Incorporating C60 as Nucleation Sites Optimizing PbI2 Films To

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Incorporating C60 as Nucleation Sites Optimizing PbI2 Films to Achieve Perovskite Solar Cells Showing Excellent Efficiency and Stability via Vapor-assisted Deposition Method Haibin Chen, Xihong Ding, Xu Pan, Tasawar Hayat, Ahmed Alsaedi, Yong Ding, and Songyuan Dai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b16627 • Publication Date (Web): 29 Dec 2017 Downloaded from http://pubs.acs.org on January 1, 2018

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ACS Applied Materials & Interfaces

Incorporating C60 as Nucleation Sites Optimizing PbI2 Films to Achieve Perovskite Solar Cells Showing Excellent Efficiency and Stability via Vapor-assisted Deposition Method Hai-Bin Chena, Xi-Hong Dinga, Xu Panb,*, Tasawar Hayatc,d, Ahmed Alsaedid, Yong Dinga,* and Song-Yuan Daia,* a Beijing Key Laboratory of Novel Thin-Film Solar Cells, North China Electric Power University, Beijing, 102206, P. R. China. b Key Laboratory of Photovoltaic and Energy Conservation Materials, Chinese Academy of Sciences, Hefei, Anhui, 230088, P. R. China. c Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan d NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia. *Corresponding author E-mail: [email protected]. Phone: +86 55165593222 E-mail: [email protected] E-mail: [email protected]. Phone: +86 1061772268

Abstract In order to achieve high quality perovskite solar cells (PSCs), the morphology and carrier transportation of perovskite films need to be optimized. Herein, C60 is employed as nucleation sites in PbI2 precursor solution to optimize the morphology of perovskite films via vapor-assisted deposition process. Accompanying with the 1

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homogeneous nucleation of PbI2, the incorporation of C60 as heterogeneous nucleation sites can lower the nucleation free energy of PbI2, which facilitates the diffusion and reaction between PbI2 and organic source. Meanwhile, C60 could enhance carrier transportation and reduce charge recombination in perovskite layer due to its high electron mobility and conductivity. In addition, the grain sizes of perovskite get larger with C60 optimizing, which can reduce the grain boundaries and voids in perovskite and prevent the corrosion of moisture. As a result, we obtain PSCs with a power conversion efficiency (PCE) of 18.33% and excellent stability. The PCEs of unsealed devices drop less than 10% in dehumidification cabinet after 100 d and remain 75% of the initial PCE during exposure to ambient air (humidity>60% RH, temperature>30ºC) for 30 d. Keywords: C60; nucleation sites; morphology; carrier transportation; perovskite solar cells; vapor-assisted deposition method

1. Introduction Organic-inorganic halide perovskites are tempting materials for solar cells owing to their low fabrication cost and excellent photovoltaic performance. The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been increased from 3.8%1 to 22.1%2 in recent years, taking advantage of high absorption coefficient, long carrier lifetime and high carrier mobility of perovskite3-7. It is vital to optimize the morphology and carrier transportation of perovskite films for high quality PSCs8-12. Electronic trap states caused by pinholes, grain boundaries and crystal defects13-14, which could gravely decrease charge carrier lifetime by enhanced non-radiative 2


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recombination15-16. The morphology of perovskite films is principally regulated by nucleation and crystal growth in one step solution deposition process10, 17. Various methods have been explored to optimize perovskite morphology, such as adding HX (X=Cl or I) acid18-20, adopting organic additives21-24, dripping anti-solvent15-16, 25, gas quenching technique26 and so on. Generally, inducing rapid nucleation and retarding crystal growth are effective methods to achieve high quality perovskite films. However, further exploration of facilitating faster nucleation and lower crystal growth with one step solution process remains challenging15. Two-step process utilizes layered deposition with decreasing the requirement for nucleation and crystal growth rates, which is benefit to get full coverage and uniform films. In two-step approach, PbI2 is first deposited on the substrate and then reacts with CH3NH3I (MAI) forming perovskite23,

27-29

. Vapor-assisted solution process

(VASP) is a derivative method of two-step deposition. The reaction rate between inorganic and organic species can be precisely controlled with VASP28-33, which is achieved by the adjustable reaction time and temperature. It is well accepted that the steps of VASP including inorganic framework deposition and subsequently in-situ reaction with desired organic vapor28,

32, 34

. The VASP exhibits better humidity

tolerance as the PbI2 precursor film is less sensitivity to moisture31, 35. The preformed PbI2 film serves not only as a framework, but also as a reactant providing "nucleation" centers for the further formation of perovskite. Therefore, the morphology of PbI2 layer would affect the final morphology and carrier property of perovskite layer29. During the crystallization process, the additives in precursor solution play a critical 3



role in optimizing the nucleation and crystallization rate and then promote the reconstruction of perovskite19, 29. Various additives were used to control nucleation and crystal growth of perovskite, such as poly (methyl methacrylate) (PMMA), [6, 6]-phenyl C61-butyric acid methyl ester (PCBM)15-16 and HX18-20. Most of the additives focus on organics or haloid acids. However, the researches on carbon and its derivatives as additives need further exploration. Herein, we adopted C60 as heterogeneous nucleation sites for the nucleation and growth of PbI2 to strengthen the electronic transportation. We fabricate PSCs with planar structure and the schematic diagram of which is shown in Figure 1. We adopt Sprio-MeOTAD as hole transport layer contacting with Au. The compact-TiO2 (c-TiO2) as electron transport layers is contacted to FTO in the device. The molecules of C60 uniformly dispersed in perovskite layer. Adopting this planar configuration, we obtain the optimal PCE of 18.33% with C60 concentration of 0.6mg ml-1 in 1, 2-dichlorobenzene (o-DCB). The stability as well as carrier transport property of PSCs with optimized C60 concentration is significantly increased compared with the control samples.

