Facilitating Electron Transportation in Perovskite Solar Cells via Water

Subscriber access provided by The Library | University of Bath

Article

Facilitating Electron Transportation in Perovskite Solar Cells via Water-Soluble Fullerenol Interlayers Tiantian Cao, Zhao-Wei Wang, Yijun Xia, Bo Song, Yi Zhou, Ning Chen, and Yongfang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b04895 • Publication Date (Web): 17 Jun 2016 Downloaded from http://pubs.acs.org on June 20, 2016

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 30

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

Facilitating Electron Transportation in Perovskite Solar Cells via Water-Soluble Fullerenol Interlayers Tiantian Cao, ‡ Zhaowei Wang, ‡ Yijun Xia, Bo Song,* Yi Zhou,* Ning Chen* and Yongfang Li Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China.

ABSTRACT TiO2 is widely-used in perovskite solar cells (Pero-SCs), but its low electrical conductivity remains a drawback for the application in electron transport layer (ETL). To overcome this problem, an easy-accessible hydroxylated fullerene, fullerenol, was employed herein as ETL modified on ITO in n-i-p type (ITO as cathode) Pero-SCs for the first time. The results showed that the insertion of a single layer of fullerenol between perovskite and TiO2 dramatically facilitates the charge transportation and decreases the interfacial resistance. As a consequence, the device performance was greatly improved, and a higher power conversion efficiency of 14.69% was achieved, which is ~17.5% enhancement comparing with that (12.50%) of the control device without the fullerenol interlayer. This work provides a new candidate of interfacial engineering for facilitating the electron transportation in Pero-SCs.

KEYWORDS Perovskite solar cells, electron transport layer, fullerenol, fullerene derivatives, charge extraction efficiency, interfacial resistance.

ACS Paragon Plus Environment

1


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 30

INTRODUCTION High-efficiency photovoltaics that converts solar energy into electrical power could meet the requirement of sustainable development.1 Very recently, organometal halide perovskite solar cells (Pero-SCs) have become research focus owing to their comparable power conversion efficiencies (PCEs) to Si-based solar cells.2 Perovskite was first employed in solar cells by Miyasaka and co-workers in 2009.3 The genuine work, however, was developed by Park and Grätzel et al in 2012, in which solid Spiro-MeOTAD was adopted instead of the liquid electrolyte and a greatly enhanced PCE of 9.7% was achieved.4 It is now widely acknowledged that perovskite, as photoabsorber, possesses remarkable features, for example, large absorption coefficient, small exciton binding energy, high charge mobility and long carrier diffusion length.5-11 Up-to-date, the highest reported PCE of Pero-SCs has reached 22.1%.12 This high efficiency of Pero-SCs promises a potential prospect for commercialization. Many efforts, such as interface manipulation,13-17 structure optimization, and perovskite film deposition, have been made to improve the performance of Pero-SCs.18-22 For n-i-p type PeroSCs, TiO2 was often used as electron transport layer (ETL). However, the low electrical conductivity of TiO223 would in some extent restrict the electron transportation and result in charge accumulation. To address this problem, a number of valuable studies have been devoted to developing more efficient electron transport materials (ETMs).24-29 For example, Jen and coworkers employed C60-SAM on the TiO2 mesoporous structure to facilitate the electron extraction.30 For planar Pero-SCs, Gong et al found that the insertion of [6, 6]-Phenyl-C61-butyric acid methyl ester (PCBM), between compact TiO2 and perovskite layers could efficiently enhance the electron transportation. However, due to the poor wettability of PbI2 on PCBM, insufficient coverage of perovskite film was obtained.31 A thin layer of carboxylic-group-


2

Page 3 of 30

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


functionalized water-soluble C60 was introduced on top of the PCBM layers for tailoring the surface wettability. After the alternation, the PCE of Pero-SCs increased ~11%. These results indicate that an interlayer of fullerene derivatives between TiO2 and perovskite layers could lead to improvement of performance of Pero-SCs. Recently, an easily-accessible water-soluble fullerene derivative, fullerenol, has drawn extensive attention because of its promising application in visible-light sensitizer,32 biomedical materials33 and fuel cells.34 Fullerenol has advantages such as one-step synthetic process from C6033 and the good solubility in water,35 as well as the excellent electron mobility.36 These features make fullerenol applicable to

electron transport material in the solar cells. Very

recently, fullerenol was proved to be a promising interfacial material for organic solar cells, with which the performance of the organic photovoltaic devices were improved.37 This result shed light on the application of fullerenol in the solar cell devices. Nevertheless, up to now, fullerenol has never been applied as buffer layer in Pero-SCs. In this study, we report a facile method which could facilitate the electron transportation and engineer the surface wettability by introducing one material. For the first time, an easyaccessible hydroxylated C60, fullerenol, was introduced as an interlayer sandwiched between TiO2 and perovskite layers. The excellent electron conductivity of fullerenol resulted in significantly enhanced electron transfer from perovskite to TiO2. Thus, the device performances in terms of detailed characteristics were improved and a high PCE of 14.69% was thus obtained. Studies of device physics demonstrated that insertion of fullerenol could lead to a high interfacial electron transfer rate between perovskite and cathode, high crystallinity of perovskite film, and in turn, decreased interfacial resistance and improved electron transportation at ETL/perovskite interfaces.


