From Blade Coating to Painting - ACS Publications - American

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Growth dynamic controllable rapid crystallization boosts the perovskite photovoltaics’ robust preparation: from blade coating to painting Jun Yin, Yichuan Lin, Chunquan Zhang, Jing Li, and Nanfeng Zheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b05172 • Publication Date (Web): 14 Jun 2018 Downloaded from http://pubs.acs.org on June 14, 2018

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ACS Applied Materials & Interfaces

Growth dynamic controllable rapid crystallization boosts the perovskite photovoltaics’ robust preparation: from blade coating to painting Jun Yin,*,† Yichuan Lin,† Chunquan Zhang,† Jing Li,*,† and Nanfeng Zheng*,§ †

Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Pen-

Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen 361005, China §

State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation

Center of Chemistry for Energy Materials, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China KEYWORDS: perovskite, photovoltaic devices, crystallization, blade-coating, painting

ABSTRACT: Perovskite based solar cells have been developed intensively in recent years due to their attractive applications in next generation photovoltaics with low cost and high efficiency. However, the fabrication processes need to be further improved to meet the requirement in actual industrial production with reliable process and scalable fabrication. Here, thermal / solvent engineering coordinately enhanced rapid crystallization strategy is reported to realize the fast and

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robust preparation of perovskite films. The modified solution based coating method enables the precursor solutions to rapidly form highly crystalline perovskite films with large crystal domains, through the effectively controlled growth dynamics, including the nucleation and lateral-growth processes. Benefitted from the specific crystallizing mechanisms, high-quality perovskite films with efficient photovoltaic performance in corresponding devices were readily produced either using the blade coating or even painting methods: average power conversion efficiency (PCE) of 16.32% was obtained when using the blade coating method and up to 16.01% average PCE was realized by the direct painting process. Most importantly, this one-step painting method is demonstrated to be fairly reliable with high repeatability, showing a promising future for perovskite films’ scalable and rapid production with controllable film uniformity and thickness.

INTRODUCTION Organometal trihalide perovskite based photovoltaics, offering low-cost fabrication process and efficient power conversion efficiency (PCE), have been intensively investigated in the past few years.1-3 Up to now, the certified efficiency has been achieved at 22.7%, which is comparable to the best record of single-crystal silicon based thin-film solar cells.4 Currently, solution based spin-coating is the mostly used deposition method for perovskite films,5 which demonstrates superior advantages of low-cost, easy operability and stable reproducibility.6 By using the modified spin-coating strategy and the developed solvent engineering, the crystalizing process has been dramatically improved and uniform perovskite films with high crystal quality can be facilely obtained. These achievements continuously boost the photovoltaic performance to new records.7-9 However, the intrinsic disadvantages for the spin-coating limit the large-area fabrication and mass production, and of which is specifically critical for further commercialization.10-11 Also, a large amount of precursor solution would be wasted due to the


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low material utilization (at around 10% or less) during the spin-coating,11 which is understandably not economical and environmentally friendly. As a rapid and effective film preparation method in organic optoelectronic filed,11-12 the blade coating technique has been introduced in perovskite solar cells (PSCs) very early for films’ rapid and scalable fabrication.13-14 Different from the commonly used spin-coating method for laboratory-scale research, the blade-coating and other related techniques, such as threedimensional (3D) printing or roll processing,15-17 were widely accepted as ideal scalablefabrication methods for mass-production with highly efficient material usage. Many efforts have been made by researchers to promote the controllable perovskite filming and efficient photovoltaic performance by this method,18-20 including introducing the antisolvent treatment19 or using the mixed-cation precursors.18,

