Improving Uniformity and Reproducibility of Hybrid Perovskite Solar

Subscriber access provided by READING UNIV

Article

Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature, Vacuum Deposition Process for NiO Hole Transport Layers x

Seong Ryul Pae, Segi Byun, Jekyung Kim, Minkyu Kim, Issam Gereige, and Byungha Shin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14499 • Publication Date (Web): 13 Dec 2017 Downloaded from http://pubs.acs.org on December 13, 2017

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 Materials & Interfaces 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 25 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 Materials & Interfaces

Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a LowTemperature, Vacuum Deposition Process for NiOx Hole Transport Layers Seong Ryul Pae1, Segi Byun1, Jekyung Kim1, Minkyu Kim1, Issam Gereige2 and Byungha Shin1* 1

Department of Materials Science and Engineering, Korea Advanced Institute of Science and

Technology, Daejeon, 34141, Korea 2

Saudi Aramco Research & Development Center, Dhahran 31311, Kingdom of Saudi Arabia

KEYWORDS perovskite, solar cell, nickel oxide, e-beam evaporation, hole transport layer

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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 25

ABSTRACT

Recently, the trend in inverted hybrid perovskite solar cells (PVSCs) has been to utilize NiOx as hole transport layers. However, the majority of reported solution-processed NiOx films require a high-temperature thermal annealing process which is unfavorable for large-scale manufacturing and suffers from lack of uniformity. We report, for the first time, e-beam evaporation as a lowtemperature, vacuum process for the deposition of NiOx hole transport layers for PVSCs. Device characterization shows that efficiency is on par with solution-processed methods, the highest efficiency at 15.4% with no obvious hysteresis. Differences are found to be due to the presence of more Ni3+ in e-beam evaporated NiOx which are responsible for a lower transmittance but higher conductivity. Most importantly, e-beam evaporated NiOx-based PVSCs show greater uniformity and reproducibility compared to those of spin-coated NiOx-based PVSCs. Finally, ebeam evaporated NiOx has the additional advantage of being a low-temperature deposition process and being applicable over large areas. This work, therefore, represents a significant step towards large-area PVSCs where e-beam evaporation can be used for the low-temperature, uniform deposition of charge transport layers such as NiOx.


2

Page 3 of 25 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 Inorganic-organic hybrid perovskite solar cells (PVSCs) have drawn considerable attention in the past few years due to the rapid increase in their power conversion efficiency (PCE), using materials that offer prospects for facile and low-cost fabrication. Since the first introduction of PVSCs for photovoltaic devices by Miyasaka and co-workers,1 extensive research has led to a remarkable progress in efficiency, recently reaching a certified PCE of 22.1% by Seok and coworkers.2 Currently, most high-efficiency PVSCs utilize the n-i-p structure which commonly consists of an expensive 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiroOMeTAD) as a hole transporting layer (HTL) and a compact and mesoporous TiO2 as an electron transporting layer (ETL).3-7 Although this structure has shown higher efficiency overall, the requirement of a high-temperature sintering process (>500 °C) and the need for an extra mesoporous layer makes this structure particularly unattractive for large-scale manufacturing of PVSCs. As an alternative, a simple and low-temperature processable p-i-n structure can be used which, most commonly, employs poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the HTL and [6,6]phenyl C61 butyric acid methyl ester/bathocuproine (PCBM/BCP) layers as the ETL.8-11 However, efficiency has generally been lower than those of their n-i-p structured counterparts. Recently, the PEDOT:PSS layer has been widely replaced with an inorganic film to overcome the stability issue often caused by the organic layers.12-22 NiOx has already proven to be an efficient HTL for fabricating inverted p-i-n PVSCs.23-26 NiOx is a low cost, easy-to-synthesize material with a wide-bandgap and good optical transparency and has a valence band that is well


3


Page 4 of 25

aligned with that of hybrid perovskites. Furthermore, the inorganic nature of NiOx provides chemical and thermal stability, unlike PEDOT:PSS whose acidic nature has been shown to be detrimental to long-term device performance and stability.27 By utilizing NiOx as the HTL, considerable progress has been made in improving the efficiency of inverted p-i-n PVSCs closer to those of their n-i-p counterparts. However, the majority of reported NiOx layers used as a HTL for hybrid perovskite devices have been prepared by Ni-containing precursor solutions or nanoparticles dispersed in polar organic solvents that undergo a high-temperature thermal annealing process, making them unfavorable for flexible devices.28 On the contrary, there have been successful reports of room-temperature solution-processed NiOx giving high efficiency devices (most notably by Choy’s group),29,30 however their use of spin-coating makes the technique fundamentally limited for large-area, uniform deposition which are important factors that need to be considered for further progress of PVSCs.31 As an alternative, the use of vacuum processes such as pulsed laser deposition and magnetron sputtering have been reported, which could potentially fulfill the requirements of a uniform, large-area deposition technique, but so far these techniques have still required a high annealing temperature or, absent of annealing, have shown low PCEs.32-36 In order to overcome such problems, we report e-beam evaporation as a low-temperature, vacuum process for the deposition of NiOx HTL for hybrid PVSCs. Device characterization shows that efficiency is on par with solution-processed methods, with the highest efficiency at 15.4% with no obvious hysteresis. Chemical analysis indicates that the difference between the NiOx films deposited via spin-coating and e-beam evaporation are on a chemical level with ebeam deposited (eb)-NiOx films showing larger Ni3+ to Ni2+ ratio which results in a more conductive but less transparent films. More importantly, eb-NiOx PVSCs show a highly