4


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Figure 1. Schematic diagram of perovskite solar cell architecture.

2. Experimental 2.1. Materials PbI2, MAI was purchased from TCI and Xi’an Polymer Light Technology Corp., respectively. DMSO, HCl, o-DCB, lithium bis (trifluoromethylsulphonyl) imide (Li-TFSI)

and

4-tert-butylpyridine

(TBP)

were

obtained

from

Aldrich.

Spiro-MeOTAD was purchased from Borun New Material Technology Co. Ltd and C60 from Alfa Aesar. All chemicals were directly used without further purification. 2.2. Device fabrication The devices were prepared as previous reports15, 36. FTO glass substrates were etched with HCl (2M) and Zn powder, and then dipped in alkali solution for 15 min. After that the glass substrates were sequentially cleaned with detergent, deionized (DI) water and ethanol for 20 min each, followed by drying with an air flow. Finally, the FTO substrates were annealed at 510ºC for 30min in a muffle furnace. TiO2 compact layer was deposited on the pre-cleaned FTO by spray pyrolysis using cold and dry air 5



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as the carrying gas at 465ºC from a precursor solution of 0.6 ml titanium diisopropoxide

and

0.4

ml

bis

(acetylacetonate)

in

7

ml

anhydrous

isoprepanol.CH3NH3PbI3 was prepared via VASP method and the following spin-coated processes were carried out in a glove box with cold and dry air (humidity≤10%, temperature≤ 20ºC). We adopted C60 as nucleation site in PbI2/DMF precursor solution and introduced o-DCB as well as HCl in precursor solution, in order to increase PbI2 solubility and the dispersity of C60. The addition volume of o-DCB and HCl were 50 µl separately and the concentration of C60/o-DCB were 0.0, 0.3, 0.6, 0.9 mg ml-1, respectively. Next, PbI2/DMF (1.3M) solution was spin-coated on the FTO substrates at 1000 rpm and 3000 rpm for 10 s and 30 s, respectively. The formed PbI2 films were annealed at 70ºC for 5 min and then reacted with MAI to synthesize perovskite as previous report28. The Spiro-MeOTAD solution was prepared by previous method37 and spin-coated on the perovskite films at 3000 rpm for 20 s. Finally, 60 nm of Au contact was deposited on top of the device by thermally evaporating. 3.1. Characterization The crystal structure and intermediate products of the films were measured by X-ray diffraction (X’Pert Pro, Netherlands) Cu Kα beam (λ=1.54 Å). We further confirmed the intermediate products with Fourier transform infrared spectroscopy (FTIR, Thermo Fisher IS50R, USA). The films morphologies were characterized by a field-emission scanning electron microscope (FE-SEM, sirion200, FEI Corp., Holland). Steady-state photoluminescence (PL) spectra of the perovskite films which 6


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were deposited onto different substrates were recorded by a spectrofluorometer (photon technology international) and analyzed by the software Fluorescence. The exciting wavelength was 473 nm and excited by a standard 450 W xenon CW lamp. The time-resolved photoluminescence spectroscopy (TRPL) were recorded on a pulsed nitro-gen/dye laser (QM400, Photo Technology International, USA). Electrochemical impedance spectra (EIS) were measured on an electrochemical workstation in the dark with a 0.9 V forward bias in a frequency range of 10−2～106 Hz. The steady state and time-resolved decay photoluminescence (PL) measurements are carried out on a Fluorescence Detector (QM400 and Laser Strobe, Photo Technology International, USA) and they are carried out on a standard 450 W xenon CW lamp and pulsed nitrogen laser, respectively. UV/Vis absorption spectra were obtained on a UV/Vis spectrophotometer (U-3900 H, Hitachi, Japan).The monochromatic IPCE spectra were conducted using a QE/IPCE measurement kit (Newport Corporation, USA).The current−voltage characteristics (J−V) curves were measured by a solar simulator (solar AAA simulator, Oriel USA) with a source meter (Keithley Instruments, Inc., OH) at 100 mW cm−2, AM 1.5 Gillumination. The active area for each device was 0.09 cm2and ensured by masking a black mask on the device. With a 50 mV s−1 of scan rate, the applied bias voltages for the reverse scan and forward scan were from 1.2 to −0.1 V and from −0.1 to 1.2 V.