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Recently, the PSCs’ efficiency has been further

improved over 19% by Huang et al by using composition engineering during the blade coating process.21 However, comparing with the widely studied spin-coating process,3 this blade-coating method still lags behind in the manipulation of the crystallizing dynamics during the instant film growth, especially towards the claimed rapid and robust deposition, as well as the demanded high crystallinity and uniformity for efficient PSCs. While for other similar robust deposition approaches, such as the painting method, which has been demonstrated by recent work to be with huge potential application in scalable processing of organic or perovskite active layers for photovoltaics,22-25 the controllable nucleation and film growth are also the key issues to realize efficient and reliable PSCs’ fabrication. In this work, the strategy of thermal controlling combined with the solvent engineering was introduced to effectively improve the rapid crystallization process of the perovskite films in the blade-coating process. With manipulating the growth dynamics of the perovskite films, uniform


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and highly crystalline MAPbI3 films with large crystal domains up to 500 µm in size were successfully produced. The obviously improved crystal quality and electrical properties of those films enabled the significantly enhanced photovoltaic performance over 12% in the blade coating based devices (champion PCE of 17.82%). More importantly, this well-verified rapid crystallization mechanism was further applied to boost the high-quality film’s fabrication via much more robust coating process, one-step precursor direct painting. Consequently, an even over 17% PCE (average of 16.01%) with high reproducibility was accomplished in the asfabricated devices. This facile film-growth manipulation approach demonstrates an attractive route for the scalable production of PSCs towards commercialization.

RESULTS AND DISCUSSION In this work, in order to improve the crystal quality and film uniformity of the perovskite films through the blade-coating process, solvent engineering7 combined with thermal controlling26 was introduced to slow down the nucleation rate and promote the lateral epitaxial growth for perovskite grains when crystalizing from the solution phase, as schematically illustrated in Figure 1. Here, the DMSO (dimethyl sulfoxide) solvent was used to form intermediate phase (MAI-PbI2-DMSO) in the precursor solution.9 Different from the conventional process (CP) in blade coating (Figure 1b), the dramatically decreased nucleation cites and lowered growth rate through the solvent engineering, during the growth-dynamic-controlled process (GDCP), were proposed to enable the lateral growth in perovskite grains so that large single crystal grains can be produced (Figure 1c). The dynamic growth process visually shown in Video S1 and Figure S1 clearly presents the decreased initial nucleation density and prolonged transformation from solution to solid phase. SEM images reveal distinguishable differences between the perovskite films prepared by the conventional (Figure 1d-f) and growth-dynamic-controlled (Figure 1g-i)


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Figure 1. (a) Schematic illustration of the blade coating method for perovskite films’ preparation, and comparison of the different growth mechanisms during the (b) conventional process (CP) and (c) growth-dynamic-controlled process (GDCP) in blade coating. (d-f) and (g-i) show the surface SEM images in different magnifications of the corresponding perovskite films fabricated by the CP and GDCP methods, respectively. The long-time electron irradiation induced crack in SEM measurement was selectively shown in (i) for comparison, indicating the flat surface with hardly resolved grain boundaries.

blade coating, respectively. Much larger crystal domains and flatter surface can be clearly resolved in the solvent engineered films compared with those by CP. Moreover, as seen from the morphologies of the front side (Figure 1i) and stripped back side (Figure S2) of the perovskite


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film, the flat surface with hardly resolved grain boundaries in large-scale, indicating a high crystallinity, was realized by the GDCP, while polycrystalline films consisted of small grains were obtained by the CP without solvent engineering (Figure 1f). Similar results were also demonstrated by the AFM topographic images shown in Figure S3, where a typical polycrystalline structure consisted of small grains was shown in the CP based film with root mean-square (RMS) roughness about 21.7 nm, in contrast with the large perovskite grains over ten microns and smooth surface with RMS roughness about 7.4 nm on the GDCP based film. Further morphological analysis (Figure S4) indicated that the average domain size was significantly increased to 389.5±15.5 µm for the GDCP based films comparing with that 80.3±5.1 µm in the CP based films, and the average grain size was increased from 266.9±12.7 nm to 17.7±1.5 µm. As shown in Figure 2a, the largely increased XRD intensity for the GDCP based perovskite film well demonstrates the significantly improved crystal quality with large crystal grains. Interestingly, the main diffraction peaks of perovskite changed to (112)/(200) and (224)/(400) planes while generally (110) plane dominates in the conventionally fabricated perovskite films.27 It is well acknowledged that the (112) and (100) planes are the most commonly recognized natural facets in the synthesized bulk single-crystal MAPbI3 with the typical rhombo-hexagonaldodecahedron shape (as seen in the inset of Figure S5).28-29 Here, the as-produced highly crystalline grains by GDCP also exhibit a similar geometric rhombic morphology with the natural facets consistent with the bulk perovskite crystals (Figure S5b). Therefore, it is reasonable to infer that the GDCP with solvent-engineering has effectively promoted the growth of the highly crystalline film from the perovskite precursor solution. And this growth mechanism, where the precursor was rapidly increased to a high temperature accompanied with


