JOUL, Volume 4

Supplemental Information

Surface-Controlled Oriented Growth

of FASnI3 Crystals for Efficient

Lead-free Perovskite Solar Cells

Xiangyue Meng, Yanbo Wang, Jianbo Lin, Xiao Liu, Xin He, Julien Barbaud, TianhaoWu, Takeshi Noda, Xudong Yang, and Liyuan Han

Supplemental data items

Figure S1. Calculated X-ray penetration depth vs incident angle. For an ideally flat surface, the value of the X-ray penetration depth Λ (i.e. the depth where the intensity is reduced to 1/e of the original intensity) can be calculated using the following expression.

16

where αi is the incident angle, λ is the X-ray wavelength, αc is the critical angle of total reflection, and β is the imaginary part of the index of refraction.

2 2 2 2 2 2

1

2 2 ( ) 4 ( )i c i c

Figure S2. GIXRD intensity as a function of incident angles before and after annealing. (A) FASnI3 and (B) FASnI3-2%FOEI perovskite films.

Figure S3. XRD pattern of the FASnI3-2%FOEI and FASnI3-20%FOEI perovskite films. (A) FASnI3-2%FOEI and (B) FASnI3-20%FOEI perovskite films.

Figure S4. Illustration of charge transport in the perovskite solar cells based on (A) highly oriented and (B) randomly packed crystals.

Figure S5. F 1s XPS spectra of the FASnI3-2%FOEI perovskite film without etching, after etching 2 nm, 5 nm and 10 nm, respectively.

Figure S6. TOF-SIMS profiles of the FASnI3-2%FOEI perovskite film.

Figure S7.

1H nuclear magnetic resonance spectra of FOEI with or without addition of SnI2 in DMSO-d6

solution.

Figure S8. The height images measured by AFM (5 um × 3 um) (A) FASnI3 perovskite film, (B) FASnI3-2%PEAI perovskite film and (C) FASnI3-2%FOEI perovskite film.

Figure S9. Nucleation from the solution-air surface. (A) FASnI3 perovskite film, (B) FASnI3-2%PEAI perovskite film and (C) FASnI3-2%FOEI perovskite film.

Figure S10. Temperature-dependent PL spectra. (A) the FASnI3 perovskite film, (B) the FASnI3-2%PEAI perovskite film, and (C) the FASnI3-2%FOEI perovskite film.

Figure S11. Activation energy of the perovskite films calculated from temperature-dependent PL spectra.

Figure S12. Contact angle of diiodomethane on (A) FASnI3, (B) FASnI3-2%PEAI and (C) FASnI3-2%FOEI perovskite films. Contact angle of glycerol on (D) FASnI3, (E) FASnI3-2%PEAI and (F) FASnI3-2%FOEI perovskite films.

Figure S13. Schematic diagram of the classical free energy diagram for nucleation as a function of particle radius.

Figure S14. DFT calculations Optimized (100) slab model of FASnI3 perovskites with (A) SnI2, (B) FAI, (C) FOEI termination. Optimized (102) slab model of FASnI3 perovskites with (D) SnI2, (E) FAI, (F) FOEI termination. Optimized (222) slab model of FASnI3 perovskites with (G) SnI2, (H) FAI, (I) FOEI termination.

Figure S15. Illustration of Wulff construction rule where the order of specific surface energy (σ) of different facets follows: σ1<σ2<σ3.

Figure S16. The photovoltaic efficiency distributions of the perovskite solar cell devices under the reverse scan.

Figure S17. J-V curves of the champion perovskite solar cell devices under the reverse scan (R) and the forward scan (F).

Figure S18. J-V curves of the champion perovskite solar cell devices with different amounts of FOEI under the reverse scan.

Figure S19. Certificated results from an accredited photovoltaic certification laboratory (Newport，USA).

The certificated efficiency is 10.16% on an aperture area of 0.0886 cm2.

Figure S20. Certification results of perovskite solar cells at Newport, USA. (A) Reverse scan, and (B) Forward scan.

Figure S21. Certification results of normalized external quantum efficiency (EQE).

Figure S22. UV-vis absorption spectra of the FASnI3, FASnI3-2%PEAI and FASnI3-2%FOEI perovskite films.

Figure S23. The suppression of Sn

4+.

The XPS results of Sn 3d core level (A) FASnI3, (B) FASnI3-2%PEAI and (C) FASnI3-2%FOEI perovskite films.

Figure S24. XRD pattern of the FASnI3-2%FEI, FASnI3-2%FOEI and FASnI3-2%FOPI perovskite films.

