Enhancing Efficiency and Stability of Perovskite Solar Cells via a Self

Aug 17, 2018 - Interfacial engineering is a simple and effective strategy that can improve the photovoltaic performance in organic–inorganic perovsk...
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Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 30607−30613

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Enhancing Efficiency and Stability of Perovskite Solar Cells via a Self-Assembled Dopamine Interfacial Layer Meihui Hou,† Haijuan Zhang,† Ze Wang,† Yingdong Xia,*,† Yonghua Chen,*,† and Wei Huang†,‡,§ †

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Key Laboratory of Flexible Electronics (KLOFE) & Institution of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), Nanjing 211816, Jiangsu, China ‡ Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University (NPU), Xi’an 710072, Shaanxi, China § Key Laboratory for Organic Electronics & Information Displays (KLOEID), and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210023, Jiangsu, China S Supporting Information *

ABSTRACT: Interfacial engineering is a simple and effective strategy that can improve the photovoltaic performance in organic−inorganic perovskite solar cells (PSCs). Herein, a dopamine (DA) self-assembled monolayer (SAM) was introduced on the top of the SnO2 electron transporting layer (ETL) to modify the SnO2/perovskite interface. The processing temperature of the present devices is around 150 °C, and the power conversion efficiency of the PSCs was significantly improved to 16.65% compared to that of the device without modification (14.05%). Such enhancement in efficiency is mainly attributed to the improved quality of perovskite films by improving the affinity of the SnO2 ETL, thus leading to better carrier transport and low charge recombination at the SnO2/ perovskite interface. Moreover, the modified device by the DA SAM exhibited enhanced stability compared to the device without modification. Our results suggest that the introduction of the DA SAM on the ETL/perovskite interface is a promising method for highly efficient and stable PSCs. KEYWORDS: high efficiency, stability, interface engineering, dopamine, perovskite solar cells

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INTRODUCTION Organic−inorganic perovskite solar cells (PSCs) have made extraordinary developments since they were first proposed by Miyasaka and co-workers in 2009.1−3 The perovskite materials exhibit outstanding optoelectronic properties, such as long exciton diffusion length,4 high charge mobility,5 tunable optical band gap,6 and high light absorption coefficient.7 In the past few years, PSCs have substantially surpassed organic solar cells and dye-sensitized solar cells with a certified power conversion efficiency (PCE) of 22.7%,8,9 which can compete with traditional commercialized polycrystalline-silicon solar cells and inorganic thin-film solar cells, such as amorphous silicon, CZTS, and CdTe thin film solar cells.1,8 Together with the advantages of simple preparation and low cost over the complex processes and high cost in the traditional solar cells, PSCs have great potential in future commercial applications. In order to improve the performance of PSCs, many efforts has been explored, such as the fabrication approach of perovskite films,2,10 the design of novel device structure,11 the composition engineering of the perovskite structure,12,13 and the interfacial modification.14−16 Among them, interfacial modification, especially the electron transporting layer (ETL)/ perovskite interface, has been widely used as an effective © 2018 American Chemical Society

method to improve the device performance by facilitating charge extraction, reducing charge recombination, avoiding the leakage current, and controlling the perovskite crystals growth.17−19 Recently, SnO2 has been demonstrated as an effective ETL in PSCs because of its good electrical and optical properties, that is, a suitable energy level, high carrier mobility, and good antireflection ability20 to improve the device electronic collection capabilities and avoid the nonstoichiometric defects of TiO2 and thermal instability of ZnO.21,22 Moreover, SnO2 thin films can be prepared at a low temperature (600 nm) with uniform and smoother surface (Figure 2c). It should be noted that solvent engineering used here is to get quick crystallization, the growth behavior of perovskite on pristine and modified SnO2 is similar without employing solvent engineering. The changed surface morphology with DA SAM modification is consistently observed using atomic force microscopy (AFM) (Figure 2e,f). After DA SAM modification, the SnO2 surface exhibits a more uniform feature with a rootmean-square (rms) surface roughness of 2.574 nm than that without modification (rms = 5.911 nm). The improved perovskite morphology demonstrated that the DA interfacial layer could act as a template to facilitate the perovskite crystal growth, thus improving the perovskite morphology and increasing the grain size. This phenomenon could be attributed to the formation of a hydrogen bond between the −NH3+ groups of DA and the halide anions of the perovskite, as demonstrated in previous reports,40 thereby increasing the surface affinity between the perovskite layer and the SnO2 ETL. Besides, the surface energy of SnO2 can be adjusted by the insert of DA; thence, we also examined the surface wettability of water on bare or DA SAM-modified SnO2, as shown in Figure S2. In fact, normally the SnO2 ETL was treated with UV−ozone (UVO). The pristine SnO2 has a large contact angle of 58.8°, while the contact angle was reduced to 6.5° and 22.3° after UVO and DA treatment, respectively, corresponding to the morphological improvement of perovskites, especially the smoother and larger crystal size on DAmodified SnO2. In addition, the interfacial contact is critical for the charge extraction; we also investigated the work function (WF) of SnO2 with different modification time. As shown in Figure S3, the WF of SnO2 ETL decreased from 4.76 to 4.56 eV, indicating that the DA modification can efficiently decrease the WF of the SnO2, which may be due to the formation of dipoles at the interface between SnO2 ETL and perovskite. The modified WF is further close to the lowest unoccupied molecular orbital of MAPbI3 perovskites (3.9 eV), thereby improving the energy level alignment and the charge extraction efficiency. We further investigated the influence of the incorporated DA SAM interfacial layer on crystallinity of perovskite films by using X-ray diffraction (XRD). The XRD patterns, shown in Figure 3a, display the crystallization of CH3NH3PbI3 perovskite grown on bare and DA SAM-modified SnO2-coated