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Figure 2. (a) XRD patterns of the perovskite films fabricated using the CP and GDCP methods. (b) Time resolved photoluminescence (TRPL) spectra of the prepared films. (c) I-V curves of the CP and GDCP based perovskite films for space charge limited current (SCLC) analysis. The device configuration for the I-V measurement was schematically shown in inset. (d) shows the absorption and steady-state PL spectra of the prepared films. (e) The optical microscopy (OM) image and (f) PL emission wavelength mapping of the CP based perovskite film, compared to (g) and (h) the corresponding images for the films fabricated using the GDCP.


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solvent’s fast evaporating, is also particularly similar with the inverse-temperature-crystallization reported by Bakr et al. for single-crystal’s rapid preparation.30 Furthermore, as discussed above, the decreased nucleation rate and reduced nucleation density through the solvent-engineering would further facilitate the single crystal grains to epitaxially grow in the lateral direction. Thus, intensively improved crystal quality with high crystallinity and much larger crystal domains were realized in the GDCP based perovskite film. It should be noticed that the feature of the unusual orientational preference to the (112)/(200) plane has also been demonstrated in the previous work, which is believed to be highly related to the initial orientation of PbI6 octahedral framework on the substrate in the early stage of the crystallization process.31-33 As well accepted that crystallization starts from the transformation of intermediates composed of perovskite precursors and solvent molecules,34 it is reasonable to argue that the edge of PbI6 octahedral framework is initially parallel to the substrate in this work when using the GDCP with solvent engineering,31 leading to a (112)/(200) initial orientation in the MAPbI3 nucleis. Consequently, synergistically induced by the controlled nucleation and epitaxial lateral growth, a (112)/(200) plane dominated perovskite film with high crystallinity was produced. The carrier lifetime of the perovskite films was estimated by time resolved photoluminescence (TRPL) spectra as illustrated in Figure 2b. Both decay curves can be well fitted using the biexponential functions, showing fast (τ1) and slow (τ2) decay components. Generally, the fast component was considered as the dynamic recombination process of carriers near the surface, while the slow part was attributed to the recombination in the inner crystals.35 Here, the extremely long lifetime of the slow component (τ2=340.0 ns) in the GDCP based film, which is comparable to that (~1 µs) in the bulk perovskite single-crystal,35 well indicated the


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highly crystalline feature with much low trap density in this perovskite. Further space charge limited current (SCLC) analysis was introduced to quantitatively evaluate the charge trap state densities in the two kinds of perovskite films.35 As shown in Figure 2c, two regions exhibited as Ohmic (I∝Vn, n=1) and trap-filled limited (TFL) (I∝Vn, n>2) responses can be clearly resolved in the curves. The trap-filled limit voltage (VTFL), which indicates the trap states are completely filled at this voltage,36 was measured to be 0.23 V and 0.09 V for the CP and GDCP based perovskite films, respectively. And the corresponding trap densities were calculated to be 1.47×1015 cm-3 and 4.45×1014 cm-3 by employing the relationship between the trap density (Ntrap) and VTFL: VTFL= qNtrapd2/2εε0

