Solution-Processed Nb:SnO2 Electron Transport ... - ACS Publications

Subscriber access provided by Fudan University

Article

Solution-processed Nb:SnO2 electron transport layer for efficient planar perovskite solar cells Xiaodong Ren, Dong Yang, Zhou Yang, Jiangshan Feng, Xuejie Zhu, Jinzhi Niu, Yucheng Liu, Wangen Zhao, and Shengzhong (Frank) Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b13362 • Publication Date (Web): 20 Dec 2016 Downloaded from http://pubs.acs.org on December 21, 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 32

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

Solution-processed Nb:SnO2 electron transport layer for efficient planar perovskite solar cells †

†,*

Xiaodong Ren, Dong Yang, Niu,

†

†

†

†

†

Zhou Yang, Jiangshan Feng, Xuejie Zhu, Jinzhi †

†‡

Yucheng Liu, Wangen Zhao, Shengzhong (Frank) Liu , ,*

AUTHOR ADDRESS †

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

Education; Shaanxi Key Laboratory for Advanced Energy Devices; Shaanxi Engineering Lab for Advanced Energy Technology; School of Materials Science & Engineering, Shaanxi Normal University, Xi’an, 710119, P. R. China ‡

Dalian Institute of Chemical Physics, Dalian National Laboratory for Clean Energy,

Chinese Academy of Sciences, Dalian, 116023, P. R. China

KEYWORDS: perovskite, Nb:SnO2, low temperature, solution processing, solar cells.

1 ACS Paragon Plus Environment


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 32

ABSTRACT: Electron transport layer (ETL), facilitating charge carrier separation and electron extraction, is a key component in planar perovskite solar cells (PSCs). We have developed an effective ETL using low-temperature solution-processed (LTSP) Nb-doped SnO2 (Nb:SnO2). Compared to the pristine SnO2, the power conversion efficiency (PCE) of PSCs based on Nb:SnO2 ETL is raised to 17.57% from 15.13%. The splendid performance is attributed to the excellent optical and electronic properties of the Nb:SnO2 material, such as smooth surface, high electron mobility, appropriate electrical conductivity, therefore a better growth platform for a high quality perovskite absorber layer. Experimental analyses reveal that the Nb:SnO2 ETL significantly enhances the electron extraction and effectively suppresses charge recombination, leading to improved solar cell performance.

1. INTRODUCTION

A new class of organic-inorganic halide perovskite materials have been developed for high performance photovoltaic and optoelectronic applications, such as solar cell, light emission diode, laser and photodetector, etc. Thanks to their remarkable photophysical properties including appropriate bandgap, high optical absorption coefficient, high charge carrier mobility1-6, low trap density and surprisingly high tolerance to defects7-11. In only a few years, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been rapidly increased from 3.8% to >22%12-23. Theoretical calculation reveals that the PCE of a single-junction PSC may be increased up to 33.5%24, which is comparable with the most popular inorganic solar 2 ACS Paragon Plus Environment

Page 3 of 32

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


cells including single-crystalline silicon, CdTe, and copper indium gallium selenide (CIGS). Moreover, it can be fabricated using facile solution-processing at low-temperature, making it particularly attractive for low cost comercialization25. Most high PCE PSCs are based on meso-superstructure with a layer of mesoscopic metal oxide such as TiO2, Al3O2, ZrO2, etc. The challenge is that it often requires complicated and high temperature >450 °C processing15,

26-27

. In comparison, the

planar-type PSC has witnessed an unprecedented development recently since its simple structure, relatively low temperature fabrication and facile preparation processes7, 28-29. In the planar-type device configuration, the perovskite absorber layer is usually sandwiched between a layer of electron transport layer (ETL) and another hole transport layer (HTL)30. The interface layers aid effective charge extraction and inhibit interfacial carrier recombination for improved cell characteristics31-32. There have been efforts studying ETL-free device configuration, however their efficiency are lower compared with the devices with ETLs31, 33. For

the

regular

PSCs

architecture,

the

2,2ˊ,7,7ˊ-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9ˊ-spirobifluorene (spiro-OMeTAD)2,

8, 34-37

and poly(triarlyamine) (PTAA)18,

21, 38

with appropriate

dopants are most often used HTLs, while a few metal oxides including TiO239-46 and ZnO47-48 are most popular ETLs, in addition some ternary compounds also used as ETLs, such as Zn2SnO449-50, SrTiO351, etc. Theoretically, an ideal ETL needs to provide: (i) good optical transparency, (ii) decent electrical conductivity, (iii) large electron mobility, (iv) low-temperature processability, and (v) well-matched energy 3 ACS Paragon Plus Environment


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 32

levels with the perovskite material52. Unfortunately, the best TiO2 and ZnO ETLs are often attained using high temperature treatment53-55. More recently, tin oxide (SnO2) is developed as an effective ETL due to its high optical transmission and low temperature preparation32, 56-57. Snaith et al. formed a SnO2 ETL by chemical bath deposition at 80 ˚C to achieve high PCE up to 17.1%58. Alex et al. employed nanocrystalline SnO2 as ETL to obtain PCE as high as 18.8%25. Miyasaka and Kuang et al. developed SnO2 films at low temperature and attained respectable efficiencies over 13%59, 60. Grätzel et al. achieved 18% PCE using atomic layer deposition61. Lately, Yan et al. raised the PCE to 19.12% by using SnO2 cooperate with fullerene62. Herein, we report our development that, by doping SnO2, we realized a more effective low-temperature solution-processed (LTSP) Nb-doped SnO2 (Nb:SnO2) ETL. Comparing to the pristine SnO2, the PCE of Nb:SnO2 based PSC is improved to 17.57% from 15.13%. The PCE improvement is attributed to improved properties including higher electron mobility, good electrical conductivity, and faster electron extraction.

