Efficiency Enhancement and Hysteresis Mitigation by Manipulation of

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Efficiency Enhancement and Hysteresis Mitigation by Manipulation of Grain Growth Conditions in Hybrid Evaporated-Spincoated Perovskite Solar Cells Saeid Rafizadeh, Karl Wienands, Patricia Samia Cerian Schulze, Alexander J. Bett, Lucio Claudio Andreani, Martin Hermle, Stefan W. Glunz, and Jan Christoph Goldschmidt ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16963 • Publication Date (Web): 04 Dec 2018 Downloaded from http://pubs.acs.org on December 5, 2018

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ACS Applied Materials & Interfaces

Efficiency Enhancement and Hysteresis Mitigation by Manipulation of Grain Growth Conditions in Hybrid Evaporated-Spincoated Perovskite Solar Cells

Saeid Rafizadeh,*,†,‡ Karl Wienands,¥ Patricia S.C. Schulze,† Alexander J. Bett,† Lucio Claudio Andreani,‡ Martin Hermle,† Stefan Glunz,†,¥ Jan Christoph Goldschmidt†

†Fraunhofer

Institute for Solar Energy Systems ISE, Freiburg, 79110, Germany.

‡University

⁑University

of Pavia, Department of Physics, Pavia, 27100, Italy.

of Freiburg, Department of Sustainable Systems Engineering (INATECH), Freiburg, 79110, Germany.

*Corresponding author. Email: [email protected], [email protected]

ACS Paragon Plus Environment

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ACS Applied Materials & Interfaces 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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KEYWORDS: Perovskite solar cells, Grain growth, Optoelectronic performance, Hysteresis, Hybrid deposition, Grain and Interface Passivation

ABSTRACT: Perovskite solar cells became a game changer in the field of photovoltaics by reaching power conversion efficiencies (PCE) beyond 23%. To achieve even higher efficiencies it is necessary to increase the understanding of crystallization, grain formation and layer ripening. In this study, by a systematic variation of the MAI concentrations we changed the stoichiometry and thereupon the crystal growth conditions in MAPbI3 perovskite solar cells, prepared by a two-step hybrid evaporation-spincoating deposition method. Utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force

miscroscopy

(AFM),

photoluminescence

(PL)

and

current-voltage

(J-V)

characterization, we found that a relatively lower concentration of MAI or in other words higher content of remnant and unconverted PbI2 correlates with smaller and stronger interconnected grains, as well as with an improved optoelectronic performance of the


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solar cells and mitigation of hysteresis. Possible explanations are grain and interface passivation by the excess PbI2 and a positive contribution of the grain boundaries to current extraction.

1. INTRODUCTION The rapid increase in the efficiency of perovskite solar cells within the past few years made them promising candidates for the future of photovoltaics. Organic-inorganic trihalide perovskites demonstrated outstanding performance due to their superior optical and electrical properties such as long diffusion length and life time, high carrier mobility and large absorption coefficient.1,2 This class of perovskites employs an ABX3 structure where A is an organic cation like methylammonium (MA) or formamidinium (FA) or inorganic cation like cesium (Cs) or rubidium (Rb). B is a metal cation like Pb or Sn and X is a halide like I, Cl or Br. So far, many investigations have been done to boost the power conversion efficiencies (PCEs) of perovskite solar cells towards the silicon's record PCE.3-13 The main goal was to reach similar efficiencies while using cheaper materials and methods. In this regard, different sensitizing methods have been utilized, ranging


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from solution processing3-8 to vacuum deposition9-12 and hybrid routes13-15, which combine vacuum and wet-chemical methods. Solution processing made it possible to easily tune the perovskite composition and to achieve band-gaps useful for tandem applications and higher stability.16-19 Vacuum deposition enabled a more controlled and reproducible sensitizing process.9 Hybrid deposition methods have shown to be able to combine high efficiency and reproducibility with a rather easy fabrication procedure.13-15 With maturing of the fabrication methods, a deepened understanding of the factors determining PCE becomes more and more important for further improvements. Especially understanding of crystallization, grain growth conditions and layer ripening20,21 is crucial as those effects determine the occurrence of defect centers that could limit the performance.22-26 Accordingly, the stoichiometry engineering and more specifically the role of excess PbI2 in perovskite structures and its impact on crystallization quality, optoelectronic properties and photovoltaic performance of different perovskite solar cells has been studied recently.27-33 However, among all these studies, perovskites produced via the highly reproducible and efficient two-step hybrid evaporation-spincoating deposition method have not been investigated. The important advantage of this


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fabrication technique for such investigations is the high level of reproducibility due to the better control over perovskite layer deposition. In this method the only solution required for perovskite formation is MAI in isopropanol (IPA) while in solution processing it is crucial to have exact contribution of the solvents and materials in perovskite solution, which is one of the main reasons for reproducibility challenges. Therefore, in this study we investigated the role of stoichiometry variation on the morphological properties and thereupon optoelectronic and photovoltaic behavior of MAPbI3 perovskite solar cells fabricated via the hybrid method, where first the inorganic PbI2 phase is deposited via thermal evaporation and then the organic MAI phase is spun to intercalate and form the perovskite phase during annealing. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to study the crystallization quality and surface morphology. Time-resolved and steadystate photoluminescence (PL) measurements are performed to evaluate the charge transportation quality. Finally, photovoltaic parameters of the solar cells are measured and compared.


