Solution coating of large-area organic semiconductor thin ... · 1 Supplementary Information Solution coating aligned single-crystalline domains of non-equilibrium organic semiconductor

1

Supplementary Information

Solution coating aligned single-crystalline domains of

non-equilibrium organic semiconductor thin films

Ying Diao1, Benjamin C-K. Tee2, Gaurav Giri1, Jie Xu1,5, Do Hwan Kim1, Hector A. Becerril1, Randall

M. Stoltenberg3, Tae Hoon Lee2, Gi Xue5, Stefan C. B. Mannsfeld4* & Zhenan Bao1*

1Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.

2Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.

3Department of Chemistry, Stanford University, Stanford, California 94305, USA.

4Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park,

California 94025, USA.

5Department of Polymer Science and Engineering, Institute of Chemistry and Chemical Engineering,

The State key Laboratory of Coordination Chemistry, The National Laboratory of Nanjing

Microstructure Study, Nanjing University, Nanjing, 210093, P. R. China.

Corresponding authors: Zhenan Bao, [email protected]; Stefan CB Mannsfeld, [email protected]

Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains

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Supplementary methods and discussion

COMSOL simulations. The detailed geometry of the simulation box is as follows. The outer diameter and inner diameter of the crescent-shaped micropillar is 35 μm and 23 μm respectively. The pillar height is 42 μm (measured from the SEM image). The center-to-center spacing between the micropillars is 50 μm. The corners of the micropillars are rounded with a radius of curvature (fillet radius in COMSOL) of 3 μm. The tilt of the blade is set as 8°. The gap of the first row of pillars to the bottom substrate is set as 3 μm. To simulate shearing motion, the bottom substrate was set as a sliding wall with speed of -0.6mm/s. The negative sign denotes the direction pointing towards the left of the simulations box (opposite to the x axis). The two side walls were set as periodic boundary conditions. The outlet (from the left bound of the simulation box, Figure S1) was set as atmospheric pressure. The inlet mass flow rate was set as the solvent evaporation rate. From the mass of solid films we calculated the solvent evaporation rate by applying the mass balance.1 Normal mass flow rate at the inlet is calculated as -1.07669 x 10-9 kg/s at the shearing conditions specified in the methods section. Simulation is performed at the steady state using the laminar fluid module. X-ray characterization of film microstructure and molecular packing. Azimuthal X-ray scans,2 high-resolution scans and grazing incidence X-ray diffraction were performed at the Stanford Synchrotron Radiation Lightsource (SSRL) on beamlines 7-2, 2-1 and 11-3. At beamline 11-3, we performed grazing incidence X-ray diffraction (GIXD) with an area detector (MAR345 image plate) for obtaining molecular packing information. The extent of deviation from the equilibrium molecular packing was inferred from the positions of (101) and (010) diffraction peaks. The beam energy is 12.73 keV. The incident angle was set as 0.12°. Two scans were performed for each sample under helium protection, one with the shearing direction parallel to the incident beam, the other perpendicular. We carried out high-resolution azimuthal X-ray scans at beamline 7-2, equipped with a point detector of 1mrad collimation. The beam energy is 8 keV. The incident angle was set as 0.12°. The detector was positioned at the (010) reflection, with the momentum transfer vector qxy= 0.81, qz= 0.21. The high-resolution scans for obtaining the correlation length were performed at beamline 2-1. The beam energy was set as 12.3 keV. The crystal analyzer was employed to reduce instrumental broardening by the soller slits. The point detector was positioned on the (001) diffraction peak (qz= 0.382). The step size of the high-resolution scan was 0.0006°. Two types of scans were performed: specular scan (thelta-2thelta scan) for obtaining out-of-plane peak width and transverse scan (rocking scan, or thelta scan) for obtaining in-plane peak width. Scherrer equation was applied for calculating the correlation length from the full width at half maximum (FWHM) of the peak. Polymorphs of TIPS-pentacene via diffraction peak analysis. Grazing Incidence X-ray Diffraction (GIXD) scans were performed at beamline 1-5 of Stanford Synchrotron Radiation Lightsource (SSRL). For films with highly aligned grains such as the ones used in this study, sample in-plane rotation is necessary to capture all diffraction peaks and detect every polymorph present in the film. To improve the data quality for detailed peak analysis, small sample areas (<3x3 mm2) were used to reduce sample-induced peak broadening and to eliminate edge effects. At least three samples were scanned for each solution shearing condition. The new data we obtained reveal at least two discrete packing states (polymorphs) in TIPS-pentacene thin films (Figure S9, Figure 4). The discerning of discrete polymorphs is made possible by the higher crystal quality and thus narrower diffraction peak widths compared to those from the previous study. When comparing the column sum of (10L) and (01L) peaks at various conditions (Figure S9), we noticed that many of the diffraction spectra are comprised of two ‘peaks’, a sharp peak at Qxy(10L) ~ 0.88 Å-1, Qxy(01L) ~ 0.77 Å-1 and a broad ‘peak’ with Qxy(10L) between 0.81 and 0.86 Å-1 and Qxy(01L) between 0.78 and 0.83 Å-1. Interestingly, with increase in shearing speed or decrease in solution concentration, the broad ‘peak’ shifts towards the sharp peak while the sharp peak positions remain invariant. This observation suggests that the broad ‘peak’ is comprised of multiple peaks, which when their relative intensities vary gives rise to an apparent shift in the position of the