Figure 3. (a) XRD patterns and (b) ultraviolet−visible (UV−vis) absorption spectra of thin-film MAPbI3 perovskites deposited on SnO2-coated substrate with different DA SAM modification times; (c) PL and (d) TRPL spectra of perovskite films deposited on SnO2 films with and without DA SAM modification.

substrates with different modification times, respectively. The crystal growth direction of the perovskite grown on different substrates was almost the same. The diffraction peaks at 14.2° and 28.4° are assigned to the (110) and (220) planes of tetragonal crystal structure of CH3NH3PbI3, according to the previous report.41 With the increase of the DA modification time, perovskite diffraction peaks became significantly enhanced, indicating that the crystallinity of perovskite films is improved. The observation agrees with the enlarged grains shown by SEM in Figure 2. Stronger crystallinity also means fewer surface defects, which would be beneficial to the performance of PSCs. Figure 3b shows ultraviolet-visible (UV−vis) absorption spectroscopy perovskite films deposited on bare and DA SAM-modified SnO2-coated substrates with different modification times. The film with DA SAM modification displays a slight increase in absorbance near the blue and green color regime, possibly related to the enhanced crystallinity of CH3NH3PbI3. In addition, we found that the absorption will decrease when the time reaches 12 h, which is due to the fact that too much DA will cause a decrease in transmittance of SnO2-coated substrate and thus influence the light absorption (Figure S4). The photoluminescence (PL) measurements, including steady-state PL and time-resolved PL (TRPL), were employed to study the impact of DA modification on the extraction of electrons and charge recombination. As shown in Figure 3c, compared to the control perovskite film, the sample with the SnO2/DA/ perovskite quenches PL much more than that with the SnO2/DA/perovskite and the PL quenching of the perovskite film formed on DA-modified SnO2 substrate is much more efficient than that grown on the bared SnO2, suggesting enhanced electron extraction ability and the reduced recombination of holes and electrons.32,42 Furthermore, when compared to the pristine perovskite film and SnO2/ perovskite layer, the PL spectra display a blue shifting of 6 nm for SnO2/DA/perovskite, indicating that the surface trap state passivation is close to the bottom surface in the perovskite film after DA SAM modification.43 The reduced surface trap states of the perovskite film may be attributed to the passivation 30609

DOI: 10.1021/acsami.8b10332 ACS Appl. Mater. Interfaces 2018, 10, 30607−30613

Research Article

ACS Applied Materials & Interfaces effect by hydrogen-bonding interactions between the −NH3+ groups of DA and the halide anions of the perovskite. In addition, the TRPL decay measurements and the stretched exponential decay lifetimes were obtained by fitting the data with a biexponential decay function,44 as shown in Figure 3d. The SnO2/DA/perovskite shows shorter lifetime (8.184 ns) than SnO2/perovskite (19.061 ns), which indicates a lower defect concentration and hence faster electron transfer from perovskite to SnO2 after the DA SAM modification and reduction of the electrons and holes recombination at the SnO2/perovskite interface. Figure 4a shows the photocurrent density−voltage (J−V) characteristics of planar PSCs with bare SnO2 (0 h) or DA

