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Intermediate Phase Intermolecular Exchange Triggered Defects Elimination in CH3NH3PbI3 towards RoomTemperature Fabrication of Efficient Perovskite Solar Cells Weidong Zhu, Dazheng Chen, Long Zhou, Chunfu Zhang, Jingjing Chang, Zhenhua Lin, Jincheng Zhang, and Yue Hao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14254 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on October 30, 2017

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ACS Applied Materials & Interfaces

Intermediate Phase Intermolecular Exchange Triggered Defects Elimination in CH3NH3PbI3 towards Room-Temperature Fabrication of Efficient Perovskite Solar Cells Weidong Zhu,* Dazheng Chen, Long Zhou, Chunfu Zhang,* Jingjing Chang, Zhenhua Lin, Jincheng Zhang,* and Yue Hao Wide Bandgap Semiconductor Technology Disciplines State Key Laboratory, School of Microelectronics, Xidian University, Xi’an 710071, P. R. China.

ABSTRACT: The solvent-engineered one-step spin-coating method has been widely used to produce full-coverage CH3NH3PbI3 films for perovskite solar cells by forming intermediate phase. However, the resultant CH3NH3PbI3 films usually contain numerous structural and compositional defects mainly resulted from the fast crystallization of intermediate phase as well as the escape of CH3NH3I species induced by the inevitably thermal annealing recipe. Herein, a facile room-temperature intermolecular exchange route is proposed to enable the conversion of intermediate phase to uniform and ultra-flat CH3NH3PbI3 films. It can effectively inhibit the formation of structural and compositional defects in the resultant films, and even repair their inherent defects. As a result, the efficiency of perovskite solar cells can be boosted to 19.45% with the stabilized value of 18.55%, which are much higher than the ones fabricated by thermal annealing. This study suggests a facile and low-cost route to room-temperature fabrication of highly efficient perovskite solar cells including the flexible ones.

KEYWORDS: CH3NH3PbI3, intermediate phase, defects, intermolecular exchange, room temperature, perovskite solar cells

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1. INTRODUCTION Organolead trihalide perovskites such as typical CH3NH3PbI3 have emerged as promising absorption materials for low-cost photovoltaic devices that are known as perovskite solar cells.1-3 Recently, the power conversion efficiency (PCE) of single-junction devices has skyrocketed over 22% from 3.8%.4,5 Such an unprecedented achievement is mainly ascribed to the excellent optoelectronic features,6-8 unique defect physics of CH3NH3PbI3 films9 as well as the great efforts focused on device architecture, interface engineering, materials and deposition strategies for each of functional layers.2,10,11 So far, it is widely recognized that pinhole-free, low-defect CH3NH3PbI3 film is essential to enable reliable device performance.2,10 Of various strategies developed for CH3NH3PbI3 film deposition,10,11 the solvent-engineered one-step spin-coating method has been widely adopted due to its simplicity,7 in which the CH3NH3PbI3 precursor solution (for example, a mixture of PbI2 and CH3NH3I in a mixture solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) ) is spin-coated onto the substrate followed by dropping anti-solvent such as toluene or diethyl ether during spinning.12,13 For this method, CH3NH3PbI3 intermediate phase film composed of CH3NH3I-PbI2-DMSO complexes firstly formed after the spinning process. It was then usually converted to full-coverage CH3NH3PbI3 film after removing the DMSO molecules by thermal annealing at ~100 °C. Nevertheless, compositional defects that relate to iodide deficiencies are easily produced in resultant CH3NH3PbI3 film by this manner due to the volatility of CH3NH3I species during annealing.14,15 In addition, because of the fast crystallization of the film it generally composes of small grains, which couples with high-density grain boundaries. Such compositional and structural defects usually act as non-radiative recombination centers in the film, which are responsible for short carrier lifetime and diffusion length, subsequently inferior solar cell performance especially low open circuit voltage (Voc).5,16,17 To address this issue, some successful attempts have been reported via engineering the intermediate phase conversion, such as incorporation of additives,16 solvent vapor recycling annealing,18 cap-mediated crystallization,19 laser-assisted annealing,20 solvent/anti-solvent designing,21-23 and so on. However, all of them inevitably involve sophisticated thermal treatment recipes with relatively high temperature that consume extra time and/or cost, making them unsuitable for industrial applications. Moreover, thermal treatment may also be a concern for device fabrication on ﬂexible substrates.24 Thus, 2


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room-temperature routes that facilitate the conversion of intermediate phase to low-defect CH3NH3PbI3 films need to be developed. Herein, we concern this vital point, and propose an intermolecular exchange route that can enable the room-temperature conversion of intermediate phase to uniform and ultra-flat CH3NH3PbI3 films. Such films that possess fewer compositional and structural defects can

dramatically boost the efficiency of perovskite solar cells. The champion cell yields the PCE of 19.45% with the stabilized value of 18.55%, which are obviously higher than those of the champion one fabricated by thermal annealing.

