Fabrication of Perovskite Films with Large Columnar Grains via

Subscriber access provided by READING UNIV

Article

Fabrication of perovskite films with large columnar grains via solventmediated Ostwald ripening for efficient inverted perovskite solar cells Xiaobing Cao, Lili Zhi, Yahui Li, Fei Fang, Xian Cui, Lijie Ci, Kongxian Ding, and Jinquan Wei ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.7b00300 • Publication Date (Web): 24 Jan 2018 Downloaded from http://pubs.acs.org on January 25, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Energy Materials is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29 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

ACS Applied Energy Materials

Fabrication of Perovskite Films with Large Columnar Grains via Solvent-Mediated Ostwald Ripening for Efficient Inverted Perovskite Solar Cells Xiaobing Cao1, Lili Zhi2, Yahui Li1, Fei Fang1, Xian Cui 1, Lijie Ci2, Kongxian Ding3, Jinquan Wei1* 1. State Key Lab of New Ceramic and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P.R. China 2. School of Materials Science & Engineering, Shandong University, Jinan 250061, Shandong, P.R. China 3. Shenzhen Jiawei Solar Lighting Co., Ltd., New Industrial Zone No. 1-4, Fuping Road, Longgang District, Shenzhen 518112, Guangdong, P.R. China *Corresponding Author. E-mail: [email protected]. Phone: +86-10-62781065.

1 Environment ACS Paragon Plus

ACS Applied Energy Materials 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

ABSTRACT Generally, residual solvent is embedded in perovskite precursor films fabricated from the Lewis adduct method. Most of research focus on the ligand function of the solvent in forming solvate complex for fabricating high quality perovskite films. But, few attentions are paid to the latent function of the solvent in the perovskite precursor films during annealing process due to its fast extravasation at high temperature. Here, we develop a sandwich configuration of substrate/perovskite precursor films/PC61BM to retard the extravasation of solvent during annealing. We find that the restrained solvent induces an obvious solvent-mediated dissolutionrecrystallization process, leading to high quality perovskite films with large columnar grains. There are mass transportation from small grains to large grains in the dissolution-recrystallization process, which follows the Ostwald ripening model. Inverted planar solar cells are fabricated basing on this annealing method. The photovoltaic performance of the solar cells are improved significantly due to its high quality perovskite films with large columnar grains.

KEYWORDS: perovskite precursor films; sandwich structure; columnar grain; dissolutionrecrystallization; Ostwald ripening; solar cell;


Page 2 of 29

Page 3 of 29 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


1. INTRODUCTION Since the solid-state mesoscopic heterojunction solar cells by using methylammonium lead iodide (CH3NH3PbI3) as light harvest layer was reported,1 a great deal of efforts were made to develop high efficient organometallic halide perovskite solar cells (PSCs). By optimizing the device structure and fabrication methods, the power conversion efficiency (PCE) of PSCs has soared to 22.1% in a few years.2 Set aside chemical composition, smooth perovskite films composed of columnar grains featuring high-crystallinity large grains, and span vertically the entire film thickness are extreme desired for high efficient perovskite solar cells to reduce nonradiative recombination site.3 In order to fabricate high performance solar cells, some approaches have been adopted to fabricate high quality perovskite films. For example, different additives were introduced into perovskite precursor solution to enhance the crystallization of perovskite films.4-6 Liao`s group developed different methods to improve the crystallization of perovskite films, such as, using perylene as a seed-mediated underlayer,7 incorporating crosslinkable fullerene into perovskite films,8 using two-dimensional material of graphitic carbon nitride to passivate the perovskite crystallization.9 Zhang et al

10

developed an electric-field to

control the polarization orientation of perovskite films to fabricate good crystallization film. Li et al.

11

developed a vacuum-flash solution processing method to obtain shiny, smooth and

crystalline perovskite films. Chen et al. 12developed a solvent- and vacuum-free route to fabricate high quality perovskite films in large-area. At the same time, some researchers focused on the multiple roles of solvent, e.g. dimethylformamide (DMF), dimethyl sulphoxide (DMSO), on fabricating high quality perovskite films. Jeon et al. developed a solvent-engineering technology to fabricate highly uniform perovskite films.