2. EXPERIMENTAL 2.1 Materials 4-tert-butylpyridine (t-BP), and Li-bis(trifluoromethanesulfonyl) imide (Li-TFSI) were purchased from Aladdin-reagent. PbI2 (99.99%), PbBr (99.99%), niobium ethoxide (99.999%), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) were ordered from Alfa-Aesar. SnCl2·2H2O (99.99%) was purchased from Aladdin. 4 ACS Paragon Plus Environment

Page 5 of 32

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


Ethanol, diethyl ether, acetonitrile, hydrobromic acid (HBr, 57 wt.% in water, 99.99%) and hydroiodic acid (HI, 57 wt.% in water, 99.99%), chlorobenzene (≥ 99.0%), formamidine (FA) and methylamine (MA) (33 wt.% in absolute ethanol) were purchased from Sinopharm Chemical Reagent Corporation Co., Ltd. Spiro-OMeTAD (≥ 99.0%) was ordered from Dalian Lichuang technology co., LTD. MABr and FAI were synthesized as reported in our earlier work to achieve record efficiencies7, 9 34. All solvents were used without any further purification. 2.2 Device fabrication The fluorine-doped tin oxide (FTO) glass was cleaned using acetone, isopropanol and ethanol separately in ultrasonic bath for 30 min each, then dried by flowing nitrogen. The FTO substrates underwent an oxygen plasma treatment for 15 minutes before used for spin-coating SnCl2·2H2O in ethanol solution. A SnO2 ETL with different thickness was prepared by spin-coating different concentration of SnCl2·2H2O at 3000 rpm in ambient56. The layers were then sintered in air at 190 °C for 60 min. The Nb:SnO2 mixed precursor solution was prepared by adding different niobium ethoxide into the SnCl2·2H2O solution. Nb:SnO2 ETLs were fabricated by spin-coating at 3000 rpm in ambient, and the films were annealed at 190 °C in air. Once cooling down to room-temperature, the samples were treated again with oxygen plasma for 15 min before the perovskite deposition. 172 mg FAI (1.0 M), 507 mg PbI2 (1.1 M), 22.4 mg MABr (0.2 M) and 73.4 mg PbBr2 (0.2 M) were dissolved in 1 mL anhydrous DMF:DMSO = 4:1 (v:v) to prepare the (FAPbI3)0.85(MAPbBr3)0.15 perovskite precursor solution61. The solution was stirred at room temperature for 12 h. 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 32

The solution was then spin-coated onto the FTO/ETL substrate by a consecutive two-step process at 1000 and 4000 rpm for 20 and 40 s, respectively. During the second step, 200 µL chlorobenzene was added onto the substrate before the spinning ended. The substrates were then heated at 150 °C for 10 min in a nitrogen filled glove box, the film color changes from orange-red to dark-brown. The 90 mg/mL spiro-OMeTAD in 1 mL chlorobenzene with addition of 36 µL t-BP and 22 µL Li-TFSI solution (520 mg in 1 mL acetonitrile) was spin-coated on the perovskite films at 5000 rpm for 40 seconds. The samples were kept in a desiccator for overnight. Finally, 80 nm gold electrodes were deposited using a thermal evaporator. 2.3 Characterization The X-ray diffraction (XRD) was carried out on a Bruker D8 (Cu Kα radiation, λ = 1.5418 Å). The absorption and transmittance spectra were measured using an UV-Vis-NIR spectrometer (Perkin-Elmer, Lambda 950). The X-ray photoelectron spectroscopy (XPS) was performed on a photoelectron spectrometer (ESCALAB 250Xi, Thermo Fisher Scientific). Field emission scanning electron microscopy (SEM, HITACHI, SU-8020) was utilized to investigate the surface morphologies for pristine SnO2, Nb:SnO2 and perovskite films. Photoluminescence (PL) (excitation at 532 nm) and time-resolved PL (TRPL) (excitation at 405 nm and emission at 760 nm) were measured with Edinburgh Instruments Ltd (FLS980). The J-V curves were measured using a computer-controlled Keithley 2400 source under ambient condition, and the illumination intensity was adjusted at 100 mW cm-2 (AM 1.5G, SAN-EI ELECTRIC XES-40S2-CE solar simulator), as calibrated by a NREL-traceable KG5 6 ACS Paragon Plus Environment

Page 7 of 32

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


filtered silicon reference cell. The device area of 9 mm2 was defined by a metal mask. All devices scanned with reverse and forward under standard test procedure at a scan rate of 0.24 V s-1. The external quantum efficiency (EQE) was characterized on the QTest Station 500TI system (Crowntech. Inc., USA). The monochromatic light intensity for EQE was calibrated using a reference silicon photodiode.

3. RESULTS AND DISCUSSION 3.1 Characterization of the SnO2 and Nb:SnO2 films The SnCl2·2H2O in ethanol solution with different Nb contents was spin-coated onto the glass substrates, followed by thermal annealing at 190 °C for 60 minutes. The composition and bonding type of the Nb:SnO2 film were measured using XPS. The typical XPS spectra of Nb:SnO2 is shown in Figure 1a. It is clear that the O, Sn and Nb peaks are centered at ~ 530, ~ 487 and ~ 495 eV, respectively. High-resolution Sn3d (Figure 1b) spectrum reveals that there are two different peaks located in 486.78 and 495.23 eV, corresponding to Sn3d5/2 and Sn3d3/2, respectively, giving a spin orbit coupling of 8.45 eV, the signature of Sn4+.63 In addition, the main binding energy of 530.45 eV is attributed to the O1s, as shown in Figure 1c, indicating the O2− state in SnO2. The higher binding energy (531.77 eV) can be assigned to the chemisorbed oxygen atoms or hydroxyl groups56. Figure 1d gives the Nb3d5/2 and Nb3d3/2 peaks at 206.87 and 209.64 eV, respectively64. It is clear from above that Nb5+ doped SnO2 is successfully attained.