2. RESULTS AND DISSCUSION

Figure 1. Schematic illustration of the procedures of CH3NH3PbI3 films formation by intermolecular exchange and conventional annealing. Figure 1 schematically illustrates the procedures of CH3NH3PbI3 film formation by intermolecular exchange. Briefly, the intermediate phase film was firstly prepared by the recipe reported by Park et al..12 For intermolecular exchange, 0.5 mL isopropanol (IPA) solution containing 3.0 mg/mL CH3NH3I and 2.0 mg/mL CH3NH3Cl that has been optimized depending on the solar cell performance was spin-coated on intermediate phase film. Thus it can be converted to CH3NH3PbI3 film. The CH3NH3PbI3 film was also prepared by thermal annealing for comparison. The experimental details can be found in the Experimental section. Figure 2a shows the X-ray diffraction (XRD) patterns of intermediate phase and CH3NH3PbI3 films. Clear diffraction peaks can be detected from intermediate phase that has been revealed to compose of CH3NH3I-PbI2-DMSO complexes.12,13 Both thermal annealing and intermolecular exchange can remove DMSO molecules from intermediate phase effectively, in turn convert to it to pure CH3NH3PbI3. This can be inferred from the characteristic diffraction peaks of the films located at 14.0o, 28.3 o and 31.8o that 3



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correspond to (110), (220) and (310) planes of tetragonal CH3NH3PbI3.10 To further confirm this inference; we have measured the Fourier transform infrared (FTIR) transmission spectra of the samples. As shown in Figure 2b, the S=O stretching bands at 1010 cm-1 that corresponds to DMSO molecules can be observed clearly from intermediate phase film, while such signal absent completely in the films after thermal annealing or intermolecular exchange. These results reveal that, as with thermal annealing, intermolecular exchange route can also fully remove DMSO molecules of intermediate phase, facilitating the formation of CH3NH3PbI3. But, compared with thermal annealing, a key superiority of intermolecular exchange route is that the intermediate phase conversion proceeds at room temperature. In addition, it is notable that the major diffraction peaks of CH3NH3PbI3 film obtained by intermolecular exchange exhibit stronger intensities than the one by thermal annealing, indicative of its better crystallinity.16,19

Figure 2. (a) XRD patterns and (b) FTIR transmission spectra of intermediate phase and CH3NH3PbI3 films deposited on insulating glass substrates.

The elemental composition of resultant CH3NH3PbI3 films was investigated by X-ray photoelectron spectroscopy (XPS). As revealed in Figure S1, clear signals that are identified to C, N, Pb, and I can be detected from both of the two samples, indicating their similar composition. However, there are some differences in atomic concentrations of Pb and I between them. To distinguish this difference, we normalized each core-level XPS spectrum to the corresponding peak intensity of I 3d5/2, and the results are shown in Figure 3a. It can be seen that peak intensities of Pb 4f for the film obtained by intermolecular exchange are much lower than those for the one by thermal annealing. And the corresponding atomic ratio of I/Pb is calculated to 2.95. These results signify that the 4


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CH3NH3PbI3 film obtained by intermolecular exchange possesses a lower iodide deficiency, namely fewer compositional defects.5,14 It is notable that the atomic ratio of I/Pb calculated from the XPS spectrum of intermediate phase film (Figure S2) is 2.56. That is to say, many compositional defects exist inherently in intermediate phase film, largely due to the solubility of PbI2 is lower than CH3NH3I that results in the preferential precipitation of PbI2 after anti-solvent dipping.25 Interestingly, such defects can be repaired effectively by intermolecular exchange recipe.