Figure S25. Chemical structure of the fluoroarene cations and J-V curves of the champion perovskite solar cell devices with different fluoroarene cations under the reverse scan.

Table S1. The calculated surface energy of plane (100), (222) and (102) for FASnI3 slabs terminated with SnI2, FAI or FOEI.

Plane Surfacetermination Surface energy (eV nm-2

)

(100)

SnI2 -0.75

FAI -0.57

FOEI -2.66

(222)

SnI2 -2.43

FAI -2.23

FOEI 1.48

(102)

SnI2 -1.31

FAI -1.77

FOEI 1.27

Table S2. Photovoltaic parameters of the best perovskite solar cell devices with different perovskites under the reverse scan.

Device Voc [V] Jsc [mA cm-2

] FF PCE[%]

FASnI3 0.538 19.41 0.664 6.93

FASnI3-2% PEAI 0.596 19.75 0.691 8.13

FASnI3-1% FOEI 0.603 20.08 0.701 8.49

FASnI3-2% FOEI 0.667 21.59 0.751 10.81

FASnI3-5% FOEI 0.645 21.13 0.743 10.13

FASnI3-10% FOEI 0.611 19.88 0.695 8.44

FASnI3-2% FEI 0.522 17.67 0.643 5.93

FASnI3-2% FOPI 0.631 20.71 0.709 9.27

Supplemental Experimental Procedures Synthesis of organic cations

BrNH3Br +

O O

O

O

O

BrNHBoc

F

F

F

F

F

OH

BrNHBoc+

F F

F

F F

O

NHBoc

F F

F

F F

O

NHBoc

+ HI

F F

F

F F

O

NH3I

1

2

FOEI Scheme S1 Synthetic route of FOEI.

Synthesis of 2-(Boc-amino)ethyl bromide (1). To a 500 mL round bottom flask was added 10g (48.8 mmol) of 1-Bromoethylamine hydrobromide and 200 mL of dichloromethane. To this was added 5.2 g (51.25 mmol) of triethylamine and the solution wasstirred at room temp until all of solid was dissolved. Then 9.6 g (43.92 mmol) of di-tert-butyldicarbonate was added to the solution. The flask was then loosely capped to release carbon dioxide produced in the reaction. The reaction was stirred at room temperature for 12 hours. Then water was added and the mixture was extracted with dichloromethane. The organic extracts were dried over MgSO4, and the solvent was evaporated to give a colorless oil. Yield: 80%. The crude product was subjected to the next reaction without further purification.

1HNMR

(400 MHz, CDCI3): δ (ppm) 5.05 (s, 1H), 3.45 (q, 2H), 3.38 (t, 2H), 1.39 (s, 9H). Synthesis of 2. To the solution of pentafluorophenol (1 g, 5.43 mmol) in 50 mL of acetonitrile was added potassium carbonate (3g 21.73 mmol). Then 2-(Boc-amino)ethyl bromide (1.8 g, 8.15 mmol) was added. The resulting reaction mixture was flushed with nitrogen and heated overnight at 65

oC

under nitrogen. Water (250 mL) was added to the reaction mixture and extracted with CH2Cl2. The organic extracts were dried over MgSO4, and then purified using silica gel column (eluent: EtOAc/hexanes = 0/100 to 20/100). A white solid (1.4 g, 79%) was obtained.

1H NMR (400 MHz,

CDCI3): δ 5.01 (s, 1H), 4.21 (t, 2H), 3.50 (t, 2H), 1.46 (s, 9H). Synthesis of FOEI. To the solution of 2 (1.4 g, 4.28 mmol) in 15 mL of dioxane was added 1.8 mL of hydroiodic acid 57% containing no stabilizer. The reaction was stirred under nitrogen at 50

oC for one

hour. The resulting solution was then evaporated to a solid. This solid was then suspended in diethyl ether and sonicated, which was then recovered by filtration and washed with a copious amount of diethyl ether. The resulting white solid was dried under vacuum for one day. Yield: 90%.

1HNMR (400

MHz, DMSO): δ (ppm) 8.01 (s, 3H), 4.36 (t, 2H), 3.25(t, 2H).

