Surface Modification of Methylamine Lead Halide Perovskite with

Subscriber access provided by UNIV OF DURHAM

Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Surface Modification of Methylamine Lead Halide Perovskite with Aliphatic Amine Hydroiodide Yingze Zhang, Mingjie Rong, Xiaoyun Yan, Xinlong Wang, Yanli Chen, Xi-You Li, and Ruimin Zhu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b01650 • Publication Date (Web): 25 Jul 2018 Downloaded from http://pubs.acs.org on July 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 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 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.

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 26 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

Langmuir

Surface Modification of Methylamine Lead Halide Perovskite with Aliphatic Amine Hydroiodide Yingze Zhang,a,‡ Mingjie Rong,a,‡ Xiaoyun Yan,a Xinlong Wang,a Yanli Chen,a Xiyou Li,a,* Ruimin Zhub,* a. College of Science, China University of Petroleum, Qingdao, China, 266580 b. Department of Chemistry, Shandong University, Jinan, China, 250014

■ ABSTRACT

By spin coating method, a thin layer of dodecylamine hydroiodide (DAHI) is introduced to the surface of perovskite CH3NH3PbIxCl3-x. This layer of DAHI successfully changes the surface of perovskite from hydrophilic to hydrophobic as revealed by the water contact angle measurement. Significantly enhanced fluorescence intensity and prolonged fluorescence lifetime are found for these modified films in comparison with those of unmodified perovskite films, suggesting the number of structure defects is reduced dramatically. The compatibility between the perovskite and hole transfer layer (HTL) is also improved, which leads to more efficient hole collection from the perovskite layer by HTL as revealed by the fluorescence spectra, fluorescence decay dynamics, as well as the transient photocurrent measurements. Moreover, the perovskite solar cells (PSCs) fabricated from these modified perovskite films exhibit significantly improved humidity stability as well as promoted photo-electron conversion

ACS Paragon Plus Environment

1

Langmuir 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

Page 2 of 26

efficiency (PCE). The result of this research reveals for the first time that the layer of aliphatic amino hydroiodide is a multiple functions layer, which can not only improve the humidity stability, but also promote the performance of PSCs by reducing the defect number and improve the compatibility between perovskite and HTL. Because the structure of aliphatic amines can be functionalized with myriad of other groups, this perovskite modification method should be very promising on promoting the performance of PSCs.

■ KEYWORDS perovskite, perovskite solar cell, surface modification, aliphatic amine hydroiodide ■ INTRODUCTION Perovskite as an excellent solar photovoltaic material inspired great attention over the past several years.1-6 The typical methylamine lead halide (MAPbX3) perovskite has a suitable band gap, strong light-absorbing ability, long carrier diffusion length, and low exciton binding energy in comparison with many other materials.7-9 In the past several years, PSCs have developed rapidly, and the highest certified PCE has reached 22.7%,10 which is close to the highest PCE of conventional photovoltaic devices such as monocrystalline silicon and CdTe.11 Generally, in the respect of PCE, PSCs has satisfied the requirements for practical application.12 However, the instability of lead halide perovskite material in moist environments is one of the biggest hindrances to the practical application of PSCs.13 In previous reports, several research groups successfully adopted surface protection strategies to minimize the effects of moisture and oxygen on the stability of perovskite thin films, thereby achieving the goal of enhancing the stability of PSCs. Wen and co-workers improved solar cell performance and stability by introducing an insulating layer of polystyrene at the


2

Page 3 of 26 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

Langmuir

perovskite/HTL interface.14 Huang et al. decorated the surface of perovskite by using trioctylphosphine oxide with three hydrophobic alkyl groups of different lengths. The resulted PSCs exhibited significantly improved humidity stability.15 In addition, molecules with hydrophobic groups such as thiols and trimethoxysilanes were also used for the surface modification of perovskites.16-20 These molecules can also improve the stability of perovskites films towards humidity, as well as the corresponding PSCs. All the examples as mentioned above proved that fabrication a layer of waterproof material or construct a hydrophobic layer on the surface of the perovskite can block the proximity of water molecules, thereby enhancing the stability of the PSCs.21 Nevertheless, the existing technologies still have drawbacks of complicated operations, limited effect on the stability improvement. It is still necessary to develop a new simple method for perovskite surface modification, which can not only promote the stability significantly, but can also improve the performance of the PSCs. In the present work, we deposited a layer of DAHI as an insulting layer onto the surface of a mixed halide perovskite CH3NH3PbIxCl3-x, a popularly used light absorbing material in solar cells because of its larger carrier migration distance and better conductivity than CH3NH3PbI3.7 The DAHI layer was deposited by spin-coating method, which can effectively prevents the decomposition of perovskite caused by the intrusion of water molecules, thereby improving the stability of the PSCs. Moreover, the DAHI layer can be adsorbed selectively to the methylammonium defect on the surface of perovskite and repair the lattice defects, which reduces the number of recombination centers of photogenerated electron and holes and prolongs the lifetime of photogenerated charge carriers. In addition, the introduction of alkyl chains can also improve the interfacial compatibility between perovskites and HTL, thus accelerating the hole collection of the HTL from perovskite. The PSCs based on this modified perovskite films