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 32

Figure 1. (a) The typical XPS survey of Nb:SnO2 film. High-resolution XPS (b) Sn3d, (c) O1s, and (d) Nb3d peaks of the Nb:SnO2 film deposited on a glass substrate.

The crystallinity and the preferred crystal orientation of pristine SnO2 and Nb:SnO2 films were analyzed using XRD, as shown in Figure 2a. The only one peak at 31.80° is attributed to the rutile type tetragonal structure of SnO2 [JCPDS50-1429], corresponding to the (111) diffraction. It is obvious that the samples remain the rutile phase irrespective of the Nb doping, whereas the (111) rutile peak slight shifts to a smaller theta angle with increased Nb doping (Figure 2b) as expected by the bigger ionic radius of Nb5+ (0.70 Å) comparing to that of Sn4+ (0.69 Å), suggesting effective Nb5+ doping into the SnO2 host lattice58.


Page 9 of 32

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 2. (a) XRD patterns of pristine SnO2 and Nb:SnO2 films with different Nb contents deposited on bare glass substrates. (b) Details of the XRD patterns at (111) peak.

Figure 3 a-b displays top-view SEM images of the SnO2 and Nb:SnO2 films, both appeared to be flat, uniform and pin-hole free. The surface morphology of the Nb:SnO2 is similar to that of the pristine SnO2 film, showing that the Nb-doping does not change the film morphology as expected. Figure 3 c-d shows AFM height images of the SnO2 and the Nb:SnO2 films, the root-mean-square (RMS) roughness is decreased from 5.73 nm to 5.08 nm by the Nb doping. Note that the smoother surface is beneficial to form a high quality perovskite layer65.



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 32

Figure 3. Top-view SEM images of (a) SnO2 and (b) Nb:SnO2 films coated on FTO substrates. AFM height images of the (c) SnO2 and (d) Nb:SnO2 films.

As electrical conductivity is a critical figure of merit for the ETL, Figure 4a and Supporting Information Table S1 shows the electrical conductivity of ETLs deposited on FTO and bare glass substrates. It is apparent that the electrical conductivity of the SnO2 film is significantly increased by the Nb-doping regardless of different substrates. Figure 4b gives optical transmission spectra of the SnO2 and Nb:SnO2, both showing excellent transmittance in the wavelength range of 400-800 nm. In addition, the electron mobility is measured using electron-only devices using space-charge-limited-current (SCLC). The details are shown in the Supporting Information. Supporting Information Figure S1 shows the current density-voltage 10 ACS Paragon Plus Environment

Page 11 of 32

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


(J-V) curves based on SnO2 and Nb:SnO2 films fitted using the Mott-Gurney law66. The electron mobility is increased from 1.02×10-4 to 2.16×10-4 cm2 V-1 s-1 by the Nb doping. A low mobility of the electron transport layer indicates more traps existed leading to charge accumulation at the interface and inferior charge transport67. The dark current-voltage (I-V) analysis for electron only devices were used to quantify the electron trap-state density in the SnO2 and Nb:SnO2 films (Supporting Information Figure S2). It is clear that the linear relationship (blue line) indicates an ohmic response of the electron only device at low bias voltage. Then the current quickly increase nonlinearly (green line) when the bias voltage exceeds the kink point, demonstrating that the trap states are completely filled. The trap state density are calculated by following equation (1):34

=

(1) 2

where e is the elementary charge of the electron, L the thickness of the SnO2 and Nb:SnO2 film, ε the relative dielectric constant of the SnO2, ε0 the vacuum permittivity, and nt the trap-state density. The VTFL can be obtained from the kink point in the dark I-V curve. The VTFL of the devices based on SnO2 (1.88 V) is higher than that of Nb:SnO2 (1.37 V). The density of electron traps in the SnO2 is determined 2.39×1015 cm-3 higher than that of the Nb:SnO2 (1.74×1015 cm-3). It is clear that Nb-doping effectively passivates electron traps, leading to higher electron mobility.



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 32

Figure 4. (a) I-V characteristics of SnO2 and Nb:SnO2 films. (b) Transmission spectra of bare FTO, pristine SnO2 and Nb:SnO2 with different Nb contents.

3.2 Photovoltaic performance The above measurements show that the SnO2 properties is significantly improved by the Nb-doping including enhanced electron mobility, smoother surface and larger electrical conductivity. The excellent performance inspired us to design and fabricate PSCs using the Nb:SnO2 ETL. Figure 5a shows the device structure, wherein the FTO is employed as the cathode, SnO2 or Nb:SnO2 film as the ETL, the (FAPbI3)0.85(MAPbBr3)0.15 as the absorber layer, the Spiro-OMeTAD as the HTL, and the gold layer as the anode. Figure 5b gives a cross-sectional SEM image of the completed device, the grain boundary are vertical to the substrate, benefiting to the carriers transport collection.36 Supporting Information Figure S3a shows the top-view SEM of the perovskite film deposited on the LTSP Nb:SnO2 ETL. The perovskite film exhibits smooth surfaces, big crystalline size and good coverage. The XRD pattern shows that the perovskite film is similar comparing to those reported in prior


Page 13 of 32

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


art

(Supporting

Information

Figure

S3b)62.

Figure 5. (a) Device structure of the PSC using LTSP Nb:SnO2 as ETL. (b) Cross-sectional SEM image of the PSC completed device.

