Easily Attainable, Efficient Solar Cell with Mass Yield of Nanorod

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Easy Attainable, Efficient solar cell with Mass Yield of Nanorods Singlecrystalline Organo-Metal Halide Perovskite-Based on Ball Milling Technique Ahmed Mourtada Elseman, Mohamed M. Rashad, and Ali M. Hassan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01183 • Publication Date (Web): 09 Aug 2016 Downloaded from http://pubs.acs.org on August 9, 2016

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ACS Sustainable Chemistry & Engineering

Easy Attainable, Efficient Solar Cell with Mass Yield of Nanorods Single-crystalline Organo-Metal Halide Perovskite Based on Ball Milling Technique

Ahmed Mourtada Elsemana*, Mohamed M. Rashada and Ali M. Hassanb

a

Electronic and Magnetic Materials Division, Advanced Materials Department, Central Metallurgical Research & Development Institute (CMRDI), P.O.Box 87 Helwan, 11421, Cairo, Egypt. b Chemistry Deparment, Faculty of Science, Al-Azhar Univeristy, Nasr city, Cairo, Egypt.

*

Corresponding author: Tel: +20227142452/4 Fax: +20227142451 E-mail addresses: [email protected]; [email protected] 1 ACS Paragon Plus Environment


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ABSTRACT Generally, nanoparticles of CH3NH3PbI3 (MLI) powders are increasingly recognized for their applications in solar cells. In this article, a new substitutional path to efficient mass yield with crucial reaction rates was proposed for the synthesis of MLI using ball mill technique. We compare between the condensation reflux strategy (RM) and the ball milling (BM) technique as synthetic routes to produce microparticles (RM-MLI) and nanoparticles (BM-MLI) from its microcrystalline powder. The change in crystal structures, microstructure and optical characteristics was investigated using XRD, FESEM, and photoluminescence emission (PL). FESEM micrographs showed a plummet straight down in particle size from 10 µm to ∼30 nm. The nanorods morphology was elucidated with transmission electron microscope (TEM). Optical absorption measurements indicate that compounds behaved the characteristic of direct band gap with Eg recorded of 1.50 and 1.56 eV for RM-MLI and BM-MLI, respectively. The two samples exhibited an intense near-IR photoluminescence (PL) emission in the 700−800 nm range at room temperature. The Hall-effect displayed as p-type semiconductors resulting from positive sign of Hall coefficient. Typically, by Cu2ZnSnS4 (CZTS) as a hole transport material, perovskite sensitized TiO2 film showed power conversion efficiency of 7.33 and 9.63 % with a fill factor record of 0.61 and 0.66 for RM-MLI and BM-MLI, respectively. Meanwhile, the results gave maximum external quantum efficiency (EQE) of 65% at 530 nm at AM 1.5G 1 sun intensity (100 mWcm2). Overall, this work gives an exceptionally simple method and efficient methodology to synthesize MLI nanoparticles with efficient power conversion.

KEYWORD: Perovskite Solar Cell, Green Chemistry, Processing, Nanorods, CZTS, Halleffect, High Power Conversion Efficiency

2 ACS Paragon Plus Environment

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INTRODUCTION Photovoltaic (PV) devices that include organic and inorganic nanomaterials to create new hybrid structures have attracted an increasing interest because of their low costs and high efficiencies.1 Accordingly, the use of organometal halide perovskite materials as organicinorganic hybrid materials has been explored for efficient light to electricity conversion in solar cells.2-4 The extensive flexibility of the perovskite material, likewise adds to the immense interest attracted.5-10. Generally, the synthesis techniques for perovskite materials assume a pertinent part on their physical and chemical properties. The variation of the homogeneity, crystallinity, stage virtue, morphology, grain size-scattering, surface zone, and numerous different parameters can be effectively adjusted by just changing material development route.11-13 Recently, green chemistry for the synthesis of materials has turned out to be a powerful and straightforward method without including high temperature treatment and consumed solvent for the synthesis of nanocrystalline powders, with compound procedures and items by creating novel responses that can optimize the wanted products and minimize by-products.14, 15 In this manner the grinding process consider as a type of green chemistry. Where the raw powders were caught between dynamic impacting balls, the internal surface of the vial causes misshaping, rewelding, and discontinuity of premixed powders were bringing about the development of fine, scattered particles in the grain-refined matrix. In this manner maintained endeavors have gone into the advancement of productive systems for perovskite arrangement. Moreover, the synthesis using ball mill technique (BM) is a desirable method for environmentally friendly, immaculate and energy efficient synthesis. Examinations on the characteristic of MLI exhibited that the morphology and crystallinity assume a focal part in the device execution.16, 17The morphology structure and grain size have an