3

Langmuir 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

Page 4 of 26

exhibited better efficiency and stability, suggesting that long alkyl ammonium should be an ideal perovskite surface modification reagent. This strategy is promising based on the large number of alkylamines available, as well as the endless possibility for the functionalization of alkylamines by other groups. ■ EXPERIMENTAL SECTION Materials All chemicals and reagents were used as received from chemical companies without any further purification. The synthesis and purification of CH3NH3I and DAHI are conducted following literature methods.22-23 Substrates are ﬂuorine-doped tin oxide conducting glass (FTO) which were washed sequentially in an ultrasonic bath of KOH/isopropyl alcohol saturated solution, distilled water, acetone and ethanol alcohol. Measurements The contact angle was measured on OCA20 contact angle measuring instrument (Dataphysics, Germany). Atomic Force Microscope (AFM) images were measured on Multimode 8 (Bruker, America). Scanning electron microscope (SEM) images were recorded on JSM-6510A (JEOL, Japan). X-ray diffraction (XRD) patterns were obatained by D8 Advance Xray diffractometer (Bruker, Germany) with Cu Kα radiation. Absorption spectra were recorded on a U-3900 UV-vis spectrophotometer (Japan Hitachi). Current-Voltage (I-V) data of PSCs, electrochemical impedance spectroscopy (EIS), and transient photo-current (TPC) decay were collected on an electrochemical workstation (CHI-760) in solar plot mode under xenon lamp irradiation. The xenon lamp used in the measurement was calibrated by a commercial standard Si cell (Newport). Steady-state and time-resolved PL spectra were recorded on FLS980 fluorescence spectrometer (Edinburgh, England). The EQEs were detected by Dual Phase LockIn Amplifier (SR830) and measured with chopped monochromatic light incident which were


4

Page 5 of 26 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

Langmuir

biased with grating spectrometer (Omni-λ300) at an equivalent solar irradiance. A calibrated silicon diode with a known spectral response was used as the reference. The devices of stability tests were stored in air at room temperature with a humidity of 60 ± 5%. The devices were tested under illumination at AM 1.5G every 12 h. EIS was tested from 0.01 Hz to 100 kHz under dark conditions and the impedance of PSCs was measured at the frequency from 0.01 Hz to 100 kHz with -0.8 V perturbation bias in the dark condition. TPC decays were tested by periodic changes of xenon lamp illumination in solar plot mode. Solar Cell Fabrication Fluorine-doped tin Oxide (FTO) glass substrates with dimension of 1.75 cm × 1.2 cm were patterned by etching with zinc powder and 2 M hydrochloric acid. The precursor solution of the dense TiO2 layer consists of 2-methoxyethanol, titanium tetraisopropoxide, and ethanolamine. The mixture was stirred at 80 oC for two hours, and then heated to 120 oC for 1 h. A dense TiO2 layer was applied to FTO by spin-coating at 4000 rpm for 20 s and sintered at 120 oC for 30 min. The mesoporous TiO2 (18NR-T TiO2 Paste Purity >99%) was then coated at 4000 rpm for 30 s, annealed at 500 oC for 30 min. For the perovskite layer, a precursor solution composed of CH3NH3I, PbI2, and PbCl2 in a molar ratio of 2:1:1 with N, Ndimethylformamide as solvent was spin-coated at 4000 rpm for 30 s and then annealed at 100oC for 60 min. Afterwards, 45 mL x mM DAHI (x = 5, 10, 20, 40) in iso-propanol was spin-coated onto the perovskite film at a speed of 5000 rpm for 30 s, and then heated at 60 oC for 5 min. The hole transport layer was subsequently deposited following the literature method.15 Finally, 60nm-thickness Au as a counter electrode was deposited by thermal evaporation at a pressure below 10-4 Pa. The active area of fabricated PSCs is 0.06 cm2. ■ RESULTS AND DISCUSSIONS


