NMR spectra were recorded on a Bruker Avance III 500 spectrometer operating at 500.13 MHz for 1H using a 5 mm 1H/13C/19F/31P gradient probe. The samples were measured in CDCl3, DMSO-d6 at ambient or in C2D2Cl4 at 120°C (for polymers). The spectra were referenced on the residual solvent peak.
Mass spectra were recorded on Maldi TOF Autoflex speed LRF, Bruker Daltonik. Dithranol and 2,5-dihydrobenzoic acid (2,5-DHBA) were used as matrixes for polymers.
GPC measurements were determined by gel permeation chromatography. For low temperature (40°C) Agilent 1260 Infinity system with two Resipore columns against polystyrene standards were used. Eluent was chloroform at 1 ml·min-1 flow rate and refractive index and Uv-vis detectors were used. Agilent 1100 Series (Agilent, USA) against polystyrene standards using a Polymer Laboratories PL-GPC 220 with two MIXED-B LS columns running with 1,2,4-trichlorobenzene as eluent at 150 °C and 1 ml·min-1 flow rate was used for high temperature analyses. Samples were dissolved over at least 7h at high temperature prior to the measurement.
UV-Vis absorption spectroscopy. An analytic Jena Specord 210 plus at a scan rate of 20 nm·s
-1 was used to record UV-Vis absorption spectra of thin polymer films prepared by drop casting on thin glass slides.
UV-Vis-nearIR absorption spectroscopy. Cary 5000 UV-Vis-NIR (Agilent Technologies) at a scan rate of 20 nm·s-1 was used to record UV-Vis-NIR absorption spectra of solutions in quartz cuvette (pathlength 1 mm) or thin polymer films prepared by drop casting/ spin coating on glass.
The atomic force microscope (AFM). The microscope (Bruker, Dimension Icon) was operated in tapping mode using silicon-SPM-sensors (BudgetSensors, Bulgaria) with spring constant of ca. 40 N/m and resonance frequency of ca 300 kHz. Thickness of the polymer layers was measured using a scratch test technique.
Electron Scanning Microscopy (ESM). The Scanning Electron Microscope, Ultra 55, (NEON 40 FIB-SEM) workstation (Carl Zeiss AG, Germany) was operated at 3 kV with InLens detector.
Chapter IV. Experimental part. Methods and instrumentation.
Page 126 Thermogravimetric analyses were carried out on a TA Instruments Q500 with a heating rate of 10 K/min under a flow of nitrogen, using Pt crucibles and 10 mg of sample for each analysis.
Differential Scanning Calorimetry. DSC was carried out with a DSC Q 1000 of TA Instruments in the temperature range of -60°C to 350°C under nitrogen atmosphere at a scan rate of 10 K/min. All samples were investigated in a heating-cooling-heating cycle. Glass transition temperature was determined using the half step method, melting peak maximum, extrapolated onset temperature and maximum of crystallization process were calculated as well as the corresponding transition enthalpies.
X-ray Scattering (for DPP polymer). Grazing incidence wide-angle X-ray measurements (GIWAXS) of thick films (about 1 μm) were performed using a Bruker D8 Discover diffractometer operating at 1.6 kW. The diffractometer is equipped with a Cu Twist tube, Ni filter (λ = 1.5418 Å), Goebel mirror, and 0.3 mm PinHole collimator for the incident beam.
The sample was mounted on an Eulerian Cradle with automatic controlled X–Y–Z stage. The GIWAXS patterns were recorded with a VÅNTEC-500 area detector using a sample-to-detector distance of 105 mm and an incident angle of 0.5°. High resolution specular data were obtained using a 2-circle diffractometer (XRD 3003 T-T, Seifert-FPM) and a point detector.
By employing a parabolic multilayer mirror, a highly parallel beam of a monochromatic Cu-Kα radiation (λ = 1.5418 Å) was obtained.
X-ray diffraction (for NDIT2). Two-dimensional transmission XRD measurements were performed using a Bruker D8 Discover diffractometer operating at 1.6 kW. The diffractometer is equipped with a Cu Twist tube, Ni filter (λ = 1.5418 Å), point focusing PolyCap™ system for parallel beam generation, and 0.3 mm PinHole collimator for the incident beam. Free standing films were investigated with the X-ray perpendicular to the films. The diffraction patterns were recorded with a VÅNTEC-500 area detector using a sample-to-detector distance of 155 mm.