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effect on the carrier mobility and indeed the achievement of the solar cell.18 Subsequently, investigation of novel morphologies and the improvement of a general strategy for structure and morphology control will make for improving the perovskite solar cell performance. The defy of producing efficient photovoltaic devices and cheap places numerous requests on the active materials. In devices based on p-i-n junction, the nanostructure characteristic plays a vital role in enhancement the efficiency.19-21 The easy synthesis of CH3NH3PbI3 (MLI) powders was previously reported by Prochowicz and coworkers.22The efficient grinding by ball milling technique provide high yield of powder and homogeneous morphology. They used gold as a cathode as well as spiro-MeOTAD as a hole transparent material (HTM). Herein, in the present work, we introduce an evaluated organohalide perovskite prepared by ball mill technique using nonpolar solvent like cyclohexane to form nanorods single-crystalline. The construction of the solar cell device using Cu2ZnSnS4 (CZTS) as a hole transport material and Al foil as a cathode based on the effectiveness of CZTS as a low cost HTM in comparison to spiro-MeOTAD was considered. Meanwhile, the comparison between the synthesized organometal halide powders using ball milling and condensation reflux strategies was also investigated. Finally, the fabrication of perovskite organo halide solar cell and the change in the power conversion were described. RESULTS AND DISCUSSION Reaction mechanism In this paper, we synthesized the perovskite material CH3NH3PbI3 by using two approaches. The first is solution growth of crystals and the second is ball milling technique. The two methods produce the target phase of material. The material obtained from the ball mill


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method is usually fast an efficient and give the desired perovskite phase without unreacted precursor as elucidated by the XRD profile. The mechanism of synthesis by ball mill can be utilizing an assortment of methodologies as shown in Figure 1a. In the first, the changes that occur in solid material trapped between colliding balls or balls and container walls during a high energy ball mill process can be demonstrated by the following approach. Once trapped between the balls, solid material is subjected to an external pressure causing a sequence of deformations which starts with reversible elastic deformations followed by pliability deformation, such as shear and snip deformations. As pressure increases, the latter becomes quite severe and finally lead to the crystallization of the material.23 Furthermore, Figure 1b illustrates the structure of CH3NH3PbI3 perovskite and Figure 1c shows the simulation of the grinding process happened for the perovskite materials. Crystal structure The formation mechanism of perovskite structure can be illustration by powder XRD patterns as shown in Figure 2. The fabricated strategy of CH3NH3PbI3 was performed using a reflux method by reacting PbI2 with CH3NH3I in the presence of DMF as solvent. These crystals were in this way overturned from yellow solution to black powder. Evidently, the XRD analysis of the synthetic perovskite shows tetragonal perovskite patterns. Reflection peaks of (211) and (310) planes maladjusted with cubic symmetry for tetragonal structure, and would be useful for the refinement between the cubic and tetragonal phase.24 For elucidation the same structure of as prepared perovskite, XRD peak positions of RM-MLI is in close agreement to BM-MLI. We can notice the width and proportional intensities of the XRD summits of BM-MLI perovskite formed by ball mill technique were somewhat diverse in view of the adjustments in their particles size as appeared in Figure 2b. From these



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XRD measurements, the ball milling synthesis produces highly crystalline CH3NH3PbI3 material and revealing no impurity extra peaks are detected in the structure of the starting methyl amine iodide and PbI2 materials; this indicates that the nanostructures of powder were of high purity and good crystallinity. The crystallite sizes of the synthesized BM-MLI powders were estimated from the squeakiest peak (220) phase of the X-ray diffraction data based on the Debye-Scherrer equation:

dRX = kλ/β Cosθ

(1)

where dRX is the crystallite size, k = 0.9 is a correction factor to account for particle shapes, β is the full width at half maximum (FWHM) of the most squeakiest diffraction peak (220) plane, λ is the wavelength of Cu target = 1.5406 Å, and θ is the Bragg angle at 25° of an X-ray powder diffraction pattern as illustrated in Figure 2.25 The XRD pattern of the CZTS nanoparticles was revealed in (ESI, Figure S1). The peaks of Cu2ZnSnS4 sample at 2θ = 28.5, 33.0, 47.3, 56.2, 59.0, 69.2, and 76.4° can be attributed to the indexed of (112), (200), (220), (312), (224), (008), and (332) planes, respectively. Besides, the XRD indicates all solidified nanoparticles with no obvious trace of the auxiliary stage.26 Microstructure A considerable area of organometal halide perovskite interface was expected to separate photogenerated excitons, yet an efficient charge extraction requires to the change of morphology that permits efficient transport of charge bearers to the electrode. From Figure 3a, b we can depict the morphology of RM-MLI perovskite powders characterized after crystallization. For the as-grown solution, the powder shows a rounded tetragonal-like morphology with particles growth which agree with XRD characterization, and the particles size is around less 10 µm. Otherwise, the Figure 3c, d represents the shape of formed perovskite particles (BM-MLI) in the


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nanoscale about 20-50 nm and the particles are regularly distributed. To evaluate and understand the microscopic structure of BM-MLI, TEM micrograph evinced in Figure 4a indicated