3


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 30

EXPERIMENTAL SECTION Materials C60

(99.5%)

was

purchased

from

Dade

Carbon

Nanotechnology

Co.,

Ltd.,

Tetrabutylammonium Hydroxide (TBAH, 40% in water) and NaOH (AR) were bought from Adamas Reagent Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd., respectively. Toluene (AR) was bought from Chinasun Specialty Products Co., Ltd., and filtrated before use. Methylammonium iodide (MAI) was synthesized in our laboratory according to the previous published literature.38 PbCl2 (99.999%) and DMF (99.8%) were purchased from Alfa-Aesar and Acros, respectively. Fabrication of Devices ITO substrates were sequentially rinsed in detergent, ultrapure water, acetone, ethanol and isopropanol by sonification each for 15 min, and then treated with UVO for 15 min to generate a hydrophilic surface after being dried in a nitrogen stream. TiO2 precursor was obtained by mixing 35 µL of HCl (2 mol/L) to 2.5 mL anhydrous ethanol, and then adding 350 µL titanium isopropoxide to the mixture. The obtained TiO2 solution was filtrated before spin-coating on top of the substrate at 2000 rpm for 50 s. The substrate was sintered at 500 °C for 30 min to obtain a compact TiO2 layer. After being dried at 120 °C for 15min, the fullerenol layer was covered on compact TiO2 by spin-coating and the substrates were then transferred into a glovebox for the following operations. The perovskite precursor solution was prepared by the dissolution of both MAI and PbCl2 (99.999%, Alfa) [molar ratio of MAI: PbCl2 = 3:1] in the anhydrous N, Ndimethylformamide (DMF, 99.8%, Acros). The obtained 40 wt% precursor solution was stirred at 60 °C for 12 h and stored in glovebox, then filtrated by a 0.45 µm filter before use. Perovskite precursor solution was spin-coated at 3000 rpm for 50 s and then annealed at 105 °C for 80 min.


4

Page 5 of 30

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


P3HT (30 mg/mL, J & K) was firstly dissolved in 1 mL of ortho-dichlorobenzene (o-DCB) and then mixed with 10.2 µL of 4-tert-butylpyridine (tBP, TCI) and 20.4 µL of Li-TFSI/acetonitrile (28.3 mg/mL, Aldrich) . This solution was further spin-coated on perovskite layer as hole transport layer (HTL) at 1500 rpm for 50 s. Finally, MoO3 (7 nm) and Ag (100 nm) were sequentially deposited by vacuum evaporation at ~ 10-4 Pa. A shadow mask was used to fix an active area of 0.0314cm2 of the sample. The devices for direct current conductivity were fabricated in a configuration of ITO/TiO2/Au and ITO/TiO2/fullerenol/Au. Au electrode (~ 80 nm) was deposited under a vacuum of ~ 10-4 Pa. Measurement and characterization Fourier Transform Infrared Spectrometer (FTIR) spectra were carried out on Bruker VERTEX 70V (Germany). Thermal gravimetric analysis (TGA) was measured on a Perkin-Elmer Pyris 6. Work function (WF) was measured in air by peak-force Kelvin probe force microscope (KPFM) mode. The current density-voltage (J-V) curves were recorded on Keithley 2400 source meter unit under simulated Air Mass 1.5 global (AM 1.5G) solar illumination with power of 100 mW/cm2 and measured in the glovebox. The incident photo-to-current conversion efficiency (IPCE) was collected on a measurement system (Enli Technology Co., Ltd., QE-R3011) in air. A spectroscopic ellipsometer (M-2000V, J.A. Woollam Co., USA) was used to measure the thicknesses of fullerenol films. The contact angles were recorded with an optical contact angle measurement instrument (Krüss DSA100, Germany). Scanning electron microscopy (SEM) images were collected on S-4700 produced by Hitachi. X-ray diffraction (XRD) patterns were recorded on a desktop diffractometer (D2 PHASER, Bruker, Germany). UV-vis spectra were measured by Cary 6000 (Agilent). Steady-state and transient photoluminescence (PL) spectra were both recorded on FLS980 (Edinburgh Instrument, UK). Transient PL spectra was


5


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

performed on Lifespec Ⅱ

Page 6 of 30

(Edinburgh Instrument, UK) with picosecond light pulser

(Hamamatsu). The alternating current impedance spectrometry (ACIS) characterization was measured by IM6 electrochemical workstation (Zahner Zennium, Germany) with a bias voltage near the respect Voc of the devices in dark condition. The effective area of the cell is 0.1842 cm2. The Z-view software was used to fit the impedance spectra to obtain the impedance parameters. RESULT AND DISCUSSION Fullerenol was synthesized by a one-step reaction.39 The details refer to the supporting information. As shown in Figure 1a, C60 (OH)24-26 was prepared from C60 reacting with NaOH in the presence of TBAH. As indicated in the FTIR spectrum of the resulting product (Figure S1, in supporting information), the characteristic vibration bands at 3310, 1590, 1368 and 1066 cm-1 could be assigned to ν O-H, ν C=C, δs C-O-H, and ν C-O vibrations, respectively.39,

40

The

appearance of these peaks confirmed the formation of hydroxylated C60. The fullerenol was dissolved in deionized water. FTIR spectroscopy was used to study the thermal stability of fullerenol. The similar spectra (Figure S2) before and after heating the samples to 120 °C indicate that no noticeable decomposition was observed. The obtained fullerenol showed excellent solubility in water and demonstrated a high thermal stability indicated by TGA (Figure S3 in supporting information) with decomposition temperature of 330 °C.


6

Page 7 of 30

(a)

(b)

(c)

-3.0

-3.20

-3.5 -3.93

-4.0

E (eV)

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


-4.5 -5.0

-4.35

-4.27 -4.60

-4.75

-5.5

-5.20 -5.44

-5.30

-6.0

Figure1. (a) The synthetic route of fullerenol. (b) Device configuration of Pero-SCs incorporated with Fullerenol as the ETL. (c) The corresponding energy level of the device materials. Figure1b & 1c present the device structure and energy level diagram of the Pero-SCs. The performances of Pero-SCs varied with the concentration of the fullerenol (i.e. corresponding to the thickness of the fullerenol film) as presented in the J-V characteristics of Figure S4, and the detailed characteristics of the Pero-SCs with/ without fullerenol ETLs are summarized in Table 1. To make a parallel comparison, except for the concentration of fullerenol, the devices were fabricated under same conditions. As reported by Zhang et al., the thickness of the buffer layers can affect the performance of the devices.41 Therefore, herein the thickness dependent photovoltaic performance were also investigated. As shown in Table 1, the PCEs of Pero-SCs increased in the beginning, and then decreased with the increasing thickness of fullerenol ETL layer. A PCE summit of 14.69% appears at the thickness of ~ 1.5 nm, in which the open circuit voltage (Voc) was 0.95 V, short circuit current density (Jsc) and fill factor (FF) were 20.91


