Enhanced Planar Perovskite Solar Cell Performance via Contact

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Article

Enhanced Planar Perovskite Solar Cell Performance via Contact Passivation of TiO2/Perovskite Interface with NaCl Doping Approach Jing Ma, Xing Guo, Long Zhou, Zhenhua Lin, Chunfu Zhang, Zhou Yang, Gang Lu, Jingjing Chang, and Yue Hao ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00602 • Publication Date (Web): 10 Jul 2018 Downloaded from http://pubs.acs.org on July 10, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29 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 Energy Materials

Enhanced Planar Perovskite Solar Cell Performance via Contact Passivation of TiO2/Perovskite Interface with NaCl Doping Approach Jing Ma,a Xing Guo,a Long Zhou,a Zhenhua Lin,a Chunfu Zhang,a Zhou Yang,b Gang Lu,c Jingjing Chang,*a Yue Haoa a

State Key Discipline Laboratory of Wide Band Gap Semiconductor Tecchnology, Shaanxi Joint Key Laboratory of Graphene, School of Microelectronics, Xidian University, 2 South Taibai Road, Xi’an, 710071, China. b

Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education;

Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China. c

Huanghe Hydropower Solar Industry Technology Co., Ltd, 369 South Yanta Road, 710061, China

KEYWORDS: perovskite solar cell, interlayer treatment, TiO2 electron transport layer, NaCl treatment, contact modification

ACS Paragon Plus Environment

1

ACS Applied Energy Materials 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 29

ABSTRACT

Perovskite solar cells (PSCs) have been developed rapidly in recent years due to the excellent photoelectric properties and development potential. In this study, high performance and hysteresis-less planar structured perovskite (MA1-yFAyPbI3-xClx) solar cell was successfully achieved via contact passivation of the compact titanium dioxide (TiO2)/perovskite interface with NaCl doping method. It was found that the sodium chloride (NaCl) doping treatment on TiO2 could significantly improve the electrical property of TiO2 electron transport layer (ETL), and passivate the trap states at TiO2/perovskite interface. Moreover, the improved interface contact between TiO2 ETL and perovskite could efficiently enhance the charge transfer and suppress the charge recombination in the device. Hence, the power conversion efficiency (PCE) of PSC device based on NaCl doped TiO2 was enhanced to 18.3 % compared with the pristine compact TiO2 based PSCs (15.1 %).

Introduction Organic-inorganic hybrid lead halide perovskite solar cells (PSCs) have attracted lots of attention due to many advantages such as low cost, facile fabrication process and high power conversion efficiency (PCE).1–5 Moreover, perovskite materials has unique properties like broad and strong light absorption, long carrier lifetime, large charge carrier diffusion length, and low exciton binding energy.6–11 Consequently, the PCE of perovskite solar cells has an amazing increase from 3.9 % to a recent record of 22.7 %.12–16 During the PSC device fabrication, planar structure is usually preferred due to its simple fabrication process and compatibility with flexible substrates.17,18 For planar structured PSC device, a sandwich configuration of electron transport layer (ETL)/hybrid perovskite layer/hole transport layer (HTL) or HTL//hybrid perovskite


2

Page 3 of 29 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


layer/ETL is commonly employed. Since the ETL plays a key role in electron extraction, electron transport and hole blocking simultaneously, suitable electron transport materials are much desired. As a result, many scientists have devoted their efforts towards investigating the ETL materials. Up to now, various inorganic ETL materials such as zinc oxide (ZnO), titanium dioxide (TiO2), tin dioxide (SnO2) etc. have been used in planar structured PSCs, and most of the planar PSCs have achieved much progress such as high performance and comparable device stability compared to mesoporous structure based PSCs.19–21 Among these ETL materials, TiO2 has been regarded as a promising candidate due to its low cost, good optoelectronics properties, and high chemical stability for ETL in PSCs. However, the pristine TiO2 exhibits low conductivity and poor film quality with much sub-band trap states.22 Hence, various approaches have been used to enhance the film conductivity, improve the energy level alignment, alleviate the charge accumulation, and enhance the charge extraction.23–26 One of simple and efficient approaches to improve the electrical properties is to utilize surface treatment or chemical doping with appropriate ions. For example, Yang et al. successfully prepared high performance PSCs and flexible devices, which could be attributed to a high quality TiO2 ETL by using magnetron sputtering and ionic liquid surface optimization.27,28 The Grätzel group

has

reported

Lithium

(Li)

doped

TiO2

layer

with

Lithium

bis(trifluoromethanesulfonyl)imide (Li-TFSI) to reduce the surface defects and improve the charge transport.29 Sargent and co-workers investigated chlorine-capped TiO2 nanocrystal film in low-temperature planar solar cells to mitigate interfacial recombination and enhance the device performance through contact passivation between perovskite and TiO2.30 Several studies have shown that the doping method has a significant effect on the band structures and trap states of the TiO2 ETL, which further affects the film important properties such as the Fermi energy level and


3


Page 4 of 29

charge transport, recombination, and collection in the PSCs.22,31 Therefore, different dopants such as Li, magnesium (Mg), niobium (Nb), yttrium (Y) etc have been investigated and applied in the electron transport layers of PSCs, and all the PSCs based on doped ETLs showed improved charge transport properties and enhanced device performance.31–34 In this study, we have successfully achieved planar structured perovskite solar cells based on TiO2 ETL and sodium chloride (NaCl) modified TiO2 ETL. It was found that the NaCl doping treatment enhanced the film conductivity and optimized the thin film morphology of perovskite. The measurements of transient photocurrent (TPC) and photovoltage (TPV) indicated the enhanced charge transfer and reduced charge recombination for the NaCl modified TiO2 based devices. Finally, we fabricated PSCs based on the NaCl modified TiO2 with an improved power conversion efficiency of 18.3 %, much higher than the devices based on pristine TiO2 (15.1 %). Experimental Section Materials Methylammonium iodide (MAI, 99.8%), Formamidinium dodide (FAI, 99.8%), and Tris [2(1H-pyrazol-1-yl)-4-tert-butylpyridine]

cobalt(III)

tris[bis

(trifluorome-thylsulfonyl)imide]