3. Result and discussion It is well known that C60 has been extensively used as electron transport layer (ETL) in PSCs to improve electron collection and eliminate photocurrent hysteresis38-39. We 7



add C60 into PbI2/DMF solution as a support to induce PbI2 nucleation and growth. The existence of C60 can strengthen the transportation of carriers and decreased charge recombination in the final perovskite films. Yet, the dispersity as well as solubility of C60 is poor in DMF solution. In order to increase the dispersity of C60, we dissolve C60 with o-DCB solution followed by dripping it into perovskite precursor solution. However, the adding of o-DCB would lower the solubility of PbI2 in DMF solution. We put HCl into DMF solution to overcome the adverse influence of o-DCB18. The addition of HCl can not only improves the solubility of PbI2 in DMF solvent18, but also inhibits the aggregation of C60 which can adsorb charged ions in precursor solution12. 3.1. Phase compositions The crystal structure of PbI2 and perovskite films were depicted by X-ray diffraction (XRD) patterns as shown in Figure 2. In Figure 2 (a), we can see the XRD patterns of PbI2 were different from previous report23 due to the addition of HCl in precursor solution. There appears strong diffraction peak at 11.68º, while the signature peak of PbI2 at 12.65º ((001) crystal face) is not obvious. The left offset of the main peak can be attributed to the introduction of HCl causing the expansion of PbI2 lattice structure18-19. As is well known that PbI2 is a semiconductor material with layer structure and the interlayer spacing can be inserted with various guest molecules, bringing about the expansion of interlayer distance along c axis18. The main peak diffraction degree would become smaller along with the increasing interplanar distance. In this work, the main diffraction peak of PbI2 films appeared at 11.68º, 8


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signifying the new phase has a longer interplanar distance compared to tetragonal PbI2. In previous researches18, 22, DMF could coordinate with PbI2 and MAI forming a MAI-PbI2-DMF complex, whose XRD exhibit some low angle peaks around 9º. The size of H+ and Cl- ion is smaller than that of MAI. We speculate H+ and Cl- ions would insert into the interlayer spacing of PbI2 and forming a new complex PbI2-DMF-xHCl17-18. FTIR was implemented to investigate the composition of intermediate phase to prove our conjecture. As shown in Figure 2 (b), the stretch vibration of C=O (ν (C=O)) appeared at 1661 cm-1 for the pure DMF and shifted to 1604 cm-1 and 1601 cm-1 for the film without and with the addition of HCl in PbI2/DMF solution, signifying the formation of PbI2-DMF and PbI2-DMF-xHCl. We could also find that the intensity of ν (C=O) absorption peak get reduced due to the formation of PbI2-DMF and PbI2-DMF-xHCl intermediates18, 40. The addition of HCl lead to the migration of absorption peak and the reduction of absorption intensity. There also appears small different nearby 2361cm-1 and 1100cm-1 in the films with and without HCl addition, further indicating that the difference of PbI2-DMF and PbI2-DMF-xHCl intermediates. More characterizations and discussions on the left offset of the main peak will be performed afterwards. We also find that the main diffraction peak intensity as well as the crystallinity of PbI2 films decreased with the increasing concentration of C60, which serves as heterogeneous nucleation sites41-42. These nucleation sites could lower the energy barrier of nucleation, leading to a fast nucleation of PbI2 and the compound, ultimately decrease the intensity of main peak and the particle size of PbI2 crystals. Meanwhile, the cavity of C60 molecule is large 9



enough to hold H+ ions. The ions of Cl- may be adsorbed around C60 to achieve a charge balance. Thus, the reduction of active HCl molecules is beneficial to reduce the intensity of compound diffraction peak. The diffraction patterns of the perovskite films (Figure 2 (c)) have strong peaks at 14.12º, 28.48º and 31.86º, corresponding to (110), (220) and (310) faces of the CH3NH3PbI3 crystal as previous reports32-34. The intensity of diffraction peak get stronger with the increasing concentration of C60. We got the strongest diffraction intensity of (110) face via adding 0.6 mg ml-1 concentration of C60/o-DCB solution into PbI2 precursor solution. Further increasing the concentration of C60, the diffraction peak intensity of (110) face is not significantly improved. In Figure 2 (b), there are not any HCl or DMF residue after the in-situ formation of perovskite, as the complexes of PbI2-DMF-xHCl are unstable at high temperature and the component of HCl can be easily removed through annealing process19-20. The main diffraction peak intensity of perovskite get enhanced with the increasing concentration of C60 and some of the weak diffraction peaks (23.44º, 26.52º and 37.76º) disappear. During the conversion from PbI2 precursor films to the final perovskite films, PbI2 grains with low crystallinity can boost film reconstruction and then optimize the perovskite grain size and suppress crystal defect29, 34. The smaller PbI2 grains with lower crystallinity have the larger reactive energy and reactivity, which could promote the diffusion and reaction with MAI. The enlarged grain size of perovskite would effectively reduce the energy of the system and make it stable. Thus we obtain the stronger diffraction peak of perovskite. The addition of C60 can further reduces the total Gibbs free energy of 10


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the system41-42, lower the surface energy of (110) and (220) planes, which exhibits the relatively higher diffraction peak intensity. (a)

(b) Transmittance (%)

0.9 0.6

Intensity (a.u)

0.3 0.0

control

with HCl without HCl DMF

ν (C=O) 10

20

30

4000

40

2θ (°)

3000

2000

1000 -1

Wavenumber (cm )

(c) 0.9

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


0.6 0.3 0.0 control

10

20

30

40

2θ (°)

