Impacts of Heterogeneous TiO2 and Al2O3 Composite Mesoporous

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Impacts of Heterogeneous TiO and AlO Composite Mesoporous Scaffold on Formamidinium Lead Trihalide Perovskite Solar Cells Youhei Numata, Yoshitaka Sanehira, and Tsutomu Miyasaka ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b11067 • Publication Date (Web): 26 Jan 2016 Downloaded from http://pubs.acs.org on January 29, 2016

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ACS Applied Materials & Interfaces

Impacts of Heterogeneous TiO2 and Al2O3 Composite Mesoporous Scaffold on Formamidinium Lead Trihalide Perovskite Solar Cells Youhei Numata*, Yoshitaka Sanehira, and Tsutomu Miyasaka* Graduate School of Engineering, Toin University of Yokohama, 1614 Kurogane-cho, Aoba, Yokohama, Kanagawa, 225-8503 Japan. Keywords, perovskite solar cell, formamidinium, metal oxide, composite material, carrier transport.

ABSTRACT

Heterogeneous TiO2 and Al2O3 composites were employed as a mesoporous scaffold in formamidinium lead trihalide (FAPbI3-xClx)-based perovskite solar cells to modify surface properties of a mesoporous layer. It was found that the quality and morphology of the perovskite film were strongly affected by the TiO2/Al2O3 ratio in the mesoporous film. The conversion efficiency of the perovskite solar cell was improved by using composite of TiO2 and Al2O3 in comparison with TiO2-based and Al2O3-based cells, yielding 11.0% for a cell with a 7:3

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TiO2/Al2O3 composite. Our investigation shows a change of electron transport path depending on a composition ratio of insulating Al2O3 to n-type semiconducting TiO2 in a mesoporous layer.

1. Introduction

Lead trihalide-based perovskite solar cells (PSCs) are one of the most promising candidates for next-generation solar cells in terms of high power conversion efficiency and significant merit in low-cost production. Since the first report of liquid junction type PSC in 2009,1 methylammonium lead trihalide (MAPbX3 X = I– and Br–) perovskite has been extensively used as visible light absorber on TiO2 films. All solid-state PSC was first made by our group in 2008,2 and its conversion efficiency was dramatically improved up to 10% in 2012,3,4 which accelerated the PSC research significantly. Today, the best conversion efficiency of PSCs reached approximately 20%,5–11 which is comparable to the value for commercial Si-based solar cells. High-efficiency PSCs using MAPbI3 perovskite as a light absorber enable short-circuit photocurrents (JSC) of these PSCs are as large as ~23 mA cm–2,12 which approaches the theoretical limit of the JSC value calculated using the photon absorption of MAPbI3 (onset: ~ 800 nm). To further increase the JSC and efficiency, a formamidinium (FA)-based perovskite has advantage over MAPbI3 in term of a wider absorption wavelength range up to 850 nm and shows higher stability.13–16 However, solution process to prepare uniform films of FA-based perovskite is generally more difficult than MAPbI3. Recently, the highest certified conversion efficiency of 20.1% was achieved based on FA-based perovskite solar cell by sequential method using with PbI2•DMSO as a precursor.10 Up to now, not only new precursor materials10,17 but also various methods of perovskite film preparation such as solution spin-coating,18–20 vapor deposition,21 and


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sequential solution treatment,22 have been energetically developed to optimize the quality of perovskite film. On the other hand, PSC devices can be roughly categorized into two: mesoscopic- and planartype.23 Mesoscopic PSCs comprise a fluorine-doped tin oxide (FTO) substrate, a compact layer, a mesoporous layer, lead (tin) trihalide perovskite, a hole transport layer (HTL), and a counter electrode (Figure 1). In contrast, the planar-type cell does not possess mesoporous layers and exhibits direct contact between the perovskite and semiconducting compact layer. Each device structure exhibits unique characteristics.24 Previously, Snaith and our group reported that the short-circuit voltage (VOC) of mesoscopic PSCs can be improved by using an Al2O3-based mesoporous layer.3 Doping25,26 and surface treatments27,28 of the mesoporous layer in PSCs have been performed to control the electronic properties of the mesoporous layer. However, heterogeneous metal-oxide film has been little examined as a mesoporous layer for PSCs, even though use of such heterogeneous films enable the control of the surface, electronic, and physicochemical properties of a mesoporous layer (e.g. the resistivity and surface wettability). Herein, we report the effects of heterogeneous TiO2 and Al2O3 composite mesoporous films on the photovoltaic properties and carrier transport of mixed halide FAPbI3-xClx-based PSCs. 2. Experimental Section 2.1. General methods All reagents and solvents were purchased from chemical companies (Tokyo Chemical Industry Co., Ltd, Wako Pure Chemical Industries, Ltd, and Sigma-Aldrich Japan). TiO2 paste (T/SP) was purchased from Solaronix. Al2O3 colloidal solution was purchased from Sigma-Aldrich. FTO glass substrates were bought from Peccel Technologies. 2.2. Experimental details 2.2.1. Preparation of Perovskite solutions