EPR spectroscopy. Continuous wave (CW) EPR spectra were recorded on an EMX-plus spectrometer (Bruker Biospin) operating at X-band, equipped with the high-sensitivity resonator ER 4119 HS-W1, and the variable temperature unit ER4141VT. Acquisition parameters were microwave power of 0.1 mW, modulation frequency of 100 kHz, modulation amplitude of 0.01 G, sweep width of 20 G, time constant of 10.24 ms, conversion time of 40.96 ms, 16 scans, and 2048 data points. The temperature was controlled within ±1 K. The liquid samples were loaded into glass capillaries (100 µL) which were flame-sealed and put into quartz tubes with inner diameter i.d.=3 mm.
Electrical measurements. Electrical conductivity of the doped films was measured by a standard method, using a commercially available Loresta-GP MCP-T610 device (Mitsubishi Chemical Analytech) with standard ESP 4-pin in a line probe (measuring range 10-3–107 Ω/sq). The distance between the current electrodes is 15 mm and between the potential electrodes is 5 mm. At least 6 measurements of square resistivity (ρs) were performed for each sample in different positions on the film surface. Conductivity σ was calculated as σ = 1/ρs ∙ t,
Chapter IV. Experimental part. Methods and instrumentation.
where t is the film thickness in cm. To perform measurements of ρs >107 Ω/sq for the undoped polymer, a Hiresta-UP MCP-HT450 device with URS standard probe was used.
Bottom-contact devices. Highly doped silicon wafers with 300 nm SiO2 were used as substrates. For the electrodes 2 nm Cr and 50 nm Au were thermally evaporated through a shadow mask at a vacuum of ~10-7 mbar. The electrodes have a width of 4.5 mm and 11 mm and the distance between two electrodes is 200 and 300 µm, respectively (see SI, Figure S9).
For the current-voltage (IV) measurement a manual probe station (Cascade Microtech GmbH) and a Keysight B1500A Semiconductor Device Parameter Analyzer were used. IV-sweeps for voltages of 0 – 10 V were performed for each substrate with the different molar doping ratios (3 sweeps for 300 µm distance and 3 sweeps for 200 µm distance). The linear current-voltage dependencies were extracted and the resistance of each sample was calculated due to the Ohm’s law
𝑅 =𝑉 𝐼.
For low conductivity samples (resistance over 107 Ohm) IV curves did not correspond to Ohm’s law and these samples were not considered. From the resistance the conductivity of the film was calculated based on Pouillet's law
𝜎 =1 𝜌= 𝑙
𝑅𝐴= 𝑙 𝑅𝑡𝑤
where ρ is the resistivity, l the distance between two electrodes, t is the thickness of the doped film, and w is the width of the electrodes. The exact distances between two electrodes were measured for every sample with optical microscopy.
Picture of the bottom contact substrate with deposited gold contacts and spin coated polymer film on it (top view). 300 µm distance between contacts on the right side of the picture and 200 µm on the top-left.
Distances between electrodes (Channel Length) were measured for every sample with optical microscopy. Width of the electrodes were 11 and 4.5 mm for two patterns, respectively.
Thin-Film Transistors (for NDIT2 polymer). The top-gate, bottom-contact OTFT devices were fabricated on glass substrates (Precision Glass & Optics, Eagle 2000). The gold source and drain electrodes (~35 nm) were deposited by thermal evaporation using a shadow mask (L = 50µm, W = 500 µm). The polymer was dissolved in the solvent at concentrations as indicated in Table 1. The solutions were stirred on a 50 C hotplate for 2 hours in nitrogen filled glove box before use, next spin coated at 2000 RPM for 60 s in the glove box, followed by 1 hour annealing on a 110 C hotplate. PMMA dielectric (70 mg/ml in butyl acetate) was spun coated and then annealed at 110 C for 30 min in the glove box as well. The substrates were cooled down to room temperature before being taken out of glove box for depositing 35 nm gold as the gate electrode. The measured capacitance of the PMMA dielectric layer is 4.0 nF/cm2. The finished devices were tested in ambient conditions.