13

In the solvent-engineering process, toluene solvent was used to remove the



excess DMSO and rapid formation of MAI-PbI2-DMSO intermediate phase. The DMSO embedded in the intermediate phase retards the reaction between PbI2 and MAI during the spincoating process, resulting in uniform perovskite films. Yang et al.14 fabricated solar cell with high efficiency above 20% through intramolecular exchange, where DMSO was intercalated into PbI2 to form PbI2-DMSO. The DMSO was replaced easily by formamidinium iodide (FAI) due to its higher affinity with PbI2 via intramolecular exchange. This process produced high quality FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Ahn et al 15developed a Lewis acid-base adduct approach to fabricate high quality perovskite films via one-step method. In this approach, a Lewis adduct of MAI∙PbI2∙DMSO was formed by spin-coating the solution containing of equimolar MAI, PbI2, and DMSO, by using diethylether to replace chlorobenzene as wash solvent. In the Lewis adduct of MAI∙PbI2∙DMSO, PbI2 act as Lewis acid, DMSO act as Lewis base. It reduced the formation rate of perovskite during the process of removing Lewis base, resulting in high quality perovskite films. Zhu et al 16 proposed a facial room temperature intermolecular exchange route to fabricate uniform and ultra-flat perovskite film with low defects. In this route, they firstly obtained a complex of MAI∙PbI2∙DMSO by using one step method. Then, a layer of MAI was spin-coated onto the complex. As a result, it formed perovskite film through intermolecular exchange between DMSO and MAI at room temperature. The formation of perovskite films at room temperature effectively avoided the structural and compositional defects in the resultant films. We also fabricated smooth perovskite films from Lewis adducts by an improved two-step method. 17-19 The intermediate product obtained from the Lewis adduct approach was perovskite precursor film embedded with residual solvent. The ultimate smooth perovskite films were ascribed to solvent modulated formation of perovskite film during molecular exchange and annealing process.20


Page 4 of 29

Page 5 of 29 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


It needs to note that most of the work focused on the ligand function of solvent in forming solvate complex for fabrication of high quality perovskite film, rather than on the annealing treatment. However, few attentions were paid to understand the latent function of the solvent embedded in the perovskite precursor films during annealing process due to its fast extravasation at high temperature. Here, we take advantage of the residual solvent embedded in perovskite precursor films to modulate the growth of the perovskite films. We pre-deposit a PC61BM layer onto the perovskite precursor film to form sandwich structure of substrate/perovskite precursor films/PC61BM, and then anneal. The PC61BM layer retards the escape of the residual solvent, which induces an obvious dissolution-recrystallization process during annealing process. As a result, it forms columnar perovskite films with large grains. Importantly, we clarify that the formation mechanism of columnar perovskite is an Ostwald ripening process, which is mediated by the residual solvent in precursor films.

2.

EXPERIMENTAL SECTION

2.1 Fabrication of devices FTO glass was cleaned according to our previous work.21 Electron block layers (1% Cs doped NiOx film) were fabricated according to Chen’s method.22 Briefly, 0.1 M Ni(Ac)2.4H2O was dissolved in 1 mL isopropanol with equivalent molar moethanolamine (NH2CH2CH2OH) and cesium acetate, the molar ration of Ni2+ and Cs+ is fixed at 100:1. The solution was stirred overnight at 70 °C. A Cs-doped NiOx film with a thickness of about 28 nm was deposited on the FTO substrate by spin-coating the solution at a speed of 2000 rpm for 30 s. The perovskite films were fabricated on the Cs-doped NiOx film through Lewis adducts by the improved two-step method. 17 In brief, PbI2/DMF (1.4 M) solution was spin-coated onto the NiOx film at a speed of 5500 rpm for 30 s. Quickly, 400 μL MAI solution (70 mg mL-1 in isopropanol) was spun on the



wet PbI2 films to obtained a perovskite precursor film with residual DMF. Traditionally, the perovskite precursor film directly annealed at 100 °C for 20 min to remove the solvent for formation perovskite films. Here, we employed a sandwich structure to obtain high quality perovskite film with large columnar grains. In this methods, a PC61BM layer (20 mg mL-1 in chlorobenzene) was spin-coated onto perovskite precursor film to form sandwich structure with a configuration of substrate/perovskite precursor films/PC61BM, and then annealed at 100 °C for 20 min to obtain perovskite films. Then, a thin layer of Bphen (BCP) (0.5 mg mL-1 in ethanol) was deposited onto the PC61BM layer by spin-coating at a speed of 5000 rpm for 30 s. Finally, 80 nm Ag was deposited onto the Bphen film to form a complete perovskite solar cell. The active area of the electrode was fixed at 0.06 cm2 during the photovoltaic characterization. 2.2 Characterization Field-emission scanning electron microscopy (SEM, MERLIN VP Compact) was used to characterize the surface morphology of the films and cross-sectional images of the solar cells. The structure and crystallization of film were measured by using X-ray diffraction diffractometer (D8Advance). The absorption spectra were recorded by using UV/Vis absorption spectrometer (Cary 5000 UV-vis-NIR, Agilent Technologies) in a range from 400 to 900 nm. The incident photon to current efficiency (IPCE) was characterized by using a QEX10 solar cell quantum efficiency measurement system (QEX10, PV measurements, USA). The photovoltaic performances of PSCs recorded by a Keithley 4200-SCS parameter analyzer under a standard solar simulator (AM 1.5G, 100 mW/cm2, 91195, Newport).