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Formamidinium iodide (FAI) was prepared according to the literature method.14 FA acetate was reacted with HI (55-58%) in ethanol (EtOH) solution for 2 h under dark condition. The solution was evaporated until minimal amount using with rotary evaporator. The solution was cooled down to r.t. and diethyether was added to precipitate pale yellow FAI crystals. The precipitates were filtrated and washed with diethylehter until residual acetic acid was completely removed. The solid was dissolved into hot EtOH and to the solution, diethylether was added. The mixture was kept in a refrigerator overnight. The pale yellow FAI crystals were filtrated by succoring funnel, washed with dietylether, and dried in vacuum dry oven. FAI and PbCl2 (3:1 in mol) were dissolved in DMF and stirred at 70°C for 1 h. 2.3. Device fabrication 2.3.1. TiO2/Al2O3 heterogeneous mesoporous substrate FTO glass substrate was etched by means of Zn powder and hydrochloric acid. The etched substrates were sequentially washed with EtOH, 5%, HellmanexTM (2%), and water by ultrasonic treatment for 15 min. TiO2 compact layer was prepared by dipping method. The etched FTO substrate was dipped into 20 mM TiCl4 aqueous solution at 70 °C for 1 h. The substrate was washed with mili-Q water and N2 browed to dry. The substrate was sintered by muffle furnace at 450 °C for 15 min. Heterogeneous TiO2 and Al2O3 mesoporous layer were prepared by spin coating method. TiO2 paste (particle size: 15 ~ 20 nm) or Al2O3 colloidal suspension (particle size: < 50 nm) were dispersed into EtOH (25 wt%). The suspensions were mixed as arbitrary ratio. The mixtures were casted onto the etched FTO substrate and spin-coated (3000 rpm for 40 sec). The as prepared films were dried at 150 °C for 10 min, and then, sintered at 500 °C for 20 min. 2.3.2. Perovskite film preparation


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Preparation of FAPbI3-xCl3x perovskite films were carried out in glove box. FAI and PbCl2 (1:3 molar ratio) were dissolved into N,N-dimethylformamide (DMF) (1 M) and stirred at 70 °C for 30 min. The precursor solution was poured onto the mesoporous substrate, which temperature kept 70°C and spin-coated (kept for 60 sec, 3000 rpm for 40 sec, and 5000 rpm for 10 sec with toluene dripping). The as prepared film was annealed at 155 °C for 90 min. 2,2',7,7'tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) (10 wt%) was dissolved in DMF and stirred at 70 °C for 1 h. The solution was cooled to r.t., and 4-tertbutylpyridine (0.020 M) and a stock solution of LiTFSI (0.063 M) in acetonitrile were added as an additive and oxidizing agent. On the perovskite films, HTM solution was spin-coated (4000 rpm for 30 sec) and kept under dry and dark condition overnight to promote oxidation. Gold was vacuum-evaporated onto the HTL as a counter electrode. For an optimized cell based on T/A 7:3, FTO substrates were dipped into TiCl4aq four times to obtain a thick and pinhole-less CL. To make HTL thinner, spin speed was accelerated to 6000 rpm, and to the HTM solution, a solution of FK102 in MeCN (10 mol%) was added as an oxidizing agent. 2.4. Measurements 2.4.1. SEM and EDX measurements SEM images and EDX measurements were performed by SU8000 (Hitachi HighTechnologies Co.) equipped with the X-ray detector (E-MAX80, HORIBA, Ltd.). XRD patterns were measured by D8 DISCOVER (Bruker-AXS K. K.) with Cu Kα radiation under operation condition of 40kV, 40mA. 2.4.2. Photovoltaic measurements Cell active area (3 × 3 mm2) was defined by a black metal mask. J-V curves were recorded using with PEC-L01 solar simulator (Peccell Technologies) under AM1.5G condition


