Perovskite solar cells, as an emerging high-efficiency and low-cost photovoltaic technology1,2,3,4,5,6, face obstacles on their way towards commercialization. Substantial improvements have been made to device stability7,8,9,10, but potential issues with lead toxicity and leaching from devices remain relatively unexplored11,12,13,14,15,16. The potential for lead leakage could be perceived as an environmental and public health risk when using perovskite solar cells in building-integrated photovoltaics17,18,19,20,21,22,23. Here we present a chemical approach for on-device sequestration of more than 96 per cent of lead leakage caused by severe device damage. A coating of lead-absorbing material is applied to the front and back sides of the device stack. On the glass side of the front transparent conducting electrode, we use a transparent lead-absorbing molecular film containing phosphonic acid groups that bind strongly to lead. On the back (metal) electrode side, we place a polymer film blended with lead-chelating agents between the metal electrode and a standard photovoltaic packing film. The lead-absorbing films on both sides swell to absorb the lead, rather than dissolve, when subjected to water soaking, thus retaining structural integrity for easy collection of lead after damage.
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The data that support the findings of this study are available from the corresponding authors upon reasonable request.
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T.X. acknowledges the support from the National Science Foundation (DMR 1806152). The work at the National Renewable Energy Laboratory was supported by the US Department of Energy under contract number DE-AC36-08GO28308 with Alliance for Sustainable Energy, Limited Liability Company (LLC), the Manager and Operator of the National Renewable Energy Laboratory. K.Z., F.Z. and J.J.B. acknowledge the support on perovskite synthesis and device fabrication and characterization from the De-risking Halide Perovskite Solar Cells programme of the National Center for Photovoltaics, funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for US Government purposes.
An application has been made for a provisional patent (US patent application number 62/853,951) related to the subject matter of this manuscript.
Peer review information Nature thanks Bert Conings, Peng Gao and Antonio Urbina for their contribution to the peer review of this work.
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Extended data figures and tables
The DMDP film thickness was varied from 0.7 to 6.89 μm. The inset shows the magnified view of the transmittance spectra.
a, Calculation of both electronic binding energies (Eb) and Gibbs free-energy (ΔG) changes of adsorption of Pb2+ by neutral and deprotonated DMDP and EDTMP at room temperature (25 °C) and 50 °C. All energies are in units of kJ mol−1. b, Schematic of binding configurations of Pb2+ ions with deprotonated DMDP and EDTMP. Configurations were obtained based on density functional theory calculations.
a, Pb concentration leaked from two-side damaged devices without any Pb-sequestrating materials and EVA packaging layer after being soaked in 40 ml of water for 3 h. Six devices were tested. The concentrations of dissolved Pb from these pristine devices were also calculated based on the density and thickness of the perovskite layers. b, Typical cross-sectional scanning electron microscopy image of the devices used in a. c, A typical verification curve of nominal Pb concentrations of various PbI2 solutions and the measured concentrations by the flame atomic absorption spectrometer. The result shows excellent accuracy and precision of the measurement system.
a, Pb-sequestering performance as a function of soaking time for DMDP films coated on glass substrates. The DMDP film thicknesses are indicated. All DMDP films are soaked in 50 ml of 1.93 × 10−5 M PbI2 aqueous solution (equivalent to 4 ppm of Pb2+) to test their Pb-absorbing capability. Five samples were measured for 2.36-μm-thick DMDP and three samples were measured for other DMDP film thickness, with the averages and standard deviations (error bars) indicated. b, Evaluation of Pb-sequestering capabilities of different EDTMP-blended films prepared by various methods. Three samples of each configuration type were measured with the averages and standard deviations (error bars) indicated. The films were soaked in 50 ml of aqueous PbI2 solution with a Pb concentration of 7 ppm. ‘5% PEO in water’ stands for the film prepared by dissolving 5 wt% PEO (viscosity-average molecular weight, about 2,000,000) in pure water as solvent, followed by adding a proper amount of EDTMP under stirring. Then the mixture was smeared into a thin film using a doctor-blade coating method with such an area that the concentration of EDTMP is 0.01 g cm−2. ACN was used as the test solvent. PVA, polyvinyl alcohol (molecular weight 86,000).
a, Schematic of integrating DMDP and EDTMP–PEO films into a PSC. b, Photos of a pristine device and a device treated with the DMDP solution showing that directly applying the DMDP in ethanol solution damaged the perovskite stack with evident yellowing associated with perovskite decomposition due to polar ethanol.