3. RESULTS AND DISCUSSION Figure 1a shows a schematic illustration of the fabrication process of perovskite films with large columnar grains. The perovskite films are deposited on the Cs-doped NiOx layer from Lewis


Page 6 of 29

Page 7 of 29 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


adduct approach via molecular exchange, which is similar to our previous work.17 When the PbI2/DMF solutions is spin-coated onto the NiOx/FTO substrates, it forms PbI2 based Lewis adducts of PbI2∙xDMF, (Stage I in Figure1a), which are identified by two characteristic XRD peaks at 9.03ºand 9.56º(see red curve in Figure 1b), corresponding to the plane (011) and (020) of PbI2∙xDMF, respectively.23 When MAI/IPA solution is spin-coated onto the PbI2∙xDMF film in the second step (Stage II in Figure1a), it forms a perovskite precursor film of MAI-PbI2-DMF with residual solvent in the films, which is identified by three characteristic peaks (marked by asterisks) in small angle region ( 5º~10º) in the XRD curve in Figure 1b. 24, 25 In the traditional annealing approach, the MAI-PbI2-DMF film was directly annealed at 100 °C to remove DMF molecule for formation of MAPbI3 film, which is donated as the control film hereinafter. In order to obtain a high quality perovskite film with large columnar grains, we pre-deposit a PC61BM layer onto perovskite precursor films to form sandwich structure of NiOx/MAI-PbI2-DMF/PC61BM, and then anneal at 100 °C for 20 min (denoted as target film hereafter, Stage III in Figure 1a). Figure 2a and b show surface morphology of the perovskite films fabricated different annealing methods. The PC61BM layer is washed by chlorobenzene for several times before SEM characterization. It clearly shows that the grain size of the perovskite films increases significantly when the perovskite precursor is annealed at 100 °C covered with a PC61BM layer. The largest grains exceeding 1 μm can be obtained in the target films. The average grain size increases from 194.8 nm to 718.6 nm calculated from SEM images by using software Nano Measure 1.2 (see Figure S1). Figure 2c and d are the corresponding cross-sectional SEM images of the perovskite films. All perovskite films have similar thickness of ~380 nm with full coverage, but the microstructure of the films exhibit obvious difference. For the control perovskite film, about 2~3 small grains can be observed across the films thickness direction. However, for the target



Page 8 of 29

perovskite film, the vertically oriented columnar grains can fully span the film entire thickness with only one grain. The perovskite films with columnar structures are beneficial to obtain high efficient PSCs due to decreasing nonradiative recombination at grain boundaries.3 In order to reconfirm the university of the annealing structure, we also replace PC61BM with Spiro-OMeTAD to form sandwich structure of substrate/perovskite precursor/ Spiro-OMeTAD. Similar to the function of PC61BM layer, it can also enlarge the perovskite grains (see Figure S2). In order to compare the crystallinity of the perovskite films, we perform x-ray diffraction (XRD) as shown in Figure 2e. As we can see, both of the XRD curves exhibit pure phase MAPbI3 without residual PbI2. The main characteristic peaks located at 14.3º, 28.6º, and 32.0ºin XRD curves are separately assigned to the (110), (220) and (310) planes of the MAPbI3.26 It is noted that the target perovskite films exhibit stronger diffusion peaks than those of control films, which reflects the improved crystallization of the target films. In order to compare the grains orientation based on XRD patters, we introduce intensity ratios of I110/I310 and I220/I310 to evaluate the effects, which are calculated by the value of the intensity of (110) and (220) peaks divided by the intensity of (310) peak, respectively.27 The intensity ratios of I110/I310 and I220/I310 of the target film are 3.35 and 1.80, respectively. However, those value are only 1.91 and 1.31 for the control perovskite film. The increased intensity ration of I110/I310 and I220/I310 indicates that the perovskite grains have a preferred orientation of (110), which is beneficial for charge transportation.27 UV absorption spectra of the perovskite films are also given in inset of Figure 2e. it clearly shows that both films have the same onset at 775 nm, which is corresponded to an optical bandgap of ~1.55 eV.

28

Compared with the control film, larger absorption intensity can be observed for the target film, especially in a range from 450 to 550 nm.


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


Figure 2f shows dark J-V curves for the hole-only devices at low voltage region. The target device exhibits a larger current density than that of the control device at the same bias voltage, showing a better hole conductivity in the target device. According to Mott–Gurney’s power law, 29-31

the hole-only devices exhibit a linear J-V relationship at low bias voltage, followed by a

nonlinear increase at the bias voltage that exceed the trap-filled limit voltage (VTFL), where all traps all filled. The value of VTFL can be determined by trap density as follows:

VTFL 

ent L2 2 0

(1)

where, e is elementary charge of the electron, L is thickness of the CH3NH3PbI3 films, nt is trap density, ε and ε0 are relative dielectric constant of MAPbI3 (ε = 32) and vacuum permittivity, respectively.30 The VTFL is 0.08 V and 0.26 V for the target device and control device, corresponding to a trap density of 1.96*1016/cm3, 6.37*1016/cm3, respectively. These values are close to those of the polycrystalline MAPbI3 films reported previously.

