Influence of Dielectric-Dependent Interfacial Widths on Device Performance in Top-Gate

Supporting Information for

Influence of dielectric-dependent interfacial widths on device performance in top-gate P(NDI2OD-T2) field-effect transistors

By Hongping Yan, Torben Schuettfort, Auke J. Kronemeijer, Christopher R. McNeill and Harald W. Ade *

Figure S1 shows the chemical structures of the semiconducting polymer poly([N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiopene)) (P(NDI2OD-T2) and the dielectrics including poly(methyl methacrylate) (PMMA), polystyrene (PS) and the fluorinated polymer CYTOP.

Figure S1. Chemical structures of the active layer P(NDI2OD-T2), and the dielectrics PMMA, PS, and CYTOP.

Dielectric/P(NDI2OD-T2) bilayers: P(NDI2OD-T2), specified with a number average molecular weight (Mn) of 25.4 kD and polydispersity index (PDI) of 4.03, was purchased from the Polyera Corporation, USA. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) with a weight average molecular weight (MW) of 1,000 kg mol-1 and 120 kg mol-1, respectively, were purchased from Sigma-Aldrich, and CYTOP CTL-809M was used as received from Asahi Glass. P(NDI2OD-T2) thin films were prepared by spin-coating from a 20 mg mL-1 dichlorobenzene solution onto electron conducting (antimony doped) silicon wafers. The film thickness was determined using a profilometer (Veeco Dektak 3) to be around 55 nm. The P(NDI2OD-T2) films were subsequently annealed at 110 ˚C for 20 min in nitrogen atmosphere and quickly cooled to room temperature. Deposition of the gate material was also performed by spin-coating from orthogonal solvents (n-butyl-acetate for PS and PMMA and perfluorotributylamine for CYTOP) using spin-conditions that yielded a film thickness of 75 nm measured with the profilometer on a pristine silicon wafer. No further heat treatment was performed on the bilayers after deposition of the gate materials. The fabrication procedures are elaborately designed to mirror the process conditions for the fabrication of top-gate FETs by Caironi et al., except for that the dielectric film thicknesses are slightly thinner.1

Data acquisition: Near edge X-ray absorption fine structure (NEXAFS) spectra of reference pristine single layer samples were acquired at beamline 5.3.2 at the Advanced Light Source (ALS).2 These spectra were used to derive the optical constants of the materials. The optical constants were then used to predict contrast and provide initial values for the fits and simulation. R-SoXR data were acquired at beamline 6.3.2 at the ALS in a high vacuum (~10-7 torr),3 following previously established protocols.4 To detect and avoid radiation damage, which can cause mass loss and spectral change,5, 6 multiple scans were taken and the samples were translated to expose a fresh sample area. Simulations and fits were performed using the non-commercial program IMD.7 The R-SoXR data and fits occasionally showed some discrepancy in the low q-region that has been traced back to spectral contamination. The q range used to extract parameters from the fits is therefore occasionally restricted to ~0.2 – 2.5 nm−1.8

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