Ionic liquid (IL) post-treatment for thin films of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is employed for the simultaneous enhancement of Seebeck coefficients and electrical conductivities. Through systematic variation of the ILs, by changing the anions while keeping the cation unchanged, changes in thermoelectric, spectroscopic, and morphological properties are investigated by means of UV−vis spectroscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS) as a function of the IL concentration. The simultaneous enhancement in the two important thermoelectric properties is ascribed to the binary nature of the ILs, which complements that of PEDOT:PSS. The anions of the ILs primarily interact with the positively charged, conducting PEDOT, while the cations interact with negatively charged insulating PSS. Therefore, post-treatment with ILs allows for primary and secondary doping of PEDOT:PSS at the same time. Differences in the obtained Seebeck coefficients for the investigated ILs are ascribed to the chemical properties of the anions. Additionally, the choice of the latter has implications on the morphology of the treated PEDOT:PSS films regarding average π−π-stacking distances of PEDOT chains, PEDOT-to-PSS ratios, and edge-on-to-face-on ratios, influencing charge transport properties macroscopically. A morphological model is presented, highlighting the influence of each IL in comparison with pristine PEDOT:PSS films.

The origin of high conductivity in polymer electrodes based on poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is investigated and the resilience against water exposure is tested. Post‐treatment with weak and strong acids, namely, hydrochloric acid (HCl), formic acid (HCOOH), nitric acid (HNO3), and sulfuric acid (H2SO4), is performed and compared to the commonly used ethylene glycol treatment. PEDOT:PSS electrodes with electrical conductivities of up to ≈3000 S cm−1 and high transmittance are obtained. The underlying mechanisms for enhanced conductivity are elucidated by means of electrical (4‐point probe), optical (UV‐Vis spectroscopy), compositional (X‐ray photo‐electron spectroscopy), and structural (grazing‐incidence wide‐angle X‐ray scattering, GIWAXS) characterizations. Selective PSS removal and structural rearrangement of PEDOT‐rich domains due to an enhanced lamellar stacking is identified as major influence on the improvement in electrical conductivity. This beneficial high order is evidenced via additional signals in the GIWAXS patterns, which are altered by subsequent H2O treatment. The PSS removal and structural rearrangement is linked to the acids' strength and dielectric constant. High conductivities are reached by efficient PSS removal via HNO3 or H2SO4 treatment with the drawback of high sensitivity against H2O. By contrast, HCl and HCOOH treatment obtaining a medium enhanced conductivity differ in the amount of PSS removal but show higher H2O resistance.

Poly­(ethylene dioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) has emerged as a promising candidate for renewable, clean, and reliable energy generation from waste heat due to its thermoelectric properties. This largely stems from its tunable and potentially high electrical conductivity. However, the resulting small Seebeck coefficients diminish the thermoelectric efficiency. We employ dedoping methods making use of acido-base and redox dedoping in order to optimize its properties. In order to tune the charge carrier concentration in PEDOT:PSS thin films, aqueous solutions of readily available inorganic salts, namely, sodium hydrogen carbonate (NaHCO3), sodium sulfite (Na2SO3), and sodium borohydride (NaBH4), are introduced in different concentrations into PEDOT:PSS solutions before thin film fabrication. This yields optimized thermoelectric properties in terms of power factors up to 100 μW/K2 m. Changes in the electronic structure are characterized using UV–vis spectroscopy and XPS, while changes in the conformation are investigated using Raman spectroscopy. The thermoelectric quantities are compared for the redox dedopants regarding the absolute number of reducing equivalents.

The ligand exchange process is a key step in fabrications of quantum dot (QD) optoelectronic devices. In this work, on the basis of grazing incidence X-ray scattering techniques, we find that the ligand exchange process with halide ions changes the PbS QD superlattice from face-centered-cubic to body-centered-cubic stacking, while the QD crystal lattice orientation also changes from preferentially “edge-up” to “corner-up”. Thus, the QDs’ shape is supposed to be the main factor for the alignment of QDs in close packed solids. Moreover, we tailor the alignment of the close packed solids by thermal treatments and further investigate their inner charge carrier dynamics by pump–probe transient absorption experiments. An overall better structure alignment optimizes the charge carrier hopping rate, as confirmed by the time dependence of the photon bleaching peak shift. The QD solid treated at 100 °C shows the best inner structure alignment with the best charge carrier hopping rate.