(FK209) were obtained from Dyesol Ltd. Spiro-OMeTAD (99.8%) was supplied by Xi’an Polymer Light Technology Corp. Toluene (anhydrous, ≥ 99.8% purity), chlorobenzene (anhydrous, 99.8% purity), acetonitrile (anhydrous, 99.8% purity), 1-butanol (anhydrous, 99.8% purity), 4-tert-butylpyridine (TBP, 98% purity), titanium diisopropoxide bis(acetylacetonate) (75wt% in isopropanol), titanium(IV) chloride (TiCl4, ≥ 98.0% purity), bis(trifluoromethane)sulfonimide lithium salt (LiTFSI, 96% purity), isopropanol (99.5% purity), and sodium chloride (NaCl, ≥99.5% purity) were purchased from Sigma-Aldrich. Lead(II) iodide (PbI2, 99.999% purity), and Lead(II) chloride (PbCl2, 99.999% purity) were bought from Alfa. Phenyl-


4

Page 5 of 29 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


C61-butyric acid methyl ester (PC61BM, 99% purity) was obtained from ADS. N,N'Dimethylformamide (DMF, 99.8% purity) was supplied by Aladdin. All chemicals and reagents were used as received without further purification. Film formation and device fabrication The device fabrication is similar with our previously reported procedure.26 Planar PSCs were fabricated on pre-patterned fluorine-doped tin oxide (FTO) glass substrates (around 2x2.5 cm2 in size, 7 Ω per square). The patterned FTO glass substrates were sequentially ultrasonic cleaned with detergent, de-ionized water, acetone, ethyl alcohol or isopropyl alcohol at 50 °C for 20 min, respectively. Then the FTO substrates were dried with nitrogen gun and treated in a UV ozone oven for 15 min. A thin compact TiO2 layer was deposited following the procedures in the literature: A 0.15 M titanium diisopropoxide bis(acetylacetonate) solution in 1-butanol was spincoated onto FTO substrates at 4000 rpm for 45 s and annealed at 125 ℃ for 5 min, and then the similar process was repeated twice with 0.3 M titanium diisopropoxide bis(acetylacetonate) solution. The as-prepared film was sintered at 500 ℃ for 15 min. After cooling down to room temperature, the coated substrates were immersed into 40 mM TiCl4 aqueous solution at 70 ℃ for 45 min. Subsequently, the film was immersed in 0.5 mg/ml and 1.0 mg/ml NaCl solution for different times before heat-treated at 500 ℃ for 15min. After that, the substrates were transferred into a nitrogen-filled glove box and spin coated with a PC61BM solution (10mg/mL in chlorobenzene) at 6000 rpm for 45 s, followed by heating at 100 ℃ for 5 min. 1.36 M PbI2 and 0.24 M PbCl2 were dissolved in the solvent of DMF and stirred for 2 h at 75 °C. 100 mg MAI:FAI (7:3 mass. ratio) were dissolved in the solvent of IPA with 1.0 vol% DMF. After that, PbX2 precursor solution was spin coated on the top of the PC61BM covered substrates at 3000 rpm for 45 s, and then the solution of MAI and FAI was spin coated on top of the PbX2


5


Page 6 of 29

substrates at 3000 rpm for 45 s. All of the films were thermally annealed on the hotplate at 100 °C for 10 min. Next, the hole transport material (HTM) was spin-coated on FTO/TiO2/PC61BM/CH3NH3PbI3-xClx substrate at 1000 rpm for 10 s and 4000 rpm for 45 s using the prepared HTM solutions. The HTM solution containing 90 mg spiro-OMeTAD in 1mL chlorobenzene with 45µL LiTFSI/acetonitrile solution (170 mg/mL), 10µL tBP, and 75µL Co(III) complex FK209/acetonitrile solution (7.5mM) was used. The devices were finished by thermally evaporated 100 nm Ag. All the devices had an effective area of 7.5 mm2 defined by a shadow mask. Measurements and characterization Photovoltaic performances were measured by using a Keithley 2400 source meter under simulated sunlight from XES-70S1 solar simulator matching the AM 1.5G standard with an intensity of 100 mW/cm2. The system was calibrated against a NREL certified silicon reference solar cell. All the measurements of the solar cells were performed under ambient atmosphere at room temperature without encapsulation. Incident photo-to-current conversion efficiencies (IPCEs) of PSCs were measured by the solar cell quantum efficiency measurement system (SCS10-X150, Zolix instrument. Co. Ltd). The morphology measurement of the perovskite layers was measured by scanning electron microscopy (SEM) (JSM-7800F). X-ray diffraction (XRD) test was conducted on Bruker D8 Advance XRD. The UV-visible absorption spectra were recorded with an UV-visible spectrophotometer (Perkin-Elmer Lambda 950). Photoluminescence spectra were collected on an HORIBA R-HR 800, and the excitation wavelength was 633 nm. Steady photoluminescence (PL) and time-resolved photoluminescence (TR-PL) were measured using the Pico Quant Fluotime 300 by using a 510 nm picosecond pulsed laser. Transient photocurrent (TPC) measurement was performed with a system excited by a 532 nm (1000 Hz,