F

F

F

F

F

NC

LiAlH4

AlCl3

F

F

F

F

F

NH2

F

F

F

F

F

NH3I

HI

3 FEI Scheme S2 Synthetic route of FEI.

Synthesis of 3. A 250 ml, three-necked flask was equipped with a reflux condenser and a mechanical stirrer. The reaction was conducted under nitrogen atmosphere. To a solution of lithiumaluminium hydride (256.5 mg, 6.76 mmol) in 10 mL of anhydrous THF, a solution of aluminium trichloride (901.4 mg, 6.76 mmol, in 10 mL THF) was added. After 5 min, a solution of 700 mg (3.38 mmol) of 2-(pentafluorophenyl)acetonitrile in 10 ml of anhydrous THF was added dropwise to the well-stirred mixture. After stirring for one hour, water was added dropwiseto decompose excess hydride. Then ammonium hydroxide solution was added continuously until the pH of the solution was 11. The aqueous layer was extracted with 30 mL of diethylether for three times. After evaporation of the solvent a yellow oil could be obtained. Yield: 68%.

1HNMR (400 MHz, CDCI3): δ (ppm) 2.88 (t, 2H), 2.77 (t, 2H).

Synthesis of FEI. To the solution of 3 (433 mg, 2.05 mmol) in anhydrous ethanol (30 mL) was added 0.69 g (3.07 mmol) of 57% hydroiodic acid containing no stabilizer. The resulting solution was purged with nitrogen gas and the reaction mixture stirred under nitrogen gas at 0°C for 2 hr. The resulting solution was then evaporated to a solid. This solid was then suspended in diethyl ether and sonicated, which was then recovered by filtration and washed with a copious amount of diethyl ether. The resulting white solid was dried under vacuum for one day. Yield: 95%.

1HNMR (400 MHz, DMSO): δ (ppm) 7.84

(s, 3H), 3.37 (t, 2H), 3.02 (m, 2H).

Br +O O

O

O

O

F

F

F

F

F

OH

+

F F

F

F F

O

+ HI

F F

F

F F

O

NH3Br Br NHBoc

NHBoc

F F

F

F F

O

NHBoc

Br NHBoc

NH3I

4

5

FOPI Scheme S3 Synthetic route of FOPI.

Synthesis of 2-(Boc-amino)propyl bromide (4). This compound was prepared as described for compound 1. Yield: 65%.

1HNMR (400 MHz, CDCI3): δ 4.77 (s, 1H), 3.40 (t, 2H), 3.23 (q, 2H), 2.01 (m,

2H), 1.39 (s, 9H). Synthesis of 5. This compound was prepared as described for compound 2. Yield: 80%.

1H NMR (400

MHz, CDCI3): δ 4.80 (s, 1H), 4.22 (t, 2H), 3.36 (t, 2H), 1.99 (m, 2H), 1.44 (s, 9H). Synthesis of FOPI. This compound was prepared as described for compound FOEI. Yield: 85%. 1HNMR (400 MHz, DMSO): δ (ppm) 7.70 (s, 3H), 4.29 (t, 2H), 3.32 (t, 2H), 2.00 (m, 2H).

DFT calculations The surface energy of the corresponding crystallographic planes can be calculated according to the following equation.

1

2

slab unitG G

A

where σ is the surface energy, Gslab is the Gibbs free energy of the slabs encased by two identical surfaces, and Gunit is the Gibbs free energy per formulary unit of perovskite in the bulk phase, including SnI2, FAI, PEAI, and FOEI. By symmetry there are two identical surfaces in ones lab, for which each surface area is denoted as A. Given that the entropic and pV contributions to the free energies change slightly throughout the condensed-phase species, the difference between the Gibbs free energy can be approximated by that between the Formation energies (E) from DFT calculations.

2 , ,( 1) 2

2

slab SnI FAI FAI PEAI orFOEIE nE n E E

A

The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE)2 exchange

correlation functional was used with norm-conserving pseudo potential3 for H atoms and the ultra-soft

pseudo potentials4 for C, F, N, O, I and Sn atoms in the Density Functional Theory (DFT) calculations.

The cutoff energies of the wave function and charge density were chosen as 25 and 255 Ry, respectively. We prepared the bulk FAI, SnI2 with initial lattice parameters from previous study.

5,6 The

bulk FOEI was prepared thanks to the previous work of PEABr.7 We replaced H in the phenyl and Br to

F and I, and added Oxygen atom. The primitive cell of FASnI3 was set to be consistent with the experimental lattice constants for bulk α-HC(NH2)SnI3.

8 Then we investigated the three types of

surfaces (SnI2, FAI and FOEI) in three directions (Figure S14). The initial surface models of FAI and FOEI were determined by shifting a bulk X-I (X: FA or FOE) to FASnI3–SnI2 surface. The initial positions of I atoms in FAI and FOEI surfaces were kept same. We kept the vacuums greater than 15Å in the vertical direction of the slab. The geometry optimizations including cell optimization were done with k-point samplings of 4x2x4, 8x4x4, and 4x4x1 for bulk FAI, SnI2, and FOEI, respectively. The geometry optimizations of surface systems were carried out with k-point of 4x4x1 with fixing the middle layer of Sn, relaxing z axis for other atoms, and relaxing the atoms of the outmost two layers of each surface. For all these calculations, the self-consistent convergence of total energy was 1x10

-8 Hartree,

and the geometries were optimized until the maximum force became smaller than 1x10-4

Hartree/bohr. We carried out these calculations using the PHASE/0 code.