It is found that the PSC performance can be significantly affected by the SnO2 ETL thickness. The device with too thick ETL leads to a high series resistance (Rs) and a small shunt resistance (Rsh), reducing the Jsc and FF. However, when the ETL is thinner, pin-holes are seen in the film, leading to direct contact between the perovskite and the FTO electrode and serious carrier recombination. In present study, the SnO2 film thickness is adjusted by controlling SnCl2·2H2O-ethanol solution concentration. Supporting Information Figure S4 shows J-V curves as a function of SnO2 ETL thickness. The key J-V parameters are summarized in Supporting Information Table S2. The PCE is optimized to 15.13% when 60 nm thick SnO2 is used by controlling the precursor concentration at 0.07 mol mL-1. Supporting Information Figure S5 shows the device performance optimized as a function of Nb contents, with key J-V parameters summarized in Supporting Information Table S3. It appears that the PCE is increased from 15.13% to 17.57% 13 ACS Paragon Plus Environment


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 32

when the Nb content is changed from 0 to 0.50%. When the Nb content is further increased to 2.00%, the PCE drops to 15.11%. It is apparent that there is an optimum Nb content for the device performance at 0.50%. Figure 6a shows the J-V curves of the champion devices based on both SnO2 and Nb:SnO2 ETLs measured under reverse and forward scan directions. Table 1 lists the key J-V parameters of the champion devices using both ETLs. The device based on the pristine SnO2 ETL using reverse scan direction gives a PCE of 15.13% with Jsc 21.65 mA cm-2, Voc 1.06 V and FF 0.659. While the Nb is doped into the SnO2 ETL, the PCE is rapidly increased to 17.57%. Comparing to the control device, all key J-V parameters are significantly improved. The larger Jsc and FF may be ascribed to the high electron mobility and electrical conductivity of the Nb:SnO2 ETL. The high Voc is likely due to the reduced charge recombination and improved electron extraction. Figure 6b shows the external quantum efficiency (EQE) and integrated current based on various ETLs. The EQE integrated current density for the pristine SnO2 based cell is 21.11 mA cm-2 and it is increased to 21.79 mA cm-2 for the Nb:SnO2 based device, in good agreement with the J-V measurement value. The reflection and transmission of a complete device are characterized, and the internal quantum efficiency (IQE) is calculated from the EQE, reflection and transmission spectra, with the results shown in Supporting Information Figure. S6. It is clear that the IQE of the Nb:SnO2 based device at ~ 480 nm is up to 99%, indicating that the carriers are effectively collected in the PSC using the Nb:SnO2 ETL.


Page 15 of 32

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 6. (a) The J-V curves of PSC devices based on pristine SnO2 and Nb:SnO2 under reverse and forward scanning directions. (b) EQE of the champion devices based on SnO2 and Nb:SnO2 ETLs. Table 1 The key parameters of champion PSCs based on pristine SnO2 and Nb:SnO2 ETLs.

SnO2

Nb:SnO2

Voc (V)

Jsc (mA cm-2)

FF

PCE (%)

Rs (Ω·cm2)

Rsh (kΩ·cm2)

reverse

1.06

21.65

0.659

15.13

8.58

2.95

forward

0.98

21.57

0.526

11.12

12.97

0.54

reverse

1.08

22.36

0.727

17.57

7.09

5.84

forward

1.04

21.51

0.570

12.75

10.84

1.49

To study the reproducibility of the material and process, we prepared more than 20 individual devices each using both SnO2 and Nb:SnO2 ETLs. Figure 7 shows the PCE histogram with the statistics summarized in Supporting Information Table S4. It is clear that all key J-V parameters displays narrower distribution with smaller standard deviation for the Nb:SnO2 based cells, indicating good reproducibility.



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 7. Histograms of PCEs measured for 20 cells using pristine SnO2 (a) and Nb:SnO2 (b) ETLs.

In addition, the stability of the devices based on SnO2 and Nb:SnO2 ETLs were studied. Using the bare devices without any encapsulation, we measured J-V on a daily basis for 12 days. In between measurements, the cells were kept in lab under ambient condition. The PCE value remained at 92% and 90% of its initial efficiency after 12 days for the devices based on SnO2 and Nb:SnO2 ETL respectively, as shown in Supporting Information Figure S7. We attribute the respectable stability to the high quality perovskite film2. In other words, Nb-doping has no negative impact on device stability.

3.3 Recombination To gain insight on the electron extraction and transport mechanism, the steady-state PL and TRPL were measured for the perovskite absorber layer deposited on both ETL based substrates. Figure 8a shows the PL spectra of the FTO/perovskite, FTO/SnO2/perovskite and FTO/Nb:SnO2/perovskite samples. The FTO/perovskite 16 ACS Paragon Plus Environment

Page 16 of 32

Page 17 of 32

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


shows apparently the highest PL intensity, indicating the serious recombination in the sample. The FTO/Nb:SnO2/perovskite sample shows the lowest, even lower than that of FTO/SnO2/perovskite, demonstrating more effective electron extraction. Figure 8b displays the TRPL spectra for the same samples. The PL decay time and amplitudes are fitted using an exponential equation (2)

() = exp (−/ ) + K (2)

where Ai is the decay amplitude, τi the decay time and K a constant for the base-line offset. All parameters are listed in Table 2.

Table 2. Parameters of the TRPL spectroscopy based on the FTO/perovskite, FTO/SnO2/perovskite and FTO/Nb:SnO2/ perovskite, respectively. τave

τ1

Amplitude τ1

τ2

Amplitude τ2

(ns)

(ns)

(%)

(ns)

(%)

FTO/perovskite

932.65

12.61

60.71

940.63

39.29

FTO/SnO2/perovskite

142.14

10.90

64.41

147.50

35.59

FTO/Nb:SnO2/perovskite

42.71

6.18

64.10

45.49

35.90

Sample

When the perovskite is deposited directly on the FTO, its PL decay time are τ1 = 12.61 ns and τ2 = 940.63 ns, respectively. When the perovskite is deposited on FTO/SnO2, both τ1 and τ2 decrease to 10.90 and 147.50 ns. For the FTO/Nb:SnO2/perovskite sample, both τ1 and τ2 are further reduced to 6.18 ns and



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

45.49 ns, respectively. Compared to the FTO/SnO2/perovskite sample, the amplitude of the relatively long decay time is reduced to 64.10%, while the corresponding amplitude of the fast decay time increased to 35.90%. The average lifetime (τave) is estimated using the equation (3).

!