6

Page 7 of 29 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


3.2 ns) pulse laser. Transient photovoltage (TPV) measurement was performed with the same system excited by a 405 nm (50 Hz, 20 ms) pulse laser. A digital oscilloscope (Tektronix, D4105) was used to record the photocurrent or photovoltage decay process with a sampling resistor of 50 Ω or 1 MΩ, respectively. Results and Discussion TiO2 ETL has been proved to play important roles on the charge extraction, recombination, as well as the device performance of the PSCs. In order to improve the interface contact properties between TiO2 ETL and perovskite film, the TiO2 ETL was modified with NaCl solution for proper time. The process was conducted by immersing the TiO2 coated FTO substrates into NaCl solutions with different concentrations for different times. It was thought that the Na+ and Clcould dope and/or passivate the trap states of TiO2 film,30 and hence, improve the interfacial properties of TiO2/perovskite. The current density – voltage (J – V) characteristics of PSCs with a device configuration of FTO/TiO2/PC60BM/perovskite/spiro-OMeTAD/Ag based on pristine TiO2 and NaCl modified TiO2 ETLs were recorded under AM 1.5G 1 sun (100 mW cm−2) simulated solar illumination conditions. The treating time was optimized and it was found that the device with TiO2 ETL treated in 0.5 mg/mL NaCl solution for 60 s gave the best performance (Table S1 and Figure S1). The photovoltaic performance parameters are summarized in Table 1. As shown in Figure 1 and Table 1, the PCE of pristine TiO2 based device was 14.2 % with an open-circuit voltage (Voc) of 1.00 V, a short-circuit current density (Jsc) of 21.6 mA/cm2, and a fill factor (FF) of 0.66. After being treated by 0.5mg/ml NaCl for 60 s, Jsc was improved to 23.4 mA/cm2 and FF was improved to 0.70 with greatly increased Voc (1.04 V), which enhanced the PCE to 17.2 %. Compared with control devices (pristine TiO2), TiO2-NaCl devices showed significantly


7


Page 8 of 29

enhancement in Voc, Jsc, and FF. A PCE as high as 18.3 % was obtained for the best device based on NaCl modified TiO2, and the Voc, Jsc and FF were 1.05 V, 23.8 mA/cm2, and 0.73, respectively, as shown in Figure 1b. For devices with 1.0 mg/mL NaCl treatment for 30 s, the best device exhibited a Voc of 1.05 V, a Jsc of 23.3 mA/cm2 and an FF of 0.74, resulting in a PCE of 18.1 %. Figure 2 shows the device statistical analysis, and it was found that the NaCl doping treatment significantly improved the electric properties of the device, including the Jsc, Voc and FF. Figure 1c exhibits the incident photo-to-electron conversion efficiency (IPCE) spectra of the PSCs with/without NaCl doping treatment. The devices based on NaCl modified TiO2 obviously showed higher IPCE value than the device with pristine TiO2, which is in good agreement with the J - V curve measurement. The integrated current densities were 21.0 and 22.8 mA/cm2 for TiO2 and TiO2-NaCl based devices, respectively.


8

Page 9 of 29

(a)

(b) Current density (mA/cm2)

Current density (mA/cm2)

10

0 TiO2 TiO2-NaCl

-10

-20 -0.2

0.0

(c)

0.2

0.4

0.6

0.8

1.0

1.2

10 5

Voc = 1.05V

0

FF = 0.73 Jsc = 23.8 mA/cm2

-5

PCE = 18.3 %

-10 -15 -20 -25 -0.2

0.0

(d)

Voltage (V)

0.2

0.4

0.6

0.8

1.0

1.2

Voltage (V)

1.05

100

1.14 kT/q

1.00

80

0.95

60

Voc (V)

IPCE (%)

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 TiO2-NaCl

40 20 0 300

1.23 kT/q

0.90 0.85

TiO2 TiO2-NaCl

0.80 0.75

400

500

600

700

Wavelength (nm)

800

1

10

100

Light intensity (mW/cm2)

Figure 1. (a) J - V characteristics of perovskite devices based on pristine TiO2 and NaCl modified TiO2. (b) J - V curve of the best device. (c) IPCEs for PSCs based on pristine TiO2 and NaCl modified TiO2. (d) Measured Voc of devices with pristine TiO2 and NaCl modified TiO2 as a function of light intensity.


9


(a)

(b) 75 Fill Factor (%)

PCE (%)

18

16

70

65

14

60 TiO2

TiO2-NaCl

(c)

(d)

TiO2

TiO2-NaCl

TiO2

TiO2-NaCl

1.08

24 1.06 23

1.04

Voc (V)

2

Jsc (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 29

22

1.02 1.00

21 0.98 20

0.96

TiO2

TiO2-NaCl

Figure 2. Statistic parameters of PCE (a), FF (b), Jsc (c) and Voc (d) for PSCs prepared under different cathode interlayer conditions without and with NaCl doping treatments. Table 1. Photovoltaic parameters of PSCs prepared on an ETL consisting of pristine TiO2 and TiO2-NaCl. The average results were derived from 16 perovskite solar cells from two batches. Voc(V)

Jsc(mA/cm2)

FF(%)

PCE(%)

Average

1.00

21.6

0.66

14.2

Best

1.02

22.1

0.67

15.1

Average

1.04

23.4

0.70

17.2

Best

1.05

23.8

0.73

18.3

ETL TiO2

TiO2-NaCl

In order to further understand the influence of NaCl doping treatment on the electrical properties of the cell, we studied the recombination mechanism of the device with TiO2 and TiO2-NaCl by measuring J - V characteristics at various light intensities from 100 to 0.1 mW/cm2.