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(100 mW cm–2). Measurement condition; Step voltage: 0.01 V, search delay: 0.05 sec, and hold time: 0.1 sec. Incident photon-to-current conversion efficiency (IPCE) spectra were observed by PEC-S20 spectrometer (Peccell Technologies). 2.4.3. Photocurrent response measurements Photocurrent responses were recorded using the same cell with photovoltaic measurements and equipments (Peccel Technologies) under 1 or 0.5 Sun with 0 or 0.3 V bias conditions. 2.4.4. Transmittance and absorption spectra measurements Transmittance of the TiO2/Al2O3 composition films and absorption spectra of FAPbI3-xClx on the TiO2/Al2O3 composition films were measured using with UV-1800 spectrometer (SHIMADZU).

3. Results and Discussion 3.1. Characterization of TiO2/Al2O3 composite mesoporous films On a FTO substrate coated with TiO2 compact layer, heterogeneous TiO2/Al2O3 composite mesoporous films were deposited. Precursor colloidal suspensions with various TiO2 and Al2O3 ratios were prepared by mixing corresponding suspensions in EtOH (25 wt%). Here, the average particle sizes of TiO2 and Al2O3 were 30 and 20 nm, respectively. The suspensions were casted onto the FTO substrate by spin coating and sintered at 500 °C for 15 min. The obtained composite mesoporous films were characterized by grazing incidence-X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) measurements. Selected XRD peaks of the mesoporous metal oxide films are shown in Figure 2. To observe the changes in the composite ratio, the (101) and (200) peaks of anatase-TiO2 at 25.28° and 48.05°, and the (400) peak of Al2O3 at 45.67° were selected as distinguishing peaks. At 26.58° and 42.62°, the (110) and (210)


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peaks of SnO2 (FTO) were observed. By increasing the Al2O3 ratio, the TiO2 peaks at 25.28° and 48.05° gradually decreased and finally disappeared, whereas the Al2O3 peak (45.67°) increased. The ratio of TiO2 to Al2O3 in the composite films was estimated by EDX measurements. For the mixed mesoporous layers, the abundance of Ti and Al ions in the composite films of 7:3, 5:5, and 3:7 are 41:59, 29:71, and 15:85, respectively. The metal ions in the composite film exist as TiO2 and Al2O3; thus, the composition ratios of TiO2 to Al2O3 are 41:30, 29:36, and 15:43, respectively. 3.2. Perovskite film preparations We prepared mixed-halide FAPbI3-xClx perovskite films by a one-step procedure using PbCl2 and FAI, as the chloride ion in the precursor solution can improve the quality of the perovskite films.3,29,30 The films were prepared in a nitrogen atmosphere. A solution containing FAI and PbCl2 (molar ratio of 3:1) in DMF was spin-coated on the mesoporous layer. To obtain uniform perovskite films, we used a toluene dripping method that was previously reported.18 The asprepared films were annealed at 155 °C for 90 min to form black FAPbI3-xClx films. The quality of the perovskite films was evaluated by XRD measurements. The XRD patterns of the perovskite films casted on the different TiO2/Al2O3 composite mesoporous films are shown in Figure 3. The XRD patterns exhibited essentially the same peak distributions for all the perovskite films, indicating that perovskite films of the same crystalline quality were formed on different composite mesoporous substrates. The absence of impurities such as yellow δ-FAPbI3,8 PbI2, and PbCl2 indicates that the films were dominantly composed of pure FAPbI3-xClx perovskite. Compared the XRD pattern of FAPbI3-xClx perovskite with that of pure FAPbI3 film prepared by sequential method, no significant difference was observed (Figure S2).