4

Page 5 of 25 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


consistent efficiency distribution between the different cells in one device, which relates to the uniformity of the NiOx films deposited via e-beam evaporation, and also shows greater reproducibility over many devices compared to those of spin-coated (sc)-NiOx PVSCs. In addition, the advantages of low-temperature deposition and the prospect of being applicable over large areas makes e-beam evaporation a very attractive deposition technique for charge transport layers for PVSCs. 2. EXPERIMENTAL SECTION 2.1 Materials. All of the chemicals and materials were purchased and used as received unless otherwise stated. CH3NH3I (MAI) was purchased from Dyesol. PbI2 (99.9985%) was purchased from Alfa Aesar. [6,6]phenyl C61 butyric acid methyl ester (PCBM) was purchased from Nano-C. NiO (3-6 mm granules, 99.995%) were purchased from iTASCO. The other materials were purchased from Sigma-Aldrich. 2.2 Device Fabrication. ITO-coated glass substrates were cleaned by sonification in acetone, ethyl alcohol and distilled water in sequence. The substrates were then treated by ultraviolet-ozone for 10 min. For sc-NiOx, nickel(II) acetate tetrahydrate (Sigma-Aldrich, ≥ 99.0%, 50 mg/ml in ethanol) was spin-coated onto the substrates at 4000 rpm for 45 s and annealed at 300 °C for 1 hour. For eb-NiOx, NiO granules were deposited via an e-beam evaporator (A-tech) at a rate of 0.5 Å/s. The CH3NH3PbI3 solutions were prepared by reacting PbI2:CH3NH3I at 1:1 molar ratio (48 wt%) in N,N-Dimethylformamide (Sigma-Aldrich, anhydrous, 99.8%). The solution was deposited onto the substrate by spin-coating at 5000 rpm for 30 s during which 150 µl of chlorobenzene (Sigma-Aldrich, anhydrous, 99.8%) was dropped after 5 s of spin-coating, a method known as solvent engineering.49 The substrate was then dried


5


Page 6 of 25

on a hot plate at 100 °C for 5 min. Subsequently, the PCBM (15 mg/ml in dichlorobenzene) and BCP (0.5 mg/ml in ethanol) were deposited via spin-coating at 1000 rpm for 40 s and 5000 rpm for 30 s, respectively. Finally, Ag contact electrodes were thermally evaporated (100 nm) in high vacuum using a shadow mask. The spin-coating of the perovskite layer alone was conducted inside a glove box. 2.3 Measurement and Characterization. J-V characteristics were measured at 25 °C under solar-simulated AM 1.5.G illumination using a K3000 Solar Simulator (McScience) and calibrated using a silicon reference cell to achieve 100 mW cm-2. The active area of all PVSCs were fixed at 0.1 cm2 using a metal shadow mask. IPCE measurements were taken using a QEXL Solar Cell Quantum Efficiency / IPCE / Spectral Response Measurement System (PV measurement). SEM images were taken using a XL30 microscope (Philips). Electrochemical impedance spectroscopy (EIS) measurements were conducted using a potentiostat (Bistat, Biologic Science Instruments) and measured under illumination condition (1 sun, 100 mW cm-2) in the frequency range of 1 MHz to 100 Hz at open-circuit potential with a 10 mV sinusoidal wave. Optical transmittance measurements were taken using a UV/VIS/NIR spectrophotometer (SolidSpec-3700). Room-temperature PL measurements were taken using a continuous-wave He-Ne laser with a wavelength of 514 nm at an excitation laser intensity of 0.01 mW cm-2. The chemical state of the nickel and oxygen were analyzed by XPS measurements, using a multipurpose X-ray photoelectron spectroscopy (Thermo VG Scientific). 3. RESULT AND DISCUSSION The NiOx thin films used in this study were first prepared by a common sol-gel method, where a nickel precursor solution (nickel(II) acetate tetrahydrate) was spin-coated onto indium tin oxide