SEM measurements, the DA SAM interfacial layer plays a critical role in improving the quality of the active layer with large grains and fewer grain boundaries, which result in obvious enhancement in Jsc and FF. We ascribed the improvement in Jsc with DA SAM modification to improved photoelectron transport and extraction, which is consistent with the above-discussed PL and TRPL measurements. Moreover, the reproducibility of the device performance was evaluated by characterizing 20 individual PSCs based on bare SnO2 ETL or SnO2/DA ETL with 6 h modification for its outstanding performance, as shown in Figure 4b. Good reproducibility was shown for the DA SAM-modified devices with a typical value over 15.5% compared to 12.5% in the devices without DA SAM modification. Our results indicate that high-performance PSCs can be repeatedly fabricated by DA modification of SnO2. The average device performance parameters are summarized in Figure S5. The devices showed a better performance after SnO2 was modified by DA SAM for Voc, Jsc, FF, and PCE, indicating that this is a simple and effective method to improve device performance. When the modification time of DA SAM is increased to 12 h, the PCE of the device is decreased to 14.16% (Table 1), which may result from the increase of the surface resistance due to the insulation nature of DA and severe charge recombination caused by reduced charge transport. Therefore, the following characterization was carried out based on the PSCs with an optimum DA SAM modification time of 6 h. The hysteresis of the devices was studied, as shown in Figure 4c. The commonly observed hysteresis is virtually negligible in the DA SAMmodified devices and the corresponding parameters are summarized in Table 2, demonstrating the reliability of our

Figure 4. (a) Best PCE of the devices with different DA treatment times and (b) histogram of efficiencies among 20 devices. (c) J−V curves measured under reverse and forward voltage scanning and (d) EQE of the devices deposited on SnO2 ETL with or without a DA SAM modification.

Table 2. Photovoltaic Parameters of 6 h DA-Modified SnO2Based Planar PSCs Investigated by Different Scanning Directions device

SAM-modified SnO2 (1, 6, 12 h) ETL under AM 1.5G illumination with a light intensity of 100 mW cm−2. The key cell parameters are summarized in Table 1. The PSC with bare

SnO2 SnO2/DA

Table 1. Photovoltaic Parameters of Planar PSCs with Different DA Modification Times time (h) 0 1 6 12

Voc (V) 1.04 1.05 1.05 1.05

± ± ± ±

0.01 0.02 0.02 0.01

Jsc (mA cm−2) 19.97 20.93 21.80 20.51

± ± ± ±

0.2 0.4 0.3 0.3

FF 0.675 0.710 0.739 0.653

± ± ± ±

14.05 15.25 16.87 14.16

± ± ± ±

Voc (V)

Jsc (mA cm−2)

FF

PCE (%)

reverse forward reverse forward

1.04 1.04 1.05 1.05

19.96 19.07 21.80 21.72

0.676 0.636 0.739 0.718

14.05 12.63 16.87 16.31

DA SAM-modified devices. Furthermore, the external quantum efficiency (EQE) measurements results are shown in Figure 4d, also confirming the enhanced improvement, where the DA SAM-modified device exhibited a broad EQE spectrum from 300 to 900 nm over 80%, which is obvious higher than device without modification. The integrated Jsc from EQE is another important parameter to prove that the Jsc of the device is enhanced by the DA SAM interlayer. Figure 5a shows the PSCs with the SnO2/DA ETL achieved a steady-state current density of 19.14 mA cm−2 and a steadystate PCE of 16.46% at a constant bias voltage of 0.86 V, suggesting that the DA SAM modification improved the electron extraction efficiency, contributing to most of the enhancement of current density and the device efficiency. Compared to the non-modified device, the performance enhancement of modified devices obviously results from the increased Jsc value (from 19.97 to 21.80 mA cm−2) and the higher FF (see Table 1). Moreover, the device stability can be enhanced when modified by DA (Figure 5b); the efficiency of the DA-modified device remains above 80%, while the pristine

PCE (%) 0.02 0.04 0.06 0.02

scanning direction

0.4 0.5 0.5 0.4

SnO2 ETL acts as a control device, giving a short-circuit photocurrent density (Jsc) of 19.97 mA cm−2, an open-circuit voltage (Voc) of 1.04 V, an FF of 0.675, and a PCE of 14.05%. In contrast, the PSCs with SnO2/DA ETL exhibit improvements in all Jsc, Voc, and FF. Especially, when the DA SAM modification time is 6 h, the device exhibits the best performance with a PCE of 16.87%, a Jsc of 21.80 mA cm−2, a Voc of 1.05 V, and an FF of 0.739. The device performance is one of the best reports compared to previous reports (Table S1). Obviously, the Jsc and FF are higher than the reported data for 21.23 mA cm−2 and 69.2, respectively,32 and those of the prior works based on metal oxide charge transporters processed in the same temperature range.45 As discussed in 30610