Figure 2. XRD patterns of PbI2 (a) and perovskite films (c) optimized with different concentrations of C60/o-DCB solution (mg ml-1). (b) FTIR curves of DMF, PbI2 films without and with HCl addition. 3.2. Film morphology The scanning electron microscopy (SEM) images of PbI2 and perovskite films deposited with different concentration of C60 are shown in Figure 3. There are numbers of quasi-spherical and irregularly shaped particles dispersing on the surface of PbI2 films, as we can see in Figure 3 (a) the top morphology of PbI2 films. There are cross-linked amorphous grains under the surface particles due to the addition of HCl in PbI2/DMF precursor solution. The PbI2 films with uniformed complexes and flake crystals measured by SEM are corresponding to the results in XRD patterns. The 11



size of the particles as well as the crystallinity of compounds decreased along with the increasing concentration of C60 which can lower the nucleation free energy barrier of PbI2. The lower crystallinity of PbI2 film would be beneficial for the completely conversion into perovskite in VASP. Figure 3 (b) exhibit the perovskite films with different concentration C60 treatment, the grain size and uniformity of perovskite are significantly improved with the increasing concentration of C60. The grain size of perovskite measured in SEM is corresponding to the diffraction peak intensity characterized with XRD. The lower magnification SEM images of perovskite films deposited with different concentrations of C60/o-DCB solution are provided in Figure S1. We get the relative larger and uniform distribution grain size when adopting 0.6 mg ml-1 C60/o-DCB solution. Further increasing the concentration of C60, the particle uniformity of perovskite grains has declined slightly and the crystal orientation get minor changed as shown in SEM and XRD patterns. The introduction of C60 in precursor solution could reduce the nucleation energy of PbI2, benefiting the diffusion and reaction between PbI2 and organic source29. We also find the enlarged perovskite grains in SEM images correspond to the intensive peak of (110) plane in XRD patterns. The addition of C60 not only acts as uniformly trigger heterogeneous nucleation over PbI2 precursor film, but also indirectly improves the grain size of perovskite. The enlarged grain size of perovskite would reduce the numbers of grain boundaries, benefiting the photoelectric performance and durability of perovskite film.

12


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13



Figure 3 Top SEM of PbI2 films (a) and perovskite films (b) deposited with different concentrations of C60/o-DCB solution (mg ml-1). 3.3. Carrier transport performance We performed PL and TRPL to analyze the carrier recombination dynamics. The PL and TRPL decays for perovskite films with control and the different concentrations of C60 deposited on glass substrate are shown in Figure 4 (a), 4 (b). The introduction of C60 would effectively strengthen the PL intensity of perovskite, as shown in Figure 4 (a). The PL intensity gets stronger with the increasing of C60 and the C60 concentration with 0.6 mg ml-1 exhibits the highest intensity which is three times as high as that of the control film. Further increasing the concentration, the PL intensity get a little decline which would be the uneven distribution of perovskite particles. The PL peak of 0.6 exhibit a bit red shift compared with that of the control sample. The increasing peak intensity as well as the red shift are due to the decrease of surface defect concentration and the reduction of spontaneous radiative recombination16. Figure 4 (b) shows the TRPL decay and fitting data with exponential function. The TRPL signal could be well fitted to mono-exponential decay ( y = A0 + Ae−∆t /τ ) and the estimated decay times are 8.10, 8.68, 11.56, 15.61 and 12.49 s for the control, 0.0, 0.3, 0.6 and 0.9 samples, respectively. Since there is no electron injection from perovskite to the glass, the slow decay process could be ascribed to the slow recombination of electron and hole in perovskite film. Herein, we get the best decay time with the addition of 0.6 mg ml-1 C60/ o-DCB. Electrochemical Impedance spectroscopy (EIS) is performed to investigate the 14


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interfacial charge transfer processes in the PSCs. Figure 4 (c) shows the Nyquist plots of PSCs with control and the different concentrations of C60, measured at 0.9 V under dark condition. The equivalent circuit can be used to analyze EIS spectra. The lower frequency arc is attributed to a charge recombination resistance (Rrec), in parallel with a chemical capacitance (Crec)43. The Rrec is the most important parameter that affects the VOC of solar cells and it could be estimated from the EIS spectra44-45. In EIS spectra, the first arc is related to the carrier transport behavior at cathode/HTM. The arc in the lower frequency results from the recombination between HTM and TiO2 which is the focus of the study46-47.

It is noted that the Rrec gets larger with the

increasing of C60, indicating the recombination in the devices with C60 optimizing is slower than that in the controlled samples. The value of Rrec are 186, 230, 358, 448 and 339 Ωfor the control, 0.0, 0.3, 0.6 and 0.9 samples, respectively. Thus, the solar cells with 0.6 mg ml-1 C60 optimizing exhibit a higher Voc due to a slower recombination. Both PL and EIS studies illustrate the faster carrier transportation and slower charge recombination of perovskite films with C60 optimizing. The mechanism of perovskite/C60 composites is illustrated in Figure 4 (d). The photo-excited electrons efficient transfer from perovskite matrix to C60, resulting in an obvious reduction in charge recombination and hence enhanced carrier transport.