7


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 30

mA/cm2 and 71.5%, respectively. In contrast, the control device without fullerenol only showed PCE of 12.50%, with Voc, Jsc and FF of 0.92V, 19.96 mA/cm2 and 65.4%, respectively. These results show that, with the insertion of fullerenol layer, the PCE of the device was notably enhanced by 17.5%, and the increase of PCE is contributed by the increase of Voc, Jsc and FF. As indicated by our recent results, C60 can also facilitate the electron transfer.42 Nevertheless, the PCE of the fullerenol-based devices was still slightly higher than that of C60-based devices (Table 1). In some extent, the Voc of Pero-SCs depends on the work function difference of two electrode contacts.43 Thus, in this study, the increase of Voc could be attributed to the lower work function of ITO/TiO2/Fullerenol (4.27 eV, Figure 1b measured by KPFM) compared with that of ITO/TiO2 (4.35 eV, Figure 1b measured by KPFM), where the decreased energy barrier between the work function of ITO/TiO2/Fullerenol electrode and the LUMO of perovskite decreases the energy loss during the electron transfer and collection. To verify the Jsc enhancement of fullerenol based devices, the J-V curves and the corresponding IPCE spectra of two typical devices with (0.5 mg/mL) / without fullerenol ETL are depicted in Figure 2a and 2b. As aforementioned, fullerenol can though enhance the performance of devices, shows a moderate decrease in hysteresis. (Figure S5 & Table S1 in supporting information) Figure 2b showed that the integrated photocurrent estimated from IPCE curve was 20.3 mA/cm2 and 19.3 mA/cm2 for two devices with / without fullerenol ETL, which is comparable to the corresponding Jsc. Moreover, the device with the fullerenol ETL demonstrates a higher IPCE, especially in 550-750 nm, and the maximum IPCE of the devices with fullerenol interlayer exceeded 90%. This higher IPCE may benefit from more efficient


8

Page 9 of 30

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


electron collection and less charge recombination through the insertion of fullerenol interlayer, which in turn, give rise to a higher Jsc. To further explore the effect of fullerenol layer on performance of the devices, especially on the enhancement of Jsc and FF, the dark J-V characteristics and photocurrent density (Jph) – effective voltage (Veff) plots were measured. Figure 2c showed that the devices with fullerenol layer possess smaller leakage current than the pristine TiO2 layer at negative voltages. The lower dark current indicates a decreased series resistance, which could prevent the current from leakage and is beneficial for the improvement of Jsc and FF. Figure 2d presented the Jph-Veff plots in double-logarithmic coordinates, which represents the effect of fullerenol layer on the Jph. The Jph is determined by the equation Jph = JL – JD, in which JL is the current densities under illumination and JD is the current densities in the dark. The Veff is calculated from the equation Veff = V0 – V. (V is applied voltage and V0 is the voltage at which Jph = 0)44, 45 Figure 2d shows the Jph of both devices possess similar trend as it first increases linearly with Veff (Veff < 0.1 V) and then reaches a saturated level at more than 1 V. Moreover, the Pero-SCs with the fullerenol layer demonstrate higher Jph at a small Veff than that based on pristine TiO2, which indicates a higher charge extraction efficiency and consequently, a higher FF.46


9


0

100

Without Fullerenol With Fullerenol

IPCE (%)

2

15

-10 -15

60 10

40

5

20

-20 0.0

0.5

0 300

1.0

V (V)

400

1

10

500

600

0 800

700

Wavelength (nm)

2

10

Intergrated Jsc (mA/cm )

20 80

2

J (mA/cm )

-5


0

10

2

Jph (mA/cm )

10

2

J (mA/cm )

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 30

-1

10

-2

10

-3

10


-4

10

1

-5

10

-1.0

-0.5

0.0

0.5

1.0

1.5

V (V)

0.1

1

Veff (V)

Figure 2. (a) Typical J-V curves, (b) IPCE spectra of devices with and without fullerenol ETL, (c) J-V characteristics plotted on a semilog scale and measured in the dark with the voltage scanned from 1.5 V to -1.0 V, scan step of 0.02 V and delay time of 200 ms. (d) Plots of Jph-Veff for different devices.


10

Page 11 of 30

Table 1. The photovoltaic performances of Pero-SCs Concentration (mg/mL)

Thickness Voc (V)

Jsc (mA/cm2)

FF (%)

PCE (%)

(nm)

/

/

0.92±0.01

19.96±0.40

65.4±1.3

12.16±0.26 (12.50)

0.3

1.0

0.92±0.01

20.45±0.22

69.7±2.2

13.16±0.21 (13.49)

0.5

1.5

0.95±0.01

20.91±0.37

71.5±0.6

14.26±0.22 (14.69)

1.0

2.8

0.95±0.01

21.27±0.27

68.9±0.9

13.99±0.24 (14.16)

1.5

4.0

0.93±0.01

20.54±0.36

68.3±1.4

12.99±0.30 (13.45)

C60

10.0

0.94±0.01

20.74±0.34

69.4±2.8

13.52±0.44 (14.32)

Average values were calculated from 8 cells, maximum PCEs were indicated in the parentheses

(a)

20

20

(b)

20

20 2

J ~ 19.59 mA/cm

PCE ~ 12.11%

5

10

5

15

15

2

J (mA/cm )

10

PCE (%)

2

15

PCE ~ 14.50% 10

10 5

5 With fullerenol

Without fullerenol

0 0

50

100

150

PCE (%)

2

J ~ 17.30 mA/cm

15

J (mA/cm )

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


0 200

0 0

50

100

150

0 200

Time (s)

Time (s)

Figure 3. Steady-state efficiencies of the Pero-SCs (a) without and (b) with fullerenol interlayer measured at constant bias voltage of 0.70 V and 0.74 V, respectively. Figure 3 shows the steady-state efficiencies of the Pero-SCs without and with fullerenol interlayer, in which efficiencies of 12.11% and 14.50% were achieved, respectively. Both the results are consistent with the performance indicated by J-V curves.