DOI: 10.1021/acsami.8b10332 ACS Appl. Mater. Interfaces 2018, 10, 30607−30613

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ACS Applied Materials & Interfaces

between the two devices is the modification of SnO2; thus, it is rational to attribute the reduced device contact resistance to the introduction of DA SAM.48 These results are consistent with the enhancement in Jsc for SnO2/DA-based PSCs (shown in Table 2). We also found that the reduced recombination was achieved in the modified devices. As seen in Figure 5f, the dark current density of the modified device is obviously lower than the device without modification, which indicates that the introduction of DA at the SnO2/perovskite interface can prevent the current leakage to a certain extent. The current leakage is mainly related to the recombination of carriers, thereby contributing to the improvement of the device efficiency. The Jsc/Voc versus light intensity characterization of the device on SnO2 with or without DA modification is shown in Figure S7. We found a good linear relationship between Jsc and light intensity. The slope of the device based on the DA-modified SnO2 is 0.97 when the pristine SnO2 device is 0.96, which is close to 1, indicating that the bimolecular recombination in the devices is almost negligible. Figure S7b shows the Voc versus light intensity, the slope represents the trap-assisted recombination. It can be seen that the slope of the device based on the original SnO2 reaches 1.65, and the DA-modified device is only about 1.18, indicating that the DA modification can significantly reduce trap-assisted recombination in the device, which is also in agreement with the conclusion in Figure 5c,d that the DA modification can help to reduce the trap-state density of the perovskite film grown SnO2, thereby contributing to good device performance.49,50

Figure 5. (a) Steady-state efficiencies of the PSCs measured at constant bias voltages of 0.86 V and integrated photocurrent density Jsc for the PSCs. (b) Stability of the devices with and without DA in air with humidity of ∼70%. Current density−voltage curves and trap density of perovskite films on (c) SnO2 and (d) SnO2/DA. (e) Nyquist plots for PSCs with or without DA, EIS was measured in dark condition. (f) J−V curves measured in the dark condition with reverse scan direction.

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CONCLUSIONS We have demonstrated that the introduction of the DA SAM is a simple and efficient method to modify the SnO2/perovskite interface and improve device performance. After the DA modification, SnO2 gets more hydrophilic and could facilitate the formation of perovskite film with better morphologies and enhanced crystallinity. Additionally, the DA SAM interlayer results in the efficient electron extraction and reduces the charge recombination. Accordingly, the device efficiency was significantly improved from 14.05 to 16.87%, which was mainly attributed to the increase of Jsc and FF. This work provides a feasible approach to achieve high-performance PSCs by utilizing DA SAM as the interfacial layer. We believe that interfacial modification is a simple and effective method to improve the performance of PSCs.

device efficiency has dropped below 50% after exposing in air for 12 days. The enhanced current density is associated with the enhanced carrier transport of the perovskite films caused by the improved perovskite film quality after modification by DA SAM, as shown in Figure S6, which displays the enhanced current density in the electron-only devices. This result further confirmed that the energy barrier at the SnO2/perovskite interface was reduced and enhanced electron transport ability. The trap-state density measurements were also conducted, as shown in Figure 5c,d. The value was calculated by the trapfilled limit voltage using the equation46 Nt =

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2ε0εrVTFL qL2

EXPERIMENTAL SECTION

Materials and Reagents. Lead iodide (PbI2, 99.99%) was purchased from TCI (Shanghai) Development Co., Ltd. Methylammonium iodide (CH3NH3I, 99.5%), spiro-OMeTAD, 99.5%, bis(trifluoromethane)sulfonamide lithium (Li-TFSI, 99%), and 4tert-butylpyridine (TBP, 98%) were obtained from Shanghai MaterWin New Materials Co., Ltd. Tin(IV) oxide SnO2 solution (15% in H2O colloidal dispersion) was purchased from Alfa Aesar (China) Chemical Co., Ltd. The other solvents were purchased from Sigma-Aldrich Co. Ltd. Unless indicated, all the chemicals were directly used without further purification. Device Fabrication and Characterization. Indium tin oxide (ITO) substrate was cleaned sequentially with detergent, deionized water, acetone, and ethanol by using an ultrasonic bath for 20 min, respectively. Before use, the ITO substrates were treated by UV−O3 for 15 min. The SnO2 solution was spin-coated onto the cleaned ITO substrate at 4000 rpm for 40 s and annealed at 150 °C for 30 min. Then, the SnO2-coated substrates were immersed into the 2 mM

where VTFL is the onset voltage of the trap-filled limit region, ε0 and εr are the vacuum permittivity and the relative dielectric constant, respectively, q is the elemental charge, and L is considered to be the thickness of the perovskite film (here, we take 250 nm, the effect of the thickness of the perovskite film before and after the modification is almost negligible). We found that the trap-state density was reduced from 7.08 × 1015 to 4.72 × 1015 cm3 after DA SAM modification. To further clarify the significant changes caused by the DA SAM modification, electrochemical impedance spectroscopy (EIS) was carried out on the devices with bare or DA-modified SnO2 ETL under 0.5 V dc bias (Figure 5e). The SnO2-based PSC shows a higher device contact resistance (950 Ω) than the SnO2/DA-based PSC (1083 Ω), suggesting better charge transport in the SnO2/DA-based device.47 The only difference 30611

