Metal halide perovskites have been the subject of intense theoretical and

experimental research in recent years due to their huge potential over their silicon based

counterparts for tunable optoelectronic applications in high-tech device innovation. The current

best perovskite for solar cell applications, with a power conversion efficiency of 22%, methyl

ammonium lead iodide (CH3NH3PbI3), is toxic due to the presence of lead and is therefore

harmful in solar cell applications despite its low concentration in solar cells. Hence, research

exploits are geared towards perovskites without lead. Unfortunately, this has taken back the

gains in PCEs by about 15%, and a lot is being done for improvement. In this paper, we

performed molecular dynamics and Monte Carlo simulations of ion-beam sputtering of lead

and tin perovskites to determine differences between the sputtering characteristics of lead

perovskite and a lead-substituted perovskite (tin perovskite). Our results show that they both

exhibit similar sputtering characteristics of linear projected ion range, and maximum yield

around 78° ion incidence

Akinpelu, A.

Oyewande, Oluwole E.

Covenant University Repository

IOP Conference Series: Earth and Environmental SciencePAPER • OPEN ACCESSProjected Range and Sputter Yield of Ne+ and Ar+in the Sputtering of Lead and Tin PerovskitesTo cite this article: Oluwole E. Oyewande and Akinwumi Akinpelu 2018 IOP Conf. Ser.: Earth Environ.Sci. 173 012045 View the article online for updates and enhancements.Related contentAnomaly in Sputtering of Aluminum underN2+ Ion BombardmentRiichirou Mitsuhashi, Hyung-Ik Lee andRyuichi Shimizu-Preliminary Study in Fabricating Fluorine-doped Tin Oxide by Using Spray PyrolysisMethodsDarsikin, Z Arifin, Nasar et al.-Angular Dependence of Sputtering Yield ofAu on Bombardment by 15 to 60 keV Ar+Shu-ichi Kojima, Kenji Kimura and Michi-hiko Mannami-This content was downloaded from IP address 165.73.192.254 on 18/09/2019 at 16:501Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045      Projected Range and Sputter Yield of Ne+ and Ar+ in the Sputtering of Lead and Tin Perovskites Oluwole E. Oyewande1, 2 and Akinwumi Akinpelu1 1Department of Physics, College of Science and Technology, Covenant University, Ota, Ogun State, Nigeria 2Department of Physics, Faculty of Sciences, University of Ibadan, Ibadan, Nigeria oluwole.oyewande@covenantuniversity.edu.ng akinwumi.akinpelu@covenantuniversity.edu.ng Abstract. Metal halide perovskites have been the subject of intense theoretical and experimental research in recent years due to their huge potential over their silicon based counterparts for tunable optoelectronic applications in high-tech device innovation. The current best perovskite for solar cell applications, with a power conversion efficiency of 22%, methyl ammonium lead iodide (CH3NH3PbI3), is toxic due to the presence of lead and is therefore harmful in solar cell applications despite its low concentration in solar cells. Hence, research exploits are geared towards perovskites without lead. Unfortunately, this has taken back the gains in PCEs by about 15%, and a lot is being done for improvement. In this paper, we performed molecular dynamics and Monte Carlo simulations of ion-beam sputtering of lead and tin perovskites to determine differences between the sputtering characteristics of lead perovskite and a lead-substituted perovskite (tin perovskite). Our results show that they both exhibit similar sputtering characteristics of linear projected ion range, and maximum yield around 78° ion incidence. Keywords: Solar cells; Sputtering; Perovskites; Sputter yield; Range of ions.  1.  Introduction Lead halide perovskites have huge potential for applications in solution-based photovoltaics (e.g. solar cells) with greater power conversion efficiencies (PCEs) than silicon-based photovoltaics [1]. However, they suffer a large setback in these applications due to the toxicity of lead and its solubility in water. There has therefore been an intense research interest with promising results in recent years on non-toxic metal replacements [2 - 6]. One advantage of perovskite based photovoltaics over their silicon based counterparts is their low-cost fabrication due to the possibility of producing them in a variety of ways, including the use of vacuum techniques [7]. A vacuum processing and fabrication technique is ion-beam sputtering of materials, which is an area of current intensive research as a cost-effective method of surface analysis, processing and fabrication of self-organized nanostructures for optoelectronic applications [8 – 14]. A new radio-frequency-sputtering method of production of lead-iodide perovskite was proposed in Ref. 15. This 21234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045      comprises of a deposition of thin films of lead sulphide, their conversion to perovskites by placement in an iodine atmosphere, and subsequent immersion into a solution of methyl ammonium (i.e. solution based). Whereas in Ref. 16, a non-solution based method of perovskite film fabrication by