Figure 3. Core-level XPS spectra of (a) Pb 4f, I 3d and (b) Cl 2p of the CH3NH3PbI3 films prepared by intramolecular exchange and conventional annealing.

Meanwhile, as shown in Figure 3b, the characteristic peak of Cl 2p was observed in the

sample obtained by intermolecular exchange, and the concentration of Cl atoms was roughly estimated to 2.3 mol% with respect to I atoms. We speculate that the observed Cl atoms are from Cl- incorporated into CH3NH3PbI3 via substituting I-. There have been several reports using XPS to probe Cl- in CH3NH3PbI3 film synthesized with the Cl-containing precursor.26-29 And, the results indicate that almost no Cl- exist in the top surface of ultimate film, which could be ascribed that Cl- can escape from the system easily during annealing.30 Herein, the film preparation proceeds at room temperature, the existence of Cl- is thus reasonable. This speculation is also supported by recent studies in which the incorporation of Cl- into CH3NH3PbI3 was theoretically and experimentally confirmed.27,28,31,32 Due to the concentration of Cl atoms is rather low, the film prepared in this work is still labeled as CH3NH3PbI3 for simplicity. The surficial morphology of CH3NH3PbI3 films was investigated by scanning electron microscope (SEM). As exhibited in Figure 4a and Figure 4c, both of the films are uniformly composed of closely packed grains and no pinholes can be found over large 5



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areas. In comparison, the CH3NH3PbI3 film obtained by intermolecular exchange has much larger grain size with the average value of ~385 nm, while the one by thermal annealing yield the average grain size of ~143 nm, as statistically shown in Figure S3. This means that the density of grain boundaries, namely structural defects in it, is much lower. From the atomic force microscopy (AFM) images shown in Figure 4b and Figure 4d, the area root-mean-squared (RMS) roughness is further estimated to 9.6 nm for the film prepared by intermolecular exchange and 5.3 nm for the one by conventional annealing. The slightly larger roughness of the film prepared by intermolecular exchange is mainly ascribed to its enlarged grain size, which induces the decrease of grain-boundary groove angle. Even so, its RMS roughness is still low extremely.

Figure 4. SEM and AFM images of CH3NH3PbI3 films prepared by intermolecular exchange (a and b) and conventional annealing (c and d).

Overall, combining all the above investigations, we come to the conclusion that intermolecular exchange route can enable the uniform and ultra-flat CH3NH3PbI3 film with fewer compositional and structural defects compared with conventional annealing, which is extremely desirable for high-performance perovskite solar cells.5,17 Moreover, this route is time-saving and low-cost relatively, possessing more potential for industrial applications. More importantly, it is carried out at room temperature, thus being compatible with flexible

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substrates. All these features make the intermolecular exchange route to be a promising one for practical applications.

Figure 5. (a) SEM images and (b) FTIR transmission spectra of intermediate phase films after spin-coating IPA, CH3NH3Cl/IPA, and CH3NH3I/IPA solutions, respectively. (c) Schematic illustration of room-temperature CH3NH3PbI3 film formation via intermolecular exchange.

Regarding detailed understanding the intermolecular exchange route, we altered the solution that is employed in this route. Three type solutions are concerned; those are IPA, IPA containing 3.3 mg/mL CH3NH3Cl, and IPA containing 7.7 mg/mL CH3NH3I. The latter two have the same molar concentration as the IPA containing 3.0 mg/mL CH3NH3I and 2.0 mg/mL CH3NH3Cl. As shown in Figure 5a and Figure 5b, the film is composed of small grains when IPA is used alone. And, clear S=O stretching bands at 1010 cm-1 that corresponds to DMSO molecules can be detected from it, indicating incomplete conversion of intermediate phase. When we employ IPA solution containing 3.3 mg/mL CH3NH3Cl, some signals of S=O stretching bands can also be detected in resultant film, while the grain size of the film becomes larger. But, no any signal of DMSO molecules can be found in the film when IPA solution containing 7.7 mg/mL CH3NH3I is used, while the grain size of the film is smaller than the one prepared with IPA solution containing 3.3 mg/mL CH3NH3Cl. These results reveal that adding CH3NH3I in IPA solution is vital for the 7