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convoluted peak. We therefore carried out peak deconvolution on the most intense diffraction peaks to find that a minimum of four peaks can be used to fit all the diffraction spectra, representative ones shown in Figure S10. The existence of at least four polymorphs can also be inferred from the fine structures of GIXD images, as exhibited in the (-11L) rod in Figure S11. However, we cannot exclude the existence of alternative solutions to the peak deconvolution, especially if more than four polymorphs are present.

Tradeoff between molecular packing control and morphology control. Higher shearing speed also resulted in increased crystal growth defects, which severely limited the chance of obtaining single-crystalline domains. Specifically, at the conditions when the desired molecular packing was obtained in the previous work,3 the film morphology was dictated by undesired spherulite formation due to random nucleation across the entire film (Figure S13A). This phenomenon is usually observed when a complete liquid film forms before nucleation occurs, i.e., the Landau-Levich regime of solution coating.1 Under this regime, controlling fluid dynamics at the meniscus front will have no effect on nucleation and crystal growth, making it impossible to obtain single-crystalline domains using FLUENCE. This limitation calls for alternative means for controlling molecular packing, which can achieve non-equilibrium molecular packing at lower shearing speeds when nucleation and crystal growth ensue at the meniscus front, concurrent with the liquid film formation, a.k.a the evaporation regime of solution coating. In this work, we are able to attain non-equilibrium molecular packing in the evaporation regime by changing the solvent and tuning the film thickness, in addition to varying the shearing speed.




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Supplementary figures

Figure S1. Streamline representation of the calculated velocity field. The streamlines are color coded to indicate the scale of velocity, in mm/s. To simulate the effect of shearing towards the right, the substrate has a sliding speed of 0.6 mm/s towards the left, while the shearing blade is fixed. Recirculation and lateral currents are highlighted using white dotted lines in B-D.





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Figure S2. Morphology comparison of TIPS-pentacene films prepared with flat shearing blade (A) and micropillar patterned blade (B), at various shearing speed. Images are taken under cross-polarized optical microscope. All images are of the same scale. Films coated with micropillar-patterned blade at shearing speed from 0.4 to 1.2 mm/s exhibit significantly increased domain size, and much lower grain boundary density and void fraction.

Figure S3. Design of nucleation control region and the resulting morphology of TIPS pentacene films. Images were taken under cross-polarized optical microscope. A-B, effect of tip angle on nucleation density and the resulting film morphology. Smaller tip angle leads to lower nucleation density, and better nucleation anchoring at the tip. C, Twin boundary formation with symmetric triangle design. D, Effect of the number of slits on crystallite ‘filtering’. The tip angle is 30°. The slit width is





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100 μm. The stripe widths in A, B, D are 500 μm. Films were solution sheared from 8mg/ml TIPS-pentacene/toluene solution, at 50 °C and 0.25 mm/s (A, B, D) or at 35 °C and 0.2 mm/s (C). These solution-shearing conditions were selected because the crystal growth is free of secondary nucleation, and as such, the nucleation control method can be investigated independent of the crystal growth control method. All other data presented in this work were based on TIPS-pentacene/mesitlyene system as specified in the methods section.