BM-

MLI was exhibited outstretched nanocrystals having rod-like morphologies with particles size of around 30.3-37.3 nm. Plainly, the indexing SAED pattern illustrated in Figure 4b for BM-MLI sample showed the axis line of crystalline nanorods with d spacing of 3.05 Å perpendicular to the (220) set of lattice planes was assigned. To understand better, we make FESEM for the thin films by the two methods in order to the study the effect of mother powder for both ball mill technique and reflux method on the shape and growth of the particles. The surface scanning for RM-MLI and BM-MLI thin films were obtained in Figure 4c, d. It can be seen that the growth of particle-like cubic in reflux system with low distributed resulting from non-stoichiometry of the reactant as shown in Figure 4c. Whereas in Figure 4d the morphology of ball milling technique revealed the view of the surface as homogeneous and vertically aligned nanorods form. Optical properties The optical properties were considered by enrollment the absorption and reflectance spectra of the formed powders in the wavelength range 200 – 1000 nm using UV–Vis-NIR spectrophotometer. The results were presented in Figure 5. It can be seen that there is a high absorption for the RM-MLI and BM-MLI samples in the wavelength range of visible light. The absorption edge shifts towards the shorter intensity direction for the RM-MLI sample which prepared by reflux method, whereas the BM-MLI nanoparticles that fabricated with ball mill technique exhibit a high intensity wavelength, which means that the band gap energy of BMMLI decreases comparing to that of the RM-MLI. Plainly, from ultra violet and visible light



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spectra (Figure 5a) there are a two peaks were spotted at ~300 and 350 nm, these peaks attributed to ligand to metal charge transfer (LMCT), and intra-atomic transitions.27, 28 The optical band gap energy (Eg) was calculated using diffuse reflectance UV-Vis measurements. The reflectance spectra for the RM-MLI and BM-MLI samples were explained in Figure 5b. From Kubelka–Munk equation, it can be calculate using these equations (2) and (3)

=

=

[ℎ] = ℎ −

(2) (3)

where R is represent the light reflected, while α and S are the absorption and scattering coefficients, respectively.29, 30 Another factors like A is a constant and depends on the transition probability, p is the power index equals 1/2 or 2 for direct or an indirect, respectively [31]. The procedures was completed by plot of (αhν)2 vs hν as shown in Figure 6. By extrapolating the straight line portion of these plots to the hν axis and from the point of intersection on the hν axis, band gap values for BM-MLI and RM-MLI equal to 1.50 and 1.56 eV, respectively. From this point, the sample was synthesized according to the ball mill technique showed an efficient in band gap energy than the traditional method used in synthesis of perovskite materials. Consequently, it is conceivable to declare that the technique used to fabricate these specimens were vital. From the results it is noticeable; the energy band gap relies on the crystallite size. In this way, it is conceivable to affirm that both the crystalline phase influence the optical band gab.32-34 Photoluminescence (PL) spectra Next to the optical properties, both intrinsic and extrinsic properties of a semiconductor material were identified using the photoluminescence spectroscopy. To extend the application 8 ACS Paragon Plus Environment

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fields of MLI and to grow new optoelectronic devices tool in view of this material system, the presence of photoluminescence quenching in our materials were indicated for (i) the generation of excitons depend on photoabsorption efficiency; (ii) The charge separation can occur at an interface due to migration rates of the excitons; (iii) and finally the powerful of charge separation.35, 36 Figure 7 displays PL emission spectra of BM-MLI and RM-MLI powders at room temperature. The PL spectra were measured with excitation band (507 nm). BM-MLI and RMMLI powders showed a broad red luminescence band around 750 nm (1.65 eV). Indeed the figure of PL intensity show BM-MLI was jumped by 40% compared to that of RM-MLI. This sensational PL was accepted because of efficient charge transfer caused by nano crystal size of materials that is prepared by ball mill technique.37, 38 Thermal analysis The majority of compounds including organic – inorganic hybrid suffer physical and chemical changes when subjected to heat energy. Under defined experimental conditions, these changes are characteristic of such substances and can be used for its qualitative and quantitative analysis. The thermal behaviors show similar trends for RM-MLI and BM-MLI perovskite as shown in Figure 8. The TGA profiles over the range 25−200 ℃ are commonly due to lack of water

molecules. Above 200 ℃ the MLI was decomposed in a continuous way, which might be because of discontinuity and thermal degradation of the organic moiety. From the curve we can see the decomposition start initially at 200 and 205 ℃ with a mass loss corresponding to

CH3NH3I and PbI2 for RM-MLI and BM-MLI, respectively. In the second step continuous loss of weights was observed up to 700 ℃ for both compounds corresponding to transformation of 9 ACS Paragon Plus Environment


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PbO2 due to the compound was decomposed in air. On the premise of TGA studies, the prospective for the decomposition of MLI was suggested in the following two steps. The perovskite particles start to disband at 250 ℃ around, with starting plummet of amine fractions

and continue up to 496 ℃. The second step in the end corrupts the lead iodide into lead oxide as

described on Table 1.39, 40 We can conclude that when the perovskites were synthesized by ball mill method, the first venture of disintegration exhibit loss in mass as compared to the perovskite synthesized by reflux method in presence of high temperature. Step -1 CH3NH3I + PbI2