15



(b) 1.0

(a)

750

800

PL intensity (Normalized)

PL Intensity / a.u.

control 0.0 0.3 0.6 0.9

700

850

control 0.0 0.3 0.6 0.9

0.8 0.6

fitting fitting fitting fitting fitting

0.4 0.2 0.0 80

90

Wavelength / nm

100

110

120

Time (ns)

(c) Rrec

RHTM

RS

250 Crec

CHTM

200

-Z″″ (Ω)

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

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150 100 50 0

0

100

200

300

400

500

Z′′ (Ω)

Figure 4 (a) PL and (b) TRPL decays for perovskite films with the control and C60 concentration of 0.6 mg ml-1 deposited on glass substrate. (c) Nyquist plots of the PSCs with the control and C60 concentration of 0.6 mg ml-1. (d) Schematic diagram of electrons transportation in perovskite film. 3.4. Devices performance Figure 5 (a) shows the J-V characteristic of PSCs employing C60 as additive under AM 1.5G illumination with light intensity of 100mW cm-2. The devices with traditional VASP (control) exhibited the best PCE of 13.29%, with VOC of 0.99 V, JSC of 18.28 mA cm-2, and FF of 0.75. The improvement in PCE is not obvious only with o-DCB optimizing, as the small amount of o-DCB has little effect on the morphology of PbI2 as well as perovskite films. With the increasing concentration of C60 in o-DCB solution, the JSC get improved, VOC increased at first and decreased subsequently. We 16


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obtain the best PCE of 18.33% with VOC of 1.11 V, JSC of 21.38 mA cm-2, and FF of 0.77, when C60 concentration is 0.6 mg ml-1 in o-DCB. The high quality perovskite films can enhance absorbance as well as the JSC of PSCs. We measured the UV-vis of perovskite films with different concentration of C60/o-DCB. As shown in Figure 5 (b), the absorption of perovskite enhanced with the increasing concentration of C60 due to the elevated grain size and crystallinity of perovskite with the optimizing of C60. When the concentration of C60 increased to 0.9 mg ml-1, the absorption decreased slightly, as the excess C60 may have adverse effects on the growth of perovskite crystals, thus lowering the absorption and VOC of PSCs. From the incident photon-to-current efficiency (IPCE) spectra in Figure 5 (c), the integrated JSC of C60 with 0.6 mg ml-1 concentration is 20.01 mA cm-2, higher than 17.63 mA cm-2 of the control. The increasing in IPCE efficiency suggests that large crystals with well-defined grains may strengthen light absorption, boost charge transport and lower charge recombination. Hysteresis is caused by defect states or surface charging induced by ion migration40. The decrease of hysteresis is owing to the larger grain size and less grain boundaries of perovskite films. Hysteresis effect of J-V curves for devices with C60 is shown in Figure 5 (d). For the device with C60 concentration of 0.6 mg ml-1as nucleation sites, the reverse scan show a PCE of 18.33%, within 6% reduction compared with forward scan (17.23%). Hence, hysteresis is suppressed and the crystallization of perovskite is enhanced confirmed by XRD and SEM patterns. The modified morphology with larger grain size of perovskite is also in favor of 17



suppressing the charge trapping and accumulation, leading to better device performance with lower hysteresis.

(b) control 0.0 0.6

20

Absorbance (a.u)

Current density (mA cm-2)

(a)

15 control 0.0 0.6

10

0.3 0.9

5

0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

500

600

Voltage (V)

800

15 60 10

40 0.6 control

20

400

500

600

700

5

Integrated Jsc (mA cm-2)

80


d 20

0 300

700

0.3 0.9

Wavelength (nm)

(c)100

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

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0 800

20 forward reverse

16 12 8 4 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

Voltage (V)

Wavelength (nm)

Figure 5. (a) J-V characteristic of PSCs employing different concentration of C60 in o-DCB (mg ml-1). (b) UV-vis spectra of perovskite films with different concentration of C60/o-DCB (mg ml-1). (c) IPCE spectra of perovskite with control and 0.6 mg ml-1concentration of C60/o-DCB solution. (d) J–V curves of the champion PSC with C60concentrationof0.6 mg ml-1measured in both reverse and forward directions, the insert picture: optical images of perovskite films with C60. We also investigated the stability of PSCs containing C60. The devices employing C60 as additive exhibit better stability than the control samples. The unsealed device with C60concentration of 0.6 mg ml-1 exhibits less than 10% decay in the dehumidification cabinet for 100 d and dropped within 25% in PCE during exposure 18


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to ambient air (humidity>60% RH, temperature>30ºC) for 30 d in the dark. In Figure 6 (a), 6 (b), we can see the devices with C60 decay slower than the control devices no matter in the open air or in dehumidification cabinet. Figure 6 (c) shows the photographs of perovskite in ambient air for 3 d and 30 d, which exhibits the better stability with C60. The degradation of PSCs mainly caused by the decomposition of active layer by moisture erosion16, 48-49. The decomposition product is PbI2, which can be confirmed by Figure S2. The main diffraction peak at 12.56º correspond to the characteristic peak of PbI2. There have two small peaks at 14.12º and 28.48º, indicating a small amount of perovskite residue. The C60 containing devices exhibited a much stronger resistance to the degradation. The addition of C60 can reduce the crystallinity of PbI2, enlarge the grain size of perovskite. The larger grains of perovskite can passivate the grain boundaries, exhibiting better resistance to the moisture erosion.

(b) control 0.0 0.6

1.0

0.3 0.9

0.8

0.6

control 0.0 0.6

1.0

Normalized PCE

(a) Normalized 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


0.3 0.9

0.8 0.6 0.4 0.2

0.4

0

20

40

60

80

0

100

(c)

0.6, 3d

5

10

15

20

25

30

Time (d)

Time (d) control, 3d

0.6, 30d

control, 30d

Figure 6 The stability of PSCs with different concentration of C60/o-DCB solution 19



(mg ml-1). (a) under dark without any encapsulation at dehumidification cabinet. (b) under dark without any encapsulation at ambient air (humidity>60% RH, temperature>30 ℃ ). (c) the photograph of perovskite films with control and C60 concentration of 0.6 mg ml-1 at dehumidification cabinet for 3 and 30 d.