30,32

The reduced trap

density can be ascribed to the reduce of grain boundary in the target perovskite films with large columnar grains. Here, we propose a formation mechanism of the columnar grains based on the Ostwald ripening model, which is used to describe the coarsening of the particles. According to the Ostwald ripening model, the relationship between chemical potential and particle radius can be described as the following formula：

  0 

2 V r

(2)

where, μ is surface chemical potential on the surface ,  0 is chemical potential for a flat surface,

 is surface energy, V is mole volume of a particle, r is particle radius.33 Therefore, the smaller particle is energetically less stable than the larger particle due to higher chemical potentials.



Here, the MAI-PbI2-DMF precursor film has residual DMF solvent (see green part in Figure 3), which plays a key role in formation of large columnar grains. The small grains are dissolved easily by DMF molecule due to their higher chemical potential. The concentration of the dissolved components near the smaller grains is always higher than that near the large grains (See purple particle in Figure 3a). Therefore, it forms a concentration gradient of the dissolved components between large grain and small grain, which leads to mass transportation from small grain to large grain according to Fick’s first law (see Figure 3b). As a result, the small grains disappear because of the continuously dissolution and the dissolved component’s mass transportation as the elongation of annealing time (see Figure 3c). Finally, the large perovskite grains coarsen by absorbing surrounding small grains via mass transportation (see Figure 3d). In the improved annealing method with a PC61BM layer. The PC61BM layer plays a key role in grain coarsening due to restraining the residual DMF solvent. The restrained DMF solvent leads continuously dissolution and transportation process, and provides enough time for the absorption of large grains from the small grains via mass transportation. In the traditional structure without a PC61BM layer, DMF molecule escapes from MAI-PbI2-DMF films quickly. As a result, the Ostwald ripening process finishes abruptly (only Figure 3b), resulting in insufficient coarsening process (without Figure 3c). It is obvious that the residual solvent embedded in MAI-PbI2-DMF plays a key role in the Ostwald ripening process. The dissolution of the small grains cannot happen if the solvent is escaped. In order to confirm the key role of solvent, we characterize the morphology of the perovskite film annealed at 100 °C for different times. The grain sizes (~193 nm) change little when the perovskite films are annealed for 5, 10 and 15 min, respectively (see Figure 4a to 4c).


Page 10 of 29

Page 11 of 29 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


The long annealing time (>5 min) makes sure for DMF to escape during annealing. The absence of DMF quenches the Ostwald ripening process, resulting in the unchanged morphology. We also characterize the evolution of the film annealed for a short time. The DMF is hardly to escape from the film in a short annealing time. The grain size increases as prolonging the annealing time (see Figure 5a to c). The coarsened grains are ascribed to occurrence of the solvent meditated Ostwald ripening during annealing. In order to observe the evolution of the grain size during annealing more clearly, we also prepare perovskite precursor films by introducing optimized DMSO into PbI2/DMF solution.19 Because DMSO has stronger Lewis basicity19,34 and higher boiling point than DMF.35 The function of Ostwald ripening in controlling the grain size is obvious (see Figure 5d to f). These results reconfirm the key roles of the residual solvent in meditating the Ostwald ripening process. We also fabricate PSCs by employing different annealing methods. By using sandwich annealing

structure,

we

fabricate

a

PSCs

with

a

configuration

of

FTO/NiOx/MAPbI3/PC61BM/BCP/Ag. The cross-sectional image of the complete device is shown in Figure 6a. It further confirms that a compact and uniform perovskite film with columnar grains are obtained by sandwich annealing structure. Figure 6b shows an energy level diagram of the solar cell, which are extracted from previous reports.22,36 We also perform details comparison of our best solar cells fabricated from different annealing methods with or without PC61BM layer under different scan directions, as shown in Figure 6c. The devices show a weak hysteresis behavior. The champion PSC annealed with PC61BM layer possesses a power conversion efficiency (PCE)=15.14%, a short-circuit (Jsc)=20.82 mAcm-2, an open voltage (Voc)=1.01V, a Fill factor (FF)=0.720. All of the photovoltaic parameters are improved significantly compared with those annealed without a PC61BM layer (Jsc=17.13 mAcm-2, Voc=0.985V, FF=0.670,