5

Langmuir 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

Page 6 of 26

Perovskite Surface Hydrophobization. The DAHI layer was deposited by spin-coating an iso-propanol solution of DAHI onto the surface of perovskite layer (Figure S1). The thickness of DAHI layer was controlled by the concentration of DAHI in solution. Figure 1 shows the results of the water contact angle tests of the perovskite films before and after modification with DAHI. The water contact angle of the non-modified perovksite film is significantly different from those of modified perovksite films. The non-modified perovskite film exhibited a contact angle of 36.0o, indicating that the surface of the unmodified perovskite solid film is hydrophilic. However, after the deposition of DAHI layer, the modified surfaces of perovskite films exhibited significantly increase on water contact angles. Moreover, the water contact angle increases along with the increase on the concentration of DAHI. The perovskite film modified with 5 mM solution presented a water contact angle of 78.57°, this angle increased to 103.20° when the concentration of DAHI increased to 20 mM. These results indicated that DAHI modification has successfully changed the perovskite surface from hydrophilic to hydrophobic, especially the one modified with 20 mM DAHI solution. It should be noted that the higher the water contact angle of the perovskite film, the more perfect cover of the perovskite film by DAHI layer should be. However, when the concentration of DAHI is larger than 20 mM (Figure S2), the water contact angle of the modified perovskite film exhibit no further increase, indicating the completely cover of the perovskite surface by DAHI layer when 20 mM DAHI were used.


6

Page 7 of 26 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

Langmuir

Figure 1. Static contact angle of the perovskite film modified with different concentrations of DAHI: (a) 0 mM; (b) 5 mM; (c) 10 mM; (d) 20 mM.

Figure 2. AFM images of perovskite films: (a) non-modified; (b) modified by 20 mM DAHI. Morphologies of Perovskite Films. The quality of the perovskite film is critical to the performance of the PSC device. Smooth perovskite film with large crystal grains favors the performance of PSCs. Contrarily, the presence of cavities in perovskite film will hinder the charge carrier transport, which is detrimental to device performance.24-27 Therefore, effects of DAHI modification on the morphologies of perovskite films were examined by AFM and SEM, and the results were shown in Figure 2 and Figure 3.


7

Langmuir 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

Page 8 of 26

As shown in Figure 2a, there are many holes and breaks in the non-modified perovskite film with a roughness Rq of 66.5 nm. After modification with a 20 mM DAHI solution, the roughness of the modified perovskite film decreased dramatically to 35.8 nm (Figure 2b), indicating the continuity of the film was improved.

Figure 3. SEM images (Magnification is 30,000) of perovskite films modified with different concentrations of DAHI (a) 0 mM; (b) 5 mM; (c) 10 mM; (d) 20 mM. The great change on the morphology of perovskite films after modification with DAHI has also been revealed by the SEM images as shown in Figure 3 and Figure S6 and S7 in Supporting Information. For the unmodified perovskite films (Figure 3a), bulky crystals can be found with distinct boundaries and large boundary gaps. In contrast, the modified films present larger crystal grains with smaller cavities and boundary gaps. The modification has obviously led to more compact film surface although obvious grain boundaries still exist. It means that the surface of the modified perovskite films becomes much smoother, in accordance with the results of AFM and SEM. Since the pin holes of the perovskite film surface has been effectively filled and the


8

Page 9 of 26 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

Langmuir

continuity has been improved, the transportation of charge carriers in this modified perovskite films will be promoted, which should be beneficial for its application in PSCs. Crystal Structure of Perovskite Films. After the deposition of DAHI layer on the surface, how the crystal structure can be affected? To answer this question, the XRD patterns of these perovskite films were recorded. The results were shown in Figure 4. The diffraction peaks for non-modified perovskite presents three peaks at 14.08o, 28.43o and 31.87o, they can be assigned to the (110), (220) and (310) planes of CH3NH3PbIxCl3-x. Compared with those of non-modified perovskite film, diffraction peaks of the modified perovskite films matched well, indicating that the surface modification did not affect the inner crystal structure of the perovskite film.28-32 But we have indeed observed broadening and even splitting of the preferential peak (110) when the concentration of DAHI is 20 mM, as shown in Figure 4b. The deposition of DAHI layer can reduce the number of defect by filling ammonium vacancy at surface. It is also possible that some methyl ammonium cations were replaced by DAHI in some special locations where the concentration of DAHI is much higher than methyl ammonium. That is why the XRD peaks became broader along with the increase on the concentration of DAHI.


9

Langmuir 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

Page 10 of 26

Figure 4. (a) XRD patterns of perovskite films modified with 0, 5, 10 and 20 mM DAHI; (b) (110) peak in a magnified scale.