10

Page 11 of 29 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 1d shows the Voc values as a function of light intensity. It is known that the device dominate recombination mechanism is bimolecular recombination when the slope of Voc versus the light intensity in the natural logarithm equals to kT/q, where k is the Boltzmann constant, T is temperature in Kelvin, and q is the elementary charge.6,35 Otherwise, the slope value should be greater than kT/q, since Voc depends on light intensity more strongly when Shockley−Read−Hall (SRH) or trap-assisted recombination is involved.35,36 From Figure 1d, it can be found that the slopes of the devices based on pristine TiO2 and NaCl modified TiO2 were 1.23 kT/q and 1.14 kT/q, respectively, implying that NaCl doping treatment reduced the interfacial trap density between the TiO2 and perovskite contact, resulting in suppressed SRH recombination.6 Therefore, the performance was enhanced. In order to understand the detailed mechanism about the charge transfer and recombination properties, TPC and TPV characteristics were performed.37 Figure 3a showed the TPC measurements under short-circuit condition, and the TPC exhibited a transient decay lifetime of 0.51µs for TiO2-NaCl, faster decay than the devices based on pristine TiO2 (1.08 µs). This indicates that the NaCl modified TiO2 based devices possess more efficient charge transfer and extraction process, which is beneficial for higher current density. The charge recombination dynamics of the working device could be probed by transient photovoltage measurement. Figure 3b showed the TPV analysis of perovskite solar cells with pristine TiO2 and NaCl modified TiO2 under open-circuit conditions, respectively. TPV exhibited a longer decay lifetime of 24.67 µs for NaCl modified TiO2 based device compared to pristine TiO2 based device (20.83 µs). This is consistent with the enhanced device parameters especially for FF and Voc observed in the J – V measurements, and it further proves that the NaCl doping treatment could efficiently suppress the charge recombination.


11


(a)

(b) 1.0

Normalized Intensity (a.u.)

Normalized 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

Page 12 of 29

TiO2

0.8

TiO2-NaCl

0.6 0.4

1.08 µs

0.2

0.51 µs

0.0

1.0 TiO2 0.8

TiO2-NaCl

0.6 0.4

24.67 µs

0.2

20.83 µs

0.0 0

1

2

3

4

5

0

20

40

60

80

100

Time (µ µs)

Time (µ µs)

Figure 3. Transient photocurrent (a) and photovoltage (b) curves of perovskite solar cells based on pristine TiO2 and NaCl modified TiO2 electron transport layers. Hysteresis behaviors of the pristine TiO2 and NaCl modified TiO2 based devices were checked by scanning the J – V curves at reverse and forward directions. The detailed parameters are summarized in Table S2 and it can be seen that the NaCl doping treatment slightly reduced the device hysteresis behavior. And the hysteresis index (defined as (PCEreverse-PCEforward)/PCEreverse) was also reduced from 12.6 % to 2.7 % after NaCl doping treatment. The measurements of current density and PCE steady-state outputs at maximum power point were also taken to further confirm that the measured result is reliable. As shown in Figure 4b and 4d, the device based on NaCl doping treatment showed a stable Jsc of 20.8 mA/cm2, yielding a stable PCE of 17.9 % at voltage bias of 0.86 V. In comparison, the devices based on pristine TiO2 showed a stable PCE of about 15.2 % at voltage bias of 0.82 V. The lower hysteresis and higher steady-state output for the perovskite solar cells with NaCl modified TiO2 electron transport layers are probably caused by the faster charge transfer and suppressed charge recombination due to the improved contact properties between perovskite and TiO2 ETL.


12

Page 13 of 29

(b) Current density (mA/cm )

10

25

20

20

16

2

2

Current density (mA/cm )

(a)

0

Reverse scan Forward scan -10

-20

12

15

Voltage bias = 0.86 V 10

8

Current density PCE

4

5 0

-0.2

0.2

0.4

0.6

0.8

1.0

0

1.2

20

40

(d)

100

120

0 140

18

25

2

2


80

Time (s)

Voltage (V) 10

60

0

Reverse scan Forward scan -10

-20

15

20

12 15 9

Voltage bias = 0.82 V

10

6

Current density PCE

5

3

0 -0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

20

Voltage (V)

40

60

80

100

PCE (%)


(c)

0.0

PCE (%)

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


120

0 140

Time (s)

Figure 4. (a) Hysteresis J – V curves of the TiO2-NaCl based device with respect to different scan directions. (b) Steady-state current density and PCE output of the TiO2-NaCl based devices at a voltage bias of 0.86 V. (c) Hysteresis J – V curves of the pristine TiO2 based device with respect to different scan directions. (d) Steady-state current density and PCE output of the pristine TiO2 based devices at a voltage bias of 0.82 V. In order to understand the relationship between NaCl doping treatment and photovoltaic performance enhancement, the TiO2 surface properties and corresponding perovskite thin film properties were investigated. Since the TiO2 surface condition has critical effect on the perovskite thin film properties, the pristine TiO2 and NaCl modified TiO2 thin film properties were studied firstly. The surface morphology of TiO2 thin films was investigated by SEM and


13


Page 14 of 29

atomic force microscopy (AFM). It is clear that NaCl doping had minimal influence on the surface morphology of TiO2 (Figure S2). The root mean square (RMS) roughness can be measured by AFM, as shown in Figure S3, and low RMS is conducive to the improvement of perovskite thin film formation. The RMS of films treated by 0.5 mg/ml NaCl for 60 s slightly decreased from 15.20 nm to 14.13 nm compared to that of pristine TiO2. The energy levels of TiO2 without and with NaCl doping treatment were studied by ultraviolet photoemission spectroscopy (UPS). As shown in Figure S4, no obvious work-function change was observed by NaCl doping treatment. Hence, the NaCl doping treatment did not induce additional energy barrier between TiO2 and conduction band of perovskite. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical states and composition of pristine TiO2 and NaCl modified TiO2 (Figure 5). The full survey spectra peaks were shown in Figure S5. The C1s peaks of all samples are calibrated at 285 eV. For the pristine TiO2, Ti 2p peak at binding energy of 464.73 eV and 458.95 eV were assigned to Ti 2p1 and Ti 2p3 at the Ti4+ oxidation state, respectively. After NaCl doping treatment, the peaks shifted to lower binding energy of 464.42 eV, and 458.63 eV, respectively (Figure 5a). According to Pauling electronegativity theory, the electrons can feasibly transfer from sodium to titanium since the Pauling electronegativity value of Ti is 1.54 and that of Na is 0.93. The electron transfer will induce more negative charge on titanium, and change the Ti4+ state to Ti3+ state, which could enhance the film conductivity.23 It has been reported that Ti3+ state can passivate the electronic defects or trap states those originate from oxygen vacancies within TiO2 lattice, which is similar with the Li+ doped case.29 Similarly, O 1s peak shifted to lower energies from 530.17 eV for pristine TiO2 to 529.87 eV for NaCl modified TiO2 (Figure 5b). In order to further confirm that the NaCl has been successfully doped into TiO2 layer, the Na 1s and Cl 2p were