6

Page 7 of 25 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


(ITO) substrates and annealed at 300 °C for 1 hour in air,19 and second by e-beam evaporation at room temperature without any post-treatment. Scanning electron microscopy (SEM) characterization was carried out to observe the difference in NiOx surface morphology between the two deposition methods. The top-view SEM images of sc-NiOx and eb-NiOx are shown in Figure 1a and b, respectively. Both films show full coverage of the substrate with compact grains, but sc-NiOx shows smaller grain sizes of 29.6 ± 5.4 nm compared to those of eb-NiOx at 38.9 ± 8.1 nm. The morphological difference between the two NiOx layers is also evident in the AFM images (Figure S1), however the RMS values of 1.59 ± 0.07 nm and 3.85 ± 0.06 nm for scNiOx and eb-NiOx, respectively, are similar. The thickness of the NiOx films on ITO, determined by cross-section SEM images (Figure S2), were optimized individually according to device performance to give a thickness of 35 nm and 100 nm for sc-NiOx and eb-NiOx, respectively. XRD patterns of sc-NiOx and eb-NiOx (Figure S3) determine a cubic structured NiOx in both cases with the improved crystallinity in the case of eb-NiOx.


7


Page 8 of 25

Figure 1. Top-view SEM images of (a) spin-coated and (b) e-beam evaporated NiOx on ITO. (c) Device structure of perovskite solar cells in this study and (d) cross-sectional SEM image of an e-beam evaporated NiOx-based device. SEM scale bars equal 500 nm. To demonstrate the compatibility of the NiOx films with PVSCs, devices with a configuration of ITO/NiOx/CH3NH3PbI3/PCBM/BCP/Ag were fabricated as illustrated in Figure 1c, using both the sc-NiOx and eb-NiOx as the HTL. Figure 1d shows a typical cross-section SEM image of a complete device using eb-NiOx as a HTL. The CH3NH3PbI3 perovskite film is shown to be uniform, fully covering the NiOx layer with an optimized thickness of around 320 nm. The topview SEM images and the XRD patterns of the perovskite deposited on sc-NiOx and eb-NiOx, (Figure S4 and Figure S5) show no major difference. These results along with the similar RMS values for the surface of the NiOx layers, make it highly unlikely that the different NiOx layers


8

Page 9 of 25 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


affect the perovskite morphology or crystallization in a different way. The PCBM/BCP layers used as the ETL in this study shows a thickness of around 50 nm. The current density-voltage (JV) curves of the best performing sc-NiOx and eb-NiOx devices under standard one sun AM 1.5G simulated solar irradiation are shown in Figure 2a and b, respectively. It is important to note that the figures show the J-V curves of different cells in one particular PVSC device prepared on one inch by one inch substrates. The best performing cell in the sc-NiOx device exhibits the highest efficiency with an open-circuit voltage (Voc) of 1.07 V, a short-circuit current density (Jsc) of 19.5 mA cm-2, and a fill factor (FF) of 0.748, resulting in a PCE of 15.7%. When e-beam evaporated NiOx films are used, the best cell in the device exhibits a Voc of 1.06 V, a slightly lower Jsc of 18.6 mA cm-2, and an increased FF of 0.778, resulting in a PCE of 15.4% (Table 1). Comparative J-V curves of the best performing cells and their corresponding incident photon to current conversion efficiency (IPCE) spectra (Figure S6 and S7) show that both devices exhibit no noticeable hysteresis and the Jsc integrated from the IPCE spectra are in good agreement with those from the J-V curve. It was found that the higher FF in eb-NiOx PVSCs was the result of lower series resistance compared to that of sc-NiOx PVSCs, evident from the slope of the J-V curve near the open-circuit voltage. This was also confirmed by the Nyquist plots shown in Figure 2c and d. The Nyquist plot fitting results of the best performing cell (Figure S8) of ebNiOx PVSCs show both a lower series resistance (Rs) and a lower charge transport resistance (Rct), with values of 6.7 Ω and 138.9 Ω, respectively, compared to sc-NiOx PVSCs at 18.3 Ω and 158.6 Ω (Figure S9). All devices investigated in this study have identical layers with the exception of the NiOx film. Therefore, it is reasonable to assume that the differences arise solely from the NiOx films where the lower Rs of the NiOx film and the lower Rct at the NiOx/perovskite interface for eb-NiOx compared to those of sc-NiOx results in the higher FF


9


Page 10 of 25

shown in the J-V curves. It is noted that the thickness of the eb-NiOx, as a result of device optimization, is larger than that of the sc-NiOx (100 nm for the eb-NiOx vs. 35 nm for the scNiOx), yet the device with the eb-NiOx exhibits the lower Rs, indicating more conductive nature of the eb-NiOx.