Figure 5. (a) The average J-V characteristics of different PSCs; (b) The comparison of PCE distribution (over 100 devices). Table 1. Photovoltaic performance of perovskite solar cells

Structure

Jsc/mAcm-2

Voc/V

FF/%

η/%

Perovskite

19.53

0.92

59.71

10.74

Perovskite/ 5 mM DAHI

20.09

0.92

60.68

11.78


19.93

0.95

63.08

11.90


20.45

0.94

63.30

12.12


19.35

0.90

59.77

10.41

PSC Performance. Figure 5 and Table 1 show the performance of the PSCs fabricated from nonand modified perovskite films. The average short-circuit photocurrent (Jsc) of the PSCs with nonmodified perovskite films is 19.53 mAcm-2, the open-circuit photovoltage (Voc) is 0.92 V, and the filled factor (FF) is 0.597. The photoelectric conversion efficiency (PCE) is 10.74%. In comparison, the corresponding parameters of the PSCs with modified perovksite films by DAHI


10

Page 11 of 26 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

Langmuir

varied significantly. When the concentration of DAHI solution was 5 mM, the PCE increased to 11.18% as the consequence of the promoted Jsc and FF. When it was increased to 10 mM, the PCE increased to 11.90%. The concentration of DAHI solution was further increased to 20 mM, PCE improved further to 12.12%. While the more concentrated DAHI solution with 40 mM was used, it did not bring further improvement on PCE of the resulted PSCs, but a decrease, which might be attributed to the increased hindrance caused by the thick insulting layer of DAHI. Therefore, the optimal modification concentration of DAHI solution was 20 mM, and the average PCE was 12.12%, with Jsc of 20.45 mAcm-2, Voc of 0.94 V, and FF of 0.633. The EQE graph of the solar cell with the best performance is compared with that of the non-modified solar cell in Figure S5 in the supporting information. It can be seen clearly that the deposition of DAHI layer (with a 20 mM solution) can improve the performance of the solar cells. The integrated current intensity is close to the measured Jsc.

Figure 6. The stability of perovskite devices modified with different concentrations of DAHI. Device Stability. The long-term stability towards humidity is critical for the commercial application of PSCs. The results as mentioned above have demonstrated that the surface of perovskite film becomes more hydrophobic after being modified with DAHI. Theoretically, it


11

Langmuir 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

Page 12 of 26

can prevent the adsorption of water molecules and thus reduce the possibility of perovskite films decomposed by water and thus improve the stability of devices. Therefore, we tested the stability of the unsealed PSCs based on non-modified and modified perovskite films by measuring the decrease on PEC along with time. Figure 6 shows the attenuation of the PCE of the PSCs at a relative humidity of 60 ± 5% at room temperature. It can be seen that the stability of the PSCs with modified perovskite films have been significantly improved. After 120 h, the PCE of the original PSCs decreases to 41.5% of the initial value. But PCE of PSCs with perovskite films modified by 5 mM DAHI can be maintained 62.3% of the initial value. Furthermore, PCE of PSCs based on the perovskite films modified by 10 mM and 20 mM DAHI can be retained 65.1% and 71.8%, respectively. Obviously, PSCs modified with 20 mM DAHI have the best stability. These results show that the stability of the PSCs can be effectively improved by modifying the perovskite/HTL interface with DAHI.


12

Page 13 of 26 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

Langmuir

Figure 7. Steady-state (excitated at 375 nm) and time-resolved PL decay (excitated at 450 nm) of unmodified and modified perovskite on FTO substrates: (a) (c) FTO/Perovskite/DAHI; (b) (d) FTO/Perovskite/DAHI/HTL. PL Spectra of Perovskite Films. For the purpose of revealing the reasons for the improvement of the PSCs performance after DAHI modification, the photoluminescence (PL) spectra were recorded, which can provide information on the recombination and migration of photo-generated electron and hole in perovskite layer.33 The emission wavelength of perovskite is 775 nm. The absorption spectra of perovskite films before and after DAHI modification are compared in Figure S3. They are almost identical, suggesting that DAHI modification does not adversely affect the light absorption of the perovskite films. Steady-state and time-resolved PL spectra were shown in Figure 7. In the absence of the charge transport layer (CTL), the emission of the perovskite material is attributed to the recombination of excitons (photo-generated electron/hole pairs) within the film.34-35 Figure 7(a) shows the steady state PL spectra of unmodified and modified perovskite films. The PL intensity of the modified samples was significantly stronger than that of unmodified perovskite films, indicating that the recombination of electrons and holes was suppressed in the modified perovskite films. This can be attributed to the interaction of the dodecylamine hydroiodide with the perovskite film, which reduced the number of the surface defects, and thus the amount of electron and hole recombination center.36 The PL decay dynamics of the perovskite films with or without DAHI modification were also comparatively measured. The results are shown in Figure 7(c). The fitting of these PL decay dynamics with a bi-exponential decay gives two lifetimes, with one around several nanoseconds and another one around a hundred of nanseconds, as shown in Table S1 of Supporting Information. The shorter-lifetime component can be attributed to the