DOI: 10.1021/acsami.8b10332 ACS Appl. Mater. Interfaces 2018, 10, 30607−30613

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ACS Applied Materials & Interfaces solution of 3-hydroxytyramine hydrochloride in deionized water for several hours to induce a DA SAM on the surface of SnO2. Then, the substrates were rinsed in ethanol and then dried under a flow of N2. The perovskite precursor solution contained 461 mg of PbI2 and 159 mg of CH3NH3I in a 1 mL mixed solvent of DMSO and DMF (VDMSO/VDMF = 1:4, stirred at 60 °C for 1 h), filtrated before used. CH3NH3PbI3 perovskite precursor solution was coated onto the SnO2 with or without modification substrate by spin-coating at 1000 rpm for 10 s and 4000 rpm for 30 s; 250 μL chlorobenzene (CB) washed the perovskite thin film when 10 s in the second spin-coating progress. The perovskite thin films were then annealed at 100 °C for about 10 min on a hotplate. After the substrates were cooled down to room temperature, the hole transport layer of spiro-OMeTAD, which was prepared by dissolving 72.3 mg of spiro-OMeTAD, 17.5 μL of LiTFSI (520 mg/mL in acetonitrile), and 28.8 μL of TBP in 1 mL of CB, was spin-coated at 3000 rpm for 30 s. Finally, 80 nm-thick of Au was thermally evaporated in a vacuum to form the electrode. Absorbance spectra were measured by using a Shimadzu UV-1750 UV−visible spectrophotometer (Japan). The steady-state PL and TRPL spectra were obtained by a Hitachi F-4600 spectrofluorometer (Japan) and FLS980, Edinburgh Instruments Ltd, respectively. The AFM images were taken by Park XE-7. The XRD data were collected by RIGAKU D/MAX-3A diffractometer. The top-view SEM image of perovskite films was investigated by Hitachi S-4800. The contact angles of SnO2 with and without modification were measured on a system of DSA1005 (KRUSS GmbH). J−V curves were acquired with a Keithley 2400 source/meter from 1.2 to −0.2 V or −0.2 to 1.2 V at 0.02 V/step under AM 1.5 by using an Enlitech SS-F5-3A solar simulator with irradiation at 100 mW cm−2. The dark J−V data were measured with the same method from 1.5 to −0.5 V in dark condition.

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peaks” Project in Jiangsu Province, China, and Startup from Nanjing Tech University.