(1)

where q is the electronic charge, d is the thickness of the perovskite film, ε0 is the vacuum permittivity, and ε is the static dielectric constant of MAPbI3 (~70).37 A significant reduction over three times in trap density was achieved in the crystallization manipulated perovskite film. Benefitted from the strongly suppressed non-radiative recombination within these trap defects, much stronger intensity in the steady-state PL emission were consequently characterized comparing with that in the polycrystalline film fabricated using the CP method (Figure 2d).30, 38 The highly crystallized perovskite film via the GDCP also presented an obvious redshift in PL spectra possibly due to the improved excitonic transitions besides free carriers’ recombination, like that frequently observed in perovskite single crystals.39-40 Additionally, the slightly increased absorbance also should be originated from the improved crystal quality of the highly crystalline perovskite film produced by GDCP.41 Once again, much more uniform and redshift emission mapping than that in the CP fabricated film, as displayed in Figure 2g-h vs Figure 2e-f, further evidenced the highly crystalline characteristic in the GDCP based perovskite films. Considering


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the relatively high uniformity in thickness and composition within the crystal domain over hundreds of micrometers (Figure S6), the ununiform emission feature within the mapping region (Figure 2f and h) should be mainly originated from the intrinsic difference in electrical properties of the perovskite grains in different sizes and crystallinity. As mentioned above, the solvent engineering and thermal controlling synergistically contribute to balancing the nucleation and grain growth during the crystallization by GDCP. So, understandably and as characterized in Figure S7(a-d), the solvent composition is critical for the growth-dynamic controlling, and thus large crystal domains with high quality can be realized in the perovskite by using the optimized solvent (DMSO) ratio in the precursor solutions. Additionally, the XRD characterization (Figure S7e) indicated that the excess DMSO solvent would cause the residual MAI-PbI2-DMSO intermediate phase and result in the declined crystallinity. Besides the solvent composition, the temperature would reasonably determine the perovskites’ nucleation and growth rate,26 so that the size enlargement in perovskite domains can be well manipulated by continuously increasing the temperature nearing the boiling point of solvent DMF (N, N-dimethylformamide ) (Figure S8), similarly as that in the previous report.38 In addition, due to the perovskite films were directly crystalized from the solution phase, the substrate with good surface wettability, such as the freshly thermal-annealed FTO substrate with compact and mesoporous layer as demonstrated in Figure S9, would be helpful to produce continuous film with large crystal domains.42 It should be noted that the continuous film grown on the hydrophilic substrate using the optimized precursor solution presents highly crystalline characteristic as evidenced in the PL mapping images and spectra of Figure S10 and S11. As comparisons, single-crystalline discrete perovskite grains are generally produced on the


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hydrophobic surface or even on the hydrophilic substrate the polycrystalline film would be fabricated if not well manipulating the precursor composition. The photovoltaic performance of the PSCs fabricated using these GDCP based films have been further evaluated. The device architecture of the PSCs can be visualized from the crosssessional SEM image in Figure 3a. Dense perovskite layer with hardly resolved crystal boundaries can be clearly observed within the device, which is consistent with the highly crystalline characteristic of the GDCP based films. Figure 3b shows the J-V curves with both

Figure 3. (a) Cross-sectional SEM image of a completed device fabricated on the GDCP based highly crystalline perovskite film. (b) J-V curves with both forward and reverse scans for the best performing cells on the two kinds of perovskite films (active area of 0.11 cm2); and (c) the corresponding IPCE spectra. (d) Histogram of PCE values obtained by the reverse J-V scan for the PSCs on CP and GDCP perovskite films.