PCE=11.30%). The statistical results of the photovoltaic parameters extracted from a series of PSCs further confirm similar trend to the best PSCs (see Figure S3). Figure 6d shows incident photon to current efficiency (IPCE) spectra of PSCs. The integrated Jsc from IPCE spectra is 19.22 and 16.27 mAcm-2, which are only about 6% mismatch with the value obtained from the reverse scans (see Figure 6c). The slight mismatch can be also observed in other groups due to measuring uncertainty of the current density or the difference in measuring base. 2,37 The IPCE spectra also reconfirm that the PSCs annealed with PC61BM layer exhibits higher quantum yield throughout the entire wavelength than that annealed without PC61BM layer, which is consistent with the photovoltaic performance. The negligible difference in the curves under different scan rate reconfirm the reliability of the performance of solar cells (see Figure 6e). Figure 6f shows the stabilized output of PSCs at the maximum point under continuous irradiation. Both Jsc and PCE change very little by soaking under one sun for 250 s, which demonstrates excellent stability of the devices. The stabilized photocurrent density and PCE obtained from Figure 6f is 18.36 mA cm-2 and 14.94 %, respectively, which match well with the values obtained from the reverse can. The increased Jsc of PSCs can be ascribed to the stronger light harvest ability in the whole wavelength (see inset in Figure 2e). The improved Voc and FF are ascribed to the large columnar grains in perovskite films, which reduce defect density significantly. 31

4. CONCLUSIONS In summary, we develop a sandwich structure to retard the escape of residual solvent embedded in perovskite precursor during annealing. The residual solvent plays a key role in fabricating high quality perovskite films with large columnar grains. The restrained solvent induces a dissolution-recrystallization process during annealing, which causes mass transport from the small grains to the large grains and grain coarsen. The small perovskite precursor grains


Page 12 of 29

Page 13 of 29 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


transfer to large columnar grains following the Ostwald ripening model. The photovoltaic performances of the perovskite solar cells are enhanced significantly due to the high quality films composed of large columnar grains.

ASSOCIATED CONTENT The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. SEM, Photographs of PbI2/DMF solution, J-V curves obtained from different direction.



AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected] (J.W.). Tel: +86-10-62781065. Notes The authors declare no competing financial interest.



ACKNOWLEDGMENTS

This work was financially supported by Shenzhen Jiawei Photovoltaic Lighting Co. Ltd., Tsinghua University Initiative Scientific Research Program (20161080165), and Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics (KF201704).



REFERENCES (1) Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon, S. J.; Humphry-Bake. R.; Yum, J. H.; Moser, J. E.; Grätzel, M.; Park, N. G. Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%. Sci. Rep. 2012, 2, 591-597. (2) 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. Il. Iodide Management in Formamidinium-Lead-Halide–Based Perovskite Layers for Efficient Solar Cells. Science, 2017, 356, 1376 –1379. (3) Marco, N. D.; Zhou, H.; Chen, Q.; Sun, P.; Liu, Z.; Meng, L.; Yao, E.-P.; Liu, Y.; Schiffer, A.; Yang, Y. Guanidinium: A Route to Enhanced Carrier Lifetime and Open-Circuit Voltage in Hybrid Perovskite Solar Cells. Nano Lett., 2016, 16, 1009− 1016. (4) Liang, P. W.; Liao, C. Y.; Chueh, C. C.; Zuo, F.; Williams, S. T.; Xin X. K.; Lin, J.; Jen, A. K. Y. Additive Enhanced Crystallization of Solution-Processed Perovskite for Highly Efficient Planar-Heterojunction Solar Cells. Adv. Mater., 2014, 26, 3748–3754. (5) Gong, X.; Li, M.; Shi, X. B.; Ma, H.; Wang, Z. K.; Liao, L. S. Controllable Perovskite Crystallization by Water Additive for High-Performance Solar Cells. Adv. Funct. Mater., 2015, 25, 6671–6678. (6) Shi, Y.; Wang, X.; Zhang, H.; Li, B.; Lu, H.; Ma, T.; Hao, C. Effects of 4- tert-butylpyridine on Perovskite Formation and Performance of Solution-Processed Perovskite Solar Cells. J. Mater. Chem. A, 2015, 3, 22191–22198. (7) Wang, Z. K.; Gong, X.; Li, M.; Hu, Y.; Wang, J. M.; Ma, H.; Liao, L. S. Induced Crystallization of Perovskites by a Perylene Underlayer for High-Performance Solar Cells. ACS Nano, 2016, 10, 5479− 5489. (8) Li, M.; Chao, Y.- H.; Kang, T.; Wang, Z. K.; Yang, Y. G.; Feng, S. L.; Hu, Y.; Gao, X. Y.; Liao, L. S.; Hsu, C. S. Enhanced Crystallization and Stability of Perovskites by a Cross-Linkable Fullerene for HighPerformance Solar Cells. J. Mater. Chem. A, 2016, 4,15088–15094.