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2. EXPERIMENTAL SECTION 2.1. Materials Spiro-MeOTAD, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), bis (trifl uoromethane) sulfonimide lithium salt (Li-TFSI,99.95%), 4-tertbutylpyridine (96%), chlorobenzene (≥99.5%), and acetonitrile (anhydrous, 99.8%) were purchased from Sigma Aldrich. Lead (II) Iodide (PbI2, 99.99%) was purchased from Tokyo Chemical Industry (TCI). Methylammonium iodide (MAI) was purchased from Greatcell Solar, and isopropanol (anhydrous, 99.5+%) was purchase from Alfa Aesar. 2.2. Solar Cell Fabrication FTO (fluorinated tin oxide) coated glass substrates were cleaned through sequential cleaning steps using an ultrasonic bath. The substrates were first sonicated in a 1% Hellmanex solution followed with two times sonication in deionized water. Then cleaning continued with sonication in isopropanol, acetone and again isopropanol respectively. Each step was done for 10 minutes. Immediately after cleaning, the substrates were heated at 400 °C for 20 minutes.


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To fabricate the solar cells with standard n-i-p structure (Figure. 1a), a 30 nm compact TiO2 electron transport layer (ETL) was deposited via electron beam evaporation.34 Subsequently, to create an electron transport bilayer, a 10 mg/ml PCBM solution in anhydrous chlorobenzene was deposited atop TiO2 by spin-coating at 3000 rpm for 30 s followed by a 10 min annealing at 80 °C. The PCBM deposition and annealing was done in a glove box under nitrogen atmosphere. The perovskite layer was deposited using a hybrid evaporation-spincoating two-step method (Figure. 1b). Accordingly, a 185 nm PbI2 layer was thermally evaporated at ~106

mbar vacuum pressure and a constant deposition rate of 0.5 Å/s. During deposition, the

substrate temperature was kept at 20 °C. To convert the PbI2 porous layer into perovskite, CH3NH3I (MAI), in isopropanol solutions with concentrations ranging from 35 mg/ml to 55 mg/ml were spin-coated at 2000 rpm for 35 s followed by 90 min annealing at 100 °C. Just before spin-coating, the MAI solutions were filtered by PTFE 0.45 μm filters to remove undissolved MAI particles. The Spiro-OMeTAD hole transport layer (HTL) solution was prepared by dissolving 72.3 mg Spiro-OMeTAD in 1 ml anhydrous chlorobenzene and doping with 28.8 μl 4-tert-


7


butylpyridine

and

17.5

μl

from

a

stoke

solution

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of

520

mg/ml

lithium

bis(trifluoromethylsulphonyl)imide in acetonitrile. The HTL layer was spin-coated at 2000 rpm for 30s. Afterwards the samples where left in ambient air over night for HTL oxidation. Finally, 80 nm gold electrodes were thermally evaporated at ~10-6 mbar vacuum pressure. Energy band diagram of the material stack is shown in Figure 1c.

Figure 1. Schematic of the solar cell structure (a), the hybrid evaporation-spin coating two-step process (b) and energy band diagram of the material stack (c).

2.3. Characterization XRD measurements were performed with a PANalytical Empyrean 2 diffractometer with Copper Kɑ1 radiation (λ = 0.154060 nm). A PIXcel-3D detector was used in “receiving slit


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mode” with a range of 1.0 mm. 2θ-θ-scans with step size of 0.02◦ and integration time of 1s were recorded. SEM images were taken using a Zeiss Auriga 60 Crossbeam Workstation, field emission SEM with InLens detector at 5 kV acceleration voltage. AFM measurements were done using a Bruker dimension edge AFM in the tapping mode. The scanned surface area was 5x5 μm with 256 data points per line. Transient photoluminescence decay spectra were measured using a fiber coupled confocal microscope.35 A pulsed laser diode (635 nm, 1.5 µJ/cm², spot diameter 0.2 mm) was used for local excitation. The emitted light was detected using a silicon single photon avalanche diode. The optical components in the light path from laser to detector were: laser bandpass filter 635 nm, cold-light mirror, sample, focusing lens with a numerical aperture of 0.26, cold-light mirror followed by 650 nm long-pass filter for suppressing spurious laser light, Ø 100 µm pinhole. All measurements were performed in ambient conditions with no significant temperature increase related to the sample illumination. Decay spectra were taken at 2-3 different positions per sample. For the spatially resolved measurements the same setup was used, utilizing a frequency-doubled Nd:YAG laser in continuous wave operation mode (532 nm, 4.5 µW, spot diameter 15 µm). Emitted photoluminescence was


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detected via a silicon line CCD, spectrally resolved by a monochromator. The current was amplified by a low-noise preamplifier. A SINUS–220 PRO solar simulator from WAVELABS with LED lamp was used to measure the photovoltaic performance. The solar spectrum was calibrated to 1sun (100 mW/cm2) using a reference silicon solar cell. Current-Voltage (J-V) characteristics were measured in reverse and forward scan directions respectively with a slow scan rate of 43 mV/s. Stabilized measurements were done, with the voltage fixed at the maximum power point as determined from the average of J-V scans. A shadow mask was used during the measurements to define a 0.16 cm2 active are. 3. RESULTS AND DISCUSSION 3.1. Morphological Properties The XRD patterns of the perovskite layers formed on a TiO2/PCBM electron transport bilayer using the MAI solutions with different concentrations are shown in Figure 2. In all samples, perovskite peaks are clearly visible, which confirms perovskite phase formation. Moreover, a diffraction peak associated with (001) crystal orientation of PbI2 is presented at 12.67°. Between the samples, the intensity of the PbI2 peak is higher in case of 40


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mg/ml MAI solution. This means that more PbI2 is present in the perovskite layer. By increasing the MAI concentrations towards 55 mg/ml, the PbI2 peak disappeared and the intensity of the perovskite peak increased. This is an indication of more perovskite phase formation and less remnant PbI2 in the formed perovskite layer.