=

∑ (3) ∑

Compared to the FTO/perovskite

sample,

the average

decay time of

FTO/SnO2/perovskite significantly is reduced to 142.14 ns from 932.65 ns. It is further dropped to 42.71 ns when the Nb:SnO2 ETL is used, demonstrating that the electron transfer is faster from the perovskite film into the Nb:SnO2 ETL, as witnessed by stronger steady-state PL quenching in the Nb:SnO2/perovskite sample (Figure 8a). The faster electron injection rate from the perovskite to the Nb:SnO2 ETL is beneficial to the charge separation and effectively suppressed charge recombination at the perovskite/ETL interface, leading to higher Jsc and Voc, in good agreement with the J-V and IPCE measurement.

Figure 8. (a) Steady-state PL spectra of the FTO/perovskite, FTO/SnO2/perovskite and FTO/Nb:SnO2/perovskite samples. (b) TRPL of perovskite absorbor deposited on different substrates. 18 ACS Paragon Plus Environment

Page 19 of 32

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. Conclusion In conclusion, we have demonstrated that LTSP Nb:SnO2 is an excellent ETL for high-performance perovskite solar cells, with the champion cell showing significantly higher PCE of 17.57% than that of devices based on pristine SnO2 ETL. The outstanding performance using the Nb:SnO2 ETL originates from improved surface morphology, higher electron mobility, larger electrical conductivity and enhanced electron

extraction.

Moreover,

considering

that

the

low-temperature

solution-processable fabrication, the Nb:SnO2 is demonstrated to be an effective ETL for low-cost PSCs.

ASSOCIATED CONTENT

Supporting Information.

The electrical conductivity of the SnO2 and Nb:SnO2 films, the current J-V curves based on SnO2 and Nb:SnO2 films fitting with the Mott-Gurney law, dark I–V curves of the electron-only devices revealing VTFL kink point behavior, top-view SEM image and XRD spectum of (FAPbI3)0.85(MAPbBr3)0.15 film, the J-V curves of the PSCs based on different thickness of SnO2 ETLs and the Nb:SnO2 ETL with different Nb contents, the IQE and stability of the PSCs based on the SnO2 and Nb:SnO2 ETLs. This material is available free of charge via the Internet at http://pubs.acs.org.



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 32

AUTHOR INFORMATION Corresponding Author *Dr. Dong Yang, [email protected]; *Prof. Shengzhong (Frank) Liu, [email protected].

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT

The authors acknowledge all support from the National Natural Science Foundation of China (61604090 and 61674098), the China Postdoctoral Science Foundation funded project (2015M580809), the Changjiang Scholar and Innovative Research Team

(IRT_14R33),

the

National

Key

Research

Program

of

China

(2016YFA0202403) and the Chinese National 1000-talent-plan program.

REFERENCES

1.

Hao, F.; Stoumpos, C. C.; Cao, D. H.; Chang, R. P. H.; Kanatzidis, M. G.,

Lead-free Solid-state Organic-inorganic Halide Perovskite Solar Cells. Nat. Photonics 2014, 8 (6), 489-494.

2.

Yang, D.; Yang, Z.; Qin, W.; Zhang, Y. L.; Liu, S. Z.; Li, C., Alternating Precursor

Layer Deposition for Highly Stable Perovskite Films Towards Efficient Solar Cells 20 ACS Paragon Plus Environment

Page 21 of 32

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


Using Vacuum Deposition. J. Mater. Chem. A 2015, 3 (18), 9401-9405.

3.

Xing, G. C.; Mathews, N.; Sun, S. Y.; Lim, S. S.; Lam, Y. M.; Gratzel, M.;

Mhaisalkar, S.; Sum, T. C., Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science 2013, 342 (6156), 344-347.

4.

Lin, Q. Q.; Armin, A.; Nagiri, R. C. R.; Burn, P. L.; Meredith, P., Electro-optics of

Perovskite Solar Cells. Nat. Photonics 2015, 9 (2), 106-112.

5.

Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon, S.

J.; Humphry-Baker, R.; Yum, J. H.; Moser, J. E.; Gratzel, M.; Park, N. G., Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591.

6.

Yin, W. J.; Shi, T.; Yan, Y., Unique Properties of Halide Perovskites as Possible

Origins of The Superior Solar Cell Performance. Adv. Mater. 2014, 26 (27), 4653-4658.

7.

Yang, D.; Zhou, X.; Yang, R. X.; Yang, Z.; Yu, W.; Wang, X. L.; Li, C.; Liu, S. Z.;

Chang, R. P. H., Surface Optimization to Eliminate Hysteresis for Record Efficiency Planar Perovskite Solar Cells. Energy Environ. Sci. 2016, 9 (10), 3071-3078.

8.

Yang, Z.; Cai, B.; Zhou, B.; Yao, T.; Yu, W.; Liu, S.; Zhang, W.-H.; Li, C., An

Up-Scalable Approach to CH3NH3PbI3 Compact Films for High-performance Perovskite Solar Cells. Nano Energy 2015, 15, 670-678.

9.

Liu, Y.; Yang, Z.; Cui, D.; Ren, X.; Sun, J.; Liu, X.; Zhang, J.; Wei, Q.; Fan, H.; 21 ACS Paragon Plus Environment


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 32

Yu, F.; Zhang, X.; Zhao, C.; Liu, S., Two-Inch-Sized Perovskite CH3NH3PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization. Adv. Mater. 2015, 27 (35), 5176-5183.

10. Liu, Y.; Zhang, Y.; Yang, Z.; Yang, D.; Ren, X.; Pang, L.; Liu, S. F., Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices. Adv. Mater. 2016, 28 (41), 9204-9209.

11. Liu, Y.; Sun, J.; Yang, Z.; Yang, D.; Ren, X.; Xu, H.; Yang, Z.; Liu, S. F., 20-mm-Large

Single-Crystalline

Formamidinium-Perovskite

Wafer for

Mass

Production of Integrated Photodetectors. Adv. Opt. Mater. 2016, 4 (11), 1829-1837.

