significantly accelerate the penetration of perovskite photovoltaic technology into the clean and renewable energy market.
Carboxylic acid cation exchange resin WAC-gel (WACG-HP, gel type, hydrogen type) and WAC-MP (WACMP, macroporous type, hydrogen type) and sulfonic acid cation exchange resin SAC-MP (SACMP-H, large Porous type), hydrogen type) purchased from ResinTech Inc. Sulfonic acid cation exchange resin SAC-gel (Amberlite® IRC120 H, gel type, hydrogen type), lead(II) iodide (99%), PTAA (average Mn) 7000–10,000), Yutongling (BCP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), 2-methoxyethanol (2-ME), 1,2-dichlorobenzene, toluene , Isopropanol, phenethylammonium chloride and Pb standard solutions (1000 ± 2 ppm) were purchased from Sigma-Aldrich. Lead(II) iodide (99.99%, trace metals) was purchased from TCI America. Formamidine iodide (FAI) and formamidine chloride were purchased from GreatCell Solar. C60 was purchased from Nano-C Inc. Copper (Cu) and chromium (Cr) used for thermal evaporation were purchased from Kurt J. Lesker.
The pre-patterned ITO glass substrate (1.5 cm x 1.5 cm for solar cells and 6.5 cm x 8.5 cm for solar modules) is first ultrasonically cleaned with soap, deionized water, isopropanol and acetone, and then treated with ultraviolet ozone for 15 minutes, then use. A PTAA solution with a concentration of 2.2 mg/mL in toluene was knife-coated on the ITO/glass substrate at a speed of 20 mm/s with a coating gap of 200 µm. Perovskite thin film coatings are similar to previous studies9. A solvent mixture containing 1.0 M FAPbI3 and 0.11 M CsPbI3 dissolved in 2-ME/DMSO was used, where the precursor was filtered through a PTFE filter with a pore size of 0.2 µm before use. Add formamidine hypophosphite, formamidine chloride and phenethylammonium chloride as additives to the solution at a molar percentage of ~1.0%, ~1.5%, and ~0.15% with respect to Pb2+ ions. The coated solid film was annealed in air at 150°C for 3 minutes. Then use C60 (30 nm), BCP (6 nm) and Cu (150 nm) to thermally evaporate the perovskite film to complete the manufacture of perovskite solar cells. For manufacturing modules, laser ablation is applied before and after the metal electrodes (30 nm Cr and 150 nm Cu) are deposited to complete the series interconnection between the module neutron cells.
The perovskite solar module is encapsulated by a back cover glass, and the top of the glass is coated with Gorilla epoxy resin, and then cured overnight. The thickness of the dried encapsulation layer is approximately 300 µm. The encapsulated perovskite solar module is placed on a hot plate at 250°C for 2 minutes to perform module delamination. The packaging glue is softened and melted, and then the blade is inserted between the ITO/glass substrate and the back cover glass at a corner of the module to separate the two glass substrates. The perovskite layer on the layered ITO/glass substrate is dissolved by DMF and used in the subsequent lead recovery process.
Different lead sources are used for lead adsorption measurement: PbI2, Cs0.1FA0.9PbI3, Pb(NO3)2 and layered perovskite solar modules with Cs0.1FA0.9PbI3 perovskite film. After stirring with 1 g of cation exchange resin at 400 rpm for different times, the lead concentration change of 10 mL of 4-40 mM PbI2 in DMF was measured to characterize the lead adsorption rate of different cation exchange resins. For the three treatments of WAC-gel, 10 mL of lead-containing solution and 1 g of WAC-gel were stirred at 400 rpm for 1 hour, and then the remaining lead-containing solution was transferred to the second 1 g of fresh WAC-gel resin. Hours, the third hour is added again to the third 1 g of fresh resin. In order to characterize the resin’s adsorption capacity for Pb2+ ions in DMF solution, the adsorption process was carried out by mixing 2 mmol PbI2 powder in different amounts of DMF solvent with 1 g WAC-gel resin under stirring for three days. The lead release process was carried out by mixing the lead-adsorbing resin with 10 mL of HNO3 aqueous solution of different concentrations at 400 rpm for 30 minutes. After the lead is released, the regeneration solution is transferred to the sedimentation tank together with the released Pb ions, and 1.5 M NaI aqueous solution is added to the sedimentation tank to form a yellow PbI2 precipitate. The PbI2 precipitate was washed with deionized water and isopropanol, collected by centrifugation, dried in vacuum and reused. The regenerated WAC gel is rinsed with deionized water before being reused for lead adsorption. The concentration of Pb and other elements in the solution was measured by inductively coupled plasma mass spectrometry (ICP-MS) Nexion 300D instrument. Before the measurement, by measuring the standard solution prepared by mixing the standard solution with different amounts of 2% HNO3 aqueous solution, draw an analytical calibration curve with a concentration between 1 ppb and 100 ppb. For each measurement, in the linear calibration curve of ICP-MS, the Pb concentration of the test solution is diluted with 2% HNO3 aqueous solution to 1 ppb and 100 ppb.