Figure 2. X-ray diffraction patterns of the perovskite layers formed with different MAI concentrations. As can be seen from the comparison of the characteristic peaks associated with (001) crystal orientation of PbI2 at 12.67° (marked with a circle) and the peaks associated with (110) crystal orientation of MAPbI3 at 14.02° (marked with a star),


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by increasing the MAI concentrations from the lower (35-40 mg/ml) to the higher (45-55 mg/ml) values, more perovskite formed and relatively less PbI2 remained.

The grain size of the perovskite samples formed with different MAI concentrations were calculated using Scherrer equation by taking the full-width-at-half-maximum (FWHM) of the dominant lattice reﬂection of 2θ at 14.02°. The results are shown in Table 1.

Table 1. Estimated perovskite grain size using Scherrer equation by taking the full-widthat-half-maximum (FWHM) of the dominant lattice reﬂection of 2θ at 14.02°.

MAI Concentration (mg/ml)

Grain Size (nm)

55

236

50

212

45

208

40

206

35

202


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Differences between the samples are also visible in the SEM top views (Figure 3), AFM maps (Figure 4) and the SEM cross sections (Figure 5). The pristine PbI2 layer is porous, which facilitates the efficient MAI intercalation and perovskite phase formation. For all MAI concentrations, highly crystalline perovskite layers were formed but with clear differences in nucleation quality and crystallites sizes. The crystallites sizes of the layers of the higher (50-55 mg/ml) MAI concentrations are slightly bigger than those with lower (35-45 mg/ml) concentrations. Comparing the quality of crystallization in case of 40 mg/ml MAI concentration, which contain excess PbI2 with 50-55 mg/ml, the crystal grains are more strongly impinged into each other. In case of the lowest MAI concentration tested (35 mg/ml), compactness of the formed perovskite layer is lower than for the other concentrations. It seems that 40 mg/ml was a threshold for the MAI concentration, for a complete perovskite phase formation, so below that concentration many voids appeared in the formed layer.


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Figure 3. SEM images of the porous PbI2 and the perovskite layers formed with different MAI concentrations. With lower MAI content the crystals tend to be slightly smaller but more strongly impinged. When the MAI concentration is too low (35 mg/l), however, voids appear.


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Figure 4. AFM images of the perovskite layers formed with 40 mg/ml and 55 mg/ml MAI concentrations. For the lower MAI concentration the crystals tend to be smaller but more strongly impinged while in case of the higher MAI concentration bigger grains with deep valleys between them and a rougher surface are formed.

The voids in case of the low 35 mg/ml concentration, as well as the gaps between the large grains for the 55 mg/ml could act as defect centers causing carrier recombination or lead to shunts, which decreases the power conversion efficiency of a solar cell.


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Figure 5. Cross-section SEM images of the perovskite layers formed with different MAI concentrations. In 40-45 mg/ml MAI concentration a compact layer is formed while in very low 35 mg/ml or very high 50-55 mg/ml concentrations, gaps appeared between crystal grains, which could act as the defect centers and decrease the efficiency of a solar cell.

3.2. Optical Properties


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The absorption spectra of the perovskite layers formed with different stoichiometries are shown in Figure 6. As can be seen, the perovskite layers of 40-45 mg/ml MAI concentrations show stronger absorption than the low 35 mg/ml and high 50 mg/ml concentrations. The differences in the absorption could be explained by the findings from the microscopic measurements. In case of 40-45 mg/ml, the formed perovskite layers were compact and uniform leading to higher absorption than for the very low or very high MAI concentrations, where voids appeared between grains reducing the compactness and uniformity of the deposited layer.


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Figure 6. UV-vis absorption spectra of the perovskite layers formed with different MAI concentrations. For 40-45 mg/ml MAI concentrations due to more compact perovskite layers formation the absorption spectra are higher than with 35 mg/ml and 50 mg/ml concentrations.

3.4. Photoluminescence Performance

Time-resolved photoluminescence (TRPL) measurements were performed to evaluate the charge extraction quality of the samples with different stoichiometries but a similar TiO2/PCBM electron transport bilayer. The measurements were performed on the halfcell level where the perovskite layers were deposited atop ETL, but no hole transport layers and metal contacts were deposited. To increase the accuracy of the PL measurements we performed three measurements on different locations for each sample (Figure 7a). A bi-exponential decay model was used to fit the PL decay data and extract the life time values (Figure 7b). As can be seen in Figure 7a, the different curves represent


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more or less the same trend for each stoichiometry. The fitted life-time values were the lowest for the 40-45 mg/ml concentrations.

Figure 7. TRPL decay curves of the perovskite layers formed with different MAI concentrations (7a) and corresponding life time values (7b). The TRPL signal is strongly quenched in case of 40-45 mg/ml MAI concentrations.

Furthermore, spectrally resolved steady-state PL measurements were done on two different locations for each sample. As can be seen in Figure 8, the two PL spectra for each stoichiometry represent the same trend. The intensity of the peaks appears to be


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correlated with the life-time values, with the lowest intensities observed for the 40-45 mg/ml indicating strong quenching. Interestingly, we also observe a blue shift with increasing MAI concentration. As the peak position is typically associated with the bandgap, this would mean that higher bandgaps are associated with higher MAI concentrations.

Figure 8. Steady-state PL curves of the perovskite layers formed with different MAI concentrations. The PL quenching efficiency is higher for the MAI concentrations of 4045 mg/ml.