13

Langmuir 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

Page 14 of 26

defect emission, while the longer-lifetime component can be assigned to the direct band emission.37 Without deposition of DAHI, the PL decay of the perovskite film was dominated by the shorter-lifetime component. But after the deposition of DAHI thin layer, the dominating PL component changed into the longer-lifetime one. This result indicates that the defect emission has been quenched by the DAHI layer and suggests the presence of more stable and long lifetime charge carriers, which is obviously favorable character for the application in PSCs. Figure 7(b) is steady-state PL spectra of modified and unmodified perovskite films assembled with HTL. The PL intensity of the modified sample was significantly lower than that of the unmodified perovskite film, indicating the presence of more efficient hole collection from the modified perovskite layer than that from the unmodified layer by HTL. This improved charge transfer across the interface between the modified perovskite layer and HTL might be attributed to the improvement on the interface compatibility between these two layers due to the DAHI modification. This is also supported by the PL dynamics as shown in Figure 7(d) and Table S1 in supporting information. Generally, the PL decay of perovskite films assembled with HTL, no matter it is modified or unmodified, is going much faster than that without HTL. This is because of the presence of efficient hole collection from perovskite by HTL.9 There are still subtle differences between the dyanmics of PL from the modified and unmodified perovskite layers in the presence of HTL. The modified perovskite layer presents a relatively faster decay, which is can be ascribed to the faster collection of holes in perovskite layer by HTL,38-39 and corresponds well with the smaller PL intensity observed in PL spectra. It must be noted that very small decrease on PL lifetimes of the modified perovskite films deposited with HTL along with the increase on the concentration of DAHI from 5 mM to 20 mM, which can be attributed to the promoted compatibility between perovskite and HTL layer. But when the concentration of DAHI


14

Page 15 of 26 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

Langmuir

further increased to 40 mM (Figure S8), both PL intensity and lifetime did not change obviously, this is because the thicker DAHI insulting layer between provksite and HTL is unfavorable for the hole collection process, even though it can improve the compatibility between perovskite and HTL.

Figure 8. EIS and TPC of PSCs: (a) Nyquist plot of unmodified and modified PSCs at -0.8 V bias; (b) Recombination resistance; (c) Charge transport resistance; (d) Series resistance; (e) Equivalent circuit; (f) Transient photocurrent decays (TPC).


15

Langmuir 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

Page 16 of 26

Electrochemical Analysis of PSCs. Electrochemical impedance spectroscopy (EIS) is a powerful technique for monitoring the interface resistance of photovoltaic devices.40-41 The Nyquist plot was recorded under dark conditions and the impedance of the PSCs was measured at the frequency from 0.01 Hz to 100 kHz with a bias voltage of -0.8 V. The results are shown in Figure 8. There are two semicircles in each Nyquist diagram. The left side is related to the charge transfer resistance (Rct), which is mainly attributed to the charge extraction and separation occurring at the interface of ETL/Perovskite or Perovskite/HTL. Moreover, the right side is related to the charge recombination resistance (Rrec) in perovskite. The recombination resistance of excitonse carriers at the corresponding interface is related to the diameter of the semicircle. The real part of the starting point represents the series resistance (Rs) of the PSCs.4245

The equivalent circuit was shown in Figure 8e. Rrec is related to the recombination of electrons from perovskite/TiO2 with HTL. As shown

in Figure 8b, the Rrec of the modified PSCs is evidently enhanced compared with the unmodified, indicating that the surface modification of perovskite by the DAHI commendably inhibits the electron-hole recombination and the leakage current.46 The reduced Rct and Rs of the PSCs with modified perovskite layer (Figure 8c, d) in comparison with that of PSCs with unmodified perovskite layer indicates that the charge extraction efficiency at the interface between HTL and perovskite is improved, which can be assigned to the improvement of the interfacial compatibility between the perovskite layer and the HTL after the DAHI deposition.47 Benefited by all the effects as mentioned above, the performance of the PSCs is then improved. Transient photocurrent decay (TPC) is performed at the short circuit current conduction, which is deemed as the charge carriers transfer process from perovskite to the counter electrodes in solar cell.

47

In the modified perovskite solar cells, the charge carriers attenuate faster


16

Page 17 of 26 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

Langmuir

(0.64ms), than that in the control one (1.13ms), demonstrating that the interfacial compatibility of the perovskite/HTL is improved (Figure 8f), which benefited the charge transfer process.47 ■ CONCLUSION By a simple spin-coating method, a thin layer of DAHI can be deposited onto the surface of perovskite film. This layer of aliphatic amine hydroiodide can change the perovskite surface from hydrophilic into hydrophobic, fill the holes in the film and reduce the roughness of the perovskite surface. But this modification does not affect the crystal structure of perovskite. The PL spectra and decay dynamics revealed that this modification by DAHI can enhance the fluorescence intensity and slow down the decay of the fluorescence, because of the structure defects on the perovskite surface have been repaired by the adsorption of ammonium head group. This modification can also increase the compatibility between the perovskite surface and hole transfer layer as suggested by the PL spectra, the PL decay dynamics, the impendence and photocurrent measurements. These modified perovskite films have been successfully fabricated into PSCs. Remarkable improvement on the performance of PSCs, including photo-electron conversion efficiency and humidity stability, have been achieved. The result of this research demonstrated successfully that modification of perovskite surface with aliphatic amine hydroidodide is an effective way to promote the humidity stability and PCE simultaneously for PSCs. Due to the fact that there are myriad of possibilities for the molecular structure functionalization of aliphatic amines, this perovskite modification strategy should be very promising on promoting the performance of PSCs. ■ ASSOCIATED CONTENT Supporting Information