Figure S4. AFM height image of single-crystalline domains corresponding to Figure 2C. The white arrow indicates the solution shearing direction. The depth profile is shown along the white dotted line. The depth of the hollows corresponds to the thickness of the film, which is 20 ± 1 nm. Crystal terraces of ~1.7nm height are also visible from this image, demonstrating high crystal quality and single-crystalline nature of the domain.

5µm

20nm





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Figure S5. Cross-polarized optical micrographs showing cases of non-single-crystalline domains. The films were solution sheared with FLUENCE at optimized conditions specified in the Methods section. The crossed arrows indicate the orientation of crossed polarizers. Rotating cross-polarizers by ~35° distinguishes single-crystalline from non-single-crystalline domains in sample 1 (A and B) and sample 2 (C and D). This figure shows that there are two types of morphology defects preventing us from attaining higher probability of single-crystalline domains. The nonidealities are either surface defect induced or twin grain boundary induced shown in Figure S6. These morphology defects occur stochastically under the same solution coating conditions.

Figure S6. Cross-polarized optical micrographs showing causes for non-single-crystalline domains: Surface defects induced (A, B) and twin grain boundary induced (C, D). C and D are images of the same sample with mirror rotations to show twin domains. The sampe has Au electrode on some of the single-crystalline domains. All films were solution sheared with FLUENCE at optimized conditions specified in the Methods section.

Figure S7. TIPS-pentacene film morphology with high probability of aligned single-crystalline domains. Nucleation control region design: tip angle is 15°; strip width is 500 μm (indicated by white





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arrows); slit size is 50 μm. Solution shearing conditions are detailed in the Methods section. The following steps were taken for attaining > 90% probability of aligned single-crystalline domains: 1) narrowing the domain size from 1 mm to 500 μm; 2) reducing surface defects by excessive substrate cleaning; 3) tuning the “slit” design to reduce meniscus instabilities, and that include adopting a ‘tapering’ design around the slit region, as shown in Figure S7 A. This helps avoid sudden stop of fluid at the slit region.

Figure S8. 200μm wide single-crystalline domains of TIPS-pentacene. A and B show the crystal morphology under different tilting angles of the cross-polarizers. Simultanous light extinction of all domains indicates highly aligned nature of the single-crystalline domains. The films were solution sheared at the same conditions detailed in the method section (135°C from 1.6mg/ml mesitylene solution at 0.6mm/s). FLUENCE was applied for obtaining the single-crystaline domains. This image, together with Figure S7 and Figure 2 demonstrate that FLUENCE can be applied to making a wide size range of single-crystalline domains (200, 500, 1000μm shown).





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Figure S10. Characterization of molecular packing by Grazing Incidence X-ray diffraction (GIXD) and corresponding diffraction peak analysis. A1-D1, GIXD images of TIPS-pentacene films prepared from 8mg/ml solution at various shearing speeds. GIXD was taken with sample in-plane rotation to capture diffraction peaks from all crystal planes of all polymorphs present. The observed brag rods (red arrows on top) are labeled with their (hk) indexes. Indexes of degenerate peaks are not shown. The amorphous ring from SiO2 (gate dielectric) is visible at q from 1.4-1.7 Å-1, whose intensity increases with decrease in film thickness. A2-D2, higher magnification images of (01L) and (10L) peaks, corresponding to the region highlighted with the white dotted box in A1. The diffracton intensities are shown on log scale. A3-D3 & A4-D4, analysis of polymorphic states via deconvolution of (01L) and (10L) peaks, with A3-D3 corresponds to (01L) and A4-D4 to (10L). Blue curve is simulated from deconvoluted peaks, and the red curve is experimentally measured, made by performing a column summation of the 2D diffraction image shown in Figure A2-D2. The simulated blue curve overlays very well with the corresponding red curve in all cases. Peak deconvolution suggests existence of at least four polymorphs of TIPS-pentacene. The four polymorphs are labeled form I, II, III, IV respectively.

