Supporting Information

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1 Supporting Information High, Anisotropic and Substrate-Independent Mobility in Polymer Field-Effect Transistors Based on Pre-Assembled Semiconducting Nanofibrils. Sara Bonacchi, Marco Gobbi, Laura Ferlauto, Marc-Antoine Stoeckel, Fabiola Liscio, Silvia Milita Emanuele Orgiu, * Paolo Samorì * University of Strasbourg, CNRS, ISIS UMR 7006, 8 allée Gaspard Monge, F Strasbourg, France. Istituto per la Microelettronica e Microsistemi (IMM) Consiglio Nazionale delle Ricerche (CNR), Via Gobetti 101, Bologna, Italy. Table of contents 1. Langmuir-Schaeffer film formation and characterization.... S2 Figure S1.... S3 1.1 UV-Vis characterization of IIDDT-C3 LS films.... S3 Figure S2.... S3 1.2 AFM Images of IIDDT-C3 spin-coated and LS films.... S4 Figure S3.... S4 FigureS4.... S D-GIXRD and XRR characterization of IIDDT-C3 LS films.....s6 Figure S5.... S6 FigureS6.... S6 Table S1.... S7 1.4 FET characterization of IIDDT-C3 LS films.... S7 Figure S7.... S7 Figure S8.... S7 Figure S9.... S8 Figure S S8 2. Langmuir-Schaeffer film transferred onto different substrates.... S9 2.1 AFM images of IIDDT-C3 films deposited on different substrates.... S9 Figure S S9 2.2 X-ray reflectivity of IIDDT-C3 films deposited on different substrates.... S10 Figure S S10 S1

2 2.3 Grazing incidence X-ray Diffraction.... S11 Figure S S12 Figure S S12 Figure S S13 Figure S S14 Table S2.... S FET analysis of IIDDT-C3 films deposited on different substrate surfaces..... S15 Figure S S15 Figure S S15 Figure S S16 Figure S S16 Table S3.... S14 3. Reference... S17 1. Langmuir-Schaeffer film formation and characterization. In order to in-depth discuss the relationship between the morphological, structural and electrical properties of the IIDDT-C3 LS films, we analyzed films obtained by using different i) volume of the IIDDT-C3 solution spread over the water/air interface, and ii) surface pressure selected for the transfer step (see Figure 1a, Main Text). In particular, we estimate the areal density ρ - such as the quantity of polymer for unit area in the different cases (expressed in µg/cm 2 ) - taking into the account the volume of polymer and the area between the barriers during the transfer (see Figure S1a,b and Table S1c). a) Surface Pression (mn/mm) LS1 LS2 LS Area (cm 2 ) b) c) LS film X cm Volume (µl) Y cm 30 cm Surface pressure (mn/m) Area (cm 2 ) ( Y x 7.5 ) 7.5 cm Areal density, ρ (µg/cm 2 ) LS LS LS S2

3 Figure S1. (a) Isotherm curve: surface pressure for all the volumes of IIDDT-C3 solution (chloroform, 0.5 mg/ml) spread over the air/water interface, as a function of the area between the barriers. For all the samples, the area at the transfer step is extrapolated by the slope of the curve at zero pressure (dashed line). (b) Schematic top-view of the LS trough top and of the barriers distance, X. (c) Table with the estimation of the LS film areal density, ρ. 1.1 UV-Vis characterization of IIDDT-C3 LS films. Figure S2a) shows the typical absorption spectra of Langmuir-Schaefer (LS) films transferred on a quartz substrate. All the LS films exhibited the characteristic dual bands of isoindigo derivatives centered at 420 nm and, at lower energy, at 650 nm and 712 nm. We reported the LS film spectra as recorded, to point out the relationship between absorbance and areal density (ρ) of LS films. Figure S2b) shows the normalized absorbance spectra of IIDDT-C3 in solution and LS film. As already reported by Lei et al., 1 the presence of a slight hypsochromic shift when going from solution to LS film indicates that IIDDT-C3 probably already forms aggregates in solution. However, the ratio between the vibration peaks 0-0 and 0-1, respectively at 715 nm and at 655 nm (Figure S2b), changes when IIDDT-C3 polymer goes from solution to films suggesting that polymer become more planar in the film with enhanced π-π stacking. 1 a) b) 0.08 Absorbance LS1 LS2 LS λ/nm Normalized Absorbance LS film Solution λ/nm Figure S2. a) Absorption spectra of LS1 (black line), LS2 (red line) and LS3 (green line) IIDDT-C3 Langmuir-Schaefer (LS) thin films transferred onto a quartz slide. b) Normalized absorption spectrum of LS3 (green line) and IIDDT-C3 in chloroform solution (C = 1 x 10-5 M) (dashed line) has been reported for comparison. S3