J–V curves of PSCs with and without the EVA coating on the metal-electrode side of the device. Both forward- and reverse-voltage scans are shown. No clear impact on cell efficiency is observed for the EVA coating.
a,b, Six types of devices with different Pb-absorber layer coating and device damage conditions were tested. All devices were sealed by EVA film on the back metal-electrode side. The details of Pb-absorber coating and device-damage conditions are given in the table on the right. Six devices for each type of sample were tested. The Pb-leakage tests were conducted at room temperature (a) and 50 °C (b) by soaking each damaged device in 40 ml of water. The error bars represent the standard deviations from six samples of each type of device. It is worth noting that the case with both sides coated and damaged outperforms the case with only one side (particularly the back side) coated and damaged. This effect can be attributed to the chemical Pb-sequestrating nature of the DMDP and EDTMP–PEO films, which yields a summed sequestration effect, namely any aqueous Pb chemically captured by the Pb-sequestrating layer on one side will no longer flow back to the other side, hence, reducing the leaked Pb via either side compared with the case where a coating layer is present on only one side.
Extended Data Fig. 8 Simulation of pristine and DMDP-coated devices on Pb sequestration at room temperature.
a,b, The two-dimensional geometry models for a pristine control device (only covered by EVA film on the metal side; a) and a device including one coated with DMDP film on the glass-side alone (and the metal side is covered with EVA; b). c,d, The simulated spatial Pb concentrations for a pristine device (c) and a DMDP-coated device after 180 min of damage by shattering the glass side and forming cracks in the glass/DMDP (d). The labelled dimensions are in mm, and the colour-scale numbers are in ppm. Note that the colour scale ranges are different in c and d.
Extended Data Fig. 9 Impact of acidic water, competitive ion (Ca2+) and flowing water on Pb sequestration.
a,b, Pb leakage of damaged PSCs in acidic water (pH = 4.2; 40 ml) at room temperature (a) and 50 °C (b). The samples with Pb absorbers have both sides of the device stack coated with the Pb-sequestrating films. All samples are covered by EVA film on the metal-electrode side. c,d, Effect of competitive ion Ca2+ (from CaCl2) on Pb sequestration by DMDP (c) and EDTMP–PEO (d) samples using 40 ml water containing 12 ppm Pb2+ and 0.1 ppm Ca2+ at room temperature. For the control tests, the water solution contains only Pb2+ ions. The error bars in a–d represent the standard deviations from three devices of each type of test condition. e, Photograph of homemade apparatus to study Pb leakage from damaged devices under flowing water to simulate rainfall conditions. The flowing water is continuously dripped on the damaged devices at a rate of 5 ml h−1 for 1.5 h facilitated by a syringe pump. The damaged devices are placed in the funnel with a tilt angle of 30° versus horizon. The rinsed water that contains Pb is collected in plastic tubes. f, Comparison of Pb-sequestration efficiency of devices under flowing water at room temperature. All devices are installed with Pb absorbers on both sides. Three devices for each type of test condition were measured.
a, Detailed device photovoltaic parameters (open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE)) from both reverse and forward J–V curves shown in Fig. 3a. b, Statistics of photovoltaic parameters of devices with and without the Pb-sequestering layers. Twelve devices were used for each type of device configuration. Error bars show the mean value, maximum/minimum values, and 25–75% region of data, which are represented by the circle, top/bottom bars, and rectangle, respectively.
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Li, X., Zhang, F., He, H. et al. On-device lead sequestration for perovskite solar cells. Nature 578, 555–558 (2020). https://doi.org/10.1038/s41586-020-2001-x
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