Shedding light on the environmental impact of the decomposition of perovskite solar cell

Perovskite materials, as the heart of perovskite solar cells (PSC), attracted great interest in the photovoltaic community since the efficiency of PSC dramatically increased to over 25% in a short period. However, the presence of Pb metal in the perovskite crystalline limits the progress of this new generation of solar cells from environmental aspects. Here, we have systematically investigated the impact of the decomposition of perovskite material on the special plant, named Coleus. The influence of the decomposition of a perovskite solar cell (p-PbI2) has a three-fold lower destruction than commercial PbI2 (s-PbI2) in the same condition. The p-PbI2 made destroying the roots and leafs slower and smoother than s-PbI2, which the amount of water absorption with the plant’s root from p-PbI2 is two-fold lower than s-PbI2. The atomic absorption spectroscopy (AAS) indicated that the amount of Pb in the first week is about 3.2 and 2.1 ppm for s-PbI2, and p-PbI2, respectively, which in following for two next weeks reached to about relatively close together and finally in the last week decreased to 1.8 ppm for s-PbI2 and increased to 2.4 ppm for p-PbI2. This paper opens new avenues and challenges about the actual scenario on the impact of perovskite materials in PSCs on the plant and live metabolisms.

www.nature.com/scientificreports/Although a large number of studies have been reported to minimize the conversion of CH 3 NH 3 PbI 3 to PbI 2 [19][20][21][22][23] , because perovskite is an ionic crystal, intense light, moisture, and heat significantly rapid this death pathway 24 .In addition, factors such as fire, heavy rain, and shock effectively destroy any solar cell 25 , which must be prevented by various chemical and physical methods.
To address these issues, self-healing polymer capsules 21 , including chemical methods and high-melting-point materials 26 , are among the most efficient physical techniques for reducing lead leakage from deconstructed perovskite solar cells containing Pb atoms.
In addition to the key role of external factors on the destroying PSC, many reports highlighted the intrinsic and internal destruction of perovskites, which generally occurs from paths 1 and 2 27 .The most important compound that remains in any degradation process of perovskite is PbI 2 which increases the lead concentration in the soil 28 .
Therefore, it is crucial to develop and extend our knowledge about the mechanism of destruction of PSC and switch to more scientific studies on the influence of destroying the PSC and producing Pb metal on earth and living organisms.
In a brilliant paper, Junming Li et al. investigated the difference between Pb produced from perovskite and PbI 2 contamination, simulated wasted soil by increasing different amounts in natural soil and using atomic absorption spectroscopy (AAS) to estimate the amount of Pb over 20 days and proposed that the amount of lead in leaves stems, and roots of mint plants (Mentha spicata), Capsicum annum (chili), and Brassica campestris (cabbage) grown in soil containing perovskite is significantly more than the amount of lead from plants grown in soils containing PbI 2 .
In following, regarding the influence of water contamination and not soil contamination, here we used the Coleus plant treated in contaminated water to assess the environmental impact of lead from halide perovskite on roots and roofs.To better observe all parts of the plant, we kept the plant in water and monitored the changes of all part of plant during the growth process for four weeks.

Experimental Materials and equipment
Plant material (Fig. 1a) was collected from the region of Gavazang located at Zanjan, IRAN (36° 39′ 51.84″ N, 4 8° 29′ 8.16″ E).Plant studies and collection of plant material, complied with relevant institutional, national, and international guidelines and legislation.
All materials are provided by Merck and Sigma Aldrich with a purity of 99%, and Atomic absorption spectroscopy was registered in an Analytikjena Model: novAA 350 Made in Germany.

Experimental steps
The procedure of preparation is constructed of three step which described in following: Step 1: The synthesis of perovskites: first, 460 mg of PbI 2 was mixed in 1mL dimethylformamide (DMF) and spin-coated on glass in the glove box, then 30 mg MAI was disolved in 1mL of 2-propanol (IPA) and spin-coated on prepared PbI 2 film and placed on a hotplate at 100 °C.The color of the deposited layer went from yellow to dark brown, which indicated the formation of perovskite film (Fig. 2, step 1).
Step 2: The plant treatments: the plant treatments have been done in two rounds: round 1: plants irrigation solution and round 2: irrigation process as shown in Fig. 2, step 2.
To investigate the influence of PbI 2 from decomposed perovskite and synthetic ones on the Coleus plant, the preparation of samples is explained as following, which schematically described in Fig. 1.(a) The reference sample dissolved drinking water , which named Cont., (b).For the preparation of the solution of synthetic PbI 2, which named s-PbI 2 , 7.3 mg of lead iodide was dissolved in 1 L of distilled water to give a solution of 3.3 ppm of lead, based on AAS measurements, and (c) to prepare the PbI 2 from decomposed perovskite, namely p-PbI 2 , perovskite film was formed two-step method, as described above.After staying the films of produced perovskite in the atmosphere for two weeks without encapsulating, when dark-brown perovskite completely turned to yellow perovskite, 9.9 mg of produced perovskite dissolved in 1 L of distilled water to give a solution of 3. 3 ppm of lead.For s-PbI 2 and p-PbL 2 the amount of Pb was set at 3.3 ppm which confirmed by AAS.
Three samples including reference, s-PbI 2 , and p-PbI 2 with lead concentrations of 2, 3.3, and 3.3 ppm, respectively, were added to tubes containing the Coleus plants for four weeks.
Step 3: the preparation of samples for AAS.After left 4 weeks, ashes of samples were prepared and 1 g of Coleus plant ash was dissolved in 100 mL distilled water, and the amount of Pb was estimated by the AAS method with the preparation of calibration curves (Fig. 2, step 3).