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3.3. Photovoltaic Performance

Using the hybrid evaporation-spincoating two-step method, we prepared solar cells with MAI concentrations ranging from 35 mg/ml to 55 mg/ml. The resulting photovoltaic parameters are shown in Figure 9. As can be seen, the short-circuit current density JSC is the highest for the samples prepared with 40-45 mg/ml MAI concentrations, which can be directly explained from the higher absorption observed for this samples. The open-circuit voltage VOC is higher for the lower concentrations of 35-45 mg/ml correlating with higher PbI2 contents. This could be attributed to passivation both of the perovskite-ETL interface and grain boundaries by the excess PbI2.36-38 The fill factor (FF) is roughly at the same level for all concentrations. Overall the highest efficiencies are achieved with 40 mg/ml MAI concentration.


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Figure 9. Photovoltaic parameters of the perovskite solar cells made with different MAI concentrations. For MAI concentrations of 40-45 mg/ml high JSC, VOC and thereupon PCE were achieved 10-15 solar cells are made and analyzed for each MAI concentration.

The photovoltaic parameters are also listed in Table 2. Additionally, we calculated the hysteresis (1-PCEfor/PCErev). We observe the lowest hysteresis levels, for 40-45 mg/ml MAI concentration, which correlates also with the highest efficiencies. This is consistent


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to models attributing hysteresis to recombination and ionic movements facilitated by low crystal quality.43-55

Table 2. Photovoltaic parameters of the perovskite solar cells made with different MAI concentrations. 10-15 solar cells are made and analyzed for each MAI concentration.

MAI (mg/ml)

35

40

45

50

55

Scan Direction

Forward

Reverse

Forward

Reverse

Forward

Reverse

Forward

Reverse

Forward

Reverse

Jsc (mA/cm2)

18.4

19.5

22.7

22.95

21.9

22

12.4

13.6

14.5

16.5

Voc (mV)

1092.2

1111.4

1090.6

1103.3

1091.5

1100.6

980.1

990

997.4

1000.6

FF (%)

54.9

64.6

69.9

74.5

55.4

62.75

59.6

72.7

41.75

60.9

PCE (%)

11

14

17.3

18.9

13.25

15.2

7.25

9.8

6.1

10

Hysteresis (%)

21.4

8.4

12.8

26

39

The J-V characteristics (a) and stabilized power conversion efficiencies (b) of the champion solar cells featuring different MAI concentrations are plotted in Figure 10. The highest stabilized efficiency of 18.2% with the lowest hysteresis has achieved from the solar cell made with 40 mg/ml MAI concentration.


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Figure 10. (a) J-V curves measured with scan rate of 43 mV/s and (b) stabilized PCE of the champion solar cells of different MAI concentrations.

4. DISCUSSION Taking all results into consideration, we find best photovoltaic performance for MAI concentrations of 40-45 mg/ml, which leads to good crystal quality, compact perovskite films with medium sized, strongly impinged grains, and consequently strong absorption that enables a high JSC. Furthermore, for those concentrations we observe strong photoluminescence quenching with short decay times and low photoluminescence intensity. Such a behaviour has been observed before and has been attributed to fast electron extraction by the ETL layer.46-48 Interestingly, a low MAI concentration


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corresponding to a higher PbI2 content was associated with higher VOC, while simultaneously photoluminescence measurements indicated a lower bandgap. Possible explanation are either surface passivation at the perovskite-ETL interface36-39 and/or at grain boundaries by the excess PbI240-42 or band edge matching between ETL and perovskite due to the excess PbI2. Such a beneficial role of slightly excess PbI2 was also reported for perovskite solar cells made with solution processing.27-33 However, to have a positive effect a precise stoichiometry is important. A band edge matching as shown in Figure 1c, would facilitate the electron extraction, which would be consistent with the TRPL measurements. With passivated surfaces, the discontinuity of the crystal at grain boundaries would also be less detrimental. In contrast, it is even possible to profit from improved charge collection close the grain boundaries.25 Hence, the smaller crystal grains observed for the sample with medium PbI2 content, would not be detrimental. Finally to further improve the efficiency and stability, interface engineering aiming at suppression of hysteresis is extremely crucial.56-58 5. CONCLUSION


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We studied the role of crystallization and grains growth conditions on morphological and optoelectronic properties as well as hysteresis behaviour by a systematic variation of MAI concentrations in MAPbI3 perovskite solar cells fabricated with a two-step hybrid evaporation-spincoating method. Stoichiometry variation strongly impacted the crystallization and grain growth. Reduction in MAI concentrations down to 40 mg/ml and accordingly increased PbI2 incorporation resulted in highly crystalline perovskite layers with smaller but more impinged grains formation. For these samples, we observed that the remnant PbI2 content correlated with higher efficiencies of photovoltaic operation, especially with higher voltages, higher currents and thus higher efficiencies, as well as less hysteresis. Possible explanations for the superior performance with lower MAI concentrations are surface and interface passivation by the PbI2 and a positive contribution of interconnected grain boundaries allowing for improved charge extraction. Even lower MAI concentrations, however, then resulted in poor crystallisation and low photovoltaic performance. Ultimately the 40 mg/ml is found to be the optimized value for the MAI concentration resulting in the champion device stabilized efficiency of 18.2%.


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AUTHOR INFORMATION Corresponding Author * Email: [email protected], [email protected] Author Contributions Saeid Rafizadeh prepared all the sample, performed the IV measurements drafted the manuscript, Karl Wienands cooperated in PbI2 layer deposition, Alexander. J. Bett and Patricia S.C. Schulze cooperated in TiO2 deposition and scientific discussions of the paper, Jan Christoph Goldschmidt conceived the concept of the work and contributed to the writing of the manuscript, Jan Christoph Goldschmidt, Lucio Claudio Andreani, Martin Hermle and Stefan W. Glunz supervised the research activities of this work and the project. Funding Sources This work was funded by the German Federal Ministry of Economic Affairs and Energy in the project “PersiST” (contract number 0324037A).