17

Langmuir 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

Page 18 of 26

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.xxxxx. A detailed schematic flow diagram of surface modification, the static contact angle of the perovskite film modified with 40 mM DAHI, absorption spectra of perovskite films and the stability of photoelectric conversion parameters of perovskite devices. ■ AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing ﬁnancial interest. Author Contributions ‡ These authors contributed equally. ■ ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (No. 21771192 and 21703287), the Natural Science Foundation of Shandong Province (ZR2017ZB0315, ZR2017MB006). X. Li also thanks Taishan Scholar Program of Shandong Province for financial support. ■ REFERENCES (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as VisibleLight Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050-6051. (2) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Grätzel, M.; Park, N.-G. Lead Iodide


18

Page 19 of 26 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

Langmuir

Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (3) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338, 643-647. (4) Dabirian, A.; Taghavinia, N. Resonant-Size Spherical Bottom Scatterers for Dye-Sensitized Solar Cells. Rsc Adv. 2013, 3, 25417-25422. (5) Chen, W.; Wu, Y.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.B.; Ashraful, I.; Grätzel, M.; Han, L. Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Charge Extraction Layers. Science 2015, 350, 944-948. (6) Tsai, H.; Nie, W.; Blancon, J.; Stoumpos, C. C.; Asadpour, R.; Harutyunyan, B.; Neukirch, A. J.; Verduzco, R.; Crochet, J. J.; Tretiak, S.; Pedesseau, L.; Even, J.; Alam, M. A.; Gupta, G.; Lou, J.; Ajayan, P. M.; Bedzyk, M. J.; Kanatzidis, M. G.; Mohite, A. D. High-Efficiency Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells. Nature 2016, 536, 312-316. (7) 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. (8) Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Low Trap-State Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science 2015, 347, 519-522.


19

Langmuir 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

Page 20 of 26

(9) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Gratzel, ̈ M.; Mhaisalkar, S.; Sum, T. C. Long-range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 2013, 342, 344-347. (10)

The best efficiency, https://www.nrel.gov/pv/assets/images/efficiencychart.png.

(11)

Green, M. A., Hishikawa, Y., Warta, W., Dunlop, E. D., Levi, D. H., Hohl-Ebinger, J.,

Ho-Baillie, A. W. Y. Solar Cell Efficiency Tables (version 50). Prog. Photovolt.: Res. Appl. 2017, 19, 565-572. (12)

Ono, L. K.; Park, N. G.; Zhu, K.; Huang, W.; Qi, Y. Perovskite Solar Cells—Towards

Commercialization. Acs Energy Lett. 2017, 2, 1749-1751. (13)

Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.;

Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Stability. Energy Environ. Sci. 2016, 9, 323-356. (14)

Wen, X.; Wu, J.; Ye, M.; Gao, D.; Lin, C. Interface Engineering via an Insulating

Polymer for Highly Efficient and Environmentally Stable Perovskite Solar Cells. Chem Commun. 2016, 52, 11355-11358. (15)

Huang, G.; Wang, C.; Zhang, H.; Xu, S.; Xu, Q.; Cui, Y. Post-Healing of Defects:

Alternative Way for Passivation of Carbon-Based Mesoscopic Perovskite Solar Cells via Hydrophobic Ligand Coordination. J. Mater. Chem. A. 2018, 6, 2449-2455. (16)

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, 94439447.


20

Page 21 of 26 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

Langmuir

(17)

Zhang, J.; Hu, Z.; Huang, L.; Yue, G.; Liu, J.; Lu, X.; Hu, Z.; Shang, M.; Han, L.; Zhu, Y.

Bifunctional Alkyl Chain Barriers for Efficient Perovskite Solar Cells. Chem Commun. 2015, 51, 7047-7050. (18)

Wang, F.; Geng, W.; Zhou, Y.; Fang, H.; Tong, C.; Loi, M. A.; Liu, L.M.; Zhao, N.