Chapter IV. Experimental part. Methods and instrumentation.
Page 128 Infrared spectroscopy. To characterize structural changes in polymer based conductive nanolayers under consideration ATR (attenuated total reflection)-FTIR (Fourier Transform infrared) spectroscopy was used. Conventional single ATR mode is known to be useful for both micro- and sub-microscales down to several hundred nm using Ge as an ATR-crystal. In the case of thinner films multiple ATR is recommended. In this work to obtain the ATR-spectra on scales around 50 nm advanced multiple ATR approach was utilized to increase device sensitivity and to break the sample thickness limit. Polymer-dopant compositions as well initial components were deposited onto Float-Zone Si-Wafer functioning both as a film substrate and as the ATR-crystal. The ATR-spectra were acquired using evacuated FTIR-spectrometer Vertex80v (Bruker) equipped with both ATR-Si-Wafer 40 mm unit (Bruker) and mercury cadmium telluride detector (InfraRed Associates). The total number of reflections was 46. The spectroscopic range was restricted to nitrile band region 2250-2050 cm-1 with 2 cm-1 spectral resolution. 300 scans were co-added to every spectrum. To compare the results properly spectral base line was corrected as well as spectra were normalized to a band of stretching vibration of nitrile group around 2190 cm-1 acting as an internal reference.
DFT calculations. We performed density functional theory (DFT) calculations as implemented in SCM ADF 1.3278, using the B3LYP279 and the PBE280 functionals and a double zeta basis set in order to determine the HOMO and LUMO energies of the model compounds and to calculate the charge transfer (CT) as well as the interaction energy of DPP(Me)TT and F6TCNNQ for various stacking configurations. In this work, the conjugated fragments were modeled by substituting methyl side groups for the C30-alkyl chains.
Furthermore, finite fragments of PDPP(Me)TT rather than full polymer chains were considered because the computation of whole chains requires too large computing efforts.
These simplifications should not strongly affect the calculation results because the charge transfer is a local effect which is not affected by those parts of the chain, which are several units distant from the stacking region. However, to ensure a correct modelling of the influence of the adjacent units, two PDPP(Me)TT fragments were modeled: the one having DPP as the middle group which is surrounded by two TT units and the other one having the TT unit surrounded by two DPP units.
Working procedure. First, we considered the isolated model compounds. In order to obtain the HOMO and LUMO energies we optimized the molecular structures using the hybrid B3LYP functional and a DZP basis. This version of DFT is well accepted for giving HOMO-LUMO gaps with better accuracy than standard GGA functionals281.
Second, we performed calculations of CT complexes by considering π-π stacks. For this, we utilized the PBE functional since the derived quantities are not affected by the unoccupied states. For cases, where we calculated both, B3LYP and PBE functionals, the CT obtained by PBE is 0.1 up to 0.2 e greater than for B3LYP. Qualitatively, however, they are in good agreement.
For considering dispersion interaction, the Grimme dispersion correction282 has been used.
At first, the dopant molecule was placed on top of the DPP-TT model at a distance of 3 Å and then systematically rotated around the stacking axis or shifted along the polymer backbone, respectively. For each of those stacks single point calculations have been performed to
Chapter IV. Experimental part. Methods and instrumentation.
evaluate the total energy as well as the charge transfer. For the latter one, we considered the Mulliken226, Hirshfeld227 as well as the Voronoi228 approaches to calculate the atomic charges.
Vibrational spectra computations. The full geometry optimizations and the corresponding harmonic vibrational frequency computations of isolated neutral F6TCNNQ and the isolated F6TCNNQ· anion radical and CT complexes were carried out using the DFT method with B3LYP functional and 6-31G(d) basis set as implemented in Gaussian 09283. The calculated harmonic vibrational frequencies and intensities were scaled by a factor of 0.9614284,285. The electrostatic potentials with an isovalue of electron density of 0.02 a.u. were calculated using Merz-Singh-Kollman procedure286.