sputtering was proposed. They confirmed that sputter processed perovskite films showed similar characteristics as their solution-processed counterparts and produced perovskite solar cells with higher PCEs. In a sputtering process, an incoming ion collides with an atom of the target material and sets off secondary collision cascades leading to kinetic and thermal agitations of the targets atoms. Noble gas ions are commonly used in sputtering experiments due to their inert nature and low reactivity with the sputtered targets. By virtue of the nature of the sputtering process and the need for kinetic details within the earliest impact times, molecular dynamics simulation can be exploited. A number of enquiries have taken this approach, focusing on specific sputtering conditions (e.g. [17- 20]). However, statistical collisional data is also required and this is obtained by statistical physics Monte Carlo simulations. A molecular dynamics simulation suite developed by Ziegler and Biersack [21 – 23], Stopping and Range of Ions in Matter (SRIM), and its more extended counterpart, TRansport of Ions in Matter (TRIM), which includes SRIM and statistical simulation and calculation of some sputtering parameters with Monte Carlo techniques, are versatile tools in this regard [24]. They are reference and very popular simulation software packages with a large number of scientific citations to them every year [23]. Signatures of the ion-target interaction are the collision cascade parameters and sputter yield. These can be drastically changed by minute changes in the target composition. It is therefore of interest to know the effect of lead replacement on the sputter characteristics of metal halide perovskites. This has not yet been studied, to the knowledge of the authors of this article. The most suitable material for this comparison is CH3NH3SnI3 which is a metal halide perovskite with similar characteristics as CH3NH3PbI3 but with a reportedly much lower PCE of 6.4% [2]. It, nonetheless, has the highest PCE among all the lead-substituted perovskites [7].However, Sn or Pb are good occupants of the B-site of a perovskite ABX3 structure, where the monovalent organic cation (e.g. methyl ammonium, CH3NH3+) occupying the position A, or the halide counter-ion (e.g. iodine, I-) occupying the X-site of the perovskite structure, can be changed to tune the properties of the perovskite. In this paper, we studied the range and sputter yield of ions in CH3NH3PbI3 (lead) and CH3NH3SnI3 (tin) perovskites for different ion energies and incidence angles by molecular dynamics and Monte Carlo simulations using SRIM and TRIM. We used ions of inert gases Ne and Ar in the sputtering of these perovskites. The rest of the paper is organized as follows. In the next section we elaborate on the methods we have used to obtain our results. For reproducibility, we provide details of the simulation set-up on the SRIM and TRIM graphical user interface and the values used for all other parameters. We present and discuss our results in section 3, and provide our conclusions in section 4.   2.  Methodology In this section we provide the specific details of our simulation. Details of the theoretical background for the calculations and simulation algorithms embedded in the TRIM and SRIM packages are discussed in the papers by Ziegler and Biersack [21, 25]. SRIM was used to perform molecular dynamics simulations of the range of inert gas ions Ne+ and Ar+, with energies varied from 1 keV to 10 keV, at normal incidence on the two targets, namely, lead perovskite CH3NH3Pb`I3 and tin perovskite CH3NH3SnI3. While TRIM was used to perform molecular dynamics and Monte Carlo simulations for the number of each component of the perovskites yielded as a result of bombardment of the perovskite by an incident ion, for varied incidence angles from 0° to 89°, and for ion energies 1 keV and 5 keV. In both SRIM and TRIM set-ups we used perovskite wafer thickness of 35 nm, and built up the lead perovskite from its composites in the stoichiometric ratio 1:3:1:3:1:3 for C, H, N, H, Pb/Sn, I, 31234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045      respectively, and densities 4.16g/cm3 [26] and 3.51g/cm3 [27] for the lead and tin perovskites, respectively. We also used 1000 ions for each simulation. A detailed calculation with full damage cascade was performed for each simulation (i.e. each complete run of TRIM or SRIM for a particular set-up).  3.  Results and discussion The results of our simulations are presented and discussed in this section. We observed the same trends for the two ions (Ne+ and Ar+), though with higher values for Ar+, and therefore present the results for only Ne ion here. Figure 1 shows the results of the projected range of the ions in the perovskites for different ion energies varied from 1 keV to 10 keV. These exhibitions of almost the same values of the linear range of the ions for the different perovskites indicate that the two materials are remarkably similar as regards their stopping power to energetic particle irradiation.     