Results and discussion
Based on the mints grown in the natural soil as a reference sample, the initial amount of Pb calculated about 12.0, 3.7, and 8.0 ppm for roots, stems, and leaves, respectively.Moreover, the amount of Pb in p-PbI 2 , especially in the stems and leaves, which are about two-fold.In brief, Junming Li et al. clearly showed that the destroying of perovskite produced a large amount of Pb compared to s-PbI 2 ones.
To illustrate what happens in the roots, the Clouse plant was treated by monitoring the roots in water and carefully studied different irrigation conditions containing perovskite and fresh PbI 2 .In this research, several plant's roots in drinking water were selected and classified into three groups and the changes were monitored for four weeks.The results as shown in Fig. 3 indicated that in series Cont., the sample control group, does not change from the first to the fourth week, while in series s-PbI 2 , and p-PbI 2 rinse the amount of lead, changing the color (green to brown), and becoming to smaller after 4 weeks.The leaves of series s-PbI 2 started to collapse in the second week, while the leaves of series p-PbI 2 began to defoliation in the third week, which finally both two samples containing PbI 2 were destroyed after four weeks.
Some studies have been done to get deeper insight into the mechanism of interaction of Pb in plants and color changing process.Instant, N. Phuong and D.C. Valeriano reported that the multifunction interaction between anthocyanin and chlorophyll changed the color from red to green 16 .In another exciting report, Farouk S Nas and Muhammad Ali confirmed that lead metal significantly limited the formation of chlorophyll by causing reduced uptake of elements such as Magnesium and Iron in plants.
Comparison of stability of samples treated with s-PbI 2 , and p-PbI 2 , the sample containing s-PbI 2 was earlier decomposed than samples p-PbI 2 , while, the reference sample without any Pb source was unchanged in this period.From these observations, it concluded that the sample containing perovskite (p-PbI 2 ) showed more stability than the commercial Pb (s-PbI 2 ) sample over the same time.To investigate the effect of destroyed perovskite and PbI 2 on the Coleus's roots, all three samples of series Cont., s-PbI 2 , and p-PbI 2 were considered, as shown in Fig. 4, as follow: in series Cont., the sample control group long, white, and clear roots after ten days, while the Coleus's roots of series s-PbI 2 , which irrigate with PbI 2 and excess water shown shortening and going to black color.Surprisingly, the p-PbI 2 -series plant roots, irrigated with excess water, produced both shapes of roots.
To find the mechanism of interaction of Pb with the plant's root, in a critical report, R. Riyazuddin et al. found that in the presence of heavy metals such as pb 2+ in samples, the amount of hydrogen peroxide as an oxidative agent was dramatically increased and consequently the roots have been completely decomposed 29 , which was earlier confirmed by Anastasia Giannakoula et al. 30 .
Given that only water-soluble substances can be absorbed by the plant, subsequent measurement of the amount of absorbed water indicated the viability of a plant.
Remarkably, we obviously found that there is a direct correlation between the amount of absorbed water by roots when were taken in the different sources of Pb involves p-PbI 2 and s-PbI 2 as well the rate of destroying of plants.The value of height of absorbed water by the plant in the tubes containing samples Cont., s-PbI 2 , and p-PbI 2 (Fig. 5a-c) were decreased from initial value from 10 cm to 7, 4 and 7.6 cm, respectively due to consume of water by Pb, which means that the value of absorbed water controlled by the type of Pb.Finally, s-PbI 2 wasted more water than perovskite and reference sample which destroyed perovskite (sample p-PbI 2 ) showed  www.nature.com/scientificreports/ the lowest water absorption, nearing sample Cont.To explain these observations, based on the results obtained by R. Riyazuddin et al., more absorption water with the plants such as stomata, xylem vessels, parenchymatous, and mesophyll cells, more toxicity of water containing heavy metals 29 .