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full conversion of intermediate phase, while CH3NH3Cl is necessary to the formation of large grains in resultant CH3NH3PbI3 film. On the basis of these results, we proposed a possible mechanism for the room-temperature conversion of intermediate phase film to low-defect CH3NH3PbI3 film by intermolecular exchange. As shown schematically in Figure 5c, after IPA solution with 3.0 mg/mL CH3NH3I and 2.0 mg/mL CH3NH3Cl being spin-coated on the intermediate phase film, DMSO molecules are exchanged easily by CH3NH3I or CH3NH3Cl at room temperature mainly due to their higher affinity toward PbI2 relative to DMSO.33,34 The exchanged DMSO molecules are then extracted from the film bulk by roving IPA. This process not only promotes the full conversion of intermediate phase film but also repairs its inherent compositional defects, leading to the formation of low-defect CH3NH3PbI3 film at room temperature. It should be noted that the introduction of CH3NH3Cl in IPA solution can induce large grains in CH3NH3PbI3 film, which is mainly ascribed that CH3NH3PbI2Cl species that formed through the reaction of CH3NH3Cl with intermediate phase can hinder the nucleation of CH3NH3PbI3 grains, thus leading to the decrease of nucleation sites. This induces the formation of larger CH3NH3PbI3 grains as previously reported.29,35,36 Moreover, the final conversion process of CH3NH3PbI2Cl species to CH3NH3PbI3 can also relatively slow down the crystallization of CH3NH3PbI3 grains, which is conductive to the improvement of their crystallinity.37,38

Figure 6. (a) Normalized UV-vis absorption spectra and (b) TRPL curves of CH3NH3PbI3 films prepared by intramolecular exchange and conventional annealing. The samples were deposited on glass substrate.

The photo-physical properties of CH3NH3PbI3 films were further examined. Figure 6a shows their UV-vis absorption spectra. The two films show similar absorption characteristic that covers the entire visible regions with the absorption edge of ~780 nm. Slightly higher absorption intensity from 550 nm to the absorption edge can be found for the CH3NH3PbI3 film prepared by intermolecular exchange. Then, the recombination 8


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dynamics of photo-induced carriers in the films were monitored by time-resolved photoluminescence (TRPL) decay measurement, as given in Figure 6b. The TRPL spectra were fitted with bi-exponential decay function coupled with two time components, in which the fast decay component (τ1) is related to surface recombination of charge carriers, while the long decay component (τ2) is attributed to their recombination in the bulk.25 Taking the weighted average of the two components, the lifetime of minority carriers is thus estimated to 36 ns for CH3NH3PbI3 film prepared by intermolecular exchange and 13 ns for the one by conventional annealing. The longer lifetime of minority carriers indicates the fewer non-radiative recombination sites in the film,6,10 which mainly originates from its lower density of compositional and structural defects. The decrease of non-radiative recombination sites is extremely conductive to boost the performance of perovskite solar cells. This is because more and more experimental and theoretical results reveal that the primary energy loss in perovskite solar cells largely results from the non-radiative recombination of charge carriers,14-17,19 as similar with other thin-film photovoltaic devices.

Figure 7. (a) Statistical PCE values of 29 solar cells fabricated by intermolecular exchange and conventional annealing. Each box as well as the sphere symbol represents the statistical PCEs distribution of 29 working devices. Whiskers indicate the outlier while box edges represent the 25/75 percentile. Small

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square symbols inside the boxes represent the mean value, while the line across the boxes represents the median. The × symbols represent the maximum and minimum values. (b) J-V curves including the reverse (from 1.2 to -0.1 V) and forward (from -0.1 to 1.2 V) scans, (c) Stabilized maximum PCE outputs, and (d) EQE spectra for the champion devices, respectively.

Table 1 Summary of photovoltaic performance parameters of champion cells fabricated by intermolecular exchange and conventional annealing recorded at forward and reverse scans. Samples

Scan

Jsc (mA/cm2)

Voc (V)

FF

PCE (%)