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 (17), 6050-6051.

13. Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J., Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites.

Science 2012, 338 (6107), 643-647.

14. 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 (7458), 316-319.

15. Liu, M.; Johnston, M. B.; Snaith, H. J., Efficient Planar Heterojunction 22 ACS Paragon Plus Environment

Page 23 of 32

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


Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501 (7467), 395-398.

16. Im, J. H.; Jang, I. H.; Pellet, N.; Gratzel, M.; Park, N. G., Growth of CH3NH3PbI3 Cuboids with Controlled Size for High-Efficiency Perovskite Solar Cells. Nat.

Nanotechnol. 2014, 9 (11), 927-932.

17. Zhou, H. P.; Chen, Q.; Li, G.; Luo, S.; Song, T. B.; Duan, H. S.; Hong, Z. R.; You, J. B.; Liu, Y. S.; Yang, Y., Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345 (6196), 542-546.

18. Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., Compositional Engineering of Perovskite Materials for High-Performance Solar Cells.

Nature 2015, 517 (7535), 476-480.

19. Nie, W. Y.; Tsai, H. H.; Asadpour, R.; Blancon, J. C.; Neukirch, A. J.; Gupta, G.; Crochet, J. J.; Chhowalla, M.; Tretiak, S.; Alam, M. A.; Wang, H. L.; Mohite, A. D., High-Efficiency Solution-Processed Perovskite Solar Cells with Millimeter-Scale Grains. Science 2015, 347 (6221), 522-525.

20. Li, X.; Bi, D.; Yi, C.; Decoppet, J. D.; Luo, J.; Zakeeruddin, S. M.; Hagfeldt, A.; Gratzel, M., A Vacuum Flash-Assisted Solution Process for High-Efficiency Large-Area Perovskite Solar Cells. Science 2016, 353 (6294), 58-62.

21. Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I., High-Performance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange. Science 2015, 348 (6240), 1234-1237. 23 ACS Paragon Plus Environment


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

22. Laboratory,

N.

R.

E.

L.

Best

Research-Cell

Page 24 of 32

Efficiencies.

http://www.nrel.gov/ncpv/images/efficiency_chart.jpg.

23. Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Correa Baena, J. P.; Decoppet, J. D.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Gratzel, M.; Hagfeldt, A., Efficient Luminescent Solar Cells Based on Tailored Mixed-Cation Perovskites. Sci Adv 2016, 2 (1), e1501170.

24. Tsai, H.; Nie, W.; Blancon, J. C.; Stoumpos, C. C.; Asadpour, R.; Harutyunyan, B.; Neukirch, A. J.; Verduzco, R.; Crochet, J. J.; Tretiak, S.; Pedesseau, L.; Even, J.; Alam, M. A.; Gupta, G.; Lou, J.; Ajayan, P. M.; Bedzyk, M. J.; Kanatzidis, M. G., High-Efficiency Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells. Nature 2016, 536 (7616), 312-316.

25. Zhu, Z.; Bai, Y.; Liu, X.; Chueh, C. C.; Yang, S.; Jen, A. K., Enhanced Efficiency and Stability of Inverted Perovskite Solar Cells Using Highly Crystalline SnO2 Nanocrystals as the Robust Electron-Transporting Layer. Adv. Mater. 2016, 28 (30), 6478-6484.

26. Etgar, L.; Gao, P.; Xue, Z.; Peng, Q.; Chandiran, A. K.; Liu, B.; Nazeeruddin, M. K.; Gratzel, M., Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells. J. Am.

Chem. Soc. 2012, 134 (42), 17396-17399.

27. Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I., Solvent Engineering for High-Performance Inorganic–Organic Hybrid Perovskite Solar Cells.

Nat. Mater. 2014, 13 (9), 897-903. 24 ACS Paragon Plus Environment

Page 25 of 32

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


28. Sun, S. Y.; Salim, T.; Mathews, N.; Duchamp, M.; Boothroyd, C.; Xing, G. C.; Sum, T. C.; Lam, Y. M., The Origin of High Efficiency in Low-Temperature Solution-Processable Bilayer Organometal Halide Hybrid Solar Cells. Energy Environ

Sci 2014, 7 (1), 399-407.

29. Wang, Q.; Shao, Y. C.; Dong, Q. F.; Xiao, Z. G.; Yuan, Y. B.; Huang, J. S., Large Fill-Factor Bilayer Iodine Perovskite Solar Cells Fabricated by A Low-Temperature Solution-Process. Energy Environ. Sci. 2014, 7 (7), 2359-2365.

30. Chueh, C. C.; Li, C. Z.; Jen, A. K. Y., Recent Progress and Perspective in Solution-Processed Interfacial Materials for Efficient and Stable Polymer and Organometal Perovskite Solar Cells. Energy Environ. Sci. 2015, 8 (4), 1160-1189.

31. Ke, W.; Fang, G.; Wan, J.; Tao, H.; Liu, Q.; Xiong, L.; Qin, P.; Wang, J.; Lei, H.; Yang, G.; Qin, M.; Zhao, X.; Yan, Y., Efficient Hole-Blocking Layer-Free Planar Halide Perovskite Thin-Film Solar Cells. Nat. Commun. 2015, 6, 6700.

32. Ke, W.; Zhao, D.; Cimaroli, A. J.; Grice, C. R.; Qin, P.; Liu, Q.; Xiong, L.; Yan, Y.; Fang, G., Effects of Annealing Temperature of Tin Oxide Electron Selective Layers on the Performance of Perovskite Solar Cells. J. Mater. Chem. A 2015, 3 (47), 24163-24168.