Saeid Rafizadeh acknowledges the scholarship support from the University of Pavia.


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Alexander J. Bett acknowledges scholarship funding from the Deutsche Bundesstiftung Umwelt (BDU).

Notes There are no conflicts of interest to declare.

ACKNOWLEDGMENT

The authors thank Harald Steidl, Jutta Zielonka, Laura Stevens and Friedemann Heinz for their support with processing and measurements.

The authors gratefully acknowledge Dr. Lutz Kirste and Mario Prescher for the XRD measurements performed at Fraunhofer Institute for Applied Solid State Physics IAF.

References (1) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-Hole Diffusion Lengths > 175 μm in Solution-Grown CH3NH3PbI3 Single Crystals. Science. 2015, 347, 967-970. (2) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L.M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science. 2013, 342, 341344. (3) Yang, W. S.; Park, B.-W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S.S.; Seo, J.; Kim, E. K.; Noh, J. H.; Seok, S. I. Iodide Management in Formamidinium-LeadHalide-Based Perovskite Layers for Efficient Solar Cells. Science. 2017, 356, 1376-1379.


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(4) Stolterfoht, M.; Wolff, C. M.; Amir, Y.; Paulke, A.; Perdigón-Toro, L.; Caprioglio, P.; Neher, D. Approaching the Fill Factor Shockley–Queisser Limit in Stable, Dopant-Free Triple Cation Perovskite Solar Cells. Energy Environ. Sci. 2017, 10, 1530-1539. (5) Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; García de Arquer, F. P.; Fan, J. Z.; Li, P.; Quan, L. N.; Zhao, Y.; Lu, Z. H., Yang, Z.; Hoogland, S.; Sargent, E. H. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation.

Science. 2017, 355, 722-726. (6) Saliba, M.; Matsui, T.; Domanski, K.; Seo, J.-Y.; Ummadisingu, A.; Zakeeruddin, S. M.; Correa-Baena, J.-P.; Tress, W. R.; Abate, A.; Hagfeldt, A.; Gratzel, M. Incorporation of Rubidium Cations into Perovskite Solar Cells Improves Photovoltaic Performance.

Science. 2016, 354, 206-209. (7) Anaraki, E. H.; Kermanpur, A.; Steier, L.; Domanski, K.; Matsui, T.; Tress, W.; Saliba, M.; Abate, A.; Grätzel, M.; Hagfeldt, A.; Correa-Baena, J.-P. Highly Efficient and Stable Planar Perovskite Solar Cells by Solution-Processed Tin Oxide. Energy Environ. Sci. 2016, 9, 3128-3134. (8) Schulze, P. S. C.; Bett, A. J.; Winkler, K.; Hinsch, A.; Lee, S.; Mastroianni, S.; Mundt, L. E.; Mundus, M.; Würfel, U.; Glunz, S. W.; Hermle, M.; Goldschmidt, J. C. Novel LowTemperature Process for Perovskite Solar Cells with a Mesoporous TiO2 Scaffold. ACS

Appl. Mater. Interfaces. 2017, 9, 30567-30574. (9) Momblona, C.; Gil-Escrig, L.; Bandiello, E.; Hutter, E. M.; Sessolo, M.; Lederer, K.; Blochwitz-Nimoth, J.; Bolink, H. J. Efficient Vacuum Deposited p-i-n and n-i-p Perovskite Solar Cells Employing Doped Charge Transport Layers. Energy Environ. Sci. 2016, 9, 3456-3463. (10) Zhao, D.; Ke, W.; Grice, C. R.; Cimaroli, A. J.; Tan, X.; Yang, M.; Collins, R. W.; Zhang, H.; Zhu, K.; Yan, Y. Annealing-Free Efficient Vacuum-Deposited Planar Perovskite Solar Cells with Evaporated Fullerenes as Electron-Selective Layers. Nano

Energy. 2016, 19, 88-97.


29


Page 30 of 37

(11) Cojocaru, L.; Wienands, K.; Kim, T. W.; Uchida, S.; Bett, A. J.; Rafizadeh, S.; Goldschmidt, J. C.; Glunz, S. W. Detailed Investigation of Evaporated Perovskite Absorbers with High Crystal Quality on Different Substrates. ACS Appl. Mater. Interfaces. 2018, 10, 26293-26302. (12) Longo, G.; Momblona, C.; La-Placa, M.-G.; Gil-Escrig, L.; Sessolo, M.; Bolink, H. J. Fully Vacuum-Processed Wide Band Gap Mixed-Halide Perovskite Solar Cells. ACS

Energy Lett. 2018, 3, 214-219. (13) Tao, C.; Neutzner, S.; Colella, L.; Marras, S.; Srimath Kandada, A. R.; Gandini, M.; Bastiani, M. D.; Pace, G.; Manna, L.; Caironi, M.; Bertarelli, C.; Petrozza, A. 17.6% Stabilized Efficiency in Low-Temperature Processed Planar Perovskite Solar Cells.