CH3NH3PbI3

(4)

Step -2 PbO2

PbI2

(5)

On the basis of DTA studies, the figure reveals strong with broadband exothermic effect at ~300 and 337 ℃ for RM-MLI and BM-MLI, respectively. Therefore, the shape of the peak depended on the transformation or chemical reaction, as well as on the heating rate or energy used to complete the reaction like ball milling technique. For the second stage, the phase was broad and sharp due to they occurred at a specific temperature until complete the phase. Kinetic and thermodynamics analyses The kinetic and thermodynamics analyses for the thermal decomposition were carried by type of methods based on thermal rate i.e. Coats-Redfern and Horowitz–Metzger. Herein, we study only the Coats-Redfern method to evaluate the kinetic parameters of the MLI.41 The final equations used to ascertain the kinetic and thermodynamic parameters and to evaluate the activation energy Ea, reaction order (n), and frequency factor (A) were as the following:

ln −

!

" = ln

#

$%&

'1 −

! %&

%

)" − !&


(6)

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= log ,-

.%

'1 −

%$2=

! %

)/0

(7)

34 35

(8)

36 35

where α is fractional weight loss, β is the thermal rate, whereas the R and E were the gas constant and the activation energy, and is. The activation energy was resulting from a plot of log2/

8 vs 1/T. Also, from Coats-Redfern method and using the following equations we can calculate ∆H, ∆S and ∆G: #?

∆: = 2.303 log ' ) @!

(9)

∆A = − 8

(10)

∆B = ∆A − 8∆:

(11)

where, h is Planck constant, T is temperature, k and A were Boltzmann constant and frequency factor, respectively. From the thermodynamics and kinetic parameters which derived by using Coats Redfern method. The findings as illustrated in Table 2 can be summarized as following: (i) The correlation coefficient was in good order by using the least square strategy. (ii) ∆S* with negative values affirm the ordered of intermediate. (iii) ∆H* with positive values indicate the decomposition processes were endothermic. (iv) The occurrence of the decomposition in the first stage revealed by Ea values at the corresponding temperatures. (v) It can be notice that the free energy ∆G* increases from first to second stages and indicate the nonspontaneous behavior.



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Hall-effect and carrier mobility Herein, the resistivity and carrier mobility of RM-MLI and BM-MLI were conducted using Hall-effect measurement. The Hall coefficients of synthesized by RM and BM pathways were positive to confirm carriers p-type for the two samples.42 Figure 9a describes the relationship between temperature and resistivity. The resistivity of CH3NH3PbI3 powders as reflux and ball mill methods was decreased with increase the temperature. The initial resistivity was 3.933 × 10D and 4.140 × 10D Ω recorded at 285 E for BM-MLI and RM-MLI, respectively.

This initial high resistivity was gradually decreased at ~309 E to become 365 and 460 Ω for BM-MLI and RM-MLI, respectively.

Figure 9b presents the electron mobility based on temperature. The change in conductivity was imputed to the movement of electron-hole pairs. As temperature was increased covalent bonds were breaker and more electron-hole pairs were available for conduction.43This means that at zero kelvins, all the electrons have occupied positions in valence band and no electrons were there in conduction band and subsequently, resistance was infinite. With increasing temperature, the electrons from valence band were acquired energy and jumped to conduction band and thus, the resistance was continued to decrease with increasing in carrier concentration of the conduction band.44 Photovoltaic performance The architecture of perovskite solar cell based on CZTS-HTMs presented in this paper was shown in Figure S2. The approach of the procedures and materials used illustrated in details within experimental section. The cell is the unpretentious best bilayer planar hetero-junction structure. The perovskite used in this device as the light absorber and CZTS work as the hole transport layer, whereas TiO2 is the electron transport layer.


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Generally, organic hole conductor employed as a p-type, the famous among them is 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-OMETAD),45,

46

which positioned as hole extraction materials so as to achieve high efficiencies. There is no doubt that spiro-OMETAD suffer from thermal degradation, low diffusion rate and high production cost beside need doping by other materials to improve the carrier density, all these factors decrease wide application in commercial photovoltaics.47,

48

In this regard, it is imperative to

develop low cost and high stable HTMs such as CZTS. Some reported used CZTS for instance Qiliang Wu et al. in the perovskite solar cell fabricated with solution process deposition method, prompting a superior performance of 12.75% and quite comparable to that obtained for perovskite based on commonly used organic HTM such as spiro-OMETAD. Other Cu derivative was applied in perovskite solar cell for example; Christians et al. introduced CuI HTM into the perovskite and achieved a power conversion of 6.0%. These limited reports demonstrate the great potential of Cu-based inorganic HTMs in high efficiency PSCs toward improved reproducibility and stability.49, 50 In comparison, (spiro-OMETAD) and CZTS as a HTM, we find that the reported essay by Prochowicz et al. accomplished a power conversion efficiency of 9.1% and our result achieved higher efficiency by low-cost HTM was 9.63% with a one-step deposition method. To the best our knowledge, this is the highest efficiency that has been reported for perovskite solar cell based Al-foil as counter electrode. Meanwhile, this method opens the way for developments of cost-effective, stable and efficient perovskite solar cell which is competitive with printing infrastructure. Device performance remains a challenge and needs to be developed through morphology structure this is achieved from development a new technique. The devices with powder