33. Pascual, J.; Kosta, I.; T. Ngo, T.; Chuvilin, A.; Cabanero, G.; Grande, H. J.; Barea, E.; Mora-Seró, I.; Delgado, J. L.; Tena-Zaera, R., Electron Transport Layer-Free Solar Cells Based on Perovskite–Fullerene Blend Films with Enhanced Performance and Stability. ChemSusChem 2016, 9 (18), 2679-2685. 25 ACS Paragon Plus Environment


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 32

34. Yang, D.; Yang, R.; Ren, X.; Zhu, X.; Yang, Z.; Li, C.; Liu, S. F., Hysteresis-Suppressed High-Efficiency Flexible Perovskite Solar Cells Using Solid-State Ionic-Liquids for Effective Electron Transport. Adv. Mater. 2016, 28 (26), 5206-5213.

35. Ren, X.; Yang, Z.; Yang, D.; Zhang, X.; Cui, D.; Liu, Y.; Wei, Q.; Fan, H.; Liu, S. F., Modulating Crystal Grain Size and Optoelectronic Properties of Perovskite Films for Solar Cells by Reaction Temperature. Nanoscale 2016, 8 (6), 3816-3822.

36. Cui, D.; Yang, Z.; Yang, D.; Ren, X.; Liu, Y.; Wei, Q.; Fan, H.; Zeng, J.; Liu, S., Color-Tuned Perovskite Films Prepared for Efficient Solar Cell Applications. The J.

Phys. Chem. C 2016, 120 (1), 42-47.

37. Yang, D.; Yang, R. X.; Zhang, J.; Yang, Z.; Liu, S. Z.; Li, C., High Efficiency Flexible Perovskite Solar Cells Using Superior Low Temperature Tio2. Energy

Environ. Sci. 2015, 8 (11), 3208-3214.

38. Heo, J. H.; Han, H. J.; Lee, M.; Song, M.; Kim, D. H.; Im, S. H., Stable Semi-Transparent CH3NH3PbI3planar Sandwich Solar Cells. Energy Environ. Sci. 2015, 8 (10), 2922-2927.

39. Wei, Q.; Yang D.; Yang Z.; Ren, X.; Liu, Y.; Feng, J.; Zhu, X.; Liu, S., Effective Solvent-Additive Enhanced Crystallization and Coverage of Absorber Layers for High Efficiency Formamidinium Perovskite Solar Cells. RSC Adv. 2016, 6 (62), 56807–56811.


Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40. Ahn, N.; Son, D. Y.; Jang, I. H.; Kang, S. M.; Choi, M.; Park, N. G., Highly Reproducible Perovskite Solar Cells with Average Efficiency of 18.3% and Best Efficiency of 19.7% Fabricated via Lewis Base Adduct of Lead(II) Iodide. J Am Chem

Soc 2015, 137 (27), 8696-8699.

41. Zhu, L.; Shi, J.; Lv, S.; Yang, Y.; Xu, X.; Xu, Y.; Xiao, J.; Wu, H.; Luo, Y.; Li, D.; Meng, Q., Temperature-Assisted Controlling Morphology and Charge Transport Property for Highly Efficient Perovskite Solar Cells. Nano Energy 2015, 15, 540-548.

42. Wozny, S.; Yang, M.; Nardes, A. M.; Mercado, C. C.; Ferrere, S.; Reese, M. O.; Zhou, W.; Zhu, K., Controlled Humidity Study on the Formation of Higher Efficiency Formamidinium Lead Triiodide-Based Solar Cells. Chem. Mater. 2015, 27 (13), 4814-4820.

43. Yang, M.; Zhou, Y.; Zeng, Y.; Jiang, C. S.; Padture, N. P.; Zhu, K., Square-Centimeter Solution-Processed Planar CH3NH3PbI3 Perovskite Solar Cells with Efficiency Exceeding 15. Adv. Mater. 2015, 27 (41), 6363-6370.

44. Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Grätzel, M., Cesium-Containing Triple Cation Perovskite Solar Cells: Improved Stability, Reproducibility and High Efficiency. Energy Environ. Sci. 2016, 9 (6), 1989-1997.

45. Yi, C.; Luo, J.; Meloni, S.; Boziki, A.; Ashari-Astani, N.; Grätzel, C.; Zakeeruddin, S. M.; Röthlisberger, U.; Grätzel, M., Entropic Stabilization of Mixed A-Cation ABX3 metal Halide Perovskites for High Performance Perovskite Solar 27 ACS Paragon Plus Environment


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 32

Cells. Energy Environ. Sci. 2016, 9 (2), 656-662.

46. Peng, W.; Wang, L. F.; Murali, B.; Ho, K. T.; Bera, A.; Cho, N.; Kang, C. F.; Burlakov, V. M.; Pan, J.; Sinatra, L.; Ma, C.; Xu, W.; Shi, D.; Alarousu, E.; Goriely, A.; He, H.; Mohammed, O. F.; Wu, T.; Bakr, O. M., Solution-Grown Monocrystalline Hybrid Perovskite Films for Hole-Transporter-Free Solar Cells. Adv. Mater. 2016, 28 (17), 3383-3390.

47. Liu, D. Y.; Kelly, T. L., Perovskite Solar Cells with a Planar Heterojunction Structure Prepared Using Room-Temperature Solution Processing Techniques. Nat.

Photonics 2014, 8 (2), 133-138.

48. Yang, J. L.; Siempelkamp, B. D.; Mosconi, E.; De Angelis, F.; Kelly, T. L., Origin of the Thermal Instability in CH3NH3PbI3 Thin Films Deposited on ZnO. Chem.

Mater. 2015, 27 (12), 4229-4236.

49. Oh, L. S.; Kim, D. H.; Lee, J. A.; Shin, S. S.; Lee, J.-W.; Park, I. J.; Ko, M. J.; Park, N.-G.; Pyo, S. G.; Hong, K. S.; Kim, J. Y., Zn2SnO4-Based Photoelectrodes for Organolead Halide Perovskite Solar Cells. J. Phys. Chem. C 2014, 118 (40), 22991-22994.

