Precise control over thin-film morphology and interfacial organization is essential for solution-processed organic electronics. We demonstrate the successful Langmuir-Blodgett (LB) fabrication of nanometer-precise, uniform PM6 and N2200 polymer films. Optimized solvent and spreading conditions yield controlled assembly of uniform and homogeneous mono- and multilayers. PM6 formed isotropic films with tangled coiled structures, while N2200 showed anisotropic domains with directional π-stacking and extended branch-like polymer chains. Nanomechanical analysis revealed a 35-40% increase in surface elasticity for multilayers versus monolayers. Surface potential measurements underlined a thickness-dependent transition from substrate-dominated electrostatics in monolayers to a bulk-like behavior in multilayers, while photoluminescence mapping confirms preservation of emissive functionality even down to a monolayer. Preliminary photoresponsivity tests with photoactive layers below 20 nm show a reproducible increase in short-circuit current density upon increasing the number of PM6 and N2200 layers from five to six each, as confirmed by measurements across multiple devices. This trend is attributed to an absorption cross section that scales with increasing layer thickness. Our results position the LB method as a robust platform for constructing ultrathin, structurally coherent, and electronically active polymer interfaces with nanometer-scale thickness control.

Understanding the decomposition and reaction mechanisms of sulfur precursors used in organometallic colloidal synthesis is critical for controlling the nucleation and growth of nanocrystals. In this work, we investigate the thermal decomposition of thiourea and various N,N '-substituted thioureas in oleylamine to elucidate their distinct decomposition mechanisms, sulfur release pathways, and the implications for strontium sulfide (SrS) nanoparticle syntheses due to these decompositions. Using a combination of in situ quadrupole mass spectrometry (QMS), NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), thermogravimetry (TGA), and DFT-calculated bond dissociation energies (BDEs), our findings reveal that substituent identity and symmetry significantly affect the decomposition onset temperatures and reaction intermediates. Unsubstituted thiourea undergoes initial isomerization with two competing subsequent fragmentation routes, releasing the gaseous products H2S and NH3, respectively. The other fragments from both routes, carbodiimide and isothiocyanic acid, react with oleylamine to form N,N '-dioleylthiourea. The N,N '-dioleylthiourea undergoes a second decomposition process, which releases H2S and the trisubstituted guanidine. Aliphatic N,N '-substituted thioureas exhibit the first fragmentation process, which releases the respective alkylamine, whereby the various chain-length substituents influence the decomposition onset temperature and the decomposition process, which releases H2S from N,N '-dioleylthiourea. Aromatic N,N '-substituted thioureas follow the same sequential decomposition mechanism, but resonance effects in N,N '-diphenylthiourea lower the decomposition temperature. These mechanistic differences are then directly correlated with the formation of strontium sulfide (SrS) nanocrystals. By tracking sulfur and amine release during synthesis, we show that the timing and concentration of reactive sulfur species, such as H2S, determine the nucleation rate, particle size, and morphology of the resulting nanocrystals. This study provides mechanistic insights into thiourea decomposition in oleylamine and establishes a direct link between the precursor structure and nanoparticle outcome. The results lay the foundation for more predictive and tunable synthesis strategies in the design of colloidal metal sulfide nanomaterials.

The inherent susceptibility of n-type organic semiconductors to molecular dioxygen (O2) results in electron trapping or in unintended p-doping, which in turn diminishes their electron mobility. This concept is challenged in the present study by exploring O2 interactions with organic charge-transfer complexes (CTCs), where electron donor-acceptor interactions generate partially delocalized electronic states. Using a CTC comprising a phenazine electron donor and a 7,7,8,8-tetracyanoquinodimethane (TCNQ) electron acceptor, we demonstrate that its exposure to O2 does not lead to electron extraction but instead enhances the charge-transfer activity. The increased electron density at the TCNQ acceptor upon CTC exposure to O2 is attributed to electron trap-states passivation by O2, without evidence of chemisorption. This passivation mitigates recombination losses, resulting in a threefold photoluminescence quantum yield increase, enhanced electrical conductivity, and improved charge-transfer state efficiency. Similar O2-mediated conductivity enhancements are observed across additional donor-acceptor pairs, proving the broader applicability of this effect, and paving the way for designing O2-enhanced advanced organic electronic materials.