Page 14 of 29

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


(9) Jiang, L. L.; Wang, Z. K.; Li, M.; Zhang, C. C.; Ye, Q. Q.; Hu, K. H. Lu, D. Z.; Fang, P. F.; Liao, L. S. Passivated Perovskite Crystallization via g-C3N4 for High-Performance Solar Cells. Adv. Funct. Mater., DOI:10.1002/adfm.201705875. (10) Zhang, C. C.; Wang, Z. K.; Li , M.; Liu, Z. Y.; Yang, J. E.; Yang, Y. G.; Gao, X. Y.; Ma, H. ElectricField Assisted Perovskite Crystallization for High-Performance Solar Cells. J. Mater. Chem. A, 2018, 6,1161–1170. (11) Li, X.; Bi, D.; Yi, C.; Décoppet, J. D.; Luo, J.; Zakeeruddin, S. M.; Hagfeldt, A.; Grätzel, M. A Vacuum Flash–Assisted Solution Process for High-Efficiency Large-Area Perovskite Solar Cells. Science, 2016, 353, 58-62. (12) Chen, H.; Ye, F.; Tang, W.; He, J.; Yin, M.; Wang, Y.; Xie, F.; Bi, E.; Yang, X.; Grätzel, M.; Han, L. A Solvent-and Vacuum-Free Route to Large-Area Perovskite Films for Efficient Solar Modules. Nature, 2017, 550, 92-95. (13) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. Il. Solvent Engineering for HighPerformance Inorganic–Organic Hybrid Perovskite Solar Cells. Nat. Mater., 2014, 13, 897-903. (14) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S. C.; Seo, J. W.; Seok, S. I. High-Performance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange. Science, 2015, 348, 12341237. (15) Ahn, N.; Son, D. Y.; Jang, I. H.; Kang, S. M.; Choi, M.; Park, N. G. Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide. J. Am. Chem. Soc., 2015, 137, 8696−8699. (16) Zhu, W.; Chen, D.; Zhou, L.; Zhang, C.; Chang, J.; Lin, Z.; Zhang, J.; Hao, Y. Intermediate Phase Intermolecular Exchange Triggered Defect Elimination in CH3NH3PbI3 toward Room-Temperature Fabrication of Efficient Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 40378−40385.



(17) Cao, X. B.; Li, Y. H.; Fang, F.; Cui, X.; Yao, Y. W.; Wei, J. Q. High Quality Perovskite Films Fabricated from Lewis Acid –Base Adduct through Molecular Exchange. RSC Adv., 2016, 6, 70925–70931. (18) Cao, X. B.; Li, C. L.; Li, Y. H.; Fang, F.; Cui, X.; Yao, Y. W.; Wei, J. Q. Enhanced Performance of Perovskite Solar Cells by Modulating the Lewis Acid–Base Reaction. Nanoscale, 2016, 8, 19804–19810. (19) Cao, X. B.; Li, C. L.; Zhi, L. L.; Li, Y. H.; Cui, X.; Yao, Y. W.; Ci, L. J.; Wei, J. Q. Fabrication of High Quality Perovskite Films by Modulating the Pb-O Bonds in Lewis Acid-Base Adducts. J. Mater. Chem. A, 2017, 5, 8416–8422. (20) Cao, X.; Zhi, L.; Li, Y.; Fang, F.; Cui, X.; Yao, Y.; Ci, L.; Ding, K.; Wei, J. Elucidating the Key Role of a Lewis Base Solvent in the Formation of Perovskite Films Fabricated from the Lewis Adduct Approach. ACS Appl. Mater. Interfaces, 2017, 9, 32868−32875. (21) Cao, X.; Zhi, L.; Li, Y.; Fang, F.; Cui, X.; Yao, Y.; Ci, L.; Ding, K.; Wei, J. Control of the Morphology of PbI2 Films for Efficient Perovskite Solar Cells by Strong Lewis Base Additives. J. Mater. Chem. C, 2017, 5, 7458−7464. (22) Chen, W.; Liu, F. Z.; Feng, X. Y.; Djurišic´, A. B.; Chan, W. K.; He, Z. B. Cesium Doped NiOx as an Efficient Hole Extraction Layer for Inverted Planar Perovskite Solar Cells. Adv. Energy Mater., 2017, 7, 1700722. (23) Zheng, H.; Wang, W.; Yang, S.; Liu, Y.; Sun, J. A Facile Way to Prepare Nanoporous PbI2 Films and Their Application in Fast Conversion to CH3NH3PbI3. RSC Adv., 2016, 6, 1611–1617. (24) Petrov, A. A.; Sokolova, I. P.; Belich, N. A.; Peters, G. S.; Dorovatovskii, P. V.; Zubavichus, Y. V.; Khrustalev, V. N.; Petrov, A. V.; Grätzel, M.; Goodilin, E. A.; Tarasov, A. B. Crystal Structure of DMFIntermediate Phases Uncovers the Link Between CH3NH3PbI3 Morphology and Precursor Stoichiometry. J. Phys. Chem. C, 2017, 121, 20739− 20743.