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(1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050−6051. (2) Liu, M.; Johnston, M. B.; Snaith, H. J. Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395−398. (3) Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Compositional Engineering of Perovskite Materials for High-Performance Solar Cells. Nature 2015, 517, 476−480. (4) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341− 344. (5) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D.D.; Higler, R.; Hüttner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J.; Atatüre, M.; Phillips, R. T.; Friend, R. H. High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421−1426. (6) Eperon, G. E.; Stranks, S. D.; Menelaou, C.; Johnston, M. B.; Herz, L. M.; Snaith, H. J. Formamidinium Lead Trihalide: a Broadly Tunable Perovskite for Efficient Planar Heterojunction Solar Cells. Energy Environ. Sci. 2014, 7, 982−988. (7) Eperon, G. E.; Burlakov, V. M.; Docampo, P.; Goriely, A.; Snaith, H. J. Morphological Control for High Performance, SolutionProcessed Planar Heterojunction Perovskite Solar Cells. Adv. Funct. Mater. 2014, 24, 151−157. (8) Yang, W. S.; Park, B.-W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S. S.; Seo, J.; Kim, E. K.; Noh, J. H.; Seok, S. I. Iodide Management in Formamidinium-Lead-Halide-Based Perovskite Layers for Efficient Solar Cells. Science 2017, 356, 1376−1379. (9) Christians, J. A.; Schulz, P.; Tinkham, J. S.; Schloemer, T. H.; Harvey, S. P.; de Villers, B. J. T.; Sellinger, A.; Berry, J. J.; Luther, J. M. Tailored interfaces of unencapsulated perovskite solar cells for >1,000 hour operational stability. Nat. Energy 2018, 3, 68−74. (10) Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J. Solvent Annealing of Perovskite-Induced Crystal Growth for PhotovoltaicDevice Efficiency Enhancement. Adv. Mater. 2014, 26, 6503−6509. (11) Salim, T.; Sun, S.; Abe, Y.; Krishna, A.; Grimsdale, A. C.; Lam, Y. M. Perovskite-Based Solar Cells: Impact of Morphology and Device Architecture on Device Performance. J. Mater. Chem. A 2015, 3, 8943−8969. (12) Wang, Z.; Shi, Z.; Li, T.; Chen, Y.; Huang, W. Stability of Perovskite Solar Cells: A Prospective on the Substitution of the A Cation and X Anion. Angew. Chem., Int. Ed. 2017, 56, 1190−1212. (13) Shi, Z.; Guo, J.; Chen, Y.; Li, Q.; Pan, Y.; Zhang, H.; Xia, Y.; Huang, W. Lead-Free Organic-Inorganic Hybrid Perovskites for Photovoltaic Applications: Recent Advances and Perspectives. Adv. Mater. 2017, 29, 1605005. (14) Cao, J.; Wu, B.; Chen, R.; Wu, Y.; Hui, Y.; Mao, B.-W.; Zheng, N. Efficient, Hysteresis-Free, and Stable Perovskite Solar Cells with ZnO as Electron-Transport Layer: Effect of Surface Passivation. Adv. Mater. 2018, 30, 1705596. (15) Liu, X.; Zhang, Y.; Shi, L.; Liu, Z.; Huang, J.; Yun, J. S.; Zeng, Y.; Pu, A.; Sun, K.; Hameiri, Z.; Stride, J. A.; Seidel, J.; Green, M. A.; Hao, X. Exploring Inorganic Binary Alkaline Halide to Passivate Defects in Low-Temperature-Processed Planar-Structure Hybrid Perovskite Solar Cells. Adv. Energy Mater. 2018, 8, 1800138. (16) Seo, J.-Y.; Uchida, R.; Kim, H.-S.; Saygili, Y.; Luo, J.; Moore, C.; Kerrod, J.; Wagstaff, A.; Eklund, M.; McIntyre, R.; Pellet, N.; Zakeeruddin, S. M.; Hagfeldt, A.; Grätzel, M. Boosting the Efficiency of Perovskite Solar Cells with CsBr-Modified Mesoporous TiO2 Beads as Electron-Selective Contact. Adv. Funct. Mater. 2018, 28, 1705763.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b10332.

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REFERENCES

Details about sample characterizations and additional figures, including XPS peaks and the contact angle of the SnO2 films, optical transmittance measurement results of SnO2-coated substrate, photovoltaic parameters statistics of planar PSCs, J−V curves of electron-only devices, Voc versus light intensity for planar PSCs, and PSC performance reported previously (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.X.). *E-mail: [email protected] (Y.C.). ORCID

Yingdong Xia: 0000-0003-4023-3231 Yonghua Chen: 0000-0002-9694-4246 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Basic Research Program of China, Fundamental Studies of Perovskite Solar Cells (grant 2015CB932200), Natural Science Foundation of China (grants 51602149, 61705102, and 91733302), Natural Science Foundation of Jiangsu Province, China (grants BK20161011, BK20160412, and BK20161010), Young 1000 Talents Global Recruitment Program of China, Jiangsu Specially-Appointed Professor program, “Six talent 30612