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Table 1. Extracted photovoltaic parameters of the devices in Figure 3b Cell

Scan direction

Voc (V)

Jsc (mA cm-2)

FF

PCE (%)

H-index (%)

CP

Reverse

1.01

21.86

0.72

15.98

16.45

Forward

1.00

21.96

0.61

13.35

Reverse

1.04

22.24

0.77

17.82

Forward

1.02

22.32

0.69

15.80

GDCP

11.34

forward and reverse scans for the champion cells on the two kinds of perovskite films. The relative higher Voc and FF enable the best performance of 17.82%-conversion efficiency (reverse scan) among the device using the GDCP based film (Table 1). Here, the hysteresis index (Hindex), which is defined as (PCEreverse−PCEforward)/PCEreverse,43 was used to evaluated the hysteresis properties of the prepared devices. The PCEreverse and PCEforward represent the power conversion efficiency (PCE) obtained from reverse and forward J-V scans, respectively. Much less hysteresis was also characterized in the GDCP based device with H-index of 11.34% versus that 16.45% in the CP based device. The estimated Jsc from incident photon-to-electron conversion efficiency (IPCE) spectrum (Figure 3c) was 20.69 and 21.23 mA cm-2 for the devices based on CP and GDCP perovskite films, respectively, which matched well with the obtained values in J-V measurement of Figure 3b. The histogram of PCE values (reverse scan) for the PSCs were statistically shown in Figure 3d. Comparing with that in the devices using polycrystalline perovskite films by CP, a remarkable PCE improvement by ~12% (from average value of 14.56% to 16.32%) was accomplished in the devices employing the GDCP realized highly crystalline films. It is clear that the significantly improved crystal quality and electrical properties were the main reasons for the improvement of photovoltaic performance. The highly crystalline perovskite film with much low trap density not only can significantly suppress the


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non-radiative recombination loss, but also could enhance the charges transportation,44 leading to an increased Jsc and FF. In addition, the correspondingly produced higher carrier concentration could further improve the quasi-Fermi level splitting, resulting in an increased Voc.45 Promisingly, the specific crystal growth mechanism demonstrated in this work can be facilely adopted to prepare high quality perovskite film through the more extensive and robust painting method, as illustrated in Figure 4a. Here, a homemade automatic painting system (Figure S12) based on a three-dimensional (3D) linear sliding module was used to prepare the perovskite films. To obtain a tender and uniform contact with substrates during the painting process, the painting head was modified using a fine, soft and absorbent material. The dust-free cloth was demonstrated to be the ideal candidate for painting perovskite solution with higher surface uniformity, when comparing with the animal hair, which usually is the raw material of writing brush or painting brush (Figure S13). Large scale (~10 cm2) and uniform perovskite films have been successfully produced by this facile painting method, as shown in Figure 4b. The rapid fabrication process can be visually seen in the supplementary Video S2. Surface SEM (Figure S14a-b) and AFM (Figure S15) images indicate that the prepared perovskite film has a similar morphology as that using the blade-coating method, which consisted of highly crystalline large perovskite grains over serval microns in size. However, different from the blade-coating approach, the painted films show distinct advantages in thickness and uniformity control, as evidenced by the cross-sectional SEM image (Figure S14c). Understandably, the direct contact mode and specific capillarity-based solution supply enabled a much controllable film forming in the painting. The dense perovskite film with highly crystalline morphology can also be resolved in the cross-sectional SEM image of a completed device, as shown in Figure 4c. A best performing cell with PCE of 17.13% (reverse scan) has been achieved on this


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Figure 4. (a) Schematic illustration of the painting method preparing perovskite films. (b) Photograph of the as-painted large-scale perovskite film. (c) Cross-sectional SEM image shows a completed device based on the painted perovskite film. (d) J-V curves with both forward and reverse scans of the best-performing cell on the painted perovskite films (active area of 0.11 cm2). (e) Histogram of the PCE values (reverse scan) for 80 devices. (f) J-V curves (reverse scan) of the large-area (1.02 cm2) device and the selected five different spots within the active area using a metal mask (aperture size of 0.09 cm2). (g) The corresponding IPCE spectra that measured at the same spots as that in the J-V measurements in (f).