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Figure 4 shows top-view SEM images of perovskite films prepared on TiO2 and Al2O3 mesoporous films with or without toluene dripping during the spin coating.18 Perovskite film on the TiO2 without toluene drip (Figure 4a) showed poor surface coverage and exhibited island like crystal shapes. With toluene dripping (Figure 4b), surface coverage was improved and the crystals were connected each other to. In contrast, the perovskite film on the Al2O3 mesoporous film with and without toluene drip showed better surface coverage compared to those on the TiO2 mesoporous films. With toluene dripping, large crystalline lumps are reduced, and although pinholes still remain, the film become homogeneous (Figure 4d). Figure 5 shows cross-sectional SEM images of the PSCs based on the different T/A composite films. Thicknesses of all mesoporous layers are ranging in approximately 300 ± 50 nm. Surface of capping layers (perovskite layer) are very rough. Thickness of a capping layer of the TiO2 based cell is ca. 200 nm, which is thinner than other cells and HTL directly contact to the mesoporous layer. To investigate a difference in surface state of the composite mesoporous films, contact angle measurement was carried out for TiO2/Al2O3 composite mesoporous films with different composition ratios. To obtain the contact angle data under same condition with perovskite film casting (vide infra), the mesoporous films were treated by UV-ozone for 10 min and heated at 70 °C before measurements. A test drop was the precursor solution of the perovskite. For the all substrates, contact angles were not measurable (0 °), indicating that surface wettability does not exhibit essential difference in the macroscopic scale. 3.3. Photovoltaic properties Figure 6 shows photocurrent density-voltage (J-V) curves and the incident photon-to-electricity conversion efficiency (IPCE) spectrum for the FAPbI3-xClx solar cells. The photovoltaic parameters are summarized in Table 1. Hysteretic J-V curves, which are typical for PSCs, were


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observed for all types of the cells on different mesoporous substrates. Because the extent of the hysteresis varied according to the composition ratio of TiO2 to Al2O3, we separately discuss the photovoltaic properties for forward scans in the JSC → VOC direction and reverse scans in the VOC → JSC direction. To take the average J–V performance, five cells were measured for each TiO2/Al2O3 composition. For the forward scans (Figure 6a), an increase in the Al2O3 ratio of the mesoporous layer caused the JSC values to increase from 11.4 ± 1.7 to 18.4 ± 3.1 mA cm–2. As described above, the SEM image of the TiO2-based FA perovskite shows many voids and poor surface coverage on the TiO2 films, and the capping layer is thin compared with those of other cells (Figure 4 and 5). Therefore, the low photocurrent density of the pure TiO2-based cells is attributed to poor light absorption. It is expected that the surface wettability of the mesoporous layer is improved by the addition of Al2O3 into the TiO2, yielding thick perovskite capping layers and better surface coverage. Figure 6d shows absorption spectra of FAPbI3-xClx perovskite films on the different TiO2/Al2O3 composition films. In visible region, absorbance of perovskite films decreased with decrease of TiO2 ratio, which is well matched with the order of JSC values. In near infrared region, absorbance of perovskite films on the TiO2-containing mesoporous films were increased compared with that on the Al2O3 mesoporous film. This is attributed to the absorption of the TiO2-containing mesoporous films (Figure S3). On the other hand, the VOC values were not significantly changed by increasing the Al2O3 ratio of the mesoporous layer, except in the pure Al2O3-based device, which exhibited a large decrease in VOC due to the low fill factor (FF). The FF was remarkably affected by the Al2O3 ratio in the mesoporous layers. When the Al2O3 ratio was increased in the mesoporous layer, the FF decreased from 0.41 ± 0.04 to 0.17 ± 0.06. Interestingly, the reverse scans did not exhibit a large difference in JSC values compared with the forward scans (Figure 6b). The VOC values and FF improved as well. This phenomenon is often


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observed in hysteretic PSCs; however, its origin remains unclear. The maximum conversion efficiency was 7.5 ± 0.8% (best efficiency: 8.7%) in a reverse scan for the cell with a T/A (7:3) composite film. Figure 6c shows the IPCE spectrum of a PSC based on a T/A (7:3) mesoporous layer. The IPCE onset reaches ~850 nm. The JSC value calculated using the IPCE is 17.3 mA cm– 2