Figure 2. J-V curves of different cells in a (a) spin-coated and (b) e-beam evaporated NiOxbased device and (c), (d) their corresponding Nyquist plots, respectively. (e) Histogram of PVSCs with (orange) spin-coated and (blue) e-beam evaporated NiOx.


10

Page 11 of 25 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


Table 1. Photovoltaic performance parameters extracted from J-V measurements under standard AM 1.5 illumination (100 mW cm-2). Cell

Voc (V)

Jsc (mA cm-2)

FF

PCE (%)

Spin-coating 1

1.09

19.7

0.727

15.6

2

1.07

19.5

0.748

15.7

3

1.03

19.1

0.577

11.3

4

1.11

17.0

0.688

13.1

E-beam evaporation 1

1.06

18.6

0.778

15.4

2

1.03

18.9

0.766

14.9

3

1.04

18.9

0.762

14.9

4

1.04

18.9

0.744

14.6

Another important feature of the eb-NiOx PVSC is the consistency of device performance over different cells in one device, evident in both the J-V curves and the Nyquist plots. Although scNiOx PVSCs have shown the highest PCE, they exhibit large fluctuations in device performance whereas eb-NiOx PVSCs show highly consistent performance. This can be attributed to the superior uniformity of the NiOx films deposited via e-beam evaporation relative to spin-coating. The superior uniformity of the eb-NiOx PVSCs, however, cannot be attributed to the larger thickness (100 nm vs. 35 nm for the sc-NiOx) because even when sc-NiOx are deposited at thicknesses to match those of eb-NiOx (100 nm), the PVSCs still show a large fluctuation between the cells across a device (Figure S10) In addition, eb-NiOx PVSCs show higher reproducibility over different cells over several devices relative to sc-NiOx PVSCs. This is


11


Page 12 of 25

evident from the PCE histogram of 50 cells from more than 10 different devices shown for both sc-NiOx and eb-NiOx (Figure 2e). Although sc-NiOx PVSCs have shown the highest efficiency, the PCE of several devices are sparsely spread out over a wide range of efficiencies giving a modest average PCE of around 12.1%, whereas eb-NiOx PVSCs show a more compact set of results with an average PCE of around 13.3%, being higher overall. These results also suggest that the non-uniformity and low-reproducibility of PVSCs may not solely be the result of the spin-coating process of the perovskite absorber itself, as was widely assumed, but rather due to the fluctuating performance of the adjacent charge transporting layers.5, 37-38 The lower Jsc of the eb-NiOx relative to sc-NiOx was investigated via UV-Vis spectra where the transmittance of the NiOx films deposited on ITO glass are shown in Figure 3a. It was found that sc-NiOx exhibits superior transmittance over the range of 400-800 nm with a slight exception at around 500 nm. The slight decrease in photocurrent density for eb-NiOx PVSCs is thus attributed to the lower light transmittance of the eb-NiOx consistent with the coloring of the film (Figure S11) which results in the reduced light absorption by the perovskite. The lower transmittance cannot be due to the thicker films of eb-NiOx as Figure 3a shows that even when they are deposited to match the thickness of sc-NiOx (35 nm), the transmittance is still far lower. Therefore, the lower transmittance can only be attributed to an intrinsic property of the eb-NiOx films. In addition, the photoluminescence (PL) spectra of the CH3NH3PbI3 absorber layer deposited on sc-NiOx and eb-NiOx are shown in Figure 3b. The relatively lower PL intensity (i.e. higher PL quenching) of the eb-NiOx compared to sc-NiOx is generally associated with a more efficient charge separation from the absorber material to the charge transport layer.39-40 This is further demonstrated with time-resolved PL decay spectra (Figure S12) where the longer lifetime of eb-NiOx at 21.8 ns compared to sc-NiOx at 14.7 ns gives evidence for a more efficient charge