Phenylalkylamine Passivation of Organolead Halide Perovskites Enabling High-Efficiency and Air-Stable Photovoltaic Cells. Adv. Mater. 2016, 28, 9986-9992. (19)

Yang, S.; Wang, Y.; Liu, P.; Cheng, Y. B.; Zhao, H. J.; Yang, H. G. Functionalization of

Perovskite Thin Films with Moisture-Tolerant Molecules. Nat. Energy. 2016, 1, 15016. (20)

Wang, Q.; Dong, Q.; Li, T.; Gruverman, A.; Huang, J. Thin Insulating Tunneling Contacts

for Efficient and Water-Resistant Perovskite Solar Cells. Adv. Mater. 2016, 28, 6734-6739. (21)

Zhao, J.; Cai, B.; Luo, Z.; Dong, Y.; Zhang, Y.; Xu, H.; Hong, B.; Yang, Y.; Li, L.; Zhang,

W.; Gao, C. Investigation of the Hydrolysis of Perovskite Organometallic Halide CH3NH3PbI3 in Humidity Environment. Sci. Rep. 2016, 6, 21976. (22)

Im, J.-H.; Lee, C.-R.; Lee, J.-W.; Park, S.-W.; Park, N. G. 6.5% Efficient Perovskite

Quantum-Dot-Sensitized Solar Cell. Nanoscale. 2011, 3, 4088−4093. (23)

Eperon, G. E.; Burlakov, V. M.; Docampo, P.; Goriely, A.; Snaith, H. J. Morphological

Control for High Performance, Solution-Processed Planar Heterojunction Perovskite Solar Cells. Adv. Funct. Mater. 2014, 24, 151-157. (24)

Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Sang, I. S. Solvent Engineering

for High-Performance Inorganic–Organic Hybrid Perovskite Solar Cells. Nature Mater. 2014, 13, 897-903. (25)

Xiao, M.; Huang, F.; Huang, W.; Dkhissi, Y.; Zhu, Y.; Etheridge, J.; Weale, A. G.; Bach,

U.; Cheng, Y.; Spiccia, L. A Fast Deposition-Crystallization Procedure for Highly Efficient


21

Langmuir 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

Page 22 of 26

Lead Iodide Perovskite Thin-Film Solar Cells. Angew. Chem. Inter. Ed. 2014, 126, 98989903. (26)

Wu, Y.; Islam, A.; Yang, X.; Qin, C.; Liu, J.; Zhang, K.; Peng, W.; Han, L. Retarding the

Crystallization of PbI2 for Highly Reproducible Planar-Structured Perovskite Solar Cells via Sequential Deposition. Energy Environ. Sci. 2014, 7, 2934-2938. (27)

Xu, Y., Zhu, L., Shi, J., Lv, S., Xu, X., Xiao, J., Dong, J.; Wu, H.; Luo, Y.; Li, D.; Men, Q.

Efficient Hybrid Mesoscopic Solar Cells with Morphology-Controlled CH3NH3PbI3-xClx Derived from Two-Stepspin Coating Method. Acs Appl Mater Inter, 2015, 7, 2242-2248. (28)

Liu, D., Wu, L., Li, C., Ren, S., Zhang, J., Li, W., Feng, l. Controlling CH3NH3PbI(3-x)Cl(x)

Film Morphology with Two-Step Annealing Method for Efficient Hybrid Perovskite Solar Cells. Acs Appl Mater Inter, 2015, 7, 16330-16337. (29)

Yantara, N.; Yanan, F.; Shi, C.; Dewi, H. A.; Boix, P. P.; Mhaisalkar, S. G.; Mathews, N.

Unravelling the Effects of Cl Addition in Single Step CH3NH3PbI3. Chem. Mater. 2015, 27, 2309-2314. (30)

Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H. S.; Wang, H. H.; Liu Y.; Li, G.; Yang, Y.

Planar Heterojunction Perovskite Solar Cells via Vapor-Assisted Solution Process. J. Am. Chem. Soc. 2014, 136, 622-625. (31)

Burschka, J.; Pellet, N.; Moon, S. J.; Humphrybaker, R., Gao, P.; Nazeeruddin, M. K.;

Grätzel, M. Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells. Nature. 2013, 499, 316-319. (32)

Chen, W.; Li, K.; Wang, Y.; Feng, X.; Liao, Z.; Su, Q.; Lin, X.; He, Z. Black Phosphorus

Quantum Dots for Hole Extraction of Typical Planar Hybrid Perovskite Solar Cells. J. Phys. Chem. Lett. 2017, 8, 591-598.


22

Page 23 of 26 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

Langmuir

(33)

Dong, Q.; Wang, Z.; Zhang, K.; Yu, H.; Huang, P.; Liu, X.; Zhou, Y.; Chen, N.; Song, B.