11


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 30

Water 77.3o

13.8o

PCBM@TiO2

DMF

6.5o

TiO2

fullerenol@TiO2

~ 0o

~ 0o 15.7o

PCBM@TiO2

TiO2

fullerenol@TiO2

Figure 4. The images of water and DMF droplet contact angles on PCBM@TiO2, TiO2 and fullerenol@TiO2 Contact angle measurement was employed to characterize the wettability on fullerenol@TiO2 and PCBM@TiO2 layer. Although facilitates the electron transportation, ETL material such as PCBM often has large contact angles due to their hydrophobic nature, which could result in deficient coverage of perovskite solutions on top of this kind of ETM layers. To overcome this problem, an additional hydrophilic layer were required to decrease the contact angle on top of the ETLs.31 In this work, however, we found that, due to its hydrophilic nature, the employment of a single layer of fullerenol could readily facilitate the full coverage of perovskite solutions. As it is demonstrated in Figure 4, water droplets on PCBM@TiO2, TiO2 and fullerenol@TiO2, have contact angles of 77.3°, 13.8°, 6.5° respectively. Fullerenol showed much smaller contact angle than PCBM. Similar trend holds for DMF, as the contact angle of DMF on fullerenol@TiO2 was about 0o. These results show that, fullerenol ETM shows a strong hydrophilic nature and could efficiently increase the perovskite solution wettability on TiO2 layer.


12

Page 13 of 30

(a)

(b)

(d)

(c) MoO3/Ag P3HT

Perovskite TiO2/Fullerenol ITO

TiO2/Fullerenol/Perovskite

Intensity(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


TiO2/Perovskite

Glass

200 nm

10

15

20

25

30

35

40

45

2θ (degree)

Figure 5. Top-view SEM images of perovskite layer on (a) TiO2 and (b) fullerenol@TiO2, (c) cross-sectional SEM image of the Pero-SC with fullerenol interlayer, (d) XRD patterns of perovskite film on TiO2 and fullerenol@TiO2. Recently researches have shown that the crystal growth and surface morphology of perovskite films have a major influence on the device performance.47 Herein, both SEM and XRD were employed to investigate how the additional fullerenol layer influences the crystallization and the surface morphology of perovskite film. The SEM images (Figure 5a, 5b & 5c) showed that both films grown on TiO2 and fullerenol@TiO2 exhibited densely covered and well-crystallized structures of perovskites. Therefore, the insertion of fullerenol layer didn’t show a major influence on the morphology of the pristine perovskite film. The obtained dense coverage and defect-free features of the perovskite films could lead to better charge transport. As indicated by UV-vis spectra (Figure S6), the perovskite film deposited on fullerenol shows a slightly higher


13


absorption, implies that the fullerenol, due to the lower contact angle, makes the growth of perovskite easier. The crystallinity of perovskite film before and after the insertion of fullerenol thin film was further investigated by XRD analysis. As shown in Figure 5d, prominent peaks at 14.19° and 28.52° were observed in XRD patterns of all perovskite films on different ETL. Compared to those of the film on TiO2, the notably enhanced intensities of these two peaks measured for the film on the fullerenol@TiO2 clearly indicated that inserting fullerenol layer enhanced crystallization of the perovskite film. This enhanced crystallization could improve the light absorption ability, facilitate charge transportation and suppress the charge recombination of the perovskite film, which is in accord with the higher Jsc and FF of the device discussed above.

150

TiO2

100

TiO2/Fullerenol

50

J (mA)

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 30

0 -50 -100 -150 -4

-2

0

2

4

V (V)

Figure 6. J-V characteristics of the ITO/TiO2/Au and ITO/TiO2/fullerenol/Au devices. To further understand why the Pero-SCs with fullerenol ETL exhibits better device performance, the direct current (DC) conductivities (σ0) of TiO2 and TiO2/fullerenol thin films were determined by measuring the current-voltage (J-V) characterization of ITO/TiO2/Au and ITO/TiO2/fullerenol/Au (Figure 6). σ0 of these two devices have been identified from the slope of the J-V plot, J = σoAd-1V,48, 49 herein, A is the area detected and d is the thickness of the film. As the thickness of TiO2 and TiO2/fullerenol thin films were recorded as about 90 nm and 91.5 nm,


14

Page 15 of 30

the corresponding conductivities of TiO2 and TiO2/fullerenol were then determined as 1.26 × 10-3 and 8.20 × 10-3 mS/cm, respectively. Thus, after inserting the fullerenol layer, the conductivity of TiO2/fullerenol becomes around 5 times higher than the pristine TiO2 electron conductor. These results indicate that the thin layer of fullerenol can greatly improve the conductivity of TiO2 film. Therefore, it is expected that the electrons generated in perovskite layer are more efficiently transported and collected by fullerenol modified TiO2 than pristineTiO2, which also corresponds to a higher FF.