14

Page 15 of 29

scanned. It can be seen that the Na 1s peak signal could be clearly observed after NaCl doping treatment (Figure 5c). However, no obvious Cl signal could be detected for TiO2-NaCl after thermal treatment. Meanwhile, the depth profiling of Na element of doped TiO2 film indicates that the NaCl doping is a surface process (Figure S6). The conductivity of TiO2 before and after NaCl doping treatment was further checked by a diode with a device structure of FTO/TiO2/Ag. As shown in Figure S7, the conductivity of NaCl modified TiO2 was enhanced about 2 times than that of pristine TiO2 layer. The enhanced film conductivity is beneficial for efficient electron transfer.

(b)

(a)

464

TiO2-NaCl

Intensity (a.u.)

Intensity (a.u.)

TiO2-NaCl

466

462

460

458

O 1s

TiO2

Ti 2p

TiO2

534

456

Binding Energy (eV)

532

530

528

526

Binding Energy (eV)

(d)

(c)

TiO2

TiO2

TiO2-NaCl

Cl 2p

TiO2-NaCl

Na 1s

Intensity (a.u.)

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


1080

1075

1070

1065

190

Binding Energy (eV)

195

200

205

210

Binding Energy (eV)

Figure 5. XPS spectra of Ti 2p peak (a), O1s peak (b), Na 1s peak (c), and Cl 2p peak (d).


15


Page 16 of 29

The trap density of TiO2 ETL was measured by the space charge limited current (SCLC) method. As shown in Figure S8, the trap-filled limit voltage (VTFL) of TiO2 and TiO2-NaCl were 0.22 V and 0.30 V respectively. According to the following equation: ்ܸி௅ =

௘௡೟ ௗమ ଶఌబ ఌ

, where e is

the elementary charge, nt is the trap density, d (~150 nm) is the film thickness, ε0 is the vacuum permittivity, and ε (~ 48) is the dielectric constant. According to the calculation results, the trap densities of TiO2 and TiO2-NaCl were 7.08×1016 cm-3 and 5.19×1016 cm-3, respectively, which indicated that NaCl doping reduced the number of TiO2 defects states. Furthermore, the electron mobility (µ) of pristine TiO2 and TiO2-NaCl was calculated using the SCLC method in Figure S8 ଽ

with the equation of ‫ߝߝ = ܬ‬଴ ߤ ଼

௏మ ௗయ

. The results showed that the electron mobility of TiO2-NaCl

increased to 7.20×10-4 cm2V-1s-1 compared to that of pristine TiO2 (3.48×10-4 cm2V-1s-1), which demonstrated that the NaCl doping could promote the electron extraction and transport. The perovskite thin films play an important role in determining the final solar cell device performance, and hence, it is desirable to study the NaCl doping treatment effect on the perovskite thin film quality. The perovskite films based on pristine TiO2, NaCl modified TiO2 were prepared under the same condition. The surface morphology of perovskites on pristine TiO2 and TiO2-NaCl ETLs was investigated by field-emission scanning electron microscopy (FESEM). As showed in Figure 6a-b and Figure S9, similar crystal morphology and crystal size were obtained. However, the perovskite crystal on TiO2-NaCl became more homogeneous than that on pristine TiO2. This indicated that NaCl doping treatment could optimize perovskite morphology so as to obtain better perovskite film comparing to pristine TiO2, which is beneficial for the light absorption and charge transport. Figure S10 shows the cross-section SEM image of TiO2-NaCl based device, and it has a planar structure in which around 500 nm perovskite layer is


16

Page 17 of 29 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


sandwiched between compact TiO2 and spiro-OMeTAD layer. X-ray diffraction (XRD) measurements were used to characterize perovskite thin film crystallinity on different interfaces, as illustrated in Figure 6c and Figure S11. All samples exhibited characteristic diffraction peaks of perovskite and TiO2. The NaCl-TiO2 based perovskite thin films slightly enhanced diffraction intensity compared to that on pristine TiO2. The UV-Vis absorption spectra of the perovskite films on pristine TiO2 and NaCl modified TiO2 were measured and shown in Figure 6d. Form UV to the near-infrared wavelength range, the light absorption of both perovskite thin films was strong, and the absorption onset was at ca. 798 – 803 nm since the perovskite optical band gap is about 1.55 eV. However, the perovskite films on NaCl modified TiO2 showed obviously stronger light absorption ability than that on pristine TiO2 from 400 – 575 nm. This could be resulted from the better crystallinity obtained due to NaCl doping treatment.