, which agrees well with that of the J-V curve. By the further optimization of the CL and HTL

on the T/A (7:3) mesoporous layer, a conversion efficiency of 10.4% with JSC = 18.49 mA cm–2, VOC = 0.92 V, and FF = 0.61 in a forward scan and η = 11.0% with JSC = 18.03 mA cm–2, VOC = 0.93 V, and FF = 0.65 in a reverse scan were achieved. 3.4. Carrier transport properties To reveal impacts of the composition ratio of TiO2 to Al2O3 on carrier transport of the PSCs, photocurrent responses were investigated on TiO2, T/A 5:5, and Al2O3-based cells. Figure 7 shows photocurrent responses measured with 0 or 0.3 V bias under 1 or 0.5 Sun conditions for the TiO2, T/A 5:5, and Al2O3-based cells. Light irradiation profile is as follows: under dark condition for 60 sec, light irradiating for 300 sec (for the Al2O3, 0 V and 1 Sun measurement: 900 sec), and light turned off and under dark condition for 60 sec. For the TiO2-based cell, the photocurrent quickly increased after light irradiation and the current was steadily observed as shown in Figure 7a under all conditions. For the Al2O3-based cell, the photocurrent gradually increased after light irradiation and reached to a maximum under 1 Sun with 0 V bias condition. Then, the photocurrent continuously decreased for a longer period compared to others (Figure 7c and S4). Photocurrent response of the T/A 5:5 film-based cell showed middle between these two cells. After the light irradiation, the photocurrent increased gradually as well as Al2O3-based cell, and then, the photocurrent was maximized and showed plateau as well as the TiO2-based cell. Under 0.5 Sun condition, the decrease in photocurrent was not observed for all cells. It is


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expected that under intense light irradiation condition, when electron generation rate exceeded electron injection rate into the electrode, a part of electrons accumulated at the interface between perovskite and the electrode or grain boundaries, suppressing electron injections into the electrode due to the charging at the interfaces. From the result of photocurrent response measurements, influences of the composite ratio of mesoporous film on carrier transport path are expected. Figure 8 shows expected electron transport path in the PSCs based on different composition ratio mesoporous films. In a TiO2based PSC, photogenerated electrons quickly injected into the meso-TiO2 reach the TCO electrode due to the wide interface between perovskite and TiO2. However, Al2O3-based PSCs, differ considerably: because of the insulation of the Al2O3, the electrons are transported exclusively through the perovskite to the TCO electrode. Furthermore, the interfacial area between perovskite and FTO (and TiO2 for other cells) is very limited compared to the TiO2based cell, decreasing electron injection per unit of time from the perovskite to the electrode. In the heterogeneous composite mesoporous layer, it is expected that increase of the Al2O3 ratio reduces the effective carrier path in the mesoporous layer. This may allow some of the electrons to travel through the perovskite to the TCO electrode. During the transportation of the electrons in the perovskite to the FTO electrode, the electrons must cross many grain boundaries. As a result, the low FF that accompanies the high Al2O3 content of the composite layer is assumed to reflect the increased internal resistance (Table 1). Additionally, difference of J–V curves between forward and reverse scans (hysteresis) become larger with increasing Al2O3 content in the mesoporous film (Figure S5). It is reported that origin of the hysteretic behavior is attributed to interface structures,31–33 difference in carrier balance,34,35 or ion migration.36–38 Our result implies that carrier injection rate at the interface between perovskite and mesoporous layer and/or TiO2


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CL dominates the hysteresis of J–V curves. Sometimes hysteretic behavior is empirically observed even though TiO2 mesoporous layer is used. It can be explained based on our assumption. When micro cracks or void exist at the interface between perovskite and mesoporous layer, carrier injection path is limited similar with Al2O3 addition and hysteretic behavior of J–V curve is expected. 4. Conclusion In conclusion, we demonstrated for the first time that the crystal morphology of FAPbI3-xClx perovskite and the photovoltaic property of its PSCs can be improved using a heterogeneous TiO2/Al2O3 composite as a mesoporous scaffold. By increasing the Al2O3 ratio in the composite mesoporous film, the JSC value was improved compared with that of pure TiO2-based solar cells. In contrast, because the series resistance was increased by increasing the Al2O3 ratio in the mesoporous layer, the FF value gradually deteriorated. As a result, the TiO2/Al2O3 (7:3) composite-based mesoporous film yielded the best conversion efficiency (6.6% in a forward scan and 8.7% in a reverse scan) among the various films tested exhibiting an improvement of 70% compared with the efficiency of a pure TiO2-based cell. By optimizing the CL and HTL, η = 10.4% in a forward scan and 11.0% in a reverse scan were achieved. Photocurrent response measurement implies that electron injection from the perovskite to electron collecting electrode is significantly affected by the T/A ratio of the mesoporous film. We will continuously attempt to optimize the cell fabrication, and a study about the relationship between mesoporous composite and hysteretic behavior of J-V curves is in progress.