9 The structures were visualized with

Visualization for Electronic and Structure Analysis (VESTA) Software.10

The surface energy of the corresponding crystallographic planes with or without FOEI based on DFT calculations are shown in Table S1. It was found that when we introduced FOEI at the surface of FASnI3 perovskite, the surface energy of (100) plane with FOEI surface was significantly reduced, compared to those with SnI2 and FAI surfaces. This suggests that the (100) plane tends to be covered by FOEI in presence of the FOEI molecule. Once the (100) plane is covered by FOEI, the growth along (100) plane is finished, and (100) surface is reserved. In contrast, the surface energy of (222) and (102) planes with FOEI surface are positive. This indicates that it is difficult to form FOEI at the (222) and (102) planes. The (222) and (102) surfaces will keep growing unless it touches the surface of another cluster. During the growth at these directions, new (100) surface can be formed, and FOEI will probably cover it soon, which increases the ratio of (100) surface over time. Finally, the ratios of other directions are quite small, which is consistent with the vanished (222) and (102) peaks from XRD results.

Supplemental Note 1 Surface segregation of FOEI

To investigate surface segregation of FOEI, depth profiling of X-ray photoelectron spectroscopy (XPS) was carried out for the FASnI3-2%FOEI film. Sample etching was performed using Ar

+ ions at a 500 V

accelerated voltage with the etching rate of about 0.2 nm s-1

. XPS spectra were obtained after etching 2 nm, 5 nm and 10 nm, respectively (Figure S5). It was observed that the intensity of the F 1s peak (688 eV) from FOEI became smaller as the Ar

+ etching time became longer. Therefore, it is concluded that

FOEI mainly exist at the top surface. Additionally, we employed time of flight secondary ion mass spectrometry (TOF-SIMS) to investigate the distribution of FOEI in the FASnI3-2%FOEI film (Figure S6). Most of FOEI molecules locate at the perovskite film top surfaces according to TOF-SIMS measurements. FOEI molecules can also be detected across the perovskite film, but FOEI molecules are too large to insert in the perovskite lattice. Therefore, some FOEI molecules also locate at the perovskite grain boundaries. In summary, FOEI molecules mainly locate at the perovskite crystal surfaces, including top surfaces and grain boundaries.

Supplemental Note 2 Activation energy calculated from temperature-dependent PL spectra.

The activation energy can be derived according to the Arrhenius equation.11

a

0

/( )I( )

1 bE k T

IT

Ae

where I(T) is the PL intensity at temperature T, I0 is the PL intensity at 0 K, A is a constant, Ea is the activation energy, and kb is the Boltzmann constant.

Supplemental Note 3 Surface energy

The surface energy of the perovskite film was calculated using Owens-Wendt method by considering both polar and dispersive components of surface energy.

12,13 These interactions will sum to form the

total surface energy of the solid perovskite film σs.

where σs

D and σs

P are the dispersive and polar components of the surface energy of the solid

perovskite film respectively. Owens-Wendt primary equation

where σl

D and σl

P are the dispersive and polar components of the surface tension of the liquid

respectively. σl is the total surface tension of the liquid. The first step for this surface energy calculation is to measure the contact angle for a purely dispersive liquid. A common liquid used here is diiodomethane, which has effectively no polar component to its surface tension (due to molecular symmetry), meaning that σl = σl

D = 50.8 mN/m. Reducing

Owens-Wendt primary equation to:

Using this equation, σs

D can be calculated directly, when the contact angle of diiodomethane on the

perovskite film is known. The next step is to measure the contact angle for a liquid with known dispersive and polar components. A common liquid used here is glycerol, where σl

P = 37.0 mN/m and σl

D = 26.4 mN/m. By inserting this

into Owens-Wendt primary equation, along with the surface tension of the liquid and previously calculated σs

D, the value of σs

P can be calculated. The total surface energy of the solid perovskite film

σs is then a sum of σsD and σs

P.

Supplemental Note 4 Nucleation According to thermodynamic theory, the total free energy of nuclei formation (ΔG) includes a bulk term (ΔGv, free energy difference between the nuclei and the solute in solution) and a surface term (ΔGs, free energy difference between the nuclei surface and the bulk of the nuclei).