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synthesized by reflux system and ball mill technique were manufactured utilizing comparative procedures and parameters. From ESI (Figure S2) which illustrated the methods and technique used in preparation of perovskite cell. The characteristics of current–voltage (J–V) were measured under simulated solar illumination (AM 1.5G, 100 mW.cm–2). The J–V curves of the two cells were illustrated in Figure 10a and the summary of device performance parameters were presented in Table 3. The device which fabricated from RM-MLI shown the lowest PCE of 7.33%, with an open circuit voltage (Voc) of 0.72 V, a short-circuit photocurrent density (Jsc) of 16.84 mA.cm–2, and a fill factor (FF) of 0.61. After used BM-MLI into the devices, Voc, Jsc, FF, and PCE raised dramatically to 0.82 V, 17.75 mA.cm–2, 0.66, and 9.63%, respectively.51The perovskite solar cell was elucidated under spot light to measure the output volt using Avometer as shown as in Figure S3. The design and FESEM of a cross section of the perovskite cell without the Al foil as electrode was revealed in Figure 10c, d. The FESEM images explained a well-structure, layer by layer and clear interfaces between each layer. We can notice that each layer in the cell was in close contact together, which reduce the resistance and become very low. The thickness of the (TiO2 + perovskite) and the CZTS layers predestined from the FE-SEM pictures is 400 nm and 140 nm, respectively. Therefore, the improvement of distribution, morphology and size in perovskite materials lead to enhance the efficiency for solar cell application. The incident photoelectric conversion efficiency (IPCE) IPCE of semiconductor pin junction energizes an electron from the valence band to the conduction band abandoning a hole. Then, pin junction clears away these transporters to an outside circuit before they can re-consolidate. The IPCE spectra of devices were revealed in Figure 10b. An enhancement within the wavelength range from 350 to 750 nm and highest


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intensity with 65% was observed for the BM-MLI device whilst, the RM-MLI device recorded about 60%. Furthermore, from EQE results could be used to calculate Jsc of the device, under normal conditions. This is basically calculated by using this equation over the spectral range of response.52

G H = I :J K. L K. MK

(12)

where Jsc is in A.m-2, St(λ) is the device spectral response, in A.W-1.nm-1 and E0(λ) the AM1.5 reference spectrum in W.m-2.nm-1. The Jsc calculated from the EQE spectra were harmonious with the values obtained from the J–V curves, which are presented in Table 3. The internal quantum efficiency IQE can be calculated based on the measurements of reflectance, transmittance and the EQE. EQE was simply calculated from this equation:

IQE =

QRQ

(13)

S T

where R is the reflectance, and T the transmittance of the sample. It can be seen that the IQE as shown as in Figure S4. To better understanding, the impact of ball mill technique on the high performance of perovskite solar cell in comparison with the traditional method. The cubic and nanorods like morphology of RM-MLI and BM-MLI thin films were affected by mother prepared materials as appeared in previous (Figure 4c and d). The technique used in the synthesis of perovskite that was found to assume a vital part in hindering the rapid reaction. At that point, the amazingly flat film was converted into a pure crystalline after annealing at 120 ℃. There is no doubt that the using of solid state reactions (grinding method) has the ability to isolate the materials in pure form. Therefore, the materials prepared by this method were stoichiometrically effective as well. The strategy for decision to acquire pure materials with exact stoichiometries and lowest number of defects was the solution method.53 15 ACS Paragon Plus Environment


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On one hand, depend on this we believe that electron or hole will be reduced due to exact ratio and higher purity of component. This return to the ball milling technique produces the perovskite in higher crystallinity. Also, the purity of material could participate to better PCE for devices obtained. On the other hand, the reflux system was suffering from synthesis of perovskite in exact stoichiometric composition due to many factors such as recrystallization process, washing, etc. in another meaning, an excess of reactant will create electron traps which lead to charge recombination and lowering power conversion efficiency. From these result, we note that there is low trap state filling effect in BM-MLI thin film rising from a uniform and closely packed of nanorods perovskite films. In contract, the RM-MLI thin film was comparatively distributed which illustrated above in (Figure 4d) with indicative of localized nucleation.54 CONCLUSIONS To sum up, we conclude synthesis of perovskite materials assumed an important role in the efficiency of solar cell. The use of ball mill technique considers as a new an alternative chemical approach and a promise avenue for the synthesis of MLI perovskite particles. By this method we obtain high crystanility and purity. The materials acquired from the BM strategy usually are fast, an efficient and give the desired perovskite phase without unreacted precursor as elucidated by the XRD. Evidences, the absorbance of light by perovskite layer produced using BM evinced a high crystallinity and a good microstructure. This work highlights the potential of low perovskites materials semiconductors in constructing new nanostructured superb materials. In addition, CZTS has been successfully applied as inorganic hole transport materials for perovskite solar cell due to low cost as well as availability. The construction perovskite solar cell showed efficiency of 7.33 and 9.63 % with a fill factor record of 0.61 and 0.66 for RM-MLI and