4 1.2 AFM Images of IIDDT-C3 spin-coated and LS films. S4

5 Figure S3. (left) AFM images of typical IIDDT-C3 polymer spin-coated and LS films transferred onto HMDS-treated SiO 2 substrate. (right) Linearly-polarized absorption spectra of IIDDT-C3 polymer LS films transferred onto a quartz substrate with the polarization parallel (continuous line) or perpendicular (dashed line) to the direction of b r. Blue arrows indicate the direction of the polymer fibrils. Figure S4. AFM images of IIDDT-C3 film obtained by a) spin-coating (1 x 1 µm 2 ) and b) LS technique (LS2 film, 2 x 2 µm 2 ). S5

6 1.3 2D-GIXRD and XRR characterization of IIDDT-C3 LS films. Figure S5. 2D-GIXRD patterns of LS2 film deposited by LS on a HMDS-SiO 2 substrate recorded with the X-ray beam (a) parallel or (b) perpendicular to the average orientation of the fibrils (see Schematic illustration in Figure 2c,d, Main Text). The extracted diffraction intensity integrated along the direction (c) perpendicular, and (d) parallel to the sample surface. Figure S6 shows the XRR curve of spin-coated and Langmuir-Schaefer films. Differently from the SC film (Figure S6a), XRR curves collected on LS films (Figure S6b,c,d) present the first two Bragg reflections at q z = 0.24 Å -1 (100) and q z = 0.50 Å -1 (200) which indicate the edge-on configuration of the polymer assembly. Figure S6. XRR curves of (a) spin-coated film (150 µl) and Langmuir-Schaefer thin films at different areal density, ρ: (b) LS1, (c) LS2 and (d) LS3. The black line is the experimental result, while the red line is the corresponding XRR fit. S6

7 Table S1: Film thickness determined by AFM (Figure S3) and XRR (Figure S5) analysis. Sample Thickness /nm (AFM data) hickness /nm (XRR data) Spin-coated film (2) LS (9) LS (7) LS (8) 1.4 FET characterization of IIDDT-C3 LS films. IIDS (A)I [I DS ] 1/2 (A) 1/ VGS (V) Figure S7. FET characteristic of IIDDT-C3 spin-coated film on HMDS-treated SiO 2 substrate. Transfer curve taken at V DS = -40 V (L = 80 µm, W = 1 mm). Average hole mobility of spin-coated film = cm 2 V -1 s -1. Figure S8. Transfer curves recorded of an IIDDT-C3 FET assembled on HMDS-treated SiO 2 substrate. The films were prepared (a) by our LS method (LS2), and b) by spin-coating. (V DS = -20V; L = 80 µm, W = 1 mm). S7

8 Figure S9. FET characteristics output curves of LS2 film on HMDS-treated SiO 2 substrate taken at various V G with carrier transport (a) parallel, and (b) perpendicular to polymer fibrils bundle orientation. a) b) I I DS (A) I [I SD ] 1/2 (A) 1/2 I DS (A) x x x V GS (V) -4.0x V GS (V) Figure S10. FET of LS3 film (a) transfer curves taken at V DS = -50 V (b) Transfer curves taken at V DS = - 50 V. The mobility values were calculated to be 2.7 cm 2 V -1 s -1 and an I ON /I OFF up to 2.5 x S8