17


Page 18 of 29

Figure 6. Top-view SEM images of perovskite films grow on (a) pristine TiO2 (b) NaCl modified TiO2. (c) XRD patterns of CH3NH3PbI3-xClx perovskite thin films on pristine TiO2 and NaCl modified TiO2. (d) UV-Vis absorption of perovskite thin films based on pristine TiO2 and NaCl modified TiO2. The steady-state photoluminescence (PL) spectra (Figure 7a) of TiO2 and NaCl modified TiO2 based perovskite films were measured to investigate the trap passivation effect at the perovskite/ETL interface and corresponding charge transfer process.38 It is interesting that the PL peak of perovskite film deposited on TiO2-NaCl showed an obvious blue-shift from 767 nm to 761 nm. This indicates that the trap states were effectively passivated as a result of improved perovskite film quality after NaCl doping treatment. Meanwhile, compared to the perovskite films deposited on pristine TiO2, the films deposited on NaCl-TiO2 exhibited obviously lower PL intensity, which indicates that efficient PL quenching occurred because of better charge transfer between ETL and perovskite film.6 Time-resolved PL (TR-PL) was further carried out to investigate the charge transfer dynamics of the photogenerated charge carriers (Figure 7b). The charge carrier lifetime could be determined by fitting the decay curves by biexponential function. The average lifetimes were calculated to be around 17.06 ns and 14.13 ns for TiO2 and NaCl modified TiO2 based perovskite films respectively (Table 2). The decreased carrier lifetime was attributed to the faster charge carrier transfer process from the perovskite to the TiO2 layer, which is helpful for efficient charge transport and extraction. This was related to the improved interface contact properties due to the enhanced conductivity, and reduced defects or traps because of NaCl passivation.


18

Page 19 of 29

5x10

(b) 1

4

767 nm

4x10

4

3x10

4

2x10

4

1x10

4

0 650

TiO2

TiO2

TiO2-NaCl

Normalized Intensity

(a) 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


761 nm

TiO2-NaCl

0.1

0.01

700

750

800

850

0

50

100

150

Time (ns)

Wavelength (nm)

Figure 7. (a) PL spectra of perovskite thin films based on TiO2 surfaces without and with NaCl doping treatment. (b) TR-PL spectra of perovskite thin films based on TiO2 surfaces without and with NaCl doping treatment. Table 2. Fitted decay times of perovskite films based on TiO2 surfaces without and with NaCl doping treatment.

τ1 (ns)

Fraction 1

τ2 (ns)

Fraction 2

τave (ns)

TiO2

5.99

63 %

22.16

37 %

17.06

TiO2-NaCl

5.40

66 %

18.96

34 %

14.13

The device stability is an important issue for perovskite solar cell application and commercialization. Hence, the device stability was also studied by storing the un-encapsulated devices in the air condition (relative humidity < 30 %). It is expected that the NaCl doping treatment enhanced the device stability from 61 % to 79 % after 168 h storage in air conditions (Figure 8). According to previous studies, UV irradiation causes fast release of O2 on TiO2 surface, and induces large amount of deep trap states, which can cause fast degradation of the perovskite solar cells due to TiO2 photocatalytic degredation effect.39,40 While NaCl doping


19


could reduce the trap states as revealed by SCLC measurement and alleviate this effect. Hence, the improved interlayer contact should be responsible for the performance stability enhancement. The performance degradation was mainly likely caused by the spiro-OMeTAD layer, since many studies have proved this issue.41,42 It was thought that the stability could be further improved by using stable hole transport layer.43–45

1.0

Normalized efficiency

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 29

79 % 0.8 0.6

61 %

0.4 TiO2 TiO2-NaCl

0.2 0.0 0

30

60

90

120

150

180

Time (h)

Figure 8. Device stability of the perovskite solar cells based on TiO2 and NaCl modified TiO2 electron transport layers. Conclusions In conclusion, TiO2 was successfully modified by immersing the TiO2 into NaCl solution. It was found that NaCl treatment can enhance the TiO2 electronic properties and optimize perovskite morphology. Meanwhile, the improved interface contact could enhance the charge transfer, and suppress the charge recombination, which could be confirmed by the time-resolved PL and TPC/TPV measurements. Using the NaCl treated TiO2 as electron transport layer, more efficient perovskite solar cell with high power conversion efficiency of 18.3% was achieved, and this efficiency is much higher than that of the PSC based on pristine-TiO2 (15.1 %). This study


20

Page 21 of 29 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


provides a facile and effective method for TiO2 modification and enhancing the photovoltaic performance of PSCs further.

ASSOCIATED CONTENT Supporting Information. Photovoltaic performance, J - V curves, AFM images, UPS spectra, XPS spectra, film conductivity, cross-section SEM image. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (61604119, 61704131), Natural Science Foundation of Shaanxi Province (2017JQ6002, 2017JQ6031), the Fundamental Research Funds for the Central Universities, and Young Talent fund of China Association for Science and Technology. REFERENCES (1)

Hodes, G. Perovskite-Based Solar Cells. Science 2013, 342, 317–318.


21


Page 22 of 29

(2)

Service, R. F. Perovskite Solar Cells Keep On Surging. Science 2014, 344, 458.

(3)

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

Gratzel, M.; Han, L. Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Charge Extraction Layers. Science 2015, 350, 944–948. (4)

Shao, Y.; Xiao, Z.; Bi, C.; Yuan, Y.; Huang, J. Origin and Elimination of Photocurrent

Hysteresis by Fullerene Passivation in CH3NH3PbI3 Planar Heterojunction Solar Cells. Nat. Commun. 2014, 5, 5784. (5)

Sun, X.; Zhang, C.; Chang, J.; Yang, H.; Xi, H.; Lu, G.; Chen, D.; Lin, Z.; Lu, X.; Zhang,

J.; Hao, Y. Mixed-Solvent-Vapor Annealing of Perovskite for Photovoltaic Device Efficiency Enhancement. Nano Energy 2016, 28, 417–425. (6)

Chang, J.; Zhu, H.; Li, B.; Isikgor, F. H.; Hao, Y.; Xu, Q.; Ouyang, J. Boosting the

Performance of Planar Heterojunction Perovskite Solar Cell by Controlling the Precursor Purity of Perovskite Materials. J. Mater. Chem. A 2016, 4, 887–893. (7) Zhou, L.; Chang, J.; Liu, Z.; Sun, X.; Lin, Z.; Chen, D.; Zhang, C.; Zhang, J.; Hao, Y. Enhanced Planar Perovskite Solar Cell Efficiency and Stability Using a perovskite/PCBM Heterojunction Formed in One Step. Nanoscale 2018, 10, 3053–3059. (8)

Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-Hole

Diffusion Lengths ≥ 175 µm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347, 967–970. (9)

Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland,

S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. a; Mohammed, O. F.;


22

Page 23 of 29 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


Sargent, E. H.; Bakr, O. M. Low Trap-State Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science 2015, 347, 519–522. (10) 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. (11) Zhang, T.; Wu, J.; Zhang, P.; Ahmad, W.; Wang, Y.; Alqahtani, M.; Chen, H.; Gao, C.; Chen, Z. D.; Wang, Z.; Li, S. High Speed and Stable Solution-Processed Triple Cation Perovskite Photodetectors. Adv. Opt. Mater. 2018, 6, 1701341. (12) 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. (13) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Grätzel, M.; Park, N.-G. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (14) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Sequential Deposition as a Route to High-Performance Perovskite-Sensitized Solar Cells. Nature 2013, 499, 316–319. (15) Park, N.-G. Organometal Perovskite Light Absorbers Toward a 20% Efficiency LowCost Solid-State Mesoscopic Solar Cell. J. Phys. Chem. Lett. 2013, 4, 2423–2429. (16) NREL—National Renewable Energy Laboratory Chart, Rev. 01-07-2018, Http:// www.nrel.gov/ncpv/images/efficiency_chart.jpg.


23


Page 24 of 29

(17) Chang, J.; Zhu, H.; Xiao, J.; Isikgor, F. H.; Lin, Z.; Hao, Y.; Zeng, K.; Xu, Q.-H.; Ouyang, J. Enhancing the Planar Heterojunction Perovskite Solar Cell Performance through Tuning the Precursor Ratio. J. Mater. Chem. A 2016, 4, 7943–7949. (18) Chang, J.; Lin, Z.; Zhu, H.; Isikgor, F. H.; Xu, Q.-H.; Zhang, C.; Hao, Y.; Ouyang, J. Enhancing the Photovoltaic Performance of Planar Heterojunction Perovskite Solar Cells by Doping the Perovskite Layer with Alkali Metal Ions. J. Mater. Chem. A 2016, 4, 16546–16552. (19) Jiang, Q.; Zhang, L.; Wang, H.; Yang, X.; Meng, J.; Liu, H.; Yin, Z.; Wu, J.; Zhang, X.; You, J. Enhanced Electron Extraction Using SnO2 for High-Efficiency Planar-Structure HC(NH2)2PbI3-Based Perovskite Solar Cells. Nat. Energy 2016, 2, 16177. (20) Zhang, P.; Wu, J.; Zhang, T.; Wang, Y.; Liu, D.; Chen, H.; Ji, L.; Liu, C.; Ahmad, W.; Chen, Z. D.; Li, S. Perovskite Solar Cells with ZnO Electron-Transporting Materials. Adv. Mater. 2017, 30, 1703737. (21) Singh, T.; Singh, J.; Miyasaka, T. Role of Metal Oxide Electron-Transport Layer Modification on the Stability of High Performing Perovskite Solar Cells. ChemSusChem 2016, 9, 2559–2566. (22) Chang, J.; Ming Kam, Z.; Lin, Z.; Zhu, C.; Zhang, J.; Wu, J. TiOx/Al Bilayer as Cathode Buffer Layer for Inverted Organic Solar Cell. Appl. Phys. Lett. 2013, 103, 173303. (23) Li, M.; Huan, Y.; Yan, X.; Kang, Z.; Guo, Y.; Li, Y.; Liao, X.; Zhang, R.; Zhang, Y. Efficient Yttrium(III) Chloride-Treated TiO2 Electron Transfer Layers for PerformanceImproved and Hysteresis-Less Perovskite Solar Cells. ChemSusChem 2018, 11, 171.


24

Page 25 of 29 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) Correa Baena, J. P.; Steier, L.; Tress, W.; Saliba, M.; Neutzner, S.; Matsui, T.; Giordano, F.; Jacobsson, T. J.; Srimath Kandada, A. R.; Zakeeruddin, S. M.; Petrozza, A.; Abate, A.; Nazeeruddin, M. K.; Grätzel, M.; Hagfeldt, A. Highly Efficient Planar Perovskite Solar Cells through Band Alignment Engineering. Energy Environ. Sci. 2015, 8, 2928–2934. (25) Gu, X.; Wang, Y.; Zhang, T.; Liu, D.; Zhang, R.; Zhang, P.; Wu, J.; Chen, Z. D.; Li, S. Enhanced Electronic Transport in Fe3+ -Doped TiO2 for High Efficiency Perovskite Solar Cells. J. Mater. Chem. C 2017, 5, 10754–10760. (26) Ma, J.; Chang, J.; Lin, Z.; Guo, X.; Zhou, L.; Liu, Z.; Xi, H.; Chen, D.; Zhang, C.; Hao, Y. Elucidating the Roles of TiCl4 and PCBM Fullerene Treatment on TiO2 Electron Transporting Layer for Highly Efficient Planar Perovskite Solar Cells. J. Phys. Chem. C 2018, 122, 1044–1053. (27) Yang, D.; Yang, R.; Zhang, J.; Yang, Z.; (Frank) Liu, S.; Li, C. High Efficiency Flexible Perovskite Solar Cells Using Superior Low Temperature TiO2. Energy Environ. Sci. 2015, 8, 3208–3214. (28) Yang, D.; Zhou, X.; Yang, R.; Yang, Z.; Yu, W.; Wang, X.; Li, C.; Liu, S. (Frank); Chang, R. P. H. Surface Optimization to Eliminate Hysteresis for Record Efficiency Planar Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 3071–3078. (29) Giordano, F.; Abate, A.; Correa Baena, J. P.; Saliba, M.; Matsui, T.; Im, S. H.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Hagfeldt, A.; Graetzel, M. Enhanced Electronic Properties in Mesoporous TiO2 via Lithium Doping for High-Efficiency Perovskite Solar Cells. Nat. Commun. 2016, 7, 10379.