(a)

(b)


Normalized intensity

PL Intensity (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


1.0

0.5


0

10

-1

10

-2

10

-3

0.0 700

1

10

10 750

800

850

0

100

Wavelength (nm)

200

300

400

500

Time (ns)

Figure 7. (a) steady-state photoluminescence (PL) spectra of perovskite@TiO2 and perovskite@fullerenol@TiO2. (b) Transient PL of Pero-SCs with and without fullerenol. The excitation wavelength was 477 nm. Steady-state PL and time-resolved PL studies were measured to further investigate the charge transportation and dynamics of the corresponding devices. Steady-state PL spectra of TiO2 and fullerenol@TiO2 are shown in Figure 7a. Perovskite film exhibits an emissive band peaked at around 790 nm. With the insertion of fullerenol, a significant fluorescence quenching of perovskite is exhibited. This quenching indicates an enhanced electron transportation from


15


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 30

perovskite to fullerenol@TiO2. Thus, the PL studies confirm that the insertion of the single layer of fullerenol could facilitate the charge transfer between the perovskite and TiO2 layer. Transient PL spectra were further employed to investigate the influence of fullerenol on the charge dissociation and recombination in Pero-SCs. Figure 7b displays the PL decay curves measured by recording the signal at 790nm and excited with a 477 nm laser (2 MHz). The PL curves were composed of a fast and a slow decay processes and fitted with a bi-exponential decay function.50-52 The fast decay component should originate from the quenching of free charges, which means that the free charges generated from the perovskite were transported to the electrodes. The slow decay component can be assigned to the radiative recombination of the free carriers before the charge collection.38,

53, 54

The detailed parameters are listed in Table 2.

Without the fullerenol interlayer, the fast and slow decay time were 5.10 and 656.64 ns with component fraction of 0.18% and 99.82%, respectively. The bigger weight fraction of slow decay indicates that, the radiative recombination of photogenerated charges, rather than the charge transport to the electrodes, is dominating in the PL decay process. For the Pero-SCs with fullerenol interlayer, the weight fraction of fast decay significantly increases from 0.18% to 16.73%. This result demonstrates that the charge carriers were separated and transported more efficiently after the insertion of the fullerenol interlayer, which agrees well with the enhanced Jsc of the Pero-SCs.


16

Page 17 of 30

Table 2. The lifetime and weight fractions of the fluorescence fitted from the transient PL spectra shown in Figure 6. ETM

τ1 (ns)

f 1(%)

τ2 (ns)

f 2(%)

without fullerenol

5.10

0.18

656.64

99.82

with fullerenol

5.99

16.73

30.15

83.07

10

(a)

(b)


)

Rs

R1

R2

CPE1

CPE2

2

Z'' (Ω cm

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


5

0 0

5

10

15

2

Z' (Ω cm )

Figure 8. (a) Nyquist plots for the Pero-SCs with and without fullerenol interlayer. (b) The equivalent circuit used for fitting the data of ACIS. The ACIS spectra were employed to investigate the internal electrical processes and influence of the fullerenol layer on the interfacial resistance of the device. As shown in Figure 8a, the Nyquist plots of Pero-SCs were measured near the corresponding Voc in the dark. The ACIS spectra consists of two semicircles. For each semicircle, the high frequency region represents the responses of the perovskite layer and lower frequency region is the response of

electrode

interlayers.55 Figure 8b illustrates the equivalent electrical circuit, which include series resistance (Rs) and resistance-constant phase elements (R||CPE). The parameters obtained by fitting of the ACIS are summarized in Table 3, where Rs is the resistance of the contacts, wires, and electrodes,

42, 56, 57

CPE is employed to depict non-ideal capacitor with CPE-T and CPE-P.58


17


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

R1||CPE1 represents the effect of the photoactive layer,

59, 60

Page 18 of 30

and R2||CPE2 corresponds to the

resistance and capacitance of the buffer interlayers.61 Herein, the configuration of the two groups of devices were controlled to the same except for the fullerenol interlayer. For a parallel comparison, the thickness of different layers as well as the measurement conditions were kept constant. Thus, it is understandable that the comparable Rss and R1s for devices without / with fullerenol interlayers were obtained. In contrast, while device with fullerenol shows a present R2 of 12.81 Ω cm2, the device with fullerenol presents a much smaller R2 of 0.94 Ω cm2. The decreased R2 of the Pero-SC with the insertion of fullerenol indicates a notably decreased buffer interlayer resistance. It suggests that with the insertion of fullerenol interlayer, electrons can be transported more easily. This result supplies a rational explanation for the enhancement in Jsc and FF for the corresponding devices. Table 3. The parameters fitted from the Nyquist plots for the n-i-p type Pero-SCs without /with fullerenol interlayers. Rs ETL

CPE1-T

R1 2

2

-2

(Ω cm )

(Ω cm )

(nF cm )

TiO2

3.98

2.91

1.27

TiO2/Fullerenol

4.23

0.98

3.66

CPE2-T

R2 CPE1-P

2

-2

CPE2-P

(Ω cm )

(µF cm )

0.85

12.81

0.02

0.95

1.22

0.94

0.24

1.01

CONCLUSIONS In conclusion, fullerenol, an easy-accessible but efficient water-soluble material, has been applied as ETL in Pero-SCs for the first time. The fullerenol was synthesized through a facile one-step process and showed the excellent electron transporting property. By introducing


18

Page 19 of 30

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


fullerenol as ETL, the energy level alignments between perovskite and cathode has been effectively improved. The wettability and SEM studies showed that, due to its hydrophilic property, the insertion of fullerenol layer didn’t show a major influence on the surface morphology of the pristine perovskite film. XRD study results confirmed the high crystallinity of the obtained perovskite film. PL and ACIS characterizations further suggest that, inserting a single fullerenol layer atop TiO2 could simultaneously facilitate the charge extraction efficiency between perovskite and TiO2 layer and decrease interfacial resistance. As a result, the device performance of Pero-SC was enhanced by ~17.5% after the insertion of the fullerenol ETL and yields a PCE of 14.69%. These results indicate that fullerenol has great potential as a promising interfacial material for solar cells. We expect that, in the near future, the application of the watersoluble fullerenol ETLs can be extended and lead to greater enhancement of device performance. ASSOCIATED CONTENT Supporting Information TGA and FT-IR of fullerenol, J-V curves of different concentration of fullerenol for the devices and other characterizations. This material is available via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] [email protected] [email protected]. Author Contributions