Page 16 of 29

Page 17 of 29 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


(25) Long, M.; Zhang, T.; Chai, Y.; Ng, C. F.; C.W. Mak, T.; Xu, J.; Yan, K. Nonstoichiometric Acid–Base Reaction as Reliable Synthetic Route to Highly Stable CH3NH3PbI3 Perovskite Film. Nat. Commun., 2016, 7, 13503. (26) Liu, D.; Wu, L.; Li, C.; Ren, S.; Zhang, J.; Li, W.; Feng, L. Controlling CH3NH3PbI3−xClx Film Morphology with Two-Step Annealing Method for Efficient Hybrid Perovskite Solar Cells. ACS Appl. Mater. Interfaces, 2015, 7, 16330−16337. (27) Wang, Y.; Li, J.; Li, Q.; Zhu, W.; Yu, T.; Chen, X.; Yin, L.; Zhou, Y.; Wang, X.; Zou, Z. PbI2 Heterogeneous-Cap-Induced Crystallization for an Efficient CH3NH3PbI3 Layer in Perovskite Solar Cells. Chem. Commun., 2017, 53, 5032-5035. (28) Yusoff, A. R. M. Nazeeruddin, M. K. Organohalide Lead Perovskites for Photovoltaic Applications. J. Phys. Chem. Lett., 2016, 7, 851− 866. (29) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-hole Diffusion Lengths >175 μm in Solution-Grown CH3NH3PbI3Single Crystals. Science, 2015, 347,967-970. (30) Zhu, W.; Kang, L.; Yu, T.; Lv, B.; Wang, Y.; Chen, X.; Wang, X.; Zhou, Y.; Zou, Z. Facile Face-Down Annealing Triggered Remarkable Texture Development in CH3NH3PbI3 Films for High-Performance Perovskite Solar Cells. ACS Appl. Mater. Interfaces, 2017, 9, 6104–6113. (31) Ke, W.; Stoumpos, C. C.; Spanopoulos, I.; Mao, L.; Chen, M.; Wasielewski, M. R.; Kanatzidis, M. G. Efficient Lead-Free Solar Cells Based on Hollow {en}MASnI3 Perovskites. J. Am. Chem. Soc., 2017, 139, 14800−14806. (32) Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J. Solvent Annealing of Perovskite-Induced Crystal Growth for Photovoltaic-Device Efficiency Enhancement. Adv. Mater., 2014, 26, 6503–6509. (33) Kim, S. Y.; Jo, H. J.; Sung, S. J.; Kim, D. H. Perspective: Understanding of Ripening Growth Model for Minimum Residual PbI2 and Its Limitation in the Planar Perovskite Solar Cells. APL Mater., 2016, 4, 100901.



(34) Friesen, D. A.; Nashiem, R. E.; Waltz, W. L. Solvent Effects on the Spectroscopic and Photophysical Properties of the trans-(1,4,8,11-Tetraazacyclotetradecane)diisothiocyanatochromium(III)Ion, trans[Cr(cyclam)(NCS)2]. Inorg. Chem., 2007, 46, 7982 −7991. (35) Hao, F.; Stoumpos, C. C.; Guo, P.; Zhou, N.; Marks, T. J.; Chang, R. P. H.; Kanatzidis, M. G. SolventMediated Crystallization of CH3NH3SnI3 Films for Heterojunction Depleted Perovskite Solar Cells. J. Am. Chem. Soc., 2015, 137, 11445−11452. (36) Chen, C.; Zhang, S.; Wu, S.; Zhang, W.; Zhu, H.; Xiong, Z.; Zhang, Y.; Chen, W. Effect of BCP Buffer Layer on Eliminating Charge Accumulation for High Performance of Inverted Perovskite Solar Cells. RSC Adv., 2017, 7, 35819–35826. (37) Wu, C. G.; Chiang, C. H.; Tseng, Z. L.; Nazeeruddin, M. K.; Hagfeldt, A. Grätzel, M. High efficiency Stable Inverted Perovskite Solar Cells without Current Hysteresis. Energy Environ. Sci., 2015, 8, 27252733.


Page 18 of 29

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


 Figures

Figure 1. (a) Schematic illustration of the fabrication process of a perovskite film with columnar grains annealed by an improved method coated with a PC61BM layer, (b) evolution of XRD patterns for different films during the formation columnar grains.



Figure 2. Surface and cross-sectional SEM images of perovskite films fabricated from different annealing methods. (a) and (c) are without a PC61BM layer, (b) and (d) are with a PC61BM layer. (e) XRD patterns of the perovskite films fabricated from different annealing methods. Inset is UV-Vis absorption spectra of the perovskite films. (f) J-V curves for the hole-only device fitting by the Mott−Gurney law at low voltage region. Inset is the configuration of the hole-only device.