Figure 1: Projected range of Ne+ ion lead (diamond symbol) and tin (square) perovskite targets for differention energies from 1 keV to 10 keV.   Sputter yield results are presented in the figures that follow, one for each element in the perovskite, namely, C, H1 (H of the methyl molecule), N, H2 (H of the ammonium molecule), Pb/Sn, I. Figure 2 shows the result for the number of C atoms ejected per incident Ne+ ion on the lead and tin perovskites at different angles of incidence varied from 0° to 89°, and for Ne+ energy of 1 keV and 5 keV. The same variables apply to Figs. 3 – 7, but for the other elements, respectively.For all results the yield is expectedly higher for higher ion energy, and a maximum yield occurs at the same θ~78° for both energies. Also, for 5 keV the yield obtained from the sputtering of tin perovskite is lower than that of the sputtering of lead perovskite for normal incidence, and then increases with angle of incidence, relative to the yield on lead perovskite, until it becomes higher around the angle of incidence at which maximum yield occurs.  0501001502002503000 2 4 6 8 10 12Projected Range (A)Ion Energy (KeV)Projected Range in PbProjectd Range in Sn41234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045       Figure 2: Sputter yield (C atoms/ion) for the ejection of C atoms from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV.     Figure 3: Sputter yield (H1 atoms/ion) for the sputter erosion of H atoms of the methyl molecule from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV.  However, for N erosion of Fig. 4, a first instance of the higher value of the sputter yield of the ion on Sn perovskite occurs at a lower angle of about 45° and then a second instance at the angle for maximum yield. Though, this could be a mere statistical fluctuation, it is noteworthy as it is exhibited in the H1 result of Fig. 3.Note that in Fig. 6 only two sets of data are available for each (Pb or Sn) since Pb is not available in tin perovskite or vice versa. The values of I atom yields are the highest Fig. 7, followed by H atom, Pb/Sn atom, N atom, and the lowest yields are those of the C atom. 00.050.10.150.20.250.30.350 20 40 60 80 100Sputter Yield Incidence Angle (Deg)1KeV Pb5KeV Pb1KeV Sn5KeV Sn00.20.40.60.811.21.41.60 20 40 60 80 100Sputter Yield Incidence Angle (Deg)1KeV of PB5KeV of PB1KeV of Sn5KeV of Sn51234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045       Figure 4: Sputter yield (N atoms/ion) for the erosion of N atoms from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV. The two H atom yields are similar, with the yield of H1 being slightly higher (about 1.4) than that of H2 (about 1.3).  Figure 5: Sputter yield (H2 atoms/ion) for the ejection of H atoms of the ammonium molecule from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV.  00.10.20.30.40.50.60.70.80 20 40 60 80 100Sputter Yield Incidence Angle (Deg)1KeV of Pb5KeV of Pb1KeV of Sn5KeV of Sn00.20.40.60.811.21.41.60 20 40 60 80 100Sputter Yield Incidence Angle (Deg)1KeV of PB5Kev of Pb1KeV of Sn5KeV of Sn61234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045       Figure 6: Sputter yield (Pb/Sn atoms/ion) for the erosion of Pb/Sn atoms from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV.   Figure 7: Sputter yield ( atoms/ion) for the erosion of I atoms from Ne+ bombardment of the perovskites at different angles of incidence and ion energy 1 keV and 5 keV.     00.10.20.30.40.50.60.70.80.90 20 40 60 80 100Sputter YieldIncidence Angle (Deg)1KeV of Pb5KeV of Pb1KV of Sn5KeV of Sn00.511.522.530 20 40 60 80 100Sputter Yield Incidence Angle (Deg)1KeV of Pb5KeV of Pb1KeV of Sn5KeV of Sn71234567890 ‘’“”2nd International Conference on Science and Sustainable Development IOP PublishingIOP Conf. Series: Earth and Environmental Science 173 (2018) 012045  doi :10.1088/1755-1315/173/1/012045      4.  Conclusion We performed molecular dynamics and Monte Carlo simulations of the ion sputtering of methyl ammonium lead iodide (lead perovskite) and its lead-substituted counterpart, methyl ammonium tin iodide (tin perovskite), as a new perspective of understanding and improving upon the desired physical properties of safer perovskite materials that are based on the possible substitutes for lead.  Currently, these substitutes give perovskites with a much lower PCE than lead perovskite. In our studies, reported in this paper, we found the sputtering results of lead perovskite and its best substitute so far, tin perovskite, to be very similar. In fact, so similar as to serve as another reason why the quest to improve upon the properties of tin perovskites, towards the desired better PCE in tin halide perovskite based solar cell applications, should not be abandoned despite its current very poor PCE.   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Projected Range and Sputter Yield of Ne+ and Ar+ in the

Sputtering of Lead and Tin Perovskites

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Projected Range and Sputter Yield of Ne+ and Ar+ in the Sputtering of Lead and Tin Perovskites

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