9 2. Langmuir-Schaeffer film transferred onto different substrates. 2.1 AFM images of IIDDT-C3 films deposited on different substrates. Figure S11. (right) Typical AFM images of bare substrates; (centre) spin-coated and (left) LS films transferred onto different substrates: (a,b,c) Quartz substrate; (d,e,f) (OTS)-treated SiO 2 substrate; (g,h,i) (PMMA)-treated SiO 2 substrate; (l,m,n) CYTOP-treated SiO 2 substrate; (o,p,q) UV-Ozone treated SiO 2 substrate. For this study, we employed the following parameters for LS film formation S9

10 and transfer (i.e., Volume = 130 µl; Surface Pressure = 40 mn/m) corresponding to an areal density ρ of 1.05 µg/cm 2, intermediate between LS2 and LS X-ray reflectivity of IIDDT-C3 films deposited on different substrates. XRR curves of the films and their relative substrates are plotted in Figure S10. In the case of LS technique, the XRR analysis 2 reveals that the choice of the substrate does not influence the amount of the material and the polymer supramolecular organization. Indeed, all XRR curves (green ones) are characterized by the same Bragg peaks coming from the lamellar stacking (001) and (002), which are characteristic of the edge-on configuration. a) Intensity (cps) LS IIDDT-C3/OTS SC IIDDT-C3/OTS OTS 002 b) Intensity (cps) LS IIDDT-C3/HMDS SC IIDDT-C3/HMDS HMDS c) Intensity (cps) q z (Å -1 ) LS IIDDT-C3/CYTOP SC IIDDT-C3/CYTOP CYTOP d) Intensity (cps) q z (Å -1 ) LS IIDDT-C3/PMMA SC IIDDT-C3/PMMA 10 8 PMMA q z (Å -1 ) q z (Å -1 ) Figure S12. XRR curves of IIDDT-C3 films deposited by spin coated (SC) and Langmuir-Schaefer (LS) techniques with their relative substrates: (a) OTS, (b) HMDS, (c) CYTOP and (d) PMMA. For the LS Bragg peak coming from the lamellar stacking are labelled. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. On the other hand, SC film morphology depends on the nature of the substrate surface. For OTS and HMDS treated-substrates, density inhomogeneities are found along the surface normal indicating a S10

11 disordered polymer organization which diverges from the edge-on configuration. For CYTOP and PMMA substrates signal from the polymer film are not detected, due to the absent of the film or the high roughness of the substrate surface, respectively. 2.3 Grazing incidence X-ray Diffraction of IIDDT-C3 films deposited on different substrate surfaces All polymer films were characterized by 2D-GIXRD measurements. 2D-GIXRD images of SC and LS films deposited on HMDS, OTS, CYTOP and PMMA surfaces are reported in Figure S11, S12, S13, and S14, respectively. Regardless the nature of the substrates, 2D-GIXRD images of LS films show lamellar peaks along the out-of-plane direction and π-π stacking peak along the in-plane direction when the incident beam is parallel to the fibril long axis direction. These findings confirm the formation of well oriented and ordered fibrils having the π-π interaction perpendicular to the fibril long axis direction. Differently, 2D-GIXRD images collected for SC films do not show any Bragg reflections coming from the films, confirming their amorphous nature as identified from XRR analysis. S11

12 Figure S13. 2D-GIXRD images of IIDDT-C3 films on HMDS deposited by (a) spin coating, and LS using an incident beam (b) parallel and (c) perpendicular to the fibril long axes. Radially integrated intensities along (d) q z and (e) q xy. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. Figure S14. 2D-GIXRD images of IIDDT-C3 films on PMMA deposited by (a) spin coating, and LS using an incident beam (b) parallel and (c) perpendicular to the fibril long axes. Radially integrated intensities along (d) q z and (e) q xy. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. S12