Electrospun nanofiber composites are a promising platform for integrating photocatalytic and electrocatalytic functionalities in environmental remediation technologies. In this study, we report the fabrication, structural characterization, and photo(electro)catalytic evaluation of polyacrylonitrile (PAN)-derived carbon nanofibers embedded with TiO2 nanoparticles (NPs). The NPs are synthesized via two distinct routes: a hydrothermally assisted sol-gel process (SG) and commercial flame-pyrolyzed P25. Aiming for a direct comparison, both fiber types were produced using identical electrospinning conditions and were thermally converted into conductive NP-carbon composites. The fibers containing TiO2 from the SG process exhibit a more homogeneous TiO2 distribution, reduced agglomeration, higher surface area (200 m²/g vs. 78 m²/g), and superior photocatalytic degradation rates of a model organic contaminant, rhodamine B (RhB), outperforming P25-containing fibers even when normalized by surface area. Photoelectrochemical measurements further demonstrate enhanced reaction kinetics under a −0.55 V bias compared to photocatalytic or electrocatalytic conditions alone, confirming the viability of these nanofiber composites for integrated photoelectrocatalysis. These findings highlight the benefits of combining SG-NP synthesis with electrospinning to develop flexible high-performance materials for pollutant degradation applications.

Abstract The most conventional atomic layer processing method, atomic layer deposition (ALD), delivers ultrathin blanket coatings with sub-nanometer thickness precision. Lateral confinement underpins the direct atomic layer processing (DALP®) family of deposition techniques. ALD chemistry applied to DALP® is a 3D printing method called atomic-layer additive manufacturing (ALAM). Here, we demonstrate the applicability of ALAM to the additive buildup of the crucial ZnS / Sb2S3 / V2O5 semiconductor stack which constitutes an functional inorganic solar cell. To this goal, ALAM processes are first optimized and evaluated for the individual materials vanadium(V) oxide, zinc sulfide, and antimony(III) sulfide. We establish the layer-by-layer growth mode controlled by self-limiting surface chemistry and characterize the materials’ structure and the smooth surface morphology of ALAM-coated areas. Finally, all three materials are 3D-printed in ALAM mode in combination with electrodes and the electron acceptor titania (TiO2) to form functional solar cells with a 120 nm thick Sb2S3 absorber layer. This novel fabrication of solar cells highlights the advantages of using direct patterning in the prototyping and optimization of photovoltaics in research and development.

Thiourea and its N,N'-substituted derivatives are widely employed as sulfur precursors in the colloidal synthesis of metal sulfide nanomaterials. Here, we demonstrate that these precursors exhibit an intrinsic limitation at elevated temperatures: prior to H2S evolution, they release reactive amines that perturb nucleation and growth. In situ mass spectrometry reveals that above 160 °C, amine evolution precedes sulfur delivery and coincides with dissolution or suppression of crystalline SrS formation in a model reaction. Mechanistic analysis further shows that all investigated thioureas converge to N,N'-dioleylthiourea (DOlTU) as a common intermediate before H2S release. By directly employing DOlTU as a sulfur precursor, we decouple amine evolution from sulfur supply and establish a continuous, temperature-dependent nanocrystal growth profile up to 250 °C. These findings identify precursor decomposition chemistry as a decisive parameter in high-temperature metal sulfide synthesis and provide a rational strategy for designing sulfur sources that enable predictable and reproducible nanocrystal formation for optoelectronic materials.

ABSTRACT Conducting polymers are widely used in bioelectronic interfaces because of their mixed ionic-electronic conductivity, mechanical compliance, and compatibility with biological systems. However, their electrochemically driven structural dynamics have received little attention as a mechanism for mechanical cell stimulation. Here, we show that electrochemical actuation of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) generates mechanical cues capable of activating endogenous mechanosensitive pathways in HEK293T cells. Transparent PEDOT:PSS films deposited on ITO exhibited a heterogeneous granular morphology and underwent potential-dependent microscopic deformation during electrochemical modulation. Direct optical tracking revealed displacement of the polymer boundary, with structural changes occurring preferentially in polymer-dense regions and propagating toward the film edge. When HEK293T cells were cultured directly on PEDOT:PSS, repeated electrochemical stimulation at -240 mV produced reproducible intracellular Ca 2+ responses. Pharmacological inhibition with GsMTx4 attenuated the calcium response, whereas blockade of voltage-gated sodium channels with tetrodotoxin largely preserved it, supporting the involvement of mechanosensitive pathways in the cellular response. These findings identify PEDOT:PSS as an electromechanical biointerface in which electrochemical modulation can introduce a mechanical component alongside the established electrical function of the interface. This mechanical contribution should therefore be considered when interpreting cellular responses to conducting polymer- based electrical stimulation and provides a basis for engineering bioelectronic interfaces that deliberately couple electrical control with mechanotransduction.