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BM-MLI, respectively. In the meantime, the external quantum efficiency (EQE) gave of 65% at 530 nm. The efficiency resulted from cell reveals that CZTS can be improving the contact between the perovskite layer and Al foils besides that the crystanility properties of MLI. EXPERIMENTAL SECTION Chemicals CH3NH2 (40 wt. % in H2O), hydroiodic acid (57 wt. % in water), Lead iodide (99.999%) and diethyl

ether

were

purchased

from

Sigma-Aldrich.

Dimethylformamide

(DMF),

Cu(CO2CH3)2.H2O, Zn(O2CCH3)2(H2O)2, SnCl4, thiourea, ethanol, chlorobenzene and acetic acid. 1-Octadecanamine (OA) (Sigma Aldrich, 98%), titanium tetraisopropoxide (Ti(isoprop)4 (Acros, 98%), indium tin oxide coated sheet glasses (ITO, 15 Ω , Sigma Aldrich) were also employed. All the chemicals were used without further purification. Synthesis of RM-MLI by reflux system Typically, 1 mol (38 mL) methylamine (CH3NH2) solution was reacted with (40 mL) hydroiodic acid (HI) and stirring at 0 °C for about 2 h to synthesize methyl ammonium iodide CH3NH3I. Then, Crystallization of CH3NH3I was achieved using evaporator at 80 °C for 3 h. The obtained CH3NH3I powder reacted with lead(II) iodide PbI2 were dissolved in DMF with stirring at 120 °C for 6 h to produce CH3NH3PbI3 (RM-MLI) precursor solution. Finally, the growth of crystals of MLI was achieved by the slow evaporation method of the solution at 50 °C. Synthesis of BM-MLI by ball milling (BM) technique 4.61 g PbI2 powder (1 mol) was blended with 1.60 g CH3NH3I powder (1 mol) to produce CH3NH3PbI3 (BM-MLI). Totally 6.21 g of the mixture was wetting in cyclohexane as suitable medium and four zirconium spheres (1.0 cm in diameter) having a total mass of 20 g were placed in the grinding bowl, under air atmosphere, equipped with a 125 cm3 jar. The weight ratio of



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Page 18 of 43

material per balls was 1 per 10. The ball-milling process was carried out at 550 rpm for 30 min (Retsch PM 200). The following image (Figure 11) illustrates the process of ball mill device and the reactant materials before and after. Fabrication of perovskite solar cell In general, ITO-coated glass sheets (surface resistivity 8-12 Ω/sq Sigma-Aldrich) were washed with soap in water, deionized water, acetone, and ethanol. A thick compact layer of TiO2 was deposited on the glass using titanium isopropoxide (99.999% purity) diluted in anhydrous ethanol and sintered for 30 mins at 500 °C. After the substrate was allowed to cool, a thick layer of TiO2 was deposited via spin coating at 1000 rpm for 1.5 min. The substrate was then heated at 500 °C for 30 min. The CH3NH3PbI3 perovskite precursor solution was prepared previous mentioned above. Then the precursor solution was made in DMF, next spin coated onto the TiO2 coated substrate under close atmosphere. After formation of the perovskite layer at 120 ℃, and was cooled down to room temperature, a 0.3 g Cu2ZnSnS4 synthesized according as mentioned in supporting information was dispersed in nitrobenzene to deposit on top of the MLI layer using spin-coating at 3000 rpm, followed by annealing for 10 min at 100 oC. Lastly, an Al foil was used to work as conducting electrode. The devices were then sealed using an epoxy resin. The active area of the devices is approximately 0.46 cm2. Physical characterization XRD patterns of the resulting products were identified by a Brucker D8-advance X-ray powder diffractometer with Cu Kα radiation (λ = 1.5406 Å). The micrographs of produced samples were examined by direct observation via field emission scanning electron microscope (FESEM) model (JSM-5400, JEOL instrument, Japan). Transmission electron microscopy (TEM) and high Resolution Transmission electron microscopy (HRTEM) were performed with a