13 Figure S15. 2D-GIXRD images of IIDDT-C3 films on CYTOP deposited by (a) spin coating, and LS using an incident (b) beam parallel and (c) perpendicular to the fibril long axes. Radially integrated intensities along (d) q z and (e) q xy. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. S13

14 Figure S16. 2D-GIXRD images of IIDDT-C3 films on OTS deposited by (a) spin coating, and LS using an incident beam (b) parallel and (c) perpendicular to the fibril long axes. Radially integrated intensities along (d) q z and (e) q xy. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. Table S2. Substrate properties (i.e., water contact angle, roughness, thickness) before and after the deposition of IIDDT-C3 polymer by using the spin-coating (SC) and the Langmuir-Schaeffer (LS) techniques. For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. Water Contact angle (at 25 C) Bare Substrate Roughnes s (nm) SC film Roughness (nm) SC Thickness (nm) [XRR data] LS film Roughness (nm) LS Thickness (nm) [XRR data] Dielectric Permittivity (ε) SiO 2 (*) HMDS PMMA Not 1.4 detectable - Not detectable OTS CYTOP (*) after 24h from UV Ozone treatment. AFM data. S14

15 2.3 FET analysis of IIDDT-C3 films deposited on different substrate surfaces. For this study, we employed the following parameters for LS film formation and transfer corresponding to an areal density ρ of 1.05 µg/cm 2, intermediate between LS2 and LS3. Figure S17. FET characteristics of IIDDT-C3 a) LS film and b) SC film on PMMA-treated SiO 2 substrate. Transfer curve taken at V DS = -40 V (L = 80 µm, W = 1 mm). For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. Figure S18. FET characteristics of IIDDT-C3 a) LS film and b) SC film on OTS-treated SiO 2 substrate. Transfer curve taken at V DS = -40 V (L = 80 µm, W = 1 mm). For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. S15

16 I DS (A) 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 1E-10 1E V GS (V) [I DS ] 1/2 (A) 1/2 Figure S19. FET characteristics of IIDDT-C3 LS film on CYTOP-treated SiO 2 substrate. Transfer curve taken at V DS = -40 V (L = 80 µm, W = 1 mm). For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. a) b) Threshold Voltage (V) HMDS OTS CYTOP PMMA On/Off HMDS OTS CYTOP PMMA Figure S2S0. (a) Threshold voltage and (b) On/Off ratio of IIDDT-C3 LS films (black square) and of SC films (white circle) transferred onto different substrates (i.e., HMDS, OTS, CYTOP and PMMA surfaces). For this study, we employed a LS film corresponding to an areal density ρ of 1.05 µg/cm 2. Table S3. Device Performance for various LS films. 4 LS Film Number of samples* Average Mobility, µ and standard deviation [cm 2 V -1 s -1 ] Average Threshold Voltage, Vth and standard deviation [V] LS ± ± 3 LS ± ± 1 LS ± ± 1 LS on OTS ± ± 2 LS on CYTOP ± ± 3 LS on PMMA ± ± 2 * For each sample, two devices were measured (L = 80 µm) to extract the average mobility. S16

17 3. Reference 1. Lei, T.; Wang, J.-Y.; Pei, J., Design, Synthesis, and Structure Property Relationships of Isoindigo- Based Conjugated Polymers. Acc. Chem. Res. 2014, 47, XRR curves were fitted using GenX program: Björck, M.; Andersson, G. GenX: an Extensible X- Ray Reflectivity Refinement Program Utilizing Differential Evolution. J. Appl. Cryst. 2007, 40, Masillamani, A.M.; Orgiu, E.; Samorì, P. Effect of the Molecular Weight of the Polymer Gate Dielectric on the Performances of Solution-Processed Ambipolar OTFTs J. Mater. Chem. C, 2013, 1, Choi, D.; Ping-Hsun, C.; McBride, M.; Reichmanis, E. Best Practices for Reporting Organic Field Effect Transistor Device Performance. Chem. Mater. 2015, 27, S17