Semiconductor nanoparticles (NPs), such as those of nickel oxide (NiO), exhibit catalytic activity toward the urea oxidation reaction (UOR), making it an attractive alternative to the kinetically slow oxygen evolution reaction (OER). Such nanomaterials have demonstrated improved electrochemical performance but experience a transformation in their electronic (defect) structure compared to bulk materials. Thus, we combine optoelectronic transient absorption (TA) with electrochemical characterization to understand the relations of electronic defect structures and morphology to the electrochemical performance of nanosized catalysts. Two distinct syntheses were performed: (I) a sol-gel Ni(OH)2 approach with subsequent calcination, forming mesoporous NiO particles, and (II) an organometallic colloidal NiO NP route. Successful formation of NiO was confirmed for all syntheses by X-ray diffraction, and morphology was explored by scanning (transmission) electron microscopy. When increasing the calcination temperature (from 250 to 700 and 850 degrees C), NiO particles from synthesis (I) grow larger and experience a removal of intra-bandgap states upon more complete formation to NiO. NiO NPs from synthesis (II) present a defined electronic structure with low defect density within the TA ranges probed, whereas an annealing step introduces delocalized defects. During electrocatalytic measurements (KOH or KOH + urea electrolyte), we distinguished surface area effects by morphology from intrinsic catalytic activities governed by defect states and correlated less defective materials with higher intrinsic activities, as well as lower charge transfer resistances. This work advances material characterization by a holistic combination of a comparably rare optoelectronic spectroscopic strategy with electrochemical characterization to understand fundamental material properties and their influence on catalytic performance, demonstrating niche investigation strategies of NiO in UOR catalysis.

ZUSAMMENFASSUNG Die intrinsische Empfindlichkeit von organischen n‐Halbleitern gegenüber molekularem Sauerstoff (O 2 ) führt zu Elektroneneinfang oder zu unbeabsichtigter p‐Dotierung, welches wiederum die Elektronenmobilität verringert. Dieser Grundsatz wird mit der vorliegenden Studie herausgefordert, in der die Wechselwirkung von O 2 mit organischen Ladungstransferkomplexen (CTCs) untersucht wird, bei denen Elektronendonor‐Akzeptor‐Wechselwirkungen teilweise delokalisierte elektronische Zustände erzeugen. Am Beispiel eines CTCs aus Phenazin als Elektronendonor und TCNQ als Elektronenakzeptor wird aufgezeigt, dass die Zugabe von O 2 nicht zum Elektroneneinfang führt , sondern stattdessen die Ladungstransferaktivität verstärkt. Die erhöhte Elektronendichte am TCNQ‐Akzeptor bei Exposition des CTC mit O 2 wird auf die Passivierung der für den Elektroneneinfang verantwortlichen Defekte durch O 2 zurückgeführt, ohne dass Anzeichen für eine chemisorptive Wechselwirkung vorliegen. Diese Passivierung mindert Rekombinationsverluste, was zur Verdreifachung der Photolumineszenz‐Quantenausbeute, einer erhöhten elektrischen Leitfähigkeit und einer verbesserten Effizienz des Ladungstransferzustandes führt. Ähnliche O 2 ‐vermittelte Leitfähigkeitssteigerungen werden auch bei weiteren Donor‐Akzeptor‐Paaren beobachtet, was die breitere Anwendbarkeit dieses Effekts belegt und den Weg ebnet zur Entwicklung von verbesserten Materialien im Bereich organische Elektronik, deren Leistungsparameter durch O 2 erhöht werden.

Atomare Kontrolle über lösungsprozessierte hybride Halogenid‐Perowskite wird experimentell durch Atomlagenabscheidung aus der Lösung (Engl. solution atomic layer deposition , sALD) erreicht. Diese Methode überträgt die oberflächenchemischen Prinzipien der Gasphasen‐ALD (gALD) auf in der Flüssigphase gelöste Präkursoren. Durch das Umgehen der Einschränkungen, die mit der für die gALD nötige Flüchtigkeit der Präkursoren verbunden sind, erweitert die sALD das Spektrum nutzbarer Reaktions‐Chemien und zugänglicher Materialklassen. Wir demonstrieren ihre Anwendbarkeit für die Abscheidung ultradünner Filme ionischer Halbleiter, indem wir ein sALD‐Verfahren für den prominentesten Halogenid‐Perowskit, Methylammonium‐Triiodidoplumbat (CH 3 NH 3 PbI 3 , „MAPI“) entwickeln. Der Prozess zeigt bei Variation der Präkursordosierung ein sättigendes, selbstlimitierendes Wachstum, wie es für ALD typisch ist, was sowohl ex‐situ als auch in‐situ nachgewiesen wird. Die durch sALD abgeschiedenen MAPI‐Filme sind hochrein, stöchiometrisch und polykristallin. Werden MAPI‐Filme paarweise und in jeweils identischer Dicke durch sALD und durch ein modernes Spin‐Coating‐Verfahren hergestellt, so übertreffen die sALD‐Filme ihre Spin‐Coating Gegenstücke deutlich hinsichtlich der Ladungsträgerlebensdauer und der Stabilität. Sie weisen zudem eine hohe Ladungsträgermobilität auf und bilden funktionale lichtabsorbierende Schichten in Solarzellen.