DOI: 10.1021/acsami.8b10332 ACS Appl. Mater. Interfaces 2018, 10, 30607−30613

Research Article

ACS Applied Materials & Interfaces (17) Fakharuddin, A.; Schmidt-Mende, L.; Garcia-Belmonte, G.; Jose, R.; Mora-Sero, I. Interfaces in Perovskite Solar Cells. Adv. Energy Mater. 2017, 7, 1700623. (18) Kim, H.; Lim, K.-G.; Lee, T.-W. Planar Heterojunction Organometal Halide Perovskite Solar Cells: Roles of Interfacial Layers. Energy Environ. Sci. 2016, 9, 12−30. (19) Bai, Y.; Chen, H.; Xiao, S.; Xue, Q.; Zhang, T.; Zhu, Z.; Li, Q.; Hu, C.; Yang, Y.; Hu, Z.; Huang, F.; Wong, K. S.; Yip, H.-L.; Yang, S. Effects of a Molecular Monolayer Modification of NiO Nanocrystal Layer Surfaces on Perovskite Crystallization and Interface Contact toward Faster Hole Extraction and Higher Photovoltaic Performance. Adv. Funct. Mater. 2016, 26, 2950−2958. (20) Wang, C.; Zhao, D.; Grice, C. R.; Liao, W.; Yu, Y.; Cimaroli, A.; Shrestha, N.; Roland, P. J.; Chen, J.; Yu, Z.; Liu, P.; Cheng, N.; Ellingson, R. J.; Zhao, X.; Yan, Y. Low-Temperature Plasma-Enhanced Atomic Layer Deposition of Tin Oxide Electron Selective Layers for Highly Efficient Planar Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 12080−12087. (21) Li, W.; Zhang, W.; Van Reenen, S.; Sutton, R. J.; Fan, J.; Haghighirad, A. A.; Johnston, M. B.; Wang, L.; Snaith, H. J. Enhanced UV-light Stability of Planar Heterojunction Perovskite Solar Cells with Caesium Bromide Interface Modification. Energy Environ. Sci. 2016, 9, 490−498. (22) Yang, J.; Siempelkamp, B. D.; Mosconi, E.; De Angelis, F.; Kelly, T. L. Origin of the Thermal Instability in CH3NH3PbI3 Thin Films Deposited on ZnO. Chem. Mater. 2015, 27, 4229−4236. (23) Anaraki, E. H.; Kermanpur, A.; Steier, L.; Domanski, K.; Matsui, T.; Tress, W.; Saliba, M.; Abate, A.; Grätzel, M.; Hagfeldt, A.; Correa-Baena, J.-P. Highly Efficient and Stable Planar Perovskite Solar Cells by Solution-Processed Tin Oxide. Energy Environ. Sci. 2016, 9, 3128−3134. (24) Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542−546. (25) Park, M.; Kim, J.-Y.; Son, H. J.; Lee, C.-H.; Jang, S. S.; Ko, M. J. Low-temperature solution-processed Li-doped SnO 2 as an effective electron transporting layer for high-performance flexible and wearable perovskite solar cells. Nano Energy 2016, 26, 208−215. (26) Yang, G.; Lei, H.; Tao, H.; Zheng, X.; Ma, J.; Liu, Q.; Ke, W.; Chen, Z.; Xiong, L.; Qin, P.; Chen, Z.; Qin, M.; Lu, X.; Yan, Y.; Fang, G. Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low-Temperature Processed Y-Doped SnO2Nanosheets as Electron Selective Layers. Small 2017, 13, 1601769. (27) Xiong, L.; Qin, M.; Yang, G.; Guo, Y.; Lei, H.; Liu, Q.; Ke, W.; Tao, H.; Qin, P.; Li, S.; Yu, H.; Fang, G. Performance enhancement of high temperature SnO2-based planar perovskite solar cells: electrical characterization and understanding of the mechanism. J. Mater. Chem. A 2016, 4, 8374−8383. (28) Ke, W.; Zhao, D.; Xiao, C.; Wang, C.; Cimaroli, A. J.; Grice, C. R.; Yang, M.; Li, Z.; Jiang, C.-S.; Al-Jassim, M.; Zhu, K.; Kanatzidis, M. G.; Fang, G.; Yan, Y. Cooperative Tin Oxide Fullerene Electron Selective Layers for High-Performance Planar Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 14276−14283. (29) Rao, H.-S.; Chen, B.-X.; Li, W.-G.; Xu, Y.-F.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y. Improving the Extraction of Photogenerated Electrons with SnO2Nanocolloids for Efficient Planar Perovskite Solar Cells. Adv. Funct. Mater. 2015, 25, 7200−7207. (30) Liu, L.; Mei, A.; Liu, T.; Jiang, P.; Sheng, Y.; Zhang, L.; Han, H. Fully Printable Mesoscopic Perovskite Solar Cells with Organic Silane Self-Assembled Monolayer. J. Am. Chem. Soc. 2015, 137, 1790−1793. (31) Zuo, L.; Gu, Z.; Ye, T.; Fu, W.; Wu, G.; Li, H.; Chen, H. Enhanced Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells through Interfacial Engineering Using Self-Assembling Monolayer. J. Am. Chem. Soc. 2015, 137, 2674−2679. (32) Yang, G.; Wang, C.; Lei, H.; Zheng, X.; Qin, P.; Xiong, L.; Zhao, X.; Yan, Y.; Fang, G. Interface Engineering in Planar Perovskite Solar Cells: Energy Level Alignment, Perovskite Morphology Control and High Performance Achievement. J. Mater. Chem. A 2017, 5, 1658−1666.