14

2 34 ln( )4

3s v b

SG G G r r k T

V

where r is the radius of the nucleus and σ is the surface energy, kb is the Boltzmann constant, T is the absolute temperature, V is the molar volume of the nucleus, and S is the supersaturation ratio, which is defined as S = C/Cs with C as the solute concentration and Cs as the solubility limit. Figure S13 shows a plot of ΔG as a function of r. It can be seen how the function reaches a maximum,

which represents the energetic barrier that needs to be surpassed to achieve nucleation (ΔG∗). The value of r at this maximum (r∗) is defined as the critical radius of nucleus size.

* 2

ln( )b

Vr

k T S

Substituting r* into ΔG gives the Gibbs free energy of formation of the critical nucleus (ΔG∗) as

3 2*

2

16G

3 ln( )b

V

k T S

Nucleation rate (i.e., the number of nuclei formed per unit time per unit volume) can be expressed by an Arrhenius-type equation.

*

exp( )b

GJ A

k T

where A also depends on supersaturation ratio. Subtituting in the expression for ΔG∗ from (1) gives:

3

2exp( )

(ln( ))

BJ A

S

Supplemental Note 5 Wulff construction theorem

After nucleation, the crystal nuclei would grow into large crystals at nearly saturated conditions (nearly equilibrium conditions). And the shape of a crystallite can be predicted by the Wulff construction theorem.

15

Constanti

ih

where σ and h are the specific surface energy and the distance from the crystallite’s center to its surface, respectively. From Wulff construction theorem, one can see that the high-energy crystal facets grow faster, their surface areas become smaller, and eventually crystals enclosed by lower energy facets form (Figure S15).

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3. Troullier, N., and Martins, J. A. (1990). straightforward method for generating soft transferable pseudopotentials. Solid State Commun.74, 613-616.

4. Vanderbilt, D. (1990). Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Phys. Rev. B 41, 7892-7895.

5. Petrov, A.A., Goodilin, E.A., Tarasov, A.B., Lazarenko, V.A., Dorovatovskii, P.V., and Khrustalev, V.N. (2017). Formamidinium iodide: crystal structure and phase transitions. Acta Cryst. E 73, 569-572.

6. Howie, R.A., Moser, W., and Trevena, I.C. (1972). The crystal structure of tin(II) iodide. Acta Cryst. B 28, 2965-2971.

7. Rademeyer, M. (2007). 2-Phenylethylammonium bromide. Acta Cryst. E 63, o221-o223. 8. Stoumpos, C.C., Malliakas, C.D., and Kanatzidis, M.G. (2013). Semiconducting Tin and Lead

Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties. Inorg. Chem. 52, 9019-9038.

9. https://azuma.nims.go.jp. 10. Momma, K., and Izumi, F. (2011). VESTA 3 for three-dimensional visualization of crystal,

volumetric and morphology data. J. Appl. Cryst. 44, 1272-1276. 11. Tan, S., Zhou, N., Chen, Y., Li, L., Liu, G., Liu, P., Zhu, C., Lu, J., Sun, W., Chen, Q., et al.

(2019). Effect of High Dipole Moment Cation on Layered 2D Organic–Inorganic Halide Perovskite Solar Cells. Adv. Energy Mater. 9, 1803024.

12. Nuriel, S., Liu, L., Barber, A.H. and Wagner, H.D. (2005). Direct measurement of multiwall nanotube surface tension. Chem. Phys. Lett. 404, 263-266.

13. Michiardi, A., Aparicio, C., Ratner, B.D., Planell, J.A., and Gil, J. (2007). The influence of surface energy on competitive protein adsorption on oxidized NiTi surfaces. Biomaterials 28, 586-594.

14. Jung, M., Ji, S.-G., Kim, G., and Seok, S.I. (2019). Perovskite precursor solution chemistry: from fundamentals to photovoltaic applications. Chem. Soc. Rev. 48, 2011-2038.

15. Zhang, J., Li, H., Kuang, Q., and Xie, Z. (2018). Toward Rationally Designing Surface Structures of Micro- and Nanocrystallites: Role of Supersaturation. Acc. Chem. Res. 51, 2880-2887.

16. Lilliu, S., Dane, T.G., Alsari, M., Griffin, J., Barrows, A.T., Dahlem, M.S., Friend, R.H., Lidzey, D.G., and Macdonald, J.E. (2016). Mapping Morphological and Structural Properties of Lead Halide Perovskites by Scanning Nanofocus XRD. Adv. Funct. Mater. 26, 8221-8230.