12

Page 13 of 25 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


extraction when using eb-NiOx. In turn, these results are consistent with the lower charge transport resistance of the eb-NiOx determined from the Nyquist plots. In order to examine the possible differences in chemical component between sc-NiOx and ebNiOx, X-ray photoelectron spectroscopy (XPS) measurements were carried out on each of the films, where the background was subtracted from the XPS spectra by using a Shirley-type background subtraction. A direct comparison between the two NiOx films at the Ni 2p and O 1s spectra are shown in Figure 3c and d, respectively. Deconvolution of the Ni 2p3/2 spectrum in the form of a Gaussian function led to two different oxidation states with peaks at 855.6 eV and 853.7 eV (Figure S13). The peak at 853.7 eV corresponds to the Ni2+ state resulting from NiO whereas the peak at 855.6 eV corresponds to the more oxidized Ni3+ state resulting from Ni2O3.41 A clear difference is shown between the sc-NiOx and eb-NiOx films in the Ni 2p3/2 spectra, where the eb-NiOx films exhibit a larger Ni3+ to Ni2+ ratio relative to that of sc-NiOx. This is again confirmed by the deconvolution of the O 1s spectrum (Figure S14) where the peak at 531.1 eV corresponds to Ni2O3 and the peak at 529.2 eV corresponds to NiO.42 Therefore, it can be concluded that while both NiOx films are non-stoichiometric, consisting of both NiO and Ni2O3, the eb-NiOx films have more excess oxygen confirmed by the larger Ni2O3 to NiO ratio (larger Ni3+ to Ni2+ ration). The electrical conductivity of NiOx is known to be strongly related to microstructural defects such as nickel vacancies and interstitial oxygen.43-44 In turn, the excess of oxygen atoms in NiOx creates vacancies in the normally occupied Ni cation sites resulting in a more p-type semiconductor behavior. Since the carriers existing in NiOx films are holes, the more oxidized eb-NiOx films are thus more electrically conductive than the sc-NiOx films. Another possible explanation is that the Ni2O3 is intrinsically more conductive than NiO. Although there is no report in the literature directly comparing the conductivities of NiO and


13


Page 14 of 25

Ni2O3 films, a more conductive Ni2O3 film that is largely present in eb-NiOx would account for the more conductive behavior. To demonstrate this, conductivity tests were performed for sc-NiOx and eb-NiOx using devices with a configuration of FTO/sc-NiOx or eb-NiOx/Au (Figure S15). The results confirm that the eb-NiOx is less resistive (and thus more conductive) than the sc-NiOx, with resistivity values of (2.51 ± 0.07) × 104 Ω cm and (9.50 ± 0.98) × 104 Ω cm, respectively. These values are similar to values reported elsewhere.45-46 These results, therefore, further confirm the previous results where the eb-NiOx PVSCs were shown to have smaller series resistance which leads to larger FF in device performance. In addition, the existence of more Ni3+ ions in eb-NiOx films is responsible for producing color centers.47-48 The coloring of the films is thus the result of defect-scattering caused by Ni3+ ions which leads to lower transmittance in eb-NiOx films and finally to lower Jsc in device performance.


14

Page 15 of 25 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 3. (a) Optical transmission spectra for ITO, and NiOx deposited on ITO via spincoating and e-beam evaporation. (b) Photoluminescence spectra of CH3NH3PbI3 on spincoated and e-beam evaporated NiOx on ITO. XPS spectra at (c) Ni 2p and (d) O 1s of the spin-coated and e-beam evaporated NiOx film. 4. CONCULSIONS In summary, we demonstrated an effective low-temperature, vacuum deposition process for NiOx HTLs for PVSCs via e-beam evaporation that overcomes several fundamental limitations of spin-coating. Device characterization shows that efficiency is on par with solution-processed methods, the highest efficiency at 15.4% with a noticeable increase in FF due to the more


15


Page 16 of 25

conductive NiOx films. More importantly, e-beam evaporation results in highly uniform devices with PCE values almost identical amongst the cells within one device. In addition, eb-NiOx PVSCs also show greater reproducibility compared to those of sc-NiOx PVSCs over several devices. Along with these advantages, e-beam evaporation of NiOx is a low-temperature process with prospects for large-area deposition, features that are highly advantageous for flexible and large-area PVSC manufacturing. The results presented here thus represent a step towards realizing large-area perovskite solar cells.

ASSOCIATED CONTENT Supporting Information. Cross-section SEM images of eb-NiOx and sc-NiOx, J-V curves of best performing cells, table of photovoltaic performance parameters under standard AM 1.5 illumination, IPCE spectra, Nyquist plot of best performing cells, equivalent circuit model to fit Nyquist plots and corresponding fitting results, J-V curves of 100 nm thick NiOx film PVSCs deposited via spin-coating, picture of sc-NiOx and eb-NiOx on ITO substrates, XPS of Ni 2p and O 1s spectra for sc-NiOx and eb-NiOx.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]

ORCID Byungha Shin: 0000-0001-6845-0305


16

Page 17 of 25 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


Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2012M3A6A7054855). This work was funded by Saudi AramcoKAIST CO2 Management Center.

REFERENCES (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) 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. (3) 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.; Gratzel, 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 (4) 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.