Shearing speed (mm/s)

0.4

0.8

1.6

2.8

A1

B1

C1

D1

A2

B2

C2

D2

0.76 0.78 0.80 0.82 0.84 0.86

350

300

250

200

150

100

50

x103

0.860.840.820.800.780.760.74

300250200150100

500

x103

20001000

0-1000

0

12

800

700

600

500

400

300

x10

3

0.840.820.800.780.76

400300200100

0

x10

3

-10-505

x10

3

0

12

3

1.7

1.6

1.5

1.4

1.3

1.2

1.1

x10

6

0.840.820.800.780.76

400300200100

0

x10

3

-10-505

x10

3

0

1

23

2.2

2.0

1.8

1.6

x10

6

0.820.800.780.760.74

600400200

0

x10

3

1050

-5-10

x10

3

0

12

I II IV

A3

B3

C3

D3

III

0.76 0.78 0.80 0.82

450

400

350

300

250

200

150

x103

0.920.900.880.860.840.820.80

300200100

0

x103

40002000

0-2000

0

1

2

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

x106

0.920.900.880.860.840.820.80

600400200

0

x103

80004000

0-4000-8000

0 1 2

3

1.3

1.2

1.1

1.0

0.9

x106

0.900.880.860.840.82

400300200100

0

x103

-40000

4000

01 2

3

1.6

1.5

1.4

1.3

x10

6

0.920.900.880.860.840.82

-4000-2000

02000

400300200100

0

x10

3

0 1

2

I II III IV

A4

B4

C4

D4

0.80 0.82 0.84 0.86 0.88 0.90 0.92

0.82 0.84 0.86 0.88 0.90 0.92 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0.75 0.85 0.95 Qxy (Å-1) Qxy (Å-1)

1.0

0.8

0.6

0.4

0.2

Qz (

Å-1

)

0.6

0.5

0.4

(01L) (10L) (01) (-11) (11) (-12)

(10)





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Figure S11. GIXD image indicating existence of four TIPS-pentacene polymorphs. A, GIXD image of the TIPS-pentacene film coated from 3.2mg/ml mesitylene solution at 0.8mm/s. The (hk) indexes ofthe (01), (10) and (-11) brag rods are shown on top. Indexes of the degenerate peaks are not shown. B, higher magnification image of the (-11) peak, corresponding to the region highlighted with the black dotted lines in A. Background substraction is applied to increase the signal-to-noise ratio. The color map used is ‘bone’ for enhancing the contrast.

Figure S12. Thickness of TIPS-pentacene films coated at various conditions. The grey dotted line indicates the film thickness below which the highest deviation from the equilibrium packing is obtained. Films with thickness above the gray dotted line exhibited mixed polymorphs.

0.60 0.80 1.00 Qxy (Å-1)

0.80

0.60

0.40

0.20

(01) (10) (-11) A I II III IV

0.96 1.10 Qxy (Å-1)

0.70

0.50

B

0.0

50.0

100.0

150.0

200.0

0 1 2 3 4 5

Thic

knes

s (n

m)

Shearing speed (mm/s)

1.6mg/ml 8.0mg/ml

0.0

50.0

100.0

150.0

200.0

0 5 10 15 20

Thic

knes

s (n

m)

Concentration (mg/ml)

0.8mm/s

~17 nm





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Figure S13. Morphology comparison of TIPS-pentacene films coated from toluene solution (A) to that from mesitylene solution (B) at respective lowest solution shearing speed when the highest deviation from equilibrium packing is obtained. Solution shearing was carried out at 8mg/ml, 90°C, 8mm/s from toluene solution, and 8mg/ml, 135°C, 2.8mm/s from mesitylene solution.

Table S1. Hole mobility of TIPS-pentacene measured perpendicular (per) and parallel (par) to the shearing direction.