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painted film, yielding a Voc of 1.05 V, Jsc of 21.96 mA cm-2, and FF of 0.74 (Figure 4d). The device also exhibits a satisfied less hysteresis with H-index of 8.00%. The integrated Jsc of 21.02 mA cm-2 from the IPCE spectrum (Figure S16) agrees well with the measured value. Figure 4e shows the histogram of the PCE values for 80 devices, which were obtained by the reverse J-V scans. The average value of 16.01% and narrow distribution of PCE values indicate that not only efficient PSCs can be facilely fabricated by this robust painting method, but also the prepared devices show a distinguished high reproducibility with the calculated standard deviation (SD) of 0.62, when comparing with that of 0.81 by the blade-coating method. Large-area (1.02 cm2) solar cells also have been fabricated to further evaluate the macroscopic uniformity across the painted single film on the substrates. As shown in Figure 4f, the J-V curve of the best-performing large-area device exhibited a satisfied PCE of 14.37% (Voc of 1.03 V, Jsc of 21.75 mA cm-2, and FF of 0.64). J-V curves measured at the selected five different areas demonstrate a small variation in Jsc ranging from 21.6 to 21.9 mA cm-2, which is also matched well with the integrated Jsc from IPCE spectra with values varying from 20.96 to 21.24 mA cm-2 (Figure 4g). These results indicate the high uniformity of the painted perovskite film in macroscopic scale at least within the 1 cm2-area. Further SEM characterization indicates that the perovskite layer only presents a small variation about ±24 nm in thickness across the large area (Figure S17). It should be noted that the decreased FF is the main parameter resulting in the obvious decrement in PCE for this large-area device when comparing with that in smallarea devices. The series resistance loss is believed to be the dominant reason for this power output decline, especially in large-area devices.46 A significant improvement in film uniformity control within the large-area device was also demonstrated for this painting approach by


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comparing the film information with those fabricated by blade coating method. (Figure S18 and S19). To further evaluate the stability performance of the painting based device, the stabilized power output and long-term air-stability were tested, with comparison to the blade coating based one (Figure S20). The results indicate that both devices have a pretty good stabilized power output and a satisfied long-term air-stability which can kept over 90% of their initial PCE values after two weeks’ aging in ambient air (RH ~20%).47 It is worth noting that slightly lower longterm stability was performed on the painting based device comparing with that on the blade coated film. The somewhat decreased crystal phase purity was considered to be the main reason,48-49 as discussed in Figure S21. In addition to the efficient and stable PSCs’ feasible preparation, this painting method also shows a specific advantage in readily controlled film thickness and transmittance, demonstrating the particular favor to the building-integrated photovoltaics or efficient tandem solar cells.50-51 As shown in Figure 5a, the thickness of the painted perovskite films can be easily adjusted by

Figure 5. (a) Absorption spectra of the perovskite films painted with different concentrations of precursor solution: 0.6, 1.0 and 2.0 M. (b) PCE metrics for 30 devices fabricated on the painted perovskite films using the three concentrations of precursor solutions.


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applying different concentrations of precursor solutions, leading to a color evolution from semitransparent to fully dark with different absorbance. Benefitted from the well-controlled film uniformity, satisfied PCE values still can be obtained in the devices fabricated by the perovskite films with different color and transmittance. An average PCE of 11.06±0.80%, 12.56±0.56% and 16.09±0.66% were obtained based on the perovskite films fabricated using 0.6, 1.0 and 2.0 M precursors, respectively (Figure 5b). The typical J-V curves for the three kinds of perovskite films was shown in Figure S22, and the photovoltaic parameters were summarized in Table S2.

CONCLUSIONS By introducing the thermal / solvent engineering, highly crystalline perovskite films with large crystal domains up to 500-µm was readily produced by using the facile blade-coating method, which is demonstrated to be originated from the highly-controlled crystal growth dynamics by balancing the nucleation and lateral-growth from solution phase. Thus, obviously improved photovoltaic performance with 12%-average PCE increment was realized employing the highly crystalline MAPbI3 perovskite films by the growth-dynamic-controlled process (GDCP), when comparing with the polycrystalline film based devices, which was fabricated using the conventional process (CP). In addition, by fully utilizing the rapid crystallization and specific film growth mechanism, high-quality, large scale and uniform perovskite films was further realized by using the more robust fabrication of painting method. The facilely obtained efficient photovoltaic performance (champion PCE of 17.13% and average PCE of 16.01%) and high repeatability well demonstrated the modified one-step painting method is a high reliable route for efficient PSCs’ mass-production.