Lead bioavailability
Screening the amount of lead in plants,s ashes of series of Cont.and s-PbI 2 by using AAS as well its bioavailability to evaluate environmental effects have been carried out and the results are shown in Fig. 6b 1 , c 1 , b 2 , and c 2 , respectively.In this study, all three samples of Cont., s-PbI 2 , and p-PbI 2 thoroughly were analyzed and each one were repeated three times for more accuracy.In summary, at the end of the first week, as shown in Fig. 6b1, samples of series s-PbI 2 shown a significant enhancement in the amount of lead compared to sample series p-PbI 2 , as shown in Fig. 6c1.In contrast to first week, from the second week to the end of the fourth week (please see Fig. 6b1), a decrease in the amount of lead of p-PbI 2 was observed, while the amount of lead of s-PbI 2 gradually increases in the same period, as shown in Fig. 6c1.Quantitatively, the amount of lead of series s-PbI 2 from first to fourth week was calculated 3.2, 2.6, 2.7, and 1.8 ppm, which for series p-PbI 2 in the same period was estimated 2.1, 2.2, 2.7 and 2.4 ppm, respectively.One of the important conditions which should check is the amount of lead in the water for series s-PbI 2 , and p-PbI 2 .In brief, the amount of lead in the water for series s-PbI 2 (Fig. 6b2) at the end of the first week, is almost zero which is much less than series p-PbI 2 , as shown in Fig. 6c2, which means that all mass of lead in 5b 2 is absorbed by the plant, confirming the highest value of 3.2 ppm for series s-PbI 2 .In following, when the irrigation was increased the amount of lead at the end of the second, third, and fourth week obtained 0.5, 1.5, and 2.5 (ppm), respectively for series s-PbI 2 (in Fig. 6b2), and 0.4, 1.2, 2.1, and 3 ppm for series p-PbI 2 as shown in Fig. 6c2.
A survey of the amount of Pb has been suspended in water shown that the initial increase of lead in series s-PbI 2 is much significant than in series p-PbI 2 .In summary, more lead absorption in the first week for series s-PbI 2 causes the Coleus plant to be poisoned and dried earlier than series p-PbI 2 , which has a gradual lead absorption.
It is important to point out that a large number studies have been focused on the impact of lead metal on the environmental issue, however the estimation of amount of iodine are not fully understood.As an instant, Eline M. et al. studied the influence of decomposition of MAPbI 3 as well a variety of perovskite precursors (PbI 2 , Pb(NO 3 ) 2 , PbBr 2 , MABr, MAI) on Arabidopsis thaliana which estimated the amount of iodine ion of 79 μM is higher than the criteria value of 50 μM, resulting the impact of iodine species into the environment issues after leakage of perovskite solar cell panels" 31 .

Conclusion
Here, we investigated the effect of perovskite decomposition from solar cells on Coleus plants, which showed that the effect of decomposed perovskite (p-PbI 2 ) on plant growth was lower than that of commercial PbI 2 (s-PbI 2 ).We found that the impact of s-PbI 2 on the root and leaf of the Coleus plant is more destroyer than p-PbI 2 .In particular, the amount of water absorption and Pb metal by roots in the s-PbI 2 sample is about two-fold more than p-PbI 2 ones.Particularly, it is proposed that the toxicity of a contaminated plant with p-PbI 2 could be found from the converting its roots to transparent thin rhizomes after one week, differently from s-pbI 2 ,s rhizomes, showing solid dark features.This interesting results show that the contamination of plants by s-pbI 2 and p-pbI 2 will be distinguished from roots and leafs without any analytical characterizations.This new achievement opens new ways and challenges for investigating the effect of perovskite materials of perovskite solar cells on the environmental issue and shedding light on the growing of the plants under the presence of destroyed PSC.More research on the influence of decomposed perovskite on plants, and animals in vivo should be done in the future to get more insights and possibilities about the commercialization of perovskite solar cells and other optoelectronic materials based on superior perovskite materials.

Figure 3 .
Figure 3. Overview of the experiment of Coleus growth in (a) irrigation water containing an initial concentration of lead of 2 ppm, (b) the concentration of lead is increased to 3.3ppm by increasing lead iodide, (c) the concentration of lead has been reduced by dissolving the yellow perovskite to 3.3 ppm.

Figure 4 .
Figure 4. Comparison of plant's root of plant in Cont., s-PbI 2 , and p-PbI 2 series samples.