Page 20 of 29

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


(a)

(c)

(b)

(d)

Mass transfer by the concentration gradient of the dissolved components

DMF molecule

Dissolved components

Figure 3. The dynamic coarsen process of the perovskite grains as elongate the annealing time based on the Ostwald ripening model. (a) initial stage, (b) early stage, (c) middle stage, (d) final stage.

(a)

Mean size =192.6 nm

100

(b)

200 300 400 Grain size (nm)

Mean size= 194.3 nm

100 200 300 400 500 600 Grain size(nm)

400 nm

400 nm

(c)

Mean size=192.8 nm

100

200 300 400 Grain size(nm)

500

400 nm

Figure 4. SEM images of the perovskite films annealed at 100 °C for long annealing times after removing the residual solvent. (a) 5 min, (b)10 min, (c)15 min.



Mean size= 95.6 nm

(a)

50

100

150

Grain size(nm)

Mean size =143.4 nm

(b)

100

200

400 nm Mean size=77.8 nm

(d) 40


400 nm

Page 22 of 29

(c)

200 300 Grain size (nm)

Mean size =176.8 nm

100


400 nm

400 nm

(e)

Mean size=119.6 nm

50


250

400 nm

400

Mean size=218.1 nm

(f) 100

200

300

400

500

Grain size (nm)

400 nm

Figure 5. SEM images of the perovskite films fabricated from for short annealing times, which still contain some residual solvent. (a) 2 s, (b) 20 s, (c) 60 s. SEM images of the perovskite films fabricated from PbI2/DMF solution added with 8% DMSO, and then annealed at 100 °C for short annealing times. (d) 10 s, (e) 40 s, (f) 120 s.


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


Figure 6. (a) Cross-sectional SEM images of a perovskite solar cell with inverted structure. (b) Energy band diagram for the PSC. (c) J-V curves of the best PSCs for the target and control PSCs. (d) IPCE spectra for the target and control PSCs. (e) J-V curves of the target PSCs under different scan rate. (f) Steady-state photocurrent and PCE of the target PSCs at the maximum power point.



TOC


Page 24 of 29

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


 Figures

Figure 1. (a) Schematic illustration of the fabrication process of a perovskite film with columnar grains annealed by an improved method coated with a PC61BM layer, (b) evolution of XRD patterns for different films during the formation columnar grains.



Figure 2. Surface and cross-sectional SEM images of perovskite films fabricated from different annealing methods. (a) and (c) are without a PC61BM layer, (b) and (d) are with a PC61BM layer. (e) XRD patterns of the perovskite films fabricated from different annealing methods. Inset is UV-Vis absorption spectra of the perovskite films. (f) J-V curves for the hole-only device fitting by the Mott−Gurney law at low voltage region. Inset is the configuration of the hole-only device.


Page 26 of 29

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


(a)

(c)

(b)

(d)

Mass transfer by the concentration gradient of the dissolved components

DMF molecule

Dissolved components

Figure 3. The dynamic coarsen process of the perovskite grains as elongate the annealing time based on the Ostwald ripening model. (a) initial stage, (b) early stage, (c) middle stage, (d) final stage.

(a)

Mean size =192.6 nm

100

(b)


Mean size= 194.3 nm

(c)

100

100 200 300 400 500 600 Grain size(nm)

400 nm

Mean size=192.8 nm


500

400 nm

400 nm

Figure 4. SEM images of the perovskite films annealed at 100 °C for long annealing times after removing the residual solvent. (a) 5 min, (b)10 min, (c)15 min. Mean size= 95.6 nm

(a)

50

100

150

Grain size(nm)

Mean size =143.4 nm

(b)

100

200

400 nm Mean size=77.8 nm

(d) 40


400 nm

(c)


Mean size =176.8 nm

100


400 nm

400 nm

(e)

Mean size=119.6 nm

50


250

400 nm

400

Mean size=218.1 nm

(f) 100

200

300

400

500

Grain size (nm)

400 nm

Figure 5. SEM images of the perovskite films fabricated from for short annealing times, which still contain some residual solvent. (a) 2 s, (b) 20 s, (c) 60 s. SEM images of the perovskite films fabricated from PbI2/DMF solution added with 8% DMSO, and then annealed at 100 °C for short annealing times. (d) 10 s, (e) 40 s, (f) 120 s.



Figure 6. (a) Cross-sectional SEM images of a perovskite solar cell with inverted structure. (b) Energy band diagram for the PSC. (c) J-V curves of the best PSCs for the target and control PSCs. (d) IPCE spectra for the target and control PSCs. (e) J-V curves of the target PSCs under different scan rate. (f) Steady-state photocurrent and PCE of the target PSCs at the maximum power point.


Page 28 of 29

Page 29 of 29 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


TOC


Fabrication of Perovskite Films with Large Columnar Grains via

Recommend Documents