EXPERIMENTAL SECTION


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Perovskite film preparation. For the blade-coated films, the freshly thermal-annealed FTO substrates with mesoporous layer were pre-heated at 150 °C and the precursor solution (PbI2:MAI=1:1 or PbI2:DMSO:MAI =1:1:1, 1 M in DMF) was kept at 70 °C. About 30 µl precursor solution was dipped at the interface of the blade and substrate, and then the bladecoater (Pushen, KTQ-200) was moved forward at a constant rate about 15 mm/s. After that, the substrates were transferred to another hot-plate heating for 5 minutes at 150 °C. For the painted films, a homemade automatic painting system based on a XYZ 3D linear sliding module was used to perform the fabrication process. A peristaltic pump was used to supply the solution into the painting head with a constant rate about 4 ml/min. After the full infiltration of the precursor solution in the painting head, the painting procedure was carried out by moving-control system with pre-loaded standard G-codes, and the typical moving speed was about 6 mm s-1. Device fabrication. Pre-patterned FTO (NSG, 14 Ω) substrates were ultrasonically cleaned by acetone and ethanol successively for 20 minutes, and then washed by DI water and dried with nitrogen gun. To deposit the compact TiO2 (c-TiO2) layer, a 0.15 M titanium diisopropoxide bis (acetylacetonate) (Alfa Asear) solution in ethanol was spin-cast on the cleaned substrates (3000 rpm for 30 s, twice), then dried at 125 °C for 5 min and annealed at 550 °C in air for 30 min. Subsequently, the substrates were treated by TiCl4 aqueous solution (50 mM) at 70 °C for 30 min and washed with DI water, followed by mesostructure TiO2 (m-TiO2) layer deposition by spin coating a commercial TiO2 paste (Dyesol 18NRT) diluted in ethanol (1:6, weight ratio) at 5000 rpm for 30 s, and then annealed at 500 °C for 30 min. After deposition of the perovskite films using the aforementioned blade-coating or painting methods, hole-transporting material (HTM) layer was deposited by spin coating a HTM solution (72.4 mg Spiro-OMeTAD, 17.5 µl Li-TFSI solution (520 mg Li-TFSI in 1ml acetonitrile) and 28.8 µl TBP in 1ml chlorobenzene solvent) at


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4000 rpm for 30 s. Finally, 100 nm-thick gold was deposited through a metal mask on the HTM layer as contact electrode by electron beam evaporation. Characterization. SEM images were obtained by a field-emission scanning electron microscopy (Hitachi S-4800). Large scale (20×20 µm2) atomic force microscopy (AFM) images were measured using an Asylum Research Cypher AFM in tapping mode. X-ray diffraction (XRD) patterns were taken by Rigaku Ultima IV X-ray Diffractometer with Cu Ka radiation. Absorption spectra of the perovskite films were recorded using a Shimadzu UV-2550 spectrophotometer. Photonluminesce (PL) mapping measurement were taken on a laser Raman microscope (RAMAN-11, Nonophoton) excited by 532 nm laser. Time-resolved PL (TRPL) spectra were recorded on a fluorescence spectrometer (FLS980, Edinburgh Photonics) excited by picosecond pulsed diode lasers (377.8 nm). J-V performance was measured by a Keithley 2400 source meter under simulated AM 1.5G illumination (100 mW cm-2, Oriel's Sol2A Class ABA Solar Simulator, Newport). The measured active area for the standard solar cells is 0.11 cm2, if without further statement. The incident photon-to-electron conversion efficiency (IPCE) spectra were measured by an optical power meter (2936-R, Newport) equipped with a power source (66920, 300 W xenon lamp, Newport) and a monochromator (Cornerstone 260, Newport). The contact angle for the different substrates were measured using a drop shape analyzer (DSA20, KRÜSS GmbH). The I-V measurements for SCLC analysis were carried out with an electrochemical workstation (CHI660D) under dark. The FTO/perovskite/Au samples were fabricated by directly blade-coating the perovskite film on the freshly thermal-annealed FTO substrates, followed by a 100 nm-thick Au layer deposition through a metal mask.