17


Page 18 of 25

(5) Burschka, J.; Pellet, N.; Moon, S. J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M. Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 2013, 499, 316-319. (6) Liu, M. Z.; Johnston, M. B.; Snaith, H. J. Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 2013, 501, 395-398. (7) Im, J. H.; Jang, I. H.; Pellet, N.; Gratzel, M.; Park, N. G. Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells. Nat. Nanotechnol. 2014, 9, 927932 (8) Nie, W. Y.; Tsai, H. H.; Asadpour, R.; Blancon, J. C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A.; Wang, H. L.; Mohite, A. D. High-efficiency solution-processed perovskite solar cells with millimeter-scale grains. Science 2015, 347, 522525. (9) Xie, F. X.; Zhang, D.; Su, H. M.; Ren, X. G.; Wong, K. S.; Gratzel, M.; Choy, W. C. H. Vacuum-Assisted Thermal Annealing of CH3NH3PbI3 for Highly Stable and Efficient Perovskite Solar Cells. ACS Nano 2015, 9, 639-646. (10) Wang, Y. L.; Dong, S. J.; Miao, Y.; Li, D.; Qin, W. J.; Cao, H. Q.; Yang, L. Y.; Li, L.; Yin, S. G. BCP as Additive for Solution-Processed PCBM Electron Transport Layer in Efficient Planar Heterojunction Perovskite Solar Cells. IEEE J. Photovolt. 2017, 7, 550-557. (11) Kim, H. S.; Jang, I. H.; Ahn, N.; Choi, M.; Guerrero, A.; Bisquert, J.; Park, N. G. Control of I-V Hysteresis in CH3NH3PbI3 Perovskite Solar Cell. J. Phys. Chem. Lett. 2015, 6, 4633-4639.


18

Page 19 of 25 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


(12) Shalan, A. E.; Oshikiri, T.; Narra, S.; Elshanawany, M. M.; Ueno, K.; Wu, H. P.; Nakamura, K.; Shi, X.; Diau, E. W. G.; Misawa, H. Cobalt Oxide (CoOx) as an Efficient HoleExtracting Layer for High Performance Inverted Planar Perovskite Solar Cells. ACS Appl. Mater. Inter. 2016, 8, 33592-33600. (13) Park, J. H.; Seo, J.; Park, S.; Shin, S. S.; Kim, Y. C.; Jeon, N. J.; Shin, H. W.; Ahn, T. K.; Noh, J. H.; Yoon, S. C.; Hwang, C. S.; Seok, S. I. Efficient CH3NH3PbI3 Perovskite Solar Cells Employing Nanostructured p-Type NiO Electrode Formed by a Pulsed Laser Deposition. Adv. Mater. 2015, 27, 4013-4019. (14) Yin, X. W.; Yao, Z. B.; Luo, Q.; Dai, X. Z.; Zhou, Y.; Zhang, Y.; Zhou, Y. Y.; Luo, S. P.; Li, J. B.; Wang, N.; Lin, H. High Efficiency Inverted Planar Perovskite Solar Cells with Solution-Processed NiOx Hole Contact. ACS Appl. Mater. Inter. 2017, 9, 2439-2448. (15) Kim, J. H.; Liang, P. W.; Williams, S. T.; Cho, N.; Chueh, C. C.; Glaz, M. S.; Ginger, D. S.; Jen, A. K. Y. High-Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution-Processed Copper-Doped Nickel Oxide HoleTransporting Layer. Adv. Mater. 2015, 27, 695-701. (16) Zhu, Z. L.; Bai, Y.; Zhang, T.; Liu, Z. K.; Long, X.; Wei, Z. H.; Wang, Z. L.; Zhang, L. X.; Wang, J. N.; Yan, F.; Yang, S. H. High-Performance Hole-Extraction Layer of Sol-GelProcessed NiO Nanocrystals for Inverted Planar Perovskite Solar Cells. Angew. Chem. Int. Edit. 2014, 53, 12571-12575. (17) Chen, W.; Wu, Y. Z.; Liu, J.; Qin, C. J.; Yang, X. D.; Islam, A.; Cheng, Y. B.; Han, L. Y. Hybrid interfacial layer leads to solid performance improvement of inverted perovskite solar cells. Energy Environ. Sci. 2015, 8, 629-640.