Average mobility (cm2 V-1 s-1) Single-crystalline Reference per 0.16 1.1 par 8.1 2.2 par/per ~50 ~2

Samples were prepared at 0.6 mm/s shearing speed from mesiytlene solution (see Methods section). par/per denotes the ratio of mobility parallel over perpendicular to the shearing direction. Charge transport anisotropy is much higher for single-crystalline domain than reference samples, which corroborates the highly aligned feature of single-crystalline domains. For reference samples, the crystal ribbons intersect due to dendritical crystal growth. In addition, the domain orientation distribution is also much broader. These factors may have resulted in higher mobility in the perpendicular direction for the reference sample.





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Figure S14. Mobility comparison at various shearing speeds. Samples were solution sheared from 1.6 mg/ml TIPS-pentacene-mesitylene solution at 135°C. Around 30 transistors tested in each case. Invariance of reference sample mobilities at various shearing speeds indicates the charge transport is grain boundary limited. For single-crystalline domain samples, maximum mobility at intermediate shearing speed may be due to interplay between morphology and molecular packing. The molecular packing was characterized with GIXD shown in Figure S9 C, D.

Figure S15. Representative transfer characteristics of the TIPS-pentacene single-crystalline devices, supplementary to device characteristics shown in Figure 5.

0

2

4

6

8

10

12

0.5 0.6 0.7 0.8

Mob

ility

, cm

^2/V

s

Shearing speed, mm/s

Control Single-crystalline Max

Referene

Single-crystalline

Max. value

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

I sd (

x10-3

A)

-100-80-60-40-200Vsd (V)

-30V-40V

-50V

-60V

-70V

-80V

-90V

Vg=-100V





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Figure S16. Optical micrograph of TIPS-pentacene single-crystalline thin-film transistors. Devices were fabricated in the top-contact, bottom-gate configuration, with 40 nm thick Au drain and source electrodes (shown as dark horizontal lines on the middle single-crystalline domain) and PTS-modified SiO2 dielectric layers (300 nm). The channel length and width were 50 μm and 1 mm, respectively. The crossed arrows denote the orientation of the crossed polarizers.

Figure S17. Film morphology of 4T-TMS (trimethylsilyl-substituted quarterthiophene), single-crystalline domains (with FLUENCE) vs. reference samples (without FLUENCE). A, a photographic image of one millimeter-wide single-crystalline OFET ‘pixels’ on a Si wafer with 300 nm SiO2 as the dielectric. B, molecular structure of 4T-TMS. C-F, optical micrographs of single-crystalline domains (C, D) and reference samples (E, F) without (C, E) and with (D, F) cross-polarizers. G & H, higher manification optical images of single-crystalline domains vs reference films. All samples were prepared via solution shearing at 140°C from 2mg/ml tetralin solution, at 0.2mm/s.





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Figure S18. Comparison of film morphology characterized by AFM: single-crystalline (with FLUENCE) vs. reference (without FLUENCE). Depth profiles are shown beneath corresponding AFM images, measured along the white dotted line. Crystal terraces of ~2nm height are visible on single-crystalline film surface, demonstrating high crystal quality and single-crystalline nature of the domain. The terrace height corresponds to the height of one 4T-TMS monolayer. In the reference sample, dendrites are evident, and the depth of hollows corresponds to the thickness of the film, which is approximately 12 nm.

1 Le Berre, M., Chen, Y. & Baigl, D. From Convective Assembly to Landau-Levich Deposition of Multilayered Phospholipid Films of Controlled Thickness. Langmuir 25, 2554-2557, doi:10.1021/la803646e (2009).

2 Rivnay, J. et al. Large modulation of carrier transport by grain-boundary molecular packing and microstructure in organic thin films. Nature Materials 8, 952-958, doi:10.1038/nmat2570 (2009).

3 Giri, G. et al. Tuning charge transport in solution-sheared organic semiconductors using lattice strain. Nature 480, 504-U124, doi:10.1038/nature10683 (2011).





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Solution coating of large-area organic semiconductor thin ... · 1 Supplementary Information Solution coating aligned single-crystalline domains of non-equilibrium organic semiconductor