19


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 30

Tiantian Cao,‡ Zhaowei Wang‡ contributed equally to this work. ACKNOWLEDGMENT Thank Mingzheng Ge for measurement of contact angle. This work was supported by the National Natural Science Foundation of China (51303118, 51302178 and 91333204), the Natural Science Foundation of Jiangsu Province (BK20130289 and BK20130295), the Ph.D. Programs Foundation of Ministry of Education of China (20133201120008), the Scientific Research Foundation for Returned Scholars, Ministry of Education of China, and A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions, the Beijing National Laboratory for Molecular Sciences (20140112), State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials. REFERENCES (1) Chu, S.; Majumdar, A., Opportunities and Challenges for a Sustainable Energy Future. Nature 2012, 488, 294-303. (2) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., HighPerformance Photovoltaic Perovskite Layers Fabricated through Intramolecular Exchange. Science 2015, 348, 1234-1237. (3) 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. (4) 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


20

Page 21 of 30

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


Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (5) 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. (6) Lin, Q.; Armin, A.; Nagiri, R. C. R.; Burn, P. L.; Meredith, P., Electro-Optics of Perovskite Solar Cells. Nat. Photonics 2015, 9, 106-112. (7) Miyata, A.; Mitioglu, A.; Plochocka, P.; Portugall, O.; Wang, J. T.-W.; Stranks, S. D.; Snaith, H. J.; Nicholas, R. J., Direct Measurement of the Exciton Binding Energy and Effective Masses for Charge Carriers in Organic-Inorganic Tri-Halide Perovskites. Nat. Phys. 2015, 11, 582-587. (8) Edri, E.; Kirmayer, S.; Mukhopadhyay, S.; Gartsman, K.; Hodes, G.; Cahen, D., Elucidating the Charge Carrier Separation and Working Mechanism of CH3NH3PbI3−xClx Perovskite Solar Cells. Nat. Commun. 2014, 5, 3461. (9) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C., Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 2013, 342, 344-347. (10) Ng, T.-W.; Chan, C.-Y.; Lo, M.-F.; Guan, Z. Q.; Lee, C.-S., Formation Chemistry of Perovskites with Mixed Iodide/Chloride Content and the Implications on Charge Transport Properties. J. Mater. Chem. A 2015, 3, 9081-9085.


21


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 30

(11) Yu, H.; Liu, X.; Xia, Y.; Dong, Q.; Zhang, K.; Wang, Z.; Zhou, Y.; Song, B.; Li, Y., Room-Temperature Mixed-Solvent-Vapor Annealing for High Performance Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 321-326. (12) www.nrel.gov/ncpv/images/efficiency_chart.jpg. (13) Shi, J.; Xu, X.; Li, D.; Meng, Q., Interfaces in Perovskite Solar Cells. Small 2015, 11, 2472-2486. (14) Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y., Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542-546. (15) Xu, Y.; Shi, J.; Lv, S.; Zhu, L.; Dong, J.; Wu, H.; Xiao, Y.; Luo, Y.; Wang, S.; Li, D.; Li, X.; Meng, Q., Simple Way to Engineer Metal-Semiconductor Interface for Enhanced Performance of Perovskite Organic Lead Iodide Solar Cells. ACS Appl. Mater. Interfaces 2014, 6, 5651-5656. (16) Min, J.; Zhang, Z.-G.; Hou, Y.; Ramirez Quiroz, C. O.; Przybilla, T.; Bronnbauer, C.; Guo, F.; Forberich, K.; Azimi, H.; Ameri, T.; Spiecker, E.; Li, Y.; Brabec, C. J., Interface Engineering of Perovskite Hybrid Solar Cells with Solution-Processed Perylene–Diimide Heterojunctions toward High Performance. Chem. Mater. 2015, 27, 227-234. (17) Zuo, L.; Gu, Z.; Ye, T.; Fu, W.; Wu, G.; Li, H.; Chen, H., Enhanced Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells through Interfacial Engineering Using SelfAssembling Monolayer. J. Am. Chem. Soc. 2015, 137, 2674-2679.


22

Page 23 of 30

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


(18) 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. (19) Xiao, Z.; Bi, C.; Shao, Y.; Dong, Q.; Wang, Q.; Yuan, Y.; Wang, C.; Gao, Y.; Huang, J., Efficient, High Yield Perovskite Photovoltaic Devices Grown by Interdiffusion of SolutionProcessed Precursor Stacking Layers. Energy Environ. Sci. 2014, 7, 2619-2623. (20) Liu, M.; Johnston, M. B.; Snaith, H. J., Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395-398. (21) 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. (22) Jiang, F.; Liu, T.; Luo, B.; Tong, J.; Qin, F.; Xiong, S.; Li, Z.; Zhou, Y., A Two-Terminal Perovskite/Perovskite Tandem Solar Cell. J. Mater. Chem. A 2016, 4, 1208-1213. (23) Tang, H.; Prasad, K.; Sanjinès, R.; Schmid, P. E.; Lévy, F., Electrical and Optical Properties of TiO2 Anatase Thin Films. J. Appl. Phys. 1994, 75, 2042. (24) Ke, W.; Fang, G.; Liu, Q.; Xiong, L.; Qin, P.; Tao, H.; Wang, J.; Lei, H.; Li, B.; Wan, J.; Yang, G.; Yan, Y., Low-Temperature Solution-Processed Tin Oxide as an Alternative Electron Transporting Layer for Efficient Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137, 67306733.