19


Page 20 of 25

(18) Wang, K. C.; Shen, P. S.; Li, M. H.; Chen, S.; Lin, M. W.; Chen, P.; Guo, T. F. LowTemperature Sputtered Nickel Oxide Compact Thin Film as Effective Electron Blocking Layer for Mesoscopic NiO/CH3NH3PbI3 Perovskite Heterojunction Solar Cells. ACS Appl. Mater. Inter. 2014, 6, 11851-11858. (19) Park, I. J.; Park, M. A.; Kim, D. H.; Park, G. D.; Kim, B. J.; Son, H. J.; Ko, M. J.; Lee, D. K.; Park, T.; Shin, H.; Park, N. G.; Jung, H. S.; Kim, J. Y. New Hybrid Hole Extraction Layer of Perovskite Solar Cells with a Planar p-i-n Geometry. J. Phys. Chem. C 2015, 119, 27285-27290. (20) Liu, Z. H.; Zhu, A. L.; Cai, F. S.; Tao, L. M.; Zhou, Y. H.; Zhao, Z. X.; Chen, Q.; Cheng, Y. B.; Zhou, H. P. Nickel oxide nanoparticles for efficient hole transport in p-i-n and n-i-p perovskite solar cells. J. Mater. Chem. A 2017, 5, 6597-6605. (21) Wang, K. C.; Jeng, J. Y.; Shen, P. S.; Chang, Y. C.; Diau, E. W. G.; Tsai, C. H.; Chao, T. Y.; Hsu, H. C.; Lin, P. Y.; Chen, P.; Guo, T. F.; Wen, T. C. p-type Mesoscopic Nickel Oxide/Organometallic Perovskite Heterojunction Solar Cells. Sci. Rep. 2014, 4, 4756. (22) Ho, P.; Bao, L. Q.; Cheruku, R.; Kim, J. H. Improved Performance of P-Type DSCs with a Compact Blocking Layer Coated by Different Thicknesses. Electron. Mater. Lett. 2016, 12, 638-644. (23) Jeng, J. Y.; Chen, K. C.; Chiang, T. Y.; Lin, P. Y.; Tsai, T. D.; Chang, Y. C.; Guo, T. F.; Chen, P.; Wen, T. C.; Hsu, Y. J. Nickel Oxide Electrode Interlayer in CH3NH3PbI3 Perovskite/PCBM Planar-Heterojunction Hybrid Solar Cells. Adv. Mater. 2014, 26, 4107-4113.


20

Page 21 of 25 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


(24) Chen, W.; Wu, Y. Z.; Yue, Y. F.; Liu, J.; Zhang, W. J.; Yang, X. D.; Chen, H.; Bi, E. B.; Ashraful, I.; Gratzel, M.; Han, L. Y. Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers. Science 2015, 350, 944-948. (25) You, J. B.; Meng, L.; Song, T. B.; Guo, T. F.; Yang, Y.; Chang, W. H.; Hong, Z. R.; Chen, H. J.; Zhou, H. P.; Chen, Q.; Liu, Y. S.; De Marco, N.; Yang, Y. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers. Nat. Nanotechnol. 2016, 11, 75-81 (26) Zhang, H.; Cheng, J. Q.; Lin, F.; He, H. X.; Mao, J.; Wong, K. S.; Jen, A. K. Y.; Choy, W. C. H. Pinhole-Free and Surface-Nanostructured NiOx Film by Room-Temperature Solution Process for High-Performance Flexible Perovskite Solar Cells with Good Stability and Reproducibility. ACS Nano 2016, 10, 1503-1511. (27) Jorgensen, M.; Norrman, K.; Krebs, F. C. Stability/degradation of polymer solar cells. Sol. Energ. Mat. Sol. C. 2008, 92, 686-714. (28) Yin, X.; Liu, J.; Ma, J.: Zhang, C.; Chen, P.; Que, M.; Yang, Y.; Que, W.; Niu, C.; Shao, J. Solvothermal derived crystalline NiOx nanoparticles for high performance perovskite solar cells. J. Power Sources 2016, 329, 398-405. (29) Zhang, H.; Cheng, J.; Li, D.; Lin, F.; Mao, J.; Liang, C.; Jen, A.; Gratzel, M.; Choy, W. Toward All Room-Temperature, Solution-Processed, High-Performance Planar Perovskite Solar Cells: A New Scheme of Pyridine-Promoted Perovskite Formation. Adv. Mater. 2017, 29 1604695.


21


Page 22 of 25

(30) Zhu, H.; Cheng, J.; Zhang, D.; Liang. C; Reckmeier, C.; Huang, H.; Rogach, A.; Choy, W. Room-Temperature Solution-Processed NiOx: PbI2 Nanocomposite Structures for Realizing High-Performance Perovskite Photodetectors. ACS Nano 2016, 10, 6808-6815. (31) Jiang, F.; Choy, W.; Li, X.; Zhang, D.; Cheng, J. Post-treatment-Free Solution-Processed Non-stoichiometric NiOx Nanoparticles for Efficient Hole-Transport Layers of Organic Optoelectronic Devices. Adv. Mater. 2015, 27, 2930-2937. (32) Park, J. H.; Seo, J.; Park, S.; Shin, S. S.; Kim, Y. C.; Jeon, N. J.; Shin, H. W.; Ahn, T. K.; Noh, J. H.; Yoon, S. C.; Hwang, C. S.; Seok, S. I. Efficient CH3NH3PbI3 Perovskite Solar Cells Employing Nanostructured p-Type NiO Electrode Formed by a Pulsed Laser Deposition. Adv. Mater. 2015, 27, 4013-4019. (33) Li, G.; Jiang, Y.; Deng, S.; Tam, A.; Xu, P.; Wong, M.; Kwok, H. Overcoming the Limitations of Sputtered Nickel Oxide for High-Efficiency and Large-Area Perovskite Solar Cells. Adv. Sci. 2017, 1700463. (34) Weber, S.; Rath, T.; Mangalam, J.; Kunert, B.; Coclite, A.; Bauch, M.; Dimopoulos, T.; Trimmel, G. Investigation of NiOx-hole transport layers in triple cation perovskite solar cells. J. Mater. Sci: Mater. Electron. 2017, DOI: 10.1007/s10854-017-8094-9 (35) Cui, J.; Meng, F.; Zhang, H.; Cao, K.; Yuan, H.; Cheng, Y.; Huang, F.; Wang, M. CH3NH3PbI3-based planar solar cells with magnetron-sputtered nickel oxide. ACS Appl. Mater. Interfaces 2014, 6, 22862-22870. (36) Wang, K.; Shen, P.; Li, M.; Chen, S.; Lin, M.; Chen, P.l Guo, T. Low-Temperature Sputtered Nickel Oxide Compact Thin Film as Effective Electron Blocking Layer for