The power conversion efficiency of perovskite solar cells and solar modules is characterized by JV measurement under a xenon lamp-based solar simulator (Oriel Sol3A, AAA solar simulator). The light intensity is calibrated to 100 mW cm-2 by a silicon reference cell (Newport 91150-KG5). For perovskite solar cells, a metal mask with an aperture area of ​​6.08 mm2 (3.8 mm × 1.6 mm) is aligned with the device area. The JV curve is measured by a Keithley 2400 source meter, the backward and forward scanning rate is 0.1 V s-1, and the delay time is 10 ms in room temperature air. In order to measure long-term operational stability, the packaged devices and modules are illuminated by 1 sun equivalent LED light. By focusing a monochromatic beam onto the device, use the Newport QE measurement kit to obtain external quantum efficiency data. The XRD pattern was obtained by Rigaku’s sixth-generation MiniFlex X-ray diffractometer.
For more information on experimental design, please see the abstract of the nature research report associated with this article.
Data supporting the results of this study can be obtained from the corresponding author upon request.
Jena, AK, Kulkarni, A. & Miyasaka, T. Halide Perovskite photovoltaics: background, current status and future prospects. Chemistry Rev. 119, 3036–3103 (2019).
Huang, J., Yuan, Y., Shao, Y. & Yan, Y. Understand the physical properties of hybrid perovskites used in photovoltaic applications. Nat. Priest. 2, 17042 (2017).
Deng, Y. et al. Customized solvent coordination for high-speed, room temperature blades of perovskite photovoltaic films. science. Advanced 5. eaax7537 (2019).
Subbiah, AS, etc. High-performance perovskite single junction and textured perovskite/silicon tandem solar cells coated by slot die. ACS Energy Corporation 5, 3034-3040 (2020).
Das, S. etc. A high-performance flexible perovskite solar cell that combines ultrasonic spraying and photon curing with low thermal budget. ACS Photonics 2, 680–686 (2015).
Yin, W.-J., Shi, T. & Yan, Y. Abnormal defect physics in CH3NH3PbI3 perovskite solar cell absorber. Application physics. Wright. 104, 063903 (2014).
Deng, Y. et al. Compensation for defects in the formamidine-cesium perovskite used to efficiently stabilize solar modules. Nat. Energy 6, 633–641 (2021).
Lu, HZ etc. Vapor-assisted deposition of high-efficiency and stable black phase FAPbI3 perovskite solar cells. Science 370, eabb8985 (2020).
Jeong, J. et al. Pseudo-halide anion engineering for α-FAPbI3 perovskite solar cells. Nature 592, 381–385 (2021).
Jung, EH, etc. High-efficiency, stable and scalable perovskite solar cells using poly(3-hexylthiophene). Nature 567, 511–515 (2019).
Jiang Q. et al. Surface passivation of perovskite films used in high-efficiency solar cells. Nat. Photonics 13, 460–466 (2019).
Chen, SS, Xiao, X., Gu, HY & Huang, JS For the iodine reduction of repeatable and high-performance perovskite solar cells and modules. science. Advanced 7, eabe8130 (2021).
Hao, F., Stoumpos, CC, Cao, DH, Chang, RPH & Kanatzidis, MG Lead-free solid-state organic-inorganic halide perovskite solar cells. Nat. Photonics 8, 489–494 (2014).
Jiang, XY, etc. The ultra-high open circuit voltage of tin perovskite solar cells designed through the electron transport layer. Nat. Community. 11, 1245 (2020).