Correlation of Thermoelectric Performance, Domain Morphology and Doping Level in PEDOT:PSS Thin Films Post-Treated with Ionic Liquids.

AbstractIonic liquid (IL) post‐treatment of poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films with ethyl‐3‐methylimidazolium dicyanamide (EMIM DCA), allyl‐3‐methylimidazolium dicyanamide (AMIM DCA), and 1‐ethyl‐3‐methylimidazolium tetracyanoborate (EMIM TCB) is compared. Doping level modifications of PEDOT are characterized using UV–Vis spectroscopy and directly correlate with the observed Seebeck coefficient enhancement. With conductive atomic force microscopy (c‐AFM) the authors investigate changes in the topographic‐current features of the PEDOT:PSS thin film surface due to IL treatment. Grazing incidence small‐angle X‐ray scattering (GISAXS) demonstrates the morphological rearrangement towards an optimized PEDOT domain distribution upon IL post‐treatment, directly facilitating the interconductivity and causing an increased film conductivity. Based on these improvements in Seebeck coefficient and conductivity, the power factor is increased up to 236 µW m−1K−2. Subsequently, a model is developed indicating that ILs, which contain small, sterically unhindered ions with a strong localized charge, appear beneficial to boost the thermoelectric performance of post‐treated PEDOT:PSS films

Increasing Photostability of Inverted Nonfullerene Organic Solar Cells by using Fullerene Derivative Additives

Organic solar cells (OSCs) recently achieved efficiencies of over 18% and are well on their way to practical applications, but still considerable stability issues need to be overcome. One major problem emerges from the electron transport material zinc oxide (ZnO), which is mainly used in the inverted device architecture and decomposes many high-performance nonfullerene acceptors due to its photocatalytic activity. In this work, we add three different fullerene derivatives—PC71BM, ICMA, and BisPCBM—to an inverted binary PBDB-TF:IT-4F system in order to suppress the photocatalytic degradation of IT-4F on ZnO via the radical scavenging abilities of the fullerenes. We demonstrate that the addition of 5% fullerene not only increases the performance of the binary PBDB-TF:IT-4F system but also significantly improves the device lifetime under UV illumination in an inert atmosphere. While the binary devices lose 20% of their initial efficiency after only 3 h, this time is increased fivefold for the most promising ternary devices with ICMA. We attribute this improvement to a reduced photocatalytic decomposition of IT-4F in the ternary system, which results in a decreased recombination. We propose that the added fullerenes protect the IT-4F by acting as a sacrificial reagent, thereby suppressing the trap state formation. Furthermore, we show that the protective effect of the most promising fullerene ICMA is transferable to two other binary systems PBDB-TF:BTP-4F and PTB7-Th:IT-4F. Importantly, this effect can also increase the air stability of PBDB-TF:IT-4F. This work demonstrates that the addition of fullerene derivatives is a transferable and straightforward strategy to improve the stability of OSCs

Thermoplastic polyester elastomers based on long-chain crystallizable aliphatic hard segments

A plant-oil derived long-chain (C23) α,ω-dicarboxylic acid and the corresponding diol provide entirely aliphatic hard segments in segmented thermoplastic polyester elastomers, with poly(tetramethylene glycol) (PTMG) or carbohydrate-based poly(trimethylene glycol) (PPDO) soft segments. Physical crosslinking is provided by their polyethylene-like crystallinity. Compared to materials derived from mid-chain (C12) analogs, thermal properties are significantly enhanced, with melting points up to 96 °C. These novel materials feature high ductility values in combination with a good elastomeric behavior.publishe

CO₂‑Switchable Cellulose Nanocrystal Hydrogels

A carbon-dioxide-switchable (CO₂-switchable) hydrogel was prepared by adding imidazole to a suspension of cellulose nanocrystals (CNCs). Sparging of CO₂ through the imidazole-containing CNC suspension led to gelation of the CNCs, which was reversible by subsequent sparging with nitrogen (N₂) to form a low-viscosity CNC suspension. The gelation process and the properties of the hydrogels have been investigated by rheology, ζ potential, pH, and conductivity measurements, and the gels were found to have interesting and reversible tunable mechanical properties. The present work describes a straightforward way to obtain switchable CNC hydrogels without the need to functionalize CNCs or add strong acids or bases. These CO₂-responsive CNC hydrogels have potential for application in stimuli-responsive adsorbents, filters, and flocculants

Ionic Liquid-Induced Inversion of the Humidity-Dependent Conductivity of Thin PEDOT:PSS Films

The humidity influence on the electronic and ionic resistance properties of thin post-treated poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films is investigated. In particular, the resistance of these PEDOT:PSS films post-treated with three different concentrations (0, 0.05, and 0.35 M) of ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is measured while being exposed to a defined humidity protocol. A resistance increase upon elevated humidity is observed for the 0 M reference sample, while the EMIM DCA post-treated samples demonstrate a reverse behavior. Simultaneously performed in situ grazing-incidence small-angle X-ray scattering (GISAXS) measurements evidence changes in the film morphology upon varying the humidity, namely, an increase in the PEDOT domain distances. This leads to a detriment in the interdomain hole transport, which causes a rise in the resistance, as observed for the 0 M reference sample. Finally, electrochemical impedance spectroscopy (EIS) measurements at different humidities reveal additional contributions of ionic charge carriers in the EMIM DCA post-treated PEDOT:PSS films. Therefrom, a model is proposed, which describes the hole and cation transport in different post-treated PEDOT:PSS films dependent on the ambient humidity

Improvement of the thermoelectric properties of PEDOT:PSS films via DMSO addition and DMSO/salt post-treatment resolved from a fundamental view

The combination of dimethyl sulfoxide (DMSO)-solvent doping and physical–chemical DMSO/salt de-doping in a sequence has been used to improve the thermoelectric (TE) properties of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) films. A high power factor of ca.105.2 µW m$^{−1}$ K$^{−2}$ has been achieved for the PEDOT:PSS film after post-treatment with 10 % sodium sulfite (Na$_2$SO$_3$) in the DMSO/salt mixture (v/v), outperforming sodium bicarbonate (NaHCO$_3$). The initial DMSO-doping treatment induces a distinct phase separation by facilitating the aggregation of the PEDOT molecules. At the same time, the subsequent DMSO/salt de-doping post-treatment strengthens the selective removal of the surplus non-conductive PSS chains. Substantial alterations in the oxidation level, chain conformations, PEDOT crystallites and their preferential orientation are observed upon treatment on the molecular level. At the mesoscale level, the purification and densification of PEDOT-rich domains enable the realization of inter-grain coupling by the formation of the electronically well-percolated network. Thereby, both electrical conductivity and Seebeck coefficient are optimized

Author Correction: Degradation mechanisms of perovskite solar cells under vacuum and one atmosphere of nitrogen

Correction to: Nature Energy https://doi.org/10.1038/s41560-021-00912-8, published online 18 October 2021 - In the version of this article initially published, there was an error in Fig. 5e. In the lower panel, second peak, the text now reading “Pb 4f$_{7/2}$” appeared originally as “Pb 4f$_{3/2}$.” The error has been corrected in the HTML and PDF versions of the article