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Supporting Information. The following files are available free of charge. Supplementary videos (MP4 video); Additional experimental details, optical images, surface and cross-sectional SEM images, AFM images, EDX mapping, substrates’ wettability characterization, PL mapping, XRD, J-V curves, stability test and the IPCE spectra (PDF). AUTHOR INFORMATION Corresponding Author *Email: [email protected] (J. Y.) *Email: [email protected] (J. L.) *Email: [email protected] (N. F. Z.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work is ﬁnancially supported by the National Basic Research Program of China (2017YFB0404100 and 2015CB932301), National Natural Science Foundation of China (61505172, 61675173 and U1405253), Natural Science Foundation of Fujian Province of China (2018J01102 and 2017H6022), Science and Technology Program of Xiamen City of China (3502Z20161223).


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Thermal/solvent engineering coordinately enhanced rapid crystallization strategy is developed to realize the fast and robust preparation of perovskite films.


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Figure 1. (a) Schematic illustration of the blade coating method for perovskite films’ preparation, and comparison of the different growth mechanisms during the (b) conventional process (CP) and (c) growthdynamic-controlled process (GDCP) in blade coating. (d-f) and (g-i) show the surface SEM images in different magnifications of the corresponding perovskite films fabricated by the CP and GDCP methods, respectively. The long-time electron irradiation induced crack in SEM measurement was selectively shown in (i) for comparison, indicating the flat surface with hardly resolved grain boundaries. 119x97mm (300 x 300 DPI)


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Figure 2. (a) XRD patterns of the perovskite films fabricated using the CP and GDCP methods. (b) Time resolved photoluminescence (TRPL) spectra of the prepared films. (c) I-V curves of the CP and GDCP based perovskite films for space charge limited current (SCLC) analysis. The device configuration for the I-V measurement was schematically shown in inset. (d) shows the absorption and steady-state PL spectra of the prepared films. (e) The optical microscopy (OM) image and (f) PL emission wavelength mapping of the CP based perovskite film, compared to (g) and (h) the corresponding images for the films fabricated using the GDCP. 140x126mm (300 x 300 DPI)



Figure 3. (a) Cross-sectional SEM image of a completed device fabricated on the GDCP based highly crystalline perovskite film. (b) J-V curves with both forward and reverse scans for the best performing cells on the two kinds of perovskite films (active area of 0.11 cm2); and (c) the corresponding IPCE spectra. (d) Histogram of PCE values obtained by the reverse J-V scan for the PSCs on CP and GDCP perovskite films. 98x74mm (300 x 300 DPI)


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Figure 4. (a) Schematic illustration of the painting method preparing perovskite films. (b) Photograph of the as-painted large-scale perovskite film. (c) Cross-sectional SEM image shows a completed device based on the painted perovskite film. (d) J-V curves with both forward and reverse scans of the best-performing cell on the painted perovskite films (active area of 0.11 cm2). (e) Histogram of the PCE values (reverse scan) for 80 devices. (f) J-V curves (reverse scan) of the large-area (1.02 cm2) device and the selected five different spots within the active area using a metal mask (aperture size of 0.09 cm2). (g) The corresponding IPCE spectra that measured at the same spots as that in the J-V measurements in (f). 148x168mm (300 x 300 DPI)



Figure 5. (a) Absorption spectra of the perovskite films painted with different concentrations of precursor solution: 0.6, 1.0 and 2.0 M. (b) PCE metrics for 30 devices fabricated on the painted perovskite films using the three concentrations of precursor solutions. 50x19mm (300 x 300 DPI)


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From Blade Coating to Painting - ACS Publications - American

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