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Figure 1. Device structure of mesoscopic FAPbI3-xCl3x perovskite solar cell. CL; compact layer.

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Figure 3. XRD patterns of FAPbI3-xClx perovskite solar cells based on TiO2/Al2O3 composite mesoporous layer. Squares indicate expected impurity peaks.


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Figure 5. Cross-sectional SEM images of FAPbI3-xClx-PSC devices based on (a) TiO2, (b) T/A 7:3, (c) T/A 1:1, (d) T/A 3:7, and (e) Al2O3 substrates.

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(c)

Photocurrent (a.u.)

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


Al2O3

0

200 300 400 Time (sec) Figure 7. Photocurrent responses of (a) TiO2, (b) T/A 5:5, and (c) Al2O3 mesoporous film-based PSCs. Red (bias = 0 V), blue (bias = 0.3 V), solid line (1 Sun), and dashed line (0.5 Sun). Black lines are tangent lines at maximum photocurrent values.

TiO 2 e– e–

100

Al2O 3

– e– e

e–

e–

– e– e

e–

e–

e–

e–

TiO 2

TiO 2 rich

Al2O 3 rich

FTO Al2O 3

Figure 8. Expected electron transport in PSCs based on mesoporous films with different T/A composition ratio.

Table 1. Photovoltaic properties of PSCs based on T/A composite mesoporous films.


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T/A ratio 10:0

JSC (mA cm–2) 11.4 ± 1.7

7:3

17.0 ± 1.0

5:5

16.5 ± 2.7

3:7

18.7 ± 1.5

0:10

18.4 ± 3.1

VOC (V)

Forward scans FF

0.71 ± 0.04 0.75 ± 0.05 0.64 ± 0.05 0.73 ± 0.06 0.60 ± 0.05

0.41 ± 0.04 0.40 ± 0.02 0.29 ± 0.04 0.27 ± 0.02 0.17 ± 0.06

η (%)

RS (Ω)

3.4 ± 0.9

179 ± 52

5.2 ± 0.8

168 ± 26

3.2 ± 1.1

304 ± 73

3.7 ± 0.6

298 ± 35

2.0 ± 1.1

1199 ± 271

JSC (mA cm–2) 11.2 ± 1.9 16.5 ± 0.6 16.4 ± 2.7 17.1 ± 1.1 16.0 ± 2.8

VOC (V) 0.75 ± 0.03 0.82 ± 0.02 0.79 ± 0.03 0.87 ± 0.04 0.83 ± 0.03

Page 18 of 25

Reverse scans FF 0.51 ± 0.04 0.55 ± 0.03 0.48 ± 0.02 0.50 ± 0.02 0.46 ± 0.02

η (%)

RS (Ω)

4.4 ± 1.2

121 ± 22 84 ± 8

7.5 ± 0.8 6.2 ± 1.1 7.4 ± 1.0 6.1 ± 1.3

147 ± 22 126 ± 13 333 ± 69

Photovoltaic data is average values of five cells. Cell area: 9 mm2.

ASSOCIATED CONTENT Supporting Information EDX and XRD data of the TiO2/Al2O3 composite mesoporous films, and J–V curves for forward and reverse scans. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *Y. Numata. E-mail: [email protected]. *T. Miyasaka. E-mail: [email protected]. Note The authors declare no competing financial interest. ACKNOWLEDGMENT This study was supported by Japan Science and Technology Agency (JST) Advanced Low Carbon Technology R&D program (ALCA). T. M. appreciates Grant-in-Aid for Scientific


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ic h 3 r O l 2 A

T iO 2

Al2O3

rich

10 µm

TiO2

FAPb(I–Cl)3

10 µm

TiO2/Al2O3 heterogeneous composite mesoporous layer


25

Impacts of Heterogeneous TiO2 and Al2O3 Composite Mesoporous

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