23


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 24 of 30

(25) Liu, D.; Kelly, T. L., Perovskite Solar Cells with a Planar Heterojunction Structure Prepared Using Room-Temperature Solution Processing Techniques. Nat. Photonics 2014, 8, 133-138. (26) Zhu, Z.; Ma, J.; Wang, Z.; Mu, C.; Fan, Z.; Du, L.; Bai, Y.; Fan, L.; Yan, H.; Phillips, D. L.; Yang, S., Efficiency Enhancement of Perovskite Solar Cells through Fast Electron Extraction: The Role of Graphene Quantum Dots. J. Am. Chem. Soc. 2014, 136, 3760-3763. (27) Wang, J. T.; Ball, J. M.; Barea, E. M.; Abate, A.; Alexander-Webber, J. A.; Huang, J.; Saliba, M.; Mora-Sero, I.; Bisquert, J.; Snaith, H. J.; Nicholas, R. J., Low-Temperature Processed Electron Collection Layers of Graphene/TiO2 Nanocomposites in Thin Film Perovskite Solar Cells. Nano Lett. 2014, 14, 724-730. (28) Tao, C.; Neutzner, S.; Colella, L.; Marras, S.; Srimath Kandada, A. R.; Gandini, M.; Bastiani, M. D.; Pace, G.; Manna, L.; Caironi, M.; Bertarelli, C.; Petrozza, A., 17.6% Stabilized Efficiency in Low-Temperature Processed Planar Perovskite Solar Cells. Energy Environ. Sci. 2015, 8, 2365-2370. (29) Li, Y.; Zhao, Y.; Chen, Q.; Yang, Y. M.; Liu, Y.; Hong, Z.; Liu, Z.; Hsieh, Y. T.; Meng, L.; Li, Y.; Yang, Y., Multifunctional Fullerene Derivative for Interface Engineering in Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137, 15540-15547. (30) Wojciechowski, K.; Stranks, S. D.; Abate, A.; Sadoughi, G.; Sadhanala, A.; Kopidakis, N.; Rumbles, G.; Li, C.-Z.; Friend, R. H.; Jen, A. K. Y.; Snaith, H. J., Heterojunction Modification for Highly Efficient Organic–Inorganic Perovskite Solar Cells. ACS Nano 2014, 8, 12701-12709.


24

Page 25 of 30

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


(31) Liu, C.; Wang, K.; Du, P.; Meng, T.; Yu, X.; Cheng, S. Z. D.; Gong, X., High Performance Planar Heterojunction Perovskite Solar Cells with Fullerene Derivatives as the Electron Transport Layer. ACS Appl. Mater. Interfaces 2015, 7, 1153-1159. (32) Park, Y.; Singh, N. J.; Kim, K. S.; Tachikawa, T.; Majima, T.; Choi, W., Fullerol-Titania Charge-Transfer-Mediated Photocatalysis Working under Visible Light. Chem. Eur. J. 2009, 15, 10843-10850. (33) Chaudhuri,

P.;

Paraskar,

A.;

Soni,

S.;

Mashelkar,

R.

A.;

Sengupta,

S.,

Fullerenol−Cytotoxic Conjugates for Cancer Chemotherapy. ACS Nano 2009, 3, 2505-2514. (34) Xing, G.; Zhang, J.; Zhao, Y.; Tang, J.; Zhang, B.; Gao, X.; Yuan, H.; Qu, L.; Cao, W.; Chai, Z.; Ibrahim, K.; Su, R., Influences of Structural Properties on Stability of Fullerenols. J. Phys. Chem. B 2004, 108, 11473-11479. (35) Zhang, G.; Liu, Y.; Liang, D.; Gan, L.; Li, Y., Facile Synthesis of Isomerically Pure Fullerenols and Formation of Spherical Aggregates from C60(OH)8. Angew. Chem. 2010, 122, 5421-5423. (36) Sardenberg, R. B.; Teixeira, C. E.; Pinheiro, M.; Figueiredo, J. M. A., Nonlinear Conductivity of Fullerenol Aqueous Solutions. ACS Nano 2011, 5, 2681-2686. (37) Wang, N.; Sun, L.; Zhang, X.; Bao, X.; Zheng, W.; Yang, R., Easily-Accessible Fullerenol as a Cathode Buffer Layer for Inverted Organic Photovoltaic Devices. RSC Adv. 2014, 4, 25886-25891.


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

Page 26 of 30

(38) Liang, P. W.; Liao, C. Y.; Chueh, C. C.; Zuo, F.; Williams, S. T.; Xin, X. K.; Lin, J.; Jen, A. K., Additive Enhanced Crystallization of Solution-Processed Perovskite for Highly Efficient Planar-Heterojunction Solar Cells. Adv. Mater. 2014, 26, 3748-3754. (39) Li, J.; Takeuchi, A.; Ozawa, M.; Li, X.; Saigo, K.; Kitazawa, K. C60 Fullerol Formation Catalysed by Quaternary Ammonium Hydroxides. J. Chem. Soc. , Chem. Commun. 1993, 17841785. (40) Long Y. Chiang, L.-Y. W., John W. Swirczewski, $Stuart Soled and Steve Cameron, Efficient

Synthesis

of

Polyhydroxylated

Fullerene

Derivatives

via

Hydrolysis

of

Polycyclosulfated Precursors. J.Org. Chem. 1994, 59, 3960-3968. (41) Zhang, Z.-G.; Li, H.; Qi, B.; Chi, D.; Jin, Z.; Qi, Z.; Hou, J.; Li, Y.; Wang, J., Amine Group Functionalized Fullerene Derivatives as Cathode Buffer Layers for High Performance Polymer Solar Cells. J. Mater. Chem. A 2013, 1, 9624-9629. (42) Wang, Z.; Dong, Q.; Xia, Y.; Yu, H.; Zhang, K.; Liu, X.; Guo, X.; Zhou, Y. Zhang, M.; Song, B., Copolymers Based on Thiazolothiazole-Dithienosilole as Hole-Transporting Materials for High Efficient Perovskite Solar Cells. Org. Electron. 2016, 33, 142-149. (43) Elumalai, N. K.; Uddin, A., Open Circuit Voltage of Organic Solar Cells: An in-Depth Review. Energy Environ. Sci. 2016, 9, 391-410. (44) Zhao, L.; Zhao, S.; Xu, Z.; Huang, D.; Zhao, J.; Li, Y.; Xu, X., The Effects of Improved Photoelectric Properties of PEDOT:PSS by Two-Step Treatments on the Performance of Polymer Solar Cells Based on PTB7-Th:PC71BM. ACS Appl. Mater. Interfaces 2016, 8, 547-552.