Energy Environ. Sci. 2015, 8, 2365-2370. (14) Fu, F.; Kranz, L.; Yoon, S.; Löckinger, J.; Jäger, T.; Perrenoud, J.; Feurer, T.; Gretener, C.; Buecheler, S.; Tiwari, A. N. Controlled Growth of PbI2 Nanoplates for Rapid Preparation of CH3NH3PbI3 in Planar Perovskite Solar Cells. Phys.Status Solidi A. 2015,

212, 2708-2717. (15) Abzieher, T.; Mathies, F.; Hetterich, M.; Welle, A.; Gerthsen, D.; Lemmer, U.; Paetzold, U. W.; Powalla, M. Additive-Assisted Crystallization Dynamics in Two-Step Fabrication of Perovskite Solar Cells. Phys.Status Solidi A, 2017, 214, 1700509. (16) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Horantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; Johnston, M. B.; Herz, L. M.; Snaith, H. J. A Mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells.

Science. 2016, 351, 151-155. (17) Bush, K. A.; Palmstrom, A. F.; Yu, Z. J.; Boccard, M.; Cheacharoen, R.; Mailoa, J. P.; McMeekin, D. P.; Hoye, R. L. Z.; Bailie, C. D.; Leijtens, T.; Peters, I. M.; Minichetti, M. C.; Rolston, N.; Prasanna, R.; Sofia, S.; Harwood, D.; Ma, W.; Moghadam, F.; Snaith, H. J.; Buonassisi, T.; Holman, Z. C.; Bent, S. F.; McGehee, M. D. 23.6%-Efficient Monolithic Perovskite/Silicon Tandem Solar Cells with Improved Stability. Nature Energy. 2017, 2, 17009.


30

Page 31 of 37 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


(18) Wu, Y.; Yan, D.; Peng, J.; Duong, T.; Wan, Y.; Phang, S. P.; Shen, H.; Wu, N.; Barugkin, C.; Fu, X.; Surve, S.; Grant, D.; Walter, D.; White, T. P.; Catchpole, K. R.; Weber, K. J. Monolithic Perovskite/Silicon-Homojunction Tandem Solar Cell with Over 22% Efficiency. Energy Environ. Sci. 2017, 10, 2472-2479. (19) Sahli, F.; Werner, J.; Kamino, B. A.; Bräuninger, M.; Monnard, R.; Paviet-Salomon, B.; Barraud, L.; Ding, L.; Diaz Leon, J. J.; Sacchetto, D.; Cattaneo, G.; Despeisse, M.; Boccard, M.; Nicolay, S.; Jeangros, Q.; Niesen, B.; Ballif, C. Fully Textured Monolithic Perovskite/Silicon Tandem Solar Cells with 25.2% Power Conversion Efficiency. Nature

Materials 2018, 17, 820-826. (20) Mokhtar, M. Z.; Chen, M.; Whittaker, E.; Hamilton, B.; Aristidou, N.; Ramadan, S.; Gholinia, A.; Haque, S. A.; O'Brien, P.; Saunders, B. R. CH3NH3PbI3 Films Prepared by Combining 1- and 2-Step Deposition: How Crystal Growth Conditions Affect Properties.

Phys.Chem.Chem.Phys. 2017, 19, 7204-7214. (21) Bi, D.; Luo, J.; Zhang, F.; Magrez, A.; Athanasopoulou, E. N.; Hagfeldt, A.; Grätzel, M. Morphology Engineering: A Route to Highly Reproducible and High Efficiency Perovskite Solar Cells. ChemSusChem. 2017, 10, 1624-1630. (22) Lee, J.-W.; Bae, S.-H.; De Marco, N.; Hsieh, Y.-T.; Dai, Z.; Yang, Y. The Role of Grain Boundaries in Perovskite Solar Cells. Materials Today Energy. 2018, 7, 149-160. (23) Roose, B.; Ummadisingu, A.; Correa-Baena, J.-P.; Saliba, M.; Hagfeldt, A.; Graetzel, M.; Steiner, U.; Abate, A. Spontaneous Crystal Coalescence Enables Highly Efficient Perovskite Solar Cells. Nano Energy. 2017, 39, 24-29. (24) Yao, Z.; Wang, W.; Shen, H.; Zhang, Y.; Luo, Q.; Yin, X.; Dai, X.; Li, J.; Lin, H. CH3NH3PbI3 Grain Growth and Interfacial Properties in Meso-Structured Perovskite Solar Cells Fabricated by Two-Step Deposition. Science and Technology of Advanced

Materials. 2017, 18, 253-262.


31


Page 32 of 37

(25) Yun, J. S.; Ho-Baillie, A.; Huang, S.; Woo, S. H.; Heo, Y.; Seidel, J.; Huang, F.; Cheng, Y.-B.; Green, M. A. Benefit of Grain Boundaries in Organic–Inorganic Halide Planar Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 875-880. (26) Li, J.-J.; Ma, J.-Y.; Ge, Q.-Q.; Hu, J.-S.; Wang, D.; Wan, L.-J. Microscopic Investigation of Grain Boundaries in Organolead Halide Perovskite Solar Cells. ACS Appl.

Mater. Interfaces. 2015, 7, 28518-28523. (27) Chen, Y.; Yerramilli, A.; Shen, Y.; Zhao, Z.; Alford, T. Effect of Excessive Pb Content in the Precursor Solutions on the Properties of the Lead Acetate Derived CH3NH3PbI3 Perovskite Solar Cells. Solar Energy Materials and Solar Cells. 2018, 174, 478-484. (28) Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Correa Baena, J.-P.; Decoppet, J.-D.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Gratzel, M.; Hagfeldt, A. Efficient Luminescent Solar Cells Based on Tailored MixedCation Perovskites. Science Advances. 2016, 2, e1501170–e1501170. (29) Liu, F.; Dong, Q.; Wong, M. K.; Djurišić, A. B.; Ng, A.; Ren, Z.; Shen, Q.; Surya, C.; Chan, W. K.; Wang, J.; Ng, A. M. C.; Liao, C.; Li, H.; Shih, K.; Wei, C.; Su, H.; Dai, J. Perovskite Solar Cells: Is Excess PbI2 Beneficial for Perovskite Solar Cell Performance?