4. Conclusion In summary, we adopt C60 to optimize the morphology and carrier transportation of perovskite films. The nucleation free energy of PbI2 get decreased with the addition of C60 which act as nucleation sites and assist the crystallization of PbI2. The grain sizes of perovskite films get larger which can effectively reduce the grain boundaries and crystal defects of perovskite on account of the formed PbI2 grains with low crystallinity can facilitate the recombination of perovskite. Furthermore, the incorporation of C60 could enhance carrier transportation and reduce charge recombination in perovskite layer because of its high electron mobility and conductivity. We obtain PSCs with 18.33% PCE and excellent stability with the optimized perovskite films. This promising method provides a simple way for the fabrication of highly efficient and stable planar PSCs. Acknowledgements This work was supported by National Basic Research Program of China under Grant No. 2016YFA0202400, 2015CB932200, the National Natural Science Foundation of China under Grant No. 21403247, and the External Cooperation Program of BIC, Chinese Academy of Sciences under Grant No. GJHZ1607.

References 20


Page 20 of 28

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


(1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. Journal of the American Chemical Society 2009, 131 (17), 6050-6051. (2) Research Cell Efficiency Records. http://www.nrel.gov/ncpv/images/efficiency chart. (3) Stranks, S.; Eperon, G.; Grancini, G.; Menelaou, C.; Alcocer, M.; Leijtens, T.; Herz, L.; Petrozza, A.; Snaith, H. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342 (6156), 341-344. (4) MM, L.; J, T.; T, M.; TN, M.; HJ, S. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338 (6107), 643-647. (5) 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. (6) Zhang, T.; Guo, N.; Li, G.; Qian, X.; Li, L.; Zhao, Y. A general non-CH3NH3X (X = I, Br) one-step deposition of CH3NH3PbX3 perovskite for high performance solar cells. Journal of Materials Chemistry A 2016, 4 (9), 3245-3248. (7) Zhang, T.; Yang, M.; Zhao, Y.; Zhu, K. Controllable Sequential Deposition of Planar CH3NH3PbI3 Perovskite Films via Adjustable Volume Expansion. Nano letters 2015, 15 (6), 3959-3963. (8) Pascoe, A. R.; Yang, M.; Kopidakis, N.; Zhu, K.; Reese, M. O.; Rumbles, G.; 21



Fekete, M.; Duffy, N. W.; Cheng, Y. B. Planar versus mesoscopic perovskite microstructures: The influence of CH3NH3PbI3 morphology on charge transport and recombination dynamics. Nano Energy 2016, 22, 439-452. (9) Bae, S.; Han, S. J.; Shin, T. J.; Jo, W. H. Two different mechanisms of CH3NH3PbI3 film formation in onestep deposition and its effect on photovoltaic properties of OPV type perovskite solar cells. Journal of Materials Chemistry A 2015, 3 (47), 23964-23972. (10) Song, T. B.; Chen, Q.; Zhou, H.; Luo, S.; Yang, Y.; You, J.; Yang, Y. Unraveling film transformations and device performance of planar perovskite solar cells. Nano Energy 2015, 12, 494-500. (11) Yao, K.; Wang, X.; Xu, Y. X.; Li, F. A general fabrication procedure for ef cient and stable planar perovskite solar cells: Morphological and interfacial control by in-situ-generated layered perovskite. Nano Energy 2015, 18, 165-175. (12) Li, F.; Wang, H.; Kufer, D.; Liang, L.; Yu, W.; Alarousu, E.; Ma, C.; Li, Y.; Liu, Z.; Liu, C. Ultrahigh Carrier Mobility Achieved in Photoresponsive Hybrid Perovskite Films via Coupling with Single-Walled Carbon Nanotubes. Advanced materials 2017, 29 (16), 1-8. (13) Agiorgousis, M. L.; Sun, Y. Y.; Zeng, H.; Zhang, S. Strong covalency-induced recombination centers in perovskite solar cell material CH3NH3PbI3. Journal of the American Chemical Society 2014, 136 (41), 14570-14575. (14) Wu, X.; Trinh, M. T.; Niesner, D.; Zhu, H.; Norman, Z.; Owen, J. S.; Yaffe, O.; Kudisch, B. J.; Zhu, X. Y. Trap states in lead iodide perovskites. Journal of the 22