Intermolecular

Forward

23.76

1.128

0.60

16.08

exchange

Reverse

23.54

1.132

0.73

19.45

Conventional

Forward

23.58

1.029

0.51

12.37

annealing

Reverse

23.36

1.057

0.69

17.03

The performance of solar cells fabricated by intermolecular exchange and conventional annealing was further investigated taking the common device configuration of FTO/c-TiO2/CH3NH3PbI3/spiro-MeOTAD/Ag. To rule out possible experimental errors during cell performance assessment, 29 cells with each type of CH3NH3PbI3 films are counted. The statistical PCEs that were recorded under reverse scan (from 1.2 to -0.1 V) with a scan rate of 100 mV/s and standard AM 1.5G illumination are shown in Figure 7a (the measured photovoltaic performance parameters are listed in Table S1 and Table S2). Thus, the average PCE can be calculated to (18.67±0.03)% for the cells fabricated by intermolecular exchange, while the value is (15.21±0.22%) for the ones by conventional annealing. This result conveys clearly that intermolecular exchange route can significantly boost the PCEs of as-fabricated cells. Moreover, the standard deviation of statistical PCEs for those cells is much smaller than the ones by conventional annealing. This means that intermolecular exchange route is not only manageable but also reproducible. To further identify the improved PCE, the light current density versus voltage (J-V) curves including the reverse and forward (from -0.1 to 1.2 V) scans for the champion cells are presented in Figure 7b. The photovoltaic parameters including short circuit current density (Jsc), Voc, fill factor (FF) and PCE are listed in Table 1. We can see that the higher PCE of the champion cell fabricated by intermolecular exchange mainly comes from its larger Voc.

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This superior feature can be originally ascribed to the low density of compositional and structural defects in CH3NH3PbI3 film produced by intermolecular exchange that gives rise to the decrease of non-radiative recombination sites.17,39 In addition, it is clearly that the J-V hysteresis is also eliminated greatly for the cell fabricated by intermolecular exchange. To further insight this difference, the photocurrent density of the cell at the bias voltage of its maximum power point was recorded as a function of time, as shown in Figure S4. It can be seen that the current density of the cell fabricated by intermolecular exchange increases rapidly to the maximum value of 21.18 mA/cm2 in about 5 s under the bias voltage of 0.876 V. At such, it yields the stabilized PCE of 18.55% as reveled in Figure 7c, which is close to the value that obtained from the light J-V curve under reverse scan. By contrast, for the cell fabricated by conventional annealing it consumes over 20 s to stabilize at the maximum current density of 17.46 mA/cm2 under the bias voltage of 0.820 V, which amounts to the much reduced real PCE of 14.32%. Such results further reveal the suppressed J-V hysteresis in the cell fabricated by intermolecular exchange. The external quantum efficiency (EQE) of the champion devices were further measured and shown in Figure 7d. The maximum of EQE spectrum for the two cells can reach over 90%, while the cell fabricated by intermolecular exchange exhibits a slightly higher EQE values than the one by conventional annealing especially in the region from 600 to 760 nm. Those features further verify the excellent photoelectric conversion characteristics of the cell fabricated by intermolecular exchange. The Jsc values integrated from the EQE spectra are 22.74 and 21.57 mA/cm2 for the cells fabricated by intermolecular exchange and conventional annealing, matching well the difference measured from the J-V curves. Based on the above results, we can conclude that intermolecular exchange can enable more efficient perovskite solar cells with smaller J-V hysteresis in contrast to conventional annealing route. 3. CONCLUSIONS In summary, the facile intermolecular exchange route can greatly promote the room-temperature conversion of intermediate phase to uniform and ultra-flat CH3NH3PbI3 film in solvent-engineered one-step spin-coating method. Moreover, it can effectively inhibit the formation of compositional and structural defects in the resultant film, and even repair its inherent defects. As a result, the 11



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efficiency of perovskite solar cells can be boosted to 19.45% with the stabilized value of 18.55%, which are much higher than the ones fabricated by thermal annealing. So, our work suggests a favorable route to room-temperature, low-cost fabrication of highly efficient perovskite solar cells including the flexible ones. 4. EXPERIMENTAL SECTION

Reagents and materials. Unless otherwise mentioned, all reagents and materials were purchased from Sigma-Aldrich, and used as received without further purification. The 2,2′,7,7′-tetrakis (N,N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (Spiro-MeOTAD, ≥99%) was purchased from Shenzhen Feiming Science and Technology Co., Ltd. (China). CH3NH3I and CH3NH3Br were purchased from Xi'an Polymer Light Technology Corp (China).