Adv. Energy Mater. 2016, 6, 1502206. (30) Kim, Y. C.; Jeon, N. J.; Noh, J. H.; Yang, W. S.; Seo, J.; Yun, J. S.; Ho-Baillie, A.; Huang, S.; Green, M. A.; Seidel, J.; Ahn, T. K.; Seok, S. I. Beneficial Effects of PbI2 Incorporated in Organo-Lead Halide Perovskite Solar Cells. Adv. Energy Mater. 2015, 6, 1502104. (31) Jacobsson, T. J.; Correa-Baena, J.-P.; Halvani Anaraki, E.; Philippe, B.; Stranks, S. D.; Bouduban, M. E. F.; Hagfeldt, A. Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells. J. Am. Chem. Soc. 2016, 138, 10331-10343.


32

Page 33 of 37 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


(32) Bi, D.; El-Zohry, A. M.; Hagfeldt, A.; Boschloo, G. Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells. ACS

Photonics. 2015, 2, 589-594. (33) Cao, D. H.; Stoumpos, C. C.; Malliakas, C. D.; Katz, M. J.; Farha, O. K.; Hupp, J. T.; Kanatzidis, M. G. Remnant PbI2, an Unforeseen Necessity in High-Efficiency Hybrid Perovskite-Based Solar Cells? APL Materials. 2014, 2, 091101. (34) Bett, A. J.; Schulze, P. S. C.; Winkler, K.; Gasparetto, J.; Ndione, P. F.; Bivour, M.; Hinsch, A.; Kohlstädt, M.; Lee, S.; Mastroianni, S.; Mundt, L. E.; Mundus, M.; Reichel, C.; Richter, A.; Veita, C.; Wienands, K.; Würfel, U.; Veurman, W.; Glunz, S. W.; Hermle, M.; Goldschmidt, J. C. Low Temperature Perovskite Solar Cells with an Evaporated TiO2 Compact Layer for Perovskite Silicon Tandem Solar Cells. Energy Procedia. 2017, 4, 567-576. (35) Mundt, L. E.; Heinz, F. D.; Albrecht, S.; Mundus, M.; Saliba, M.; Correa-Baena, J.P.; Anaraki, E. H.; Korte, L.; Gratzel, M.; Hagfeldt, A.; Rech, B.; Schubert, M. C.; Glunz, S. W. Nondestructive Probing of Perovskite Silicon Tandem Solar Cells Using Multiwavelength Photoluminescence Mapping. IEEE Journal of Photovoltaics. 2017, 7, 1081-1086. (36) Peng, J.; Khan, J. I.; Liu, W.; Ugur, E.; Duong, T.; Wu, Y.; Shen, H.; Wang, K.; Dang, H.; Aydin, E.; Yang, X.; Wan, Y.; Weber, K. J.; Catchpole, K. R.; Laquai, F.; De Wolf, S.; White, T. P. A Universal Double-Side Passivation for High Open-Circuit Voltage in Perovskite Solar Cells: Role of Carbonyl Groups in Poly(methyl methacrylate). Adv.

Energy Mater. 2018, 8, 1801208. (37) Stolterfoht, M.; Wolff, C. M.; Márquez, J. A.; Zhang, S.; Hages, C. J.; Rothhardt, D.; Albrecht, S.; Burn, P. L.; Meredith, P.; Unold, T.; Neher, D. Visualization and Suppression of Interfacial Recombination for High-Efficiency Large-Area pin Perovskite Solar Cells. Nature Energy 2018, https://doi.org/10.1038%2Fs41560-018-0219-8.


33


Page 34 of 37

(38) Wu, Y.; Yang, X.; Chen, W.; Yue, Y.; Cai, M.; Xie, F.; Bi, E.; Islam, A.; Han, L. Perovskite Solar Cells with 18.21% Efficiency and Area over 1 cm2 Fabricated by Heterojunction Engineering. Nature Energy 2016, 1, doi:10.1038/nenergy.2016.148. (39) Xing, Y.; Sun, C.; Yip, H.-L.; Bazan, G. C.; Huang, F.; Cao, Y. New Fullerene Design Enables Efficient Passivation of Surface Traps in High Performance p-i-n Heterojunction Perovskite Solar Cells. Nano Energy 2016, 26, 7-15. (40) Ummadisingu, A.; Grätzel, M. Revealing the Detailed Path of Sequential Deposition for Metal Halide Perovskite Formation. Science Advances 2018, 4, e1701402. (41) Zhao, P.; Kim, B. J.; Jung, H. S. Passivation in Perovskite Solar Cells: A Review.

Materials Today Energy. 2018, 7, 267-286. (42) Lee, J.-W.; Bae, S.-H.; De Marco, N.; Hsieh, Y.-T.; Dai, Z.; Yang, Y. The Role of Grain Boundaries in Perovskite Solar Cells. Materials Today Energy. 2018, 7, 149-160. (43) Turren-Cruz, S.-H.; Saliba, M.; Mayer, M. T.; Juárez-Santiesteban, H.; Mathew, X.; Nienhaus, L.; Tress, W.; Erodici, M.; Sher, M.-P.; Bawendi, M. J.; Grätzel, M.; Abate, A.; Hagfeldt, A.; Correa-Baena, J.-P. Enhanced Charge Carrier Mobility and Lifetime Suppress Hysteresis and Iimprove Efficiency in Planar Perovskite Solar Cells. Energy