Page 22 of 28

Page 23 of 28 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


American Chemical Society 2015, 137 (5), 2089-2096. (15) Bi, D.; Yi, C.; Luo, J.; Décoppet, J. D.; Zhang, F.; Shaik, M. Z.; Li, X.; Hagfeldt, A.; Grätzel, M. Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%. Nature Energy 2016, 1 (10), 16142. (16) Fei, Z.; Wen, S., Jing, L.; Norman, P.; Chen, Y.; Xiong, L.; Xiao, Z.; T. D.; Xiang, L.; Shi, W.; Yin, X.; Shaik, Z.; Dong, B.; Michael, G. Isomer-Pure Bis-PCBM-Assisted Crystal Engineering of Perovskite Solar Cells Showing Excellent Efficiency and Stability. Advanced materials 2017, 29 (17), 1-7. (17) Liu, J.; Lin, J.; Xue, Q.; Ye, Q.; He, X.; Ouyang, L.; Zhuang, D.; Liao, C.; Yip, H. L.; Mei, J.; Lau, W. M. Growth and evolution of solution-processed CH3NH3PbI3-xClx layer for highly efficient planar-heterojunction perovskite solar cells. Journal of Power Sources 2016, 301, 242-250. (18) Duan, B.; Ren, Y.; Xu, Y.; Chen, W.; Ye, Q.; Huang, Y.; Zhu, J.; Dai, S. Identification and characterization of a new intermediate to obtain high quality perovskite films with hydrogen halides as additives. Inorg. Chem. Front. 2017, 4 (3), 473-480. (19) Li, G.; Zhang, T.; Zhao, Y. Hydrochloric acid accelerated formation of planar CH3NH3PbI3 perovskite with high humidity tolerance. J. Mater. Chem. A 2015, 3 (39), 19674-19678. (20) Yang, L.; Wang, J.; Leung, W. W. Lead Iodide Thin Film Crystallization Control for High-Performance and Stable Solution-Processed Perovskite Solar Cells. ACS applied materials & interfaces 2015, 7 (27), 14614-14649. 23



(21) Lee, J. W.; Kim, H. S.; Park, N. G. Lewis Acid-Base Adduct Approach for High Efficiency Perovskite Solar Cells. Accounts of chemical research 2016, 49 (2), 311-9. (22) Zuo, L.; Dong, S.; De Marco, N.; Hsieh, Y. T.; Bae, S. H.; Sun, P.; Yang, Y. Morphology Evolution of High Efficiency Perovskite Solar Cells via Vapor Induced Intermediate Phases. Journal of the American Chemical Society 2016, 138 (48), 15710-15716. (23) Zhang, H.; Cheng, J.; Li, D.; Lin, F.; Mao, J.; Liang, C.; Jen, A. K.; Gratzel, M.; Choy, W. C. Toward All Room-Temperature, Solution-Processed, High-Performance Planar Perovskite Solar Cells: A New Scheme of Pyridine-Promoted Perovskite Formation. Advanced materials 2017, 29 (13), 1-7. (24) Bao, X.; Wang, Y.; Zhu, Q.; Wang, N.; Zhu, D.; Wang, J.; Yang, A.; Yang, R. Efficient planar perovskite solar cells with large fill factor and excellent stability. Journal of Power Sources 2015, 297, 53-58. (25) Bi, D.; Tress, W.; Dar, M. I.; Peng, G.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Baena, J. P. C. Efficient luminescent solar cells based on tailored mixed-cation perovskites. Science advances 2016, 2 (1), 1-7. (26) Zhang, M.; Yun, J. S.; Ma, Q.; Zheng, J.; Lau, C. F. J.; Deng, X.; Kim, J.; Kim, D.; Seidel, J.; Green, M. A.; Huang, S.; HoBaillie, A. W. Y. High-Efficiency Rubidium-Incorporated Perovskite Solar Cells by Gas Quenching. ACS Energy Letters 2017, 2 (2), 438-444. (27) Ko, H.; Sin, D. H.; Kim, M.; Cho, K. Predicting the Morphology of Perovskite Thin Films Produced by Sequential Deposition Method: A Crystal Growth Dynamics 24


Page 24 of 28

Page 25 of 28 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


Study. Chemistry of Materials 2017, 29 (3), 1165-1174. (28) Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H. S.; Wang, H. H.; Liu, Y.; Li, G.; Yang, Y. Planar heterojunction perovskite solar cells via vapor-assisted solution process. Journal of the American Chemical Society 2014, 136 (2), 622-625. (29) Yin, J.; Qu, H.; Cao, J.; Tai, H.; Li, J.; Zheng, N. Vapor-assisted crystallization control toward high performance perovskite photovoltaics with over 18% efficiency in the ambient atmosphere. J. Mater. Chem. A 2016, 4 (34), 13203-13210. (30) Hsiao, S. Y.; Lin, H. L.; Lee, W. H.; Tsai, W. L.; Chiang, K. M.; Liao, W. Y.; Re-Wu, C. Z.; Chen, C. Y.; Lin, H. W.. Efficient All-Vacuum Deposited Perovskite Solar Cells by Controlling Reagent Partial Pressure in High Vacuum. Advanced materials 2016, 28 (32), 7013-7019. (31) Lee, W. H.; Chen, C. Y.; Li, C. S.; Hsiao, S. Y.; Tsai, W. L.; Huang, M. J.; Cheng, C. H.; Wu, C. I.; Lin, H. W. Boosting thin-film perovskite solar cell efficiency through vacuum-deposited sub-nanometer small-molecule electron interfacial layers. Nano Energy 2017, 38, 66-71. (32) Zhou, H.; Chen, Q.; Yang, Y. Vapor-assisted solution process for perovskite materials and solar cells. MRS Bulletin 2015, 40 (08), 667-673. (33) Chen, C. W.; Kang, H. W.; Hsiao, S. Y.; Yang, P. F.; Chiang, K. M.; Lin, H. W. Efficient and uniform planar-type perovskite solar cells by simple sequential vacuum deposition. Advanced materials 2014, 26 (38), 6647-6652. (34) Pang, S.; Zhou, Y.; Wang, Z.; Yang, M.; Krause, A. R.; Zhou, Z.; Zhu, K.; Padture, N. P.; Cui, G. Transformative Evolution of Organolead Triiodide Perovskite 25