Preparation of CH3NH3PbI3 film. Patterned FTO glass substrate with sheet resistance of 7 Ω/sq was cleaned by the recipe described elsewhere.19,20 A compact TiO2 layer with the optimized thickness of ~60 nm was coated onto the pre-cleaned FTO substrate by spin-coating TiO2 sol at 3000 rpm for 30 s. The TiO2 sol was prepared by the recipe described by Wang et al..40 After the spin-coating process, the sample was thermal annealing at 480 °C for 60 min in air. After naturally cooling down to room temperature, the TiO2/FTO substrate was obtained. The CH3NH3PbI3 intermediate phase film was deposited onto the as-prepared substrate in a glovebox by the recipe reported by Park et al..12 In detail, 50 µL of precursor solution that contains 0.160 g CH3NH3I, 0.461 g of PbI2, 0.078 g of DMSO, and 0.600 g of DMF was dropped onto the TiO2/FTO substrate, followed by spinning at 4500 rpm for 25 s. During the first 6 s of the above spin process, 0.5 mL of anhydrous diethyl ether was injected on the rotated substrate via an injection syringe. Thus, the CH3NH3PbI3 intermediate phase film can be obtained. For the intermolecular exchange, 0.5 mL IPA solution containing 3.0 mg/mL CH3NH3I and 2.0 mg/mL CH3NH3Cl was spin-coated on intermediate phase film at 3000 s for 60 s in glovebox. After the spinning process, the intermediate phase film can be converted to CH3NH3PbI3 film. The CH3NH3PbI3 film was also prepared by thermal annealing the intermediate phase film at 100 °C for 10 min for comparison.

Fabrication of solar cells. The hole transport material (HTM) with the layer thickness of ~100 nm was deposited on CH3NH3PbI3 film by spin-coating 100 µL of HTM solution at 3000 rpm for 30 s. The HTM solution was prepared by dissolving 0.075 g spiro-MeOTAD, 28.8 µL TBP, 12


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and 17.5 µL lithium Li-TFSI in acetonitrile (0.520 g/mL) into 1 mL chlorobenzene. After being preserved in the dark in dry box for 24 h, an Ag counter electrode with the thickness of ~100 nm and specific area of 0.28 cm2 was deposited on the top HTM layer by the thermal evaporation technique.

Thus,

the

perovskite

solar

cells

with

the

configuration

of

FTO/c-TiO2/CH3NH3PbI3/spiro-MeOTAD/Ag can be obtained.

Characterization. XRD patterns were collected in the range of 10-60° with the sweep speed of 10° min-1 using a Bruker D8 Advance XRD Instrument. The elemental composition of film was measured by XPS (PHI 5000 VersaProbe) using Al Kα monochromatic radiation. SEM images were acquired with a Zeiss Supra-40 Field-Emission SEM. AFM images were obtained using a Veeco NanoScope IV Multi-Mode AFM operated in tapping mode. FTIR transmission spectra of the samples were recorded with a Nicolet Nexus 870 FTIR spectrometer. UV-vis absorption spectra were tested with a Shimadzu UV-1800 Spectrophotometer. TRPL curves were recorded using the time-correlated single-photon counting technique (Picoharp 300). The samples were photoexcited using a 505 nm laser beam pulsed at 5 MHz. J-V curves of the cells were measured on a Keithley 2400 Digital Source-Meter under standard AM1.5 illumination (100 mW cm−2) cast by an Oriel 92251A-1000 sunlight simulator calibrated by the standard reference of a Newport silicon solar cell. A black mask with a circular aperture (0.09 cm2) was applied on top of the solar cell. The EQE spectra of cells were recorded with a 300 W xenon lamp (Oriel 6258) and a Cornerstone 260 Oriel 74125 Monochromator. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. XPS survey spectra of the CH3NH3PbI3 films prepared by intramolecular exchange and conventional annealing, core-level XPS spectra of Pb 4f and I 3d for the intermediate phase film, statistical grain size distributions, the stabilized current density outputs at the maximum power point for the champion devices fabricated by intramolecular exchange and conventional annealing, and measured photovoltaic performance parameters 29 solar cells fabricated by intramolecular exchange and conventional annealing. AUTHOR INFORMATION 13



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Corresponding Author *E-mail: [email protected]; [email protected]; [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported primarily by National Natural Science Foundation of China under Grant 61334002 and 61106063, and Class General Financial Grant from the China Postdoctoral Science Foundation (Grant No. 2016M602771).

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Intermediate Phase Intermolecular Exchange ... - ACS Publications

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