Environ. Sci. 2018, 11, 78-86. (44) Bergmann, V. W.; Guo, Y.; Tanaka, H.; Hermes, I. M.; Li, D.; Klasen, A.; Bretschneider, S. A.; Nakamura, E.; Berger, R.; Weber, S. A. L. Local Time-Dependent Charging in a Perovskite Solar Cell. ACS Appl. Mater. Interfaces. 2016, 8, 19402-19409. (45) Tang, Z.; Bessho, T.; Awai, F.; Kinoshita, T.; Maitani, M. M.; Jono, R.; Murakami, T. N.; Wang, H.; Kubo, T.; Uchida, S.; Segawa, H. Hysteresis-Free Perovskite Solar Cells Made of Potassium-Doped Organometal Halide Perovskite. Scientific Reports. 2017, 7. doi:10.1038/s41598-017-12436-x. (46) Patel, J. B.; Wong-Leung, J.; Van Reenen, S.; Sakai, N.; Wang, J. T. W.; Parrott, E. S.; Liu, M.; Snaith, H. J.; Herz, L. M.; Johnston, M. B. Influence of Interface Morphology


34

Page 35 of 37 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


on Hysteresis in Vapor-Deposited Perovskite Solar Cells. Adv. Electron. Mater. 2017, 3, 1600470. (47) Kegelmann, L.; Wolff, C. M.; Awino, C.; Lang, F.; Unger, E. L.; Korte, L.; Thomas, D.; Dieter, N.; Bernd, R.; Albrecht, S. It Takes Two to Tango—Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis. ACS Appl. Mater. Interfaces. 2017, 9, 17245-17255. (48) Peng, J.; Wu, Y.; Ye, W.; Jacobs, D. A.; Shen, H.; Fu, X.; Wan, Y.; Duong, T.; Wu, N.; Barugkin, C.; Nguyen, H. T.; Zhong, D.; Li, J.; Lu, T.; Liu, Y.; Lockrey, M. N.; Weber, K. J.; Catchpole, K. R.; White, T. P. Interface Passivation Using Ultrathin Polymer– Fullerene Films for High-Efficiency Perovskite Solar Cells with Negligible Hysteresis.

Energy Environ. Sci. 2017, 10, 1792-1800. (49) Wong, K. K.; Fakharuddin, A.; Ehrenreich, P.; Deckert, T.; Abdi-Jalebi, M.; Friend, R.

H.;

Schmidt-Mende,

L.

Interface-Dependent

Radiative

and

Nonradiative

Recombination in Perovskite Solar Cells. J. Phys. Chem. C. 2018, 122, 10691-10698. (50) Yadav, P.; Turren-Cruz, S.-H.; Prochowicz, D.; Tavakoli, M. M.; Pandey, K.; Zakeeruddin, S. M.; Grätzel, M.; Hagfeldt, A.; Saliba, M. Elucidation of Charge Recombination and Accumulation Mechanism in Mixed Perovskite Solar Cells. J. Phys.

Chem. C. 2018, 122, 15149-15154. (51) Kim, G. Y.; Senocrate, A.; Yang, T.-Y.; Gregori, G.; Grätzel, M.; Maier, J. Large Tunable Photoeffect on Ion Conduction in Halide Perovskites and Implications for Photodecomposition. Nature Materials. 2018, 17, 445-449. (52) Shao, Y.; Fang, Y.; Li, T.; Wang, Q.; Dong, Q.; Deng, Y.; Yuan, Y.; Wei, H.; Wang, M.; Gruverman, A.; Shield, J.; Huang, J. Grain Boundary Dominated Ion Migration in Polycrystalline Organic–Inorganic Halide Perovskite Films. Energy Environ. Sci. 2016, 9, 1752-1759.


35


Page 36 of 37

(53) Ip, A. H.; Quan, L. N.; Adachi, M. M.; McDowell, J. J.; Xu, J.; Kim, D. H.; Sargent, E. H. A Two-Step Route to Planar Perovskite Cells Exhibiting Reduced Hysteresis. Appl.

Phys. Lett. 2015, 106, 143902. (54) Wang, F.; Bai, S.; Tress, W.; Hagfeldt, A.; Gao, F. Defects Engineering for HighPerformance Perovskite Solar Cells. npj Flexible Electronics 2018, 2, https://doi.org/10.1038%2Fs41528-018-0035-z. (55) Hermes, I. M.; Hou, Y.; Bergmann, V. W.; Brabec, C. J.; Weber, S. A. L. The Interplay of Contact Layers: How the Electron Transport Layer Influences Interfacial Recombination and Hole Extraction in Perovskite Solar Cells. J. Phys. Chem. Lett. 2018, https://doi.org/10.1021%2Facs.jpclett.8b02824. (56) Yang, D.; Yang, R.; Wang, K., Wu, C.; Zhu, X.; Feng, J.; Ren, X.; Fang, G.; Priya, S.; Liu, S. High Efficiency Planar-Type Perovskite Solar Cells with Negligible Hysteresis Using EDTA-Complexed SnO2. Nature Communications 2018, 9, 3239. (57) Yang, D.; Zhou, X.; Yang, R.; Yang, Z.; Yu, W.; Wang, X.; Li, C.; Liu, S (F).; Chang, R. P. H. Surface Optimization to Eliminate Hysteresis for Record Efficiency Planar Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 3071-3078. (58) Yang, D.; Yang, R.; Ren, X., Zhu, X., Yang, Z.; Li, C., Liu, S. F. HysteresisSuppressed High-Efficiency Flexible Perovskite Solar Cells Using Solid-State IonicLiquids for Effective Electron Transport. Adv Mater. 2016, 28, 5206-5213.

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Efficiency Enhancement and Hysteresis Mitigation by Manipulation of

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