Page 26 of 28

Thin Films from Strong Room-Temperature Solid-Gas Interaction between HPbI3-CH3NH2 Precursor Pair. Journal of the American Chemical Society 2016, 138 (3), 750-753. (35) Tsai, W. L.; Lee, W. H.; Chen, C. Y.; Hsiao, S. Y.; Shiau, Y. J.; Hsu, B. W.; Lee, Y. C.; Lin, H. W. Very high hole drift mobility in neat and doped molecular thin films for normal and inverted perovskite solar cells. Nano Energy 2017, 41, 681-686. (36) Liu, X.; Kong, F.; Guo, F.; Cheng, T.; Chen, W.; Yu, T.; Chen, J.; Tan, Z.; Dai, S. Influence of π-linker on triphenylamine-based hole transporting materials in perovskite solar cells. Dyes and Pigments 2017, 139, 129-135. (37) Zhang, X. H.; Ye, J. J.; Zhu, L. Z.; Zheng, H. Y.; Liu, X. P.; Xu, P.; Dai, S. High Consistency Perovskite Solar Cell with a Consecutive Compact and Mesoporous TiO2 Film by One-Step Spin-Coating. ACS applied materials & interfaces 2016, 8 (51), 35440-35446. (38)

Yoon,

H.;

Kang,

S.

M.;

Lee,

J.

K.;

Choi,

M.

Hysteresis-free

low-temperature-processed planar perovskite solar cells with 19.1% efficiency. Energy & Environmental Science 2016, 9 (7), 2262-2266. (39) Ke, W.; Zhao, D.; Grice, C. R.; Cimaroli, A. J.; Ge, J.; Tao, H.; Lei, H.; Fang, G.; Yan,

Y.

Efficient

planar

perovskite

solar

cells

using

room-temperature

vacuum-processed C60 electron selective layers. J. Mater. Chem. A 2015, 3 (35), 17971-17976. (40) Ge, L.; Taiyang, Z.; Yixin, Z. Hydrochloric acid accelerated formation of planar CH3NH3PbI3 perovskite with high humidity tolerance. J. Mater. Chem. A 2015, 3 (39), 26


Page 27 of 28 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


19674-19678. (41) Cacciuto, A.; Auer, S.; Frenkel, D. Onset of heterogeneous crystal nucleation in colloidal suspensions. Nature 2004, 428 (6981), 404-406. (42) Stefan A.; Frenkel, D. Suppression of crystal nucleation in polydisperse colloids due to increase of the surface free energy. Nature 2001, 413 (6857), 711-713. (43) Wu, G.; Zhang, Y.; Kaneko, R.; Kojima, Y.; Shen, Q.; Islam, A.; Sugawa, K.; Otsuki, J. A 2,1,3-Benzooxadiazole Moiety in a D–A–D-type Hole-Transporting Material for Boosting the Photovoltage in Perovskite Solar Cells. The Journal of Physical Chemistry C 2017, 121 (33), 17617-17624. (44) Liu, X.; Kong, F.; Ghadari, R.; Jin, S.; Chen, W.; Yu, T.; Hayat, T.; Alsaedi, A.; Guo, F.; Tan, Z. A. Thiophene–Arylamine Hole-Transporting Materials in Perovskite Solar Cells:Substitution Position Effect. (45) Yi, L.; Jun, Z.; Yang, H.; Feng, L.; Mei, L.; Shuanghong,, C.; Linhua H.; Junwang, T.; Jianxi, Y.; Dai, S. Mesoporous SnO2 nanoparticle films as electron-transporting material in perovskite solar cells. RSC Adv. 2015, 5 (36), 28424-28429. (46) Liu, X.; Kong, F.; Cheng, T.; Chen, W.; Tan, Z.; Yu, T.; Guo, F.; Chen, J.; Yao, J.; Dai, S. Tetraphenylmethane-Arylamine Hole-Transporting Materials for Perovskite Solar Cells. ChemSusChem 2017, 10 (5), 968-975. (47) Liu, X.; Kong, F.; Jin, S.; Chen, W.; Yu, T.; Hayat, T.; Alsaedi, A.; Wang, H.; Tan, Z.; Chen, J.; Dai, S. Molecular Engineering of Simple Benzene-Arylamine Hole-Transporting Materials for Perovskite Solar Cells. ACS applied materials & 27



interfaces 2017, 9 (33), 27657-27663. (48) Chen, B.; Lin, J.; Suen, N.; Tsao, C.; Chu, T.; Hsu, Y.; Chan, T.; Chan, Y.; Yang, J.; Chiu, C. Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells. Advanced materials 2014, 26 (22), 3748-3754. (49) Chen, B.; Lin, J.; Suen, N.; Tsao, C.; Chu, T.; Hsu, Y.; Chan, T.; Chan, Y.; Yang, J.; Chiu, C. In Situ Identification of Photo- and Moisture-Dependent Phase Evolution of Perovskite Solar Cells. ACS Energy Letters 2017, 2 (2), 342-348.

Table of Content 25


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

control C60

PCE=18.33% 20 15 10 5 0 0.0

0.2

0.4

0.6

0.8

1.0

Voltage (V)

28


1.2

Page 28 of 28

Incorporating C60 as Nucleation Sites Optimizing PbI2 Films To

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