Page 19 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


JEOL-JEM-1230 microscope. The UV-Vis absorption and diffuse reflectance spectrum were recorded

at

room

temperature

using

UV-VIS-NIR

spectrophotometer

(Jasco-V-570

spectrophotometer, Japan) fitted with integrating sphere reflectance unit (ISN) in the wavelength range 200 - 2000 nm. Photoluminescence (PL) spectra were performed at room temperature with a fluorescence spectrophotometer equipped with 50 W xenon lamp (Shimadzu RF-5301PC, Kyoto, Japan). Hall-effect measurements were performed on a 4-probe sample holder placed between the plates of an electromagnet. The magnetic field was varied in the 0.5 T range. The CH3NH3PbI3 films were fulfilled with a HMS 5,000 Hall-effect measurement system at room temperature in the dark using Van der Pauw geometry. The electron density and electron mobility were calculated from Hall measurements. Device performance was tested in ambient conditions using a Keithley 2420 source meter unit under simulated 100 mW cm-2 (AM 1.5G) irradiation from a solar simulator (Solar Light Co. Inc.). An NREL certified silicon reference cell was used to calibrate the integrated light-output from the simulator to 100 mW cm-2 at 25 °C. The incident photon to current conversion efficiency (IPCE) measurement system (PVE 300, Bentham) comprised a Xenon lamp, a monochromator, a chopper, a lock-in amplifier and calibrated silicon photodetector was employed for external quantum efficiency (EQE). EQE measurements of solar cell devices were acquired under continuous illumination of monochromated light from a tungsten lamp. The PVE300 permits the quick and accurate determination of solar cell spectral response/ EQE (IPCE). The additional measurement of cell transmittance and reflectance allows the determination of IQE.



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ASSOCIATED CONTENT Supporting Information Addition of methods used for synthesis of TiO2 and CZTS nanoparticles, XRD patterns of Cu2ZnSnS4, Scheme of cell preparation and finally internal quantum efficiency (IQE). This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author Ahmed Mourtada Elseman *Tel: +20227142452/4

Fax: +20227142451

E-mail addresses: [email protected]; [email protected] Notes The authors declare no competing financial interest. Acknowledgements The authors would like to extend their sincere appreciation to Dr. A. E. Shalan for suggestions in editing my manuscript and thanks to Central Metallurgical Research and Development Institute, Egypt for its financial support to pursue that work. References (1) Jayawardena K. D. G. I.; Rozanski L. J.; Mills C. A.; Beliatis M. J.; Nismy N. A.; Silva S. R. P. Inorganics-in-Organics: recent developments and outlook for 4G polymer solar cells. Nanoscale 2013, 5(18), 8411-8427. (2) Burschka J.; Pellet N.; Moon S. J.; Humphry-Baker R.; Gao P.; Nazeeruddin M. K. et al. Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 2013, 10, 499(7458), 316–319.


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Page 28 of 43

List of Tables

Table 1: Thermal gravimetric analysis for RM-MLI and BM-MLI Compound

Stages

Calculated

Found

Assignment

RM-MLI

First Step

25.63

24.96

CH3NH3I

& BM-MLI

Second Step

47.28

47.32

PbO2


Page 29 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2: Kinetic data of the thermal decomposition of RM-MLI and BM-MLI by Coats-Redfern method Coats – Redfern Compd.

Steps

Cs

∝

A S

-1

Ea KJ mol

-1

R2

∆H*

∆S*

∆G*

KJ mol-1

KJ mol-1K-1

KJ mol-1

1st

0.05

0.008

2.03x103

28.054

0.876

25.654

-0.161

79.907

2nd

0.04

0.02

1.08x1013

176.097

0.809

144.287

-0.113

151.343

1st

0.05

0.008

2.05x103

30.082

0.986

27.3523

-0.163

80.927

2nd

0.04

0.02

1.16x1014

188.579

0.947

183.236

-0.114

159.379

RM-MLI

BM-MLI



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Page 30 of 43

Table 3: Photovoltaic characteristics of cells measured under illumination with standard AM 1.5G simulated sunlight (100 mW/cm2) Perovskite

2

Voc

Jsc(mA/cm )

RM-MLI

0.72

BM-MLI

0.82

Jsc(mA/cm2)

FF

η(%)

16.84

60.50%

7.33

16.64

17.75

66.00%

9.63

17.50


calc.

Page 31 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure Captions

Figure 1

(a) The approach and mechanism of synthesis in ball mill technique. (b) The structure of CH3NH3PbI3 perovskite. (c) Simulation of the grinding process happened for the perovskite materials.

Figure 2

Left side is the XRD patterns and Right side is the 3D simulation of (a) RM-MLI; (b) BM-MLI.

Figure 3

FESEM images of (a) and (b) showing the growth crystal of the RM-MLI compounds obtained from the reflux method. (c) and (d) showing the nanoparticles of BM-MLI prepared compound by ball mill

Figure 4

Representative (a) TEM image (b) Indexing SAED pattern for BM-MLI crystalline showing the nanoparticles of prepared compound by ball mill, Surface FESEM images of (c) showing the cubic growth crystal of the RM-MLI thin film (d) showing the nanorods of BM-MLI thin film

Figure 5

(a) Absorbance and (b) Diffuse reflectance spectra of the RM-MLI and BM-MLI powders synthesized by reflux and ball mill technique.

Figure 6

Band gap energy of produced RM-MLI and BM-MLI powders by reflux and ball mill strategies.