(33) Jiang, Q.; Chu, Z.; Wang, P.; Yang, X.; Liu, H.; Wang, Y.; Yin, Z.; Wu, J.; Zhang, X.; You, J. Planar-Structure Perovskite Solar Cells with Efficiency beyond 21%. Adv. Mater. 2017, 29, 1703852. (34) Goh, C.; Scully, S. R.; McGehee, M. D. Effects of Molecular Interface Modification in Hybrid Organic-Inorganic Photovoltaic Cells. J. Appl. Phys. 2007, 101, 114503. (35) Ogomi, Y.; Morita, A.; Tsukamoto, S.; Saitho, T.; Shen, Q.; Toyoda, T.; Yoshino, K.; Pandey, S. S.; Ma, T.; Hayase, S. All-Solid Perovskite Solar Cells with HOCO-R-NH3+I- Anchor-Group Inserted between Porous Titania and Perovskite. J. Phys. Chem. C 2014, 118, 16651−16659. (36) Cao, J.; Yin, J.; Yuan, S.; Zhao, Y.; Li, J.; Zheng, N. Thiols as Interfacial Modifiers to Enhance the Performance and Stability of Perovskite Solar Cells. Nanoscale 2015, 7, 9443−9447. (37) 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. (38) Zheng, L.; Zhang, D.; Ma, Y.; Lu, Z.; Chen, Z.; Wang, S.; Xiao, L.; Gong, Q. Morphology Control of the Perovskite Films for Efficient Solar Cells. Dalton Trans. 2015, 44, 10582−10593. (39) Pujari, S. P.; Scheres, L.; Marcelis, A. T. M.; Zuilhof, H. Covalent Surface Modification of Oxide Surfaces. Angew. Chem., Int. Ed. 2014, 53, 6322−6356. (40) Abate, A.; Saliba, M.; Hollman, D. J.; Stranks, S. D.; Wojciechowski, K.; Avolio, R.; Grancini, G.; Petrozza, A.; Snaith, H. J. Supramolecular Halogen Bond Passivation of Organic-Inorganic Halide Perovskite Solar Cells. Nano Lett. 2014, 14, 3247−3254. (41) Zheng, L.; Ma, Y.; Chu, S.; Wang, S.; Qu, B.; Xiao, L.; Chen, Z.; Gong, Q.; Wu, Z.; Hou, X. Improved Light Absorption and Charge Transport for Perovskite Solar Cells with Rough Interfaces by Sequential Deposition. Nanoscale 2014, 6, 8171−8176. (42) Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; de Arquer, F. P. G.; Fan, J. Z.; Quintero-Bermudez, R.; Yuan, M.; Zhang, B.; Zhao, Y.; Fan, F.; Li, P.; Quan, L. N.; Zhao, Y.; Lu, Z.-H.; Yang, Z.; Hoogland, S.; Sargent, E. H. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation. Science 2017, 355, 722−726. (43) Sun, C.; Wu, Z.; Yip, H.-L.; Zhang, H.; Jiang, X.-F.; Xue, Q.; Hu, Z.; Hu, Z.; Shen, Y.; Wang, M.; Huang, F.; Cao, Y. AminoFunctionalized Conjugated Polymer as an Efficient Electron Transport Layer for High-Performance Planar-Heterojunction Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1501534. (44) 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. (45) Haque, M. A.; Sheikh, A. D.; Guan, X.; Wu, T. Metal oxides as efficient charge transporters in perovskite solar cells. Adv. Energy Mater. 2017, 7, 1602803. (46) Bube, R. H. Trap Density Determination by Space-ChargeLimited Currents. J. Appl. Phys. 1962, 33, 1733−1737. (47) Wang, Z.; Xia, Y.; Chao, L.; Pan, Y.; Li, M.; Li, R.; Du, B.; Chen, Y.; Huang, W. Solution Processed Nano-ZnMgO Interfacial Layer for Highly Efficient Inverted Perovskite Solar Cells. J. Energy Chem. 2018, DOI: 10.1016/j.jechem.2018.03.001. (48) Zhou, G.; Wu, J.; Zhao, Y.; Li, Y.; Shi, J.; Li, Y.; Wu, H.; Li, D.; Luo, Y.; Meng, Q. Application of Cesium on the Restriction of Precursor Crystallization for Highly Reproducible Perovskite Solar Cells Exceeding 20% Efficiency. ACS Appl. Mater. Interfaces 2018, 10, 9503−9513. (49) Liu, Y.; Chen, Q.; Duan, H.-S.; Zhou, H.; Yang, Y.; Chen, H.; Luo, S.; Song, T.-B.; Dou, L.; Hong, Z.; Yang, Y. A dopant-free organic hole transport material for efficient planar heterojunction perovskite solar cells. J. Mater. Chem. A 2015, 3, 11940−11947. (50) Cowan, S. R.; Street, R. A.; Cho, S.; Heeger, A. J. Transient photoconductivity in polymer bulk heterojunction solar cells: competition between sweep-out and recombination. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 035205.

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DOI: 10.1021/acsami.8b10332 ACS Appl. Mater. Interfaces 2018, 10, 30607−30613