25


Page 26 of 29

(30) Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; García de Arquer, F. P.; Fan, J. Z.; QuinteroBermudez, R.; Yuan, M.; Zhang, B.; Zhao, Y.; Fan, F.; Li, P.; Quan, L. N.; Zhao, Y.; Lu, Z.-H.; Yang, Z.; Hoogland, S.; Sargent, E. H. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation. Science 2017, 355, 722–726. (31) Liu, D.; Li, S.; Zhang, P.; Wang, Y.; Zhang, R.; Sarvari, H.; Wang, F.; Wu, J.; Wang, Z.; Chen, Z. D. Efficient Planar Heterojunction Perovskite Solar Cells with Li-Doped Compact TiO2 Layer. Nano Energy 2017, 31, 462–468. (32) Zhang, H.; Shi, J.; Xu, X.; Zhu, L.; Luo, Y.; Li, D.; Meng, Q. Mg-Doped TiO2 Boosts the Efficiency of Planar Perovskite Solar Cells to Exceed 19%. J. Mater. Chem. A 2016, 4, 15383–15389. (33) Peng, J.; Duong, T.; Zhou, X.; Shen, H.; Wu, Y.; Mulmudi, H. K.; Wan, Y.; Zhong, D.; Li, J.; Tsuzuki, T.; Weber, K. J.; Catchpole, K. R.; White, T. P. Efficient Indium-Doped TiOx Electron Transport Layers for High-Performance Perovskite Solar Cells and Perovskite-Silicon Tandems. Adv. Energy Mater. 2017, 7, 1601768. (34) Chen, B.-X.; Rao, H.; Li, W.; Xu, Y.; Chen, H.; Kuang, D.; Su, C. Achieving HighPerformance Planar Perovskite Solar Cell with Nb-Doped TiO2 Compact Layer by Enhanced Electron Injection and Efficient Charge Extraction. J. Mater. Chem. A 2016, 4, 5647–5653. (35) Koster, L. J. A.; Mihailetchi, V. D.; Ramaker, R.; Blom, P. W. M. Light Intensity Dependence of Open-Circuit Voltage of Polymer : Fullerene Solar Cells. Appl. Phys. Lett. 2005, 86, 123509.


26

Page 27 of 29 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


(36) Mandoc, M. M.; Veurman, W.; Koster, L. J. a.; de Boer, B.; Blom, P. W. M. Origin of the Reduced Fill Factor and Photocurrent in MDMO-PPV:PCNEPV All-Polymer Solar Cells. Adv. Funct. Mater. 2007, 17, 2167–2173. (37) Li, Y.; Zhao, Y.; Chen, Q.; Yang, Y.; 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. (38) Sun, C.; Wu, Z.; Yip, H.-L.; Zhang, H.; Jiang, X.-F.; Xue, Q.; Hu, Z.; Hu, Z.; Shen, Y.; Wang, M.; Huang, F.; Cao, Y. Amino‐Functionalized Conjugated Polymer as an Efficient Electron Transport Layer for High‐Performance Planar‐Heterojunction Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1501534. (39) Zhang, P.; Wu, J.; Wang, Y.; Sarvari, H.; Liu, D.; Chen, Z. D.; Li, S. Enhanced Efficiency and Environmental Stability of Planar Perovskite Solar Cells by Suppressing Photocatalytic Decomposition. J. Mater. Chem. A 2017, 5, 17368–17378. (40) Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; García de Arquer, F. P.; Fan, J. Z.; QuinteroBermudez, R.; Yuan, M.; Zhang, B.; Zhao, Y.; Fan, F.; Li, P.; Quan, L. N.; Zhao, Y.; Lu, Z.-H.; Yang, Z.; Hoogland, S.; Sargent, E. H. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation. Science 2017, 355, 722–726. (41) Leijtens, T.; Eperon, G. E.; Noel, N. K.; Habisreutinger, S. N.; Petrozza, A.; Snaith, H. J. Stability of Metal Halide Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500963. (42) Roose, B.; Gödel, K. C.; Pathak, S.; Sadhanala, A.; Baena, J. P. C.; Wilts, B. D.; Snaith, H. J.; Wiesner, U.; Grätzel, M.; Steiner, U.; Abate, A. Enhanced Efficiency and Stability of


27


Page 28 of 29

Perovskite Solar Cells Through Nd-Doping of Mesostructured TiO2. Adv. Energy Mater. 2016, 6, 1501868. (43) Bella, F.; Griffini, G.; Correa-Baena, J.-P.; Saracco, G.; Gratzel, M.; Hagfeldt, A.; Turri, S.; Gerbaldi, C. Improving Efficiency and Stability of Perovskite Solar Cells with Photocurable Fluoropolymers. Science 2016, 354, 203–206. (44) Liu, Z.; Chang, J.; Lin, Z.; Zhou, L.; Yang, Z.; Chen, D.; Zhang, C.; Liu, S. F.; Hao, Y. High-Performance Planar Perovskite Solar Cells Using Low Temperature, Solution-CombustionBased Nickel Oxide Hole Transporting Layer with Efficiency Exceeding 20%. Adv. Energy Mater. 2018, 1703432. (45) You, J.; Meng, L.; Song, T.-B.; Guo, T.-F.; Yang, Y. (Michael); Chang, W.-H.; Hong, Z.; Chen, H.; Zhou, H.; Chen, Q.; Liu, Y.; 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.


28

Page 29 of 29 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 Graphic


29

Enhanced Planar Perovskite Solar Cell Performance via Contact

Recommend Documents