22

Page 23 of 25 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


Mesoscopic NiO/CH3NH3PbI3 Perovskite Heterojunction Solar Cells. Appl. Mater. Interfaces 2014, 6, 11851-11858. (37) Wang, F.; Yu, H.; Xu, H. H.; Zhao, N. HPbI3: A New Precursor Compound for Highly Efficient Solution-Processed Perovskite Solar Cells. Adv. Funct. Mater. 2015, 25, 1120-1126. (38) Yu, H.; Wang, F.; Xie, F. Y.; Li, W. W.; Chen, J.; Zhao, N. The Role of Chlorine in the Formation Process of "CH3NH3PbI3-xCl(x)" Perovskite. Adv. Funct. Mater. 2014, 24, 71027108. (39) Abrusci, A.; Stranks, S. D.; Docampo, P.; Yip, H. L.; Jen, A. K. Y.; Snaith, H. J. HighPerformance Perovskite-Polymer Hybrid Solar Cells via Electronic Coupling with Fullerene Monolayers. Nano Lett. 2013, 13, 3124-3128. (40) Docampo, P.; Ball, J. M.; Darwich, M.; Eperon, G. E.; Snaith, H. J. Efficient organometal trihalide perovskite planar-heterojunction solar cells on flexible polymer substrates. Nat. Commun. 2013, DOI: 10.1038/ncomms3761 (41) Mansour, A.; Melendres, C. Characterization of Ni2O3⋅ 6H2O by XPS. Surface Science Spectra 1994, 3, 263-270. (42) Chen, Y. S.; Kang, J. F.; Chen, B.; Gao, B.; Liu, L. F.; Liu, X. Y.; Wang, Y. Y.; Wu, L.; Yu, H. Y.; Wang, J. Y.; Chen, Q.; Wang, E. G. Microscopic mechanism for unipolar resistive switching behaviour of nickel oxides. J. Phys. D Appl. Phys. 2012, 45, 065303. (43) Fasaki, I.; Koutoulaki, A.; Kompitsas, M.; Charitidis, C. Structural, electrical and mechanical properties of NiO thin films grown by pulsed laser deposition. Appl. Surf. Sci. 2010, 257, 429-433.


23


Page 24 of 25

(44) Reddy, A. M.; Byun, C. W.; Joo, S. K.; Reddy, A. S.; Reddy, P. S. Preparation and Characterization of Nickel Oxide Thin Films by Direct Current Reactive Magnetron Sputtering at Different Substrate Temperatures. Electron. Mater. Lett. 2014, 10, 887-892. (45) Guo, W.; Hui, K. N.; Hui, K. S. High conductivity nickel oxide thin films by a facile sol-gel method. Mater. Lett. 2013, 92, 291-295. (46) Hassan, A. Study of Optical and Electrical Properties of Nickel Oxide (NiO) Thin Films Deposited by Using a Spray Pyrolysis Technique. J. Mod. Phys. 2014, 5, 2184-2191. (47) Patel, K.; Desai, M.; Panchal, C.; Rehani, B. p-type transparent NiO thin films by e-beam evaporation techniques. J. Nano- Electron. Phys. 2011, 3, 376-382. (48) Pereira, S.; Goncalves, A.; Correia, N.; Pinto, J.; Pereira, L.; Martins, R.; Fortunato, E. Electrochromic behavior of NiO thin films deposited by e-beam evaporation at room temperature. Sol. Energ. Mat. Sol. C. 2014, 120, 109-115. (49) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells. Nat. Mater. 2014, 13, 897903.


24

Page 25 of 25 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 GRAPHICS


25

Improving Uniformity and Reproducibility of Hybrid Perovskite Solar

Recommend Documents