The relation of the thermoelectric figure of merit and the nanocomposite morphology is studied for thermoelectric thin films consisting of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with different amounts of silicon nanoparticles (Si‐NPs). An increase in the figure of merit of up to 150% is found for an Si‐NP concentration of 0.5 wt% as compared to pristine PEDOT:PSS films. The improvement originates from a disruption in the molecular ordering and therefore reduced electrical conductivity, which leads to an increased Seebeck coefficient, while also reducing thermal conductivity for higher concentrations through phonon scattering. The thermal conductivity is measured with steady‐state IR thermography on free‐standing PEDOT:PSS/Si‐NP composite films, enabling a full determination of the figure of merit. The morphology is investigated with grazing incidence resonant tender X‐ray scattering (GIR‐TeXS) around the sulfur K‐absorption edge. Without need for extrinsic labeling, GIR‐TeXS measurements have varying scattering contrast conditions for the components of the ternary system. By comparing the scattered intensities at different photon energies with the corresponding scattering contrast, the Si‐NPs are found to be preferentially dispersed in the large and medium‐sized PEDOT‐rich domains. The changes in size for the PEDOT‐rich domains as function of Si‐NP concentration cause improvement of the thermoelectric properties of the films.

Thermoelectric generators pose a promising approach in renewable energies as they can convert waste heat into electricity. In order to build high efficiency devices, suitable thermoelectric materials, both n-and p-type, are needed. Here, the n-type high-mobility polymer poly[N,N′-bis(2-octyldodecyl) naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene) (P(NDI2OD-T2)) is focused upon. Via solution doping with 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline (N-DPBI), a maximum power factor of (1.84 ± 0.13) µW K −2 m −1 is achieved in an in-plane geometry for 5 wt% dopant concentration. Additionally, UV-vis spectroscopy and grazingincidence wide-angle X-ray scattering are applied to elucidate the mechanisms of the doping process and to explain the discrepancy in thermoelectric performance depending on the charge carriers being either transported in-plane or cross-plane. Morphological changes are found such that the crystallites, built-up by extended polymer chains interacting via lamellar and π-π stacking, re-arrange from face-to edge-on orientation upon doping. At high doping concentrations, dopant molecules disturb the crystallinity of the polymer, hindering charge transport and leading to a decreased power factor at high dopant concentrations. These observations explain why an intermediate doping concentration of N-DPBI leads to an optimized thermoelectric performance of P(NDI2OD-T2) in an in-plane geometry as compared to the cross-plane case.

Mesoporous titania is a cheap and widely used material for photovoltaic applications. To enable a large-scale fabrication and a controllable pore size, we combined a block copolymer-assisted sol-gel route with spray coating to fabricate titania films, in which the block copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) is used as a structure-directing template. Both the macroscale and nanoscale are studied. The kinetics and thermodynamics of the spray deposition processes are simulated on a macroscale, which shows a good agreement with the large-scale morphology of the spray-coated films obtained in practice. On the nanoscale, the structure evolution of the titania films is probed with in situ grazing incidence small-angle X-ray scattering (GISAXS) during the spray process. The changes of the PS domain size depend not only on micellization but also on solvent evaporation during the spray coating. Perovskite (CHNHPbI) solar cells (PSCs) based on sprayed titania film are fabricated, which showcases the suitability of spray-deposited titania films for PSCs.

Scattering techniques are a powerful tool for probing thin-film nanomorphologies but often require additional characterization by other methods. We applied the well-established grazing-incidence small-angle X-ray scattering (GISAXS) technique for a selection of energies around the absorption edge of sulfur to exploit the resonance effect (grazing incidence resonant tender X-ray scattering, GIR-TeXS) of the sulfur atoms within a poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) sample to gain information about the composition of the film morphology. With this approach, it is possible not only to identify structures within the investigated thin film but also to link them to a particular material combination.