26

Page 27 of 30

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


(45) Li, Z.; Zhang, X.; Liu, C.; Zhang, Z.; Li, J.; Shen, L.; Guo, W.; Ruan, S., Enhanced Electron Extraction Capability of Polymer Solar Cells via Employing Electrostatically SelfAssembled Molecule on Cathode Interfacial Layer. ACS Appl. Mater. Interfaces 2016, 8, 82248231. (46) Chen, J. D.; Cui, C.; Li, Y. Q.; Zhou, L.; Ou, Q. D.; Li, C.; Li, Y.; Tang, J. X., SingleJunction Polymer Solar Cells Exceeding 10% Power Conversion Efficiency. Adv. Mater. 2015, 27, 1035-1041. (47) Xiao, Z.; Dong, Q.; Bi, C.; Shao, Y.; Yuan, Y.; Huang, J., Solvent Annealing of Perovskite-Induced Crystal Growth for Photovoltaic-Device Efficiency Enhancement. Adv. Mater. 2014, 26, 6503-6509. (48) Heo, J. H.; Han, H. J.; Kim, D.; Ahn, T. K.; Im, S. H., Hysteresis-Less Inverted CH3NH3PbI3Planar Perovskite Hybrid Solar Cells with 18.1% Power Conversion Efficiency. Energy Environ. Sci. 2015, 8, 1602-1608. (49) Obrzut, J.; Page, K. A., Electrical Conductivity and Relaxation in Poly(3Hexylthiophene). Phys. Rev. B 2009, 80, 195211. (50) Pellet, N.; Gao, P.; Gregori, G.; Yang, T. Y.; Nazeeruddin, M. K.; Maier, J.; Gratzel, M., Mixed-Organic-Cation Perovskite Photovoltaics for Enhanced Solar-Light Harvesting. Angew. Chem. Int. Ed. 2014, 53, 3151-3157. (51) Yeo, J.-S.; Kang, R.; Lee, S.; Jeon, Y.-J.; Myoung, N.; Lee, C.-L.; Kim, D.-Y.; Yun, J.M.; Seo, Y.-H.; Kim, S.-S.; Na, S.-I., Highly Efficient and Stable Planar Perovskite Solar Cells


27


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 28 of 30

with Reduced Graphene Oxide Nanosheets as Electrode Interlayer. Nano Energy 2015, 12, 96104. (52) 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, 5552-5558. (53) Chen, Q.; Zhou, H.; Song, T. B.; Luo, S.; Hong, Z.; Duan, H. S.; Dou, L.; Liu, Y.; Yang, Y., Controllable Self-Induced Passivation of Hybrid Lead Iodide Perovskites toward High Performance Solar Cells. Nano Lett. 2014, 14, 4158-4163. (54) Ponseca, C. S., Jr.; Savenije, T. J.; Abdellah, M.; Zheng, K.; Yartsev, A.; Pascher, T.; Harlang, T.; Chabera, P.; Pullerits, T.; Stepanov, A.; Wolf, J. P.; Sundstrom, V., Organometal Halide Perovskite Solar Cell Materials Rationalized: Ultrafast Charge Generation, High and Microsecond-Long Balanced Mobilities, and Slow Recombination. J. Am. Chem. Soc. 2014, 136, 5189-5192. (55) Liu, X.; Jiao, W.; Lei, M.; Zhou, Y.; Song, B.; Li, Y., Crown-Ether Functionalized Fullerene as a Solution-Processable Cathode Buffer Layer for High Performance Perovskite and Polymer Solar Cells. J. Mater. Chem. A 2015, 3, 9278-9284. (56) Liu, X.; Lei, M.; Zhou, Y.; Song, B.; Li, Y., High Performance Planar p-i-n Perovskite Solar Cells with Crown-Ether Functionalized Fullerene and LiF as Double Cathode Buffer Layers. Appl. Phys. Lett. 2015, 107, 063901. (57) Trevisan, R.; Döbbelin, M.; Boix, P. P.; Barea, E. M.; Tena-Zaera, R.; Mora-Seró, I.; Bisquert, J., PEDOT Nanotube Arrays as High Performing Counter Electrodes for Dye


28

Page 29 of 30

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


Sensitized Solar Cells. Study of the Interactions among Electrolytes and Counter Electrodes. Adv. Energy Mater. 2011, 1, 781-784. (58) Ecker, B.; Egelhaaf, H.-J.; Steim, R.; Parisi, J.; von Hauff, E., Understanding S-Shaped Current–Voltage Characteristics in Organic Solar Cells Containing a TiOx Interlayer with Impedance Spectroscopy and Equivalent Circuit Analysis. J. Phys. Chem. C 2012, 116, 1633316337. (59) Yan, L.; Song, Y.; Zhou, Y.; Song, B.; Li, Y., Effect of PEI Cathode Interlayer on Work Function and Interface Resistance of ITO Electrode in the Inverted Polymer Solar Cells. Org. Electron. 2015, 17, 94-101. (60) Liu, X.; Yu, H.; Yan, L.; Dong, Q.; Wan, Q.; Zhou, Y.; Song, B.; Li, Y., Triple Cathode Buffer Layers Composed of PCBM, C60, and LiF for High-Performance Planar Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 6230-6237. (61) Lin, H.-W.; Lu, C.-W.; Lin, L.-Y.; Chen, Y.-H.; Lin, W.-C.; Wong, K.-T.; Lin, F., Pyridine-Based Electron Transporting Materials for Highly Efficient Organic Solar Cells. J. Mater. Chem. A 2013, 1, 1770-1777.

TOC:


29


0

+

-5 2

J (mA/cm )

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

Ag MoO3 P3HT Perovskite Fullerenol TiO2 Substrate

Page 30 of 30

-

-10 -15


Voc = 0.96 V Jsc = 21.14 mA/cm2 FF = 72.12% PCE = 14.69%

-20 0.0

0.5

1.0

V (V)


30

Facilitating Electron Transportation in Perovskite Solar Cells via Water

Recommend Documents