Figure 7

Photoluminescence spectra of RM-MLI and BM-MLI powders by reflux and ball mill with excitation spectrum at 507 nm.

Figure 8

TGA and DTA analysis for the as (a) RM-MLI; (b) BM-MLI particles as function of the temperature

Figure 9

(a) Resistivity as a function of temperature (b) Charge Mobility as a function of temperature for RM-MLI and BM-MLI

Figure 10

(a) I–V characteristics and (b) EQE of perovskite solar cell made from the RM-MLI and BM-MLI nanoparticles (c) and (d) cross sectional of cell device explain the depositing layer.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figures

(a)

(b)

(c)

Figure 1: (a) The approach and mechanism of synthesis in ball mill technique. (b) The structure of CH3NH3PbI3 perovskite. (c) Simulation of the grinding process happened for the perovskite materials.


Page 32 of 43

Page 33 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2: Left side is the XRD patterns and Right side is the 3D simulation of (a) RM-MLI; (b) BM-MLI



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a

Page 34 of 43

b

d

c

Figure 3: FESEM images of (a) and (b) showing the growth crystal of the RM-MLI compounds obtained from the reflux method. (c) and (d) showing the nanoparticles of BM-MLI prepared compound by ball mill


Page 35 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

b

100 nm

d

c

500 nm

10 um

Figure 4: Representative (a) TEM image (b) Indexing SAED pattern for BM-MLI crystalline showing the nanoparticles of prepared compound by ball mill, Surface FESEM images of (c) showing the cubic growth crystal of the RM-MLI thin film (d) showing the nanorods of BMMLI thin film



a

b 1.0

RM-MLI BM-MLI

300 nm

100

RM-MLI BM-MLI 80

Reflectance %

0.8

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 43

350 nm 0.6

0.4

60

40

20

0.2

300

400

500

600

700

800

900

1000

0 200

400

600

800

Wavelength (nm)

Wavelength (nm)

Figure 5: (a) Absorbance and (b) Diffuse reflectance spectra of the RM-MLI and BM-MLI powders synthesized by reflux and ball mill technique


1000

Page 37 of 43

160000

BM-MLI RM-MLI

140000

2

120000

(F(R)hυ)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100000 80000 60000 40000

Eg= 1.50

20000

Eg= 1.56

0

1.2

1.3

1.4

1.5

1.6

1.7

Energy (eV)

Figure 6: Band gap energy of produced RM-MLI and BM-MLI powders by reflux and ball mill strategies



700

RM-MLI BM-MLI

600 500

PL intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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400 300 200 100 0 650

700

750

800

850

900

Wavelength(nm)

Figure 7: Photoluminescence spectra of RM-MLI and BM-MLI powders by reflux and ball mill with excitation spectrum at 507 nm


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a

b 100

0.6

480oC

0.6

o

500 C

100

300oC

0.4 0.3

60

0.2 40

0.1

0.5 o

337.46 C

80

Weight %

Weight %

80

0.4 0.3

60

0.2 40

0.1

0.0

20

0.0

20

0

100

200

300

400

500

600

700

-0.1 800

-0.1

0

100

Temprature (oC)

200

300

400

500

600

Temprature (oC)

Figure 8: TGA and DTA analysis for the as (a) RM-MLI; (b) BM-MLI particles as function of the temperature


700

o

RM-MLI (Deriv. Weight)

0.5

Deriv. Weight (%/ C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



. b

3500 3000 2500 2000 1500 1000

BM-MLI RM-MLI

45 -1 -1

RM-MLI BM-MLI

4000

44

2

4500

Mobility (cm V s )

a

Resistivity (Ω cm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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43

500

42 41 40

0 280

290

300

310

320

330

340

280

290

300

310

320

330

340

Temperature (K)

Temperature (K)

Figure 9: (a) Resistivity as a function of temperature (b) Charge Mobility as a function of temperature for RM-MLI and BM-MLI


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a

BM-MLI RM-MLI

18

b RM-MLI BM-MLI

70

15

60

12

50

EQE %

Current Density (mA/cm2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9 6

40 30

3 20 0 10 -3 0 0.0

0.2

0.4

0.6

400

0.8

500

600

700

Wavelength(nm)

Voc (V)

c

d

Al foil

CZTS MLI+TiO2 ITO Glass

Figure 10: (a) I–V characteristics and (b) EQE of perovskite solar cell made from the RM-MLI and BM-MLI nanoparticles (c) and (d) cross sectional of cell device explain the depositing layer.


800


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 11: Simulation image of Jar of ball mill device used in grinding process


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Graphical abstract Easy Attainable, Efficient Solar Cell with Mass Yield of Nanorods Single-crystalline Organo-Metal Halide Perovskite Based on Ball Milling Technique Ahmed Mourtada Elseman, Mohamed M. Rashad and Ali M. Hassan

Synopsis: Starting materials were trapped between colliding balls and container walls during ball milling process to form CH3NH3PbI3 nanorods.


Easily Attainable, Efficient Solar Cell with Mass Yield of Nanorod

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