50. Bera, A.; Sheikh, A. D.; Haque, M. A.; Bose, R.; Alarousu, E.; Mohammed, O. F.; Wu, T., Fast Crystallization and Improved Stability of Perovskite Solar Cells with Zn2SnO4 Electron Transporting Layer: Interface Matters. ACS Appl. Mater. Interfaces 2015, 7 (51), 28404-28411.


Page 29 of 32

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


51. Bera, A.; Wu, K.; Sheikh, A.; Alarousu, E.; Mohammed, O. F.; Wu, T., Perovskite Oxide SrTiO3 as an Efficient Electron Transporter for Hybrid Perovskite Solar Cells. J.

Phys. Chem. C 2014, 118 (49), 28494-28501.

52. Jung, J. W.; Chueh, C. C.; Jen, A. K., A Low-Temperature, Solution-Processable, Cu-Doped Nickel Oxide Hole-Transporting Layer via the Combustion Method for High-Performance Thin-Film Perovskite Solar Cells. Adv. Mater.78 2015, 27 (47), 7874-7880.

53. Tiwana, P.; Docampo, P.; Johnston, M. B.; Snaith, H. J.; Herz, L. M., Electron Mobility and Injection Dynamics in Mesoporous Zno, Sno(2), And Tio(2) Films Used in Dye-Sensitized Solar Cells. ACS Nano 2011, 5 (6), 5158-5166.

54. Abayev, I.; Zaban, A.; Fabregat-Santiago, F.; Bisquert, J., Electronic Conductivity in Nanostructured Tio2 Films Permeated with Electrolyte. physica status solidi (a) 2003, 196 (1), R4-R6.

55. Mahmood, K.; Swain, B. S.; Jung, H. S., Controlling the Surface Nanostructure of ZnO and Al-doped ZnO Thin Films Using Electrostatic Spraying for Their Application in 12% Efficient Perovskite Solar Cells. Nanoscale 2014, 6 (15), 9127-9138.

56. 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 (21), 6730-6733. 29 ACS Paragon Plus Environment


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

57. Liu, X.; Tsai, K. W.; Zhu, Z.; Sun, Y.; Chueh, C. C.; Jen, A. K. Y., A Low-Temperature, Solution Processable Tin Oxide Electron-Transporting Layer Prepared by the Dual-Fuel Combustion Method for Efficient Perovskite Solar Cells.

Adv. Mater. Interfaces 2016, 3 (13), 1600122.

58. McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Horantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; Johnston, M. B.; Herz, L. M.; Snaith, H. J., A Mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells. Science 2016, 351 (6269), 151-155.

59. Song, J. X.; Zheng, E. Q.; Bian, J.; Wang, X. F.; Tian, W. J.; Sanehira, Y.; Miyasaka, T., Low-Temperature SnO2-Based Electron Selective Contact for Efficient and Stable Perovskite Solar Cells. J.Mater. Chem. A 2015, 3 (20), 10837-10844.

60. Rao, H. S.; Chen, B. X.; Li, W. G.; Xu, Y. F.; Chen, H. Y.; Kuang, D. B.; Su, C. Y., Improving the Extraction of Photogenerated Electrons with SnO2 Nanocolloids for Efficient Planar Perovskite Solar Cells. Adv. Func. Mater. 2015, 25 (46), 7200-7207.

61. Baena, J. P. C.; Steier, L.; Tress, W.; Saliba, M.; Neutzner, S.; Matsui, T.; Giordano, F.; Jacobsson, T. J.; Kandada, A. R. S.; Zakeeruddin, S. M.; Petrozza, A.; Abate, A.; Nazeeruddin, M. K.; Gratzel, M.; Hagfeldt, A., Highly Efficient Planar Perovskite Solar Cells Through Band Alignment Engineering. Energy Environ. Sci. 2015, 8 (10), 2928-2934.

62. Ke, W.; Zhao, D.; Xiao, C.; Wang, C.; Cimaroli, A. J.; Grice, C. R.; Yang, M.; Li, Z.; Jiang, C.-S.; Al-Jassim, M.; Zhu, K.; Kanatzidis, M. G.; Fang, G.; Yan, Y., 30 ACS Paragon Plus Environment

Page 30 of 32

Page 31 of 32

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


Cooperative Tin Oxide Fullerene Electron Selective Layers for High-Performance Planar Perovskite Solar Cells. J. Mater. Chem. A 2016, 4 (37), 14276-14283.

63. Xiong, L.; Qin, M.; Yang, G.; Guo, Y.; Lei, H.; Liu, Q.; Ke, W.; Tao, H.; Qin, P.; Li, S.; Yu, H.; Fang, G., Performance Enhancement of High Temperature Sno2-Based Planar Perovskite Solar Cells: Electrical Characterization and Understanding of the Mechanism. J. Mater. Chem. A 2016, 4 (21), 8374-8383.

64. Chen, B.-X.; Rao, H.-S.; Li, W.-G.; Xu, Y.-F.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y., Achieving High-Performance Planar Perovskite Solar Cell with Nb-doped TiO2 Compact Layer by Enhanced Electron Injection and Efficient Charge Extraction. J.

Mater. Chem. A 2016, 4 (15), 5647-5653.

65. Yang, D.; Zhou, L. Y.; Yu, W.; Zhang, J.; Li, C., Work-Function-Tunable Chlorinated Graphene Oxide as an Anode Interface Layer in High-Efficiency Polymer Solar Cells. Adv. Energy Mater. 2014, 4 (15), 1400591.

66. Goodman, A. M.; Rose, A., Double Extraction of Uniformly Generated Electron-Hole Pairs from Insulators with Noninjecting Contacts. J. Appl. Phys. 1971,

42 (7), 2823-2830.

67. 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, 1, 16177.



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 32 of 32

Table of Contents


Solution-Processed Nb:SnO2 Electron Transport ... - ACS Publications

Recommend Documents