Easily Accessible Polymer Additives for Tuning the Crystal-Growth of Perovskite ThinFilms for Highly Efficient Solar Cells. Nanoscale. 2016, 8, 5552. (34)

Swarnkar, A.; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag, A. Colloidal

CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots. Angew. Chem. Int. Ed. 2016, 54, 15424-15428. (35)

Zhu, R.; Gao, C.; Sun, T.; Shen, L.; Sun, D.; Li, X. Surface Decorating of CH3NH3PbBr3

Nanoparticles

with

the

Chemically

Adsorbed

Perylenetetracarboxylic

Diimide.

Langmuir. 2016, 32, 3294-3299. (36)

Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith,

H. J. Enhanced Photoluminescence and Solar Cell Performance via Lewis Base Passivation of Organic-Inorganic Lead Halide Perovskites. Acs Nano. 2014, 8, 9815-9821. (37)

Gonzalezpedro, V.; Juarezperez, E. J.; Arsyad, W. S.; Barea, E. M.; Fabregatsantiago, F.;

Morasero, I.; et al. General Working Principles of CH3NH3PbX3 Perovskite Solar Cells. Nano. Lett. 2014, 14, 888-893. (38)

Li, J.; Duan, C.; Wang, N.; Zhao, C.; Han, W.; Jiang, L.; Wang, J.; Zhao, Y.; Huang, C.;

Jiu, T. Controllable Spatial Configuration on Cathode Interface for Enhanced Photovoltaic Performance and Device Stability. Acs Appl Mater Inter. 2018, 10, 17401-17408. (39)

Li, J.; Jiu, T.; Duan, C.; Wang, Y.; Zhang, H.; Jian, H.; Zhao, Y.; Wang, N.; Huang, C.; Li,

Y. Improved Electron Transport in MAPbI3 Perovskite Solar Cells Based on Dual Doping Graphdiyne. Nano Energy. 2018, 46, 331-337.


23

Langmuir 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

(40)

Page 24 of 26

Fabregat-Santiago, F.; Garcia-Belmonte, G.; Mora-Seró, I.; Bisquert, J. Characterization

of Nanostructured Hybrid and Organic Solar Cells by Impedance Spectroscopy. Phys. Chem. Chem. Phys. 2011, 13, 9083. (41)

Hou, X.; Hu, Y.; Liu, H.; Mei, A.; Li, X.; Duan, M.；Zhang, G.; Rong, Y.; Han, H. Effect

of Guanidinium on Mesoscopic Perovskite Solar Cells. J. Mater. Chem. A. 2017, 5, 73-78. (42)

Kim, H.-S; Lee, J.-W; Yantara, N.; Boix, P.-P,; Kulkarni, S.-A; Mhaisalkar, S.; Grätzel,

M.; Park, N.-G. High Efficiency Solid State Sensitized Solar Cell Based on Submicrometer Rrutile TiO2 Nanorod and CH3NH3PbI3 Perovskite Sensitizer. Nano Lett. 2013, 13, 24122417. (43)

Huang, X.; Hu, Z.; Xu, J.; Wang, P.; Wang, L.; Zhang, J.; Zhu, Y. Low-Temperature

Processed SnO2, Compact Layer by Incorporating TiO2, Layer Toward Efficient Planar Heterojunction Perovskite Solar Cells. Sol. Energy. Mat. Sol. C. 2017, 164, 87-92. (44)

Chen, W.; Wu, Y.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.; Ashraful, I.;

Grätzel, M. Han, M. Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Charge Extraction Layers. Science 2015, 350, 944-948. (45)

Papavassiliou, G. C.; Pagona, G., Karousis, N.; Mousdis, G. A.; Koutselas, I.;

Vassilakopoulou, A. Nanocrystalline/Microcrystalline Materials Based on Lead-Halide Units. J. Mater. Chem. 2012, 22, 8271-8280. (46)

Li, J.; Zhao, M.; Zhao, C.; Jian, H.; Wang, N.; Yao, L.; Huang, C.; Zhao, Y.; Jiu, T.

Graphdiyne-Doped P3CT-K as an Efficient Hole-Transport Layer for MAPbI3 Perovskite Solar Cells. Acs Appl Mater Inter. 2018. 10.1021/acsami.8b02611.


24

Page 25 of 26 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

Langmuir

(47)

Chen, R.; Hou, D.; Lu, C.; Zhang, J.; Tian, H.; Zeng, Z.; Xiong, Q.; Hu, Z,; Zhu, Y.; Han,

L. Zinc Ion as Effective Film Morphology Controller in Perovskite Solar Cells. Sustain. Energy. Fuels. 2018, 2, 1093-1100.


25

Langmuir 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

Page 26 of 26

Abstract Graphic A thin layer of dodecylamine hydroiodide deposited to the surface of perovskite CH3NH3PbIxCl3x

can improve the stability, reduce the number of defects, and increase compatibility between the

provskite layer and hole transfer layer, and finally improve the performance of PSCs.


26

Surface Modification of Methylamine Lead Halide Perovskite with

Recommend Documents