Charge transfer and recombination dynamics are key to understanding and optimizing photovoltaic devices. However, metallic contacts are typically used to fabricate devices, making them incompatible with transmission spectroscopic techniques such as transient absorption spectroscopy (TAS). Omission of the top contact to avoid this issue results in mismatched results and has limited previous work examining the dynamics in thin-film Sb2S3-based devices. In this work, this challenge is overcome by developing a new methodology, adding a protective layer of ZnO over hole transport materials, allowing fabrication of transparent (i.e., bifacial) solar cell devices. Photovoltaic characterization reveals similar J-V curves between reference and bifacial cells. Examination with TAS reveals a modified mechanism that builds off of previously proposed models for similar systems. Optical modeling supports the understanding of several important changes to the mechanism. These results provide a path toward the investigation of photo-driven dynamics under more realistic operating conditions.

Solution-processing of high structural quality organic thin films offers access to the production of sustainable, flexible, and low-cost carbon-based electronic devices. We report on the preparation of well-defined poly(methyl methacrylate) (PMMA) dielectric films by means of the Langmuir-Blodgett (LB) method in the mono- and multilayer regimes. The sequential multilayer fabrication in separate LB compressions involves a reimmersion of the produced layers into the water subphase. This results in a modification of the PMMA film morphology due to water absorption. With the benefit of real-time control via compression isotherms, fabrication of defined multilayer films in a single step by high-degree compression allows avoidance of a forced presence of the polymer inside water. Unlike previously proposed polymer dielectrics that exceed 100-600 nm in thickness to compensate for potential morphological defects, we demonstrate that LB-prepared PMMA films of only about 35 nm thickness serve as insulating layers in organic field-effect transistors. Fabricated C13-BTBT-based devices demonstrate a high charge-carrier mobility and low-voltage operation due to negligible electrical shorts within the insulating PMMA film.

Investigating novel chalcogenide nanomaterials, specifically quantum confined colloidal nanocrystals, to improve the sustainability and performance of optoelectronic devices is of key importance to drive future research and make commercialization possible. We seek to exploit the unique features enabled by semiconducting inorganic metal chalcogenide quantum dots (QDs) for controlling the life and fate of charge carriers in photoelectrodes. These features include solution-processability, the size-dependent band gap, and the adjustment of the energy levels facilitated by the choice of ligands. CuInS 2 QDs are first discussed as a model alternative material for Pb- and Cd-containing chalcogenide QDs in photoelectrochemical cells. Using surface ligand exchange reactions, we shift the energy levels of the material which is demonstrated through a combination of electrochemical impedance spectroscopy (EIS) and spectroelectrochemistry – termed energy-resolved EIS – with additional supporting characterization of FT-IR, XRD, PL, and transient absorption spectroscopy. These materials are then employed as hole-transport materials for Sb 2 S 3 solar cells as the valence band and Fermi levels are tuned to provide an optimal hole-contact. We work towards finding the limiting factors and developing strategies for switching from the well-understood PbS QD and CdTe devices to those using CuInS 2 and Sb 2 S 3 and to overcome the challenges of fast non-radiative carrier recombination present in these materials. For example, enabling efficient ligand exchange with metal halide salts (ZnCl 2 , InCl 3 ) and organic thiols (ethane dithiol and mercaptopropionic acid), as well as finding the ideal layer thicknesses (balancing light absorption and charge transport) are important steps for the investigation and improvement of photoelectrochemical device performance because these factors directly influence the carrier dynamics that need to be controlled. We seek to use the gained knowledge to provide general lessons learned and enable further studies on sustainable light absorbing nanomaterials and their applications.

Bottom-up syntheses of carbon nanodots (CND) using solvothermal treatment of citric acid are known to afford nanometer-sized, amorphous polycitric acid-based materials. The addition of suitable co-reactants in the form of in situ synthesized N -hetero-π-conjugated chromophores facilitates hereby the overall functionalization. Reports regarding the influence of CND on the properties of, for example, N -hetero-π-conjugated chromophores are scarce. Thus, our incentive was to design a CND model that features phenazine (P-CND) – a well-known N -hetero-π-conjugated chromophore – to investigate the influence of the CND matrix on its redox chemistry as well as photochemistry. The scope of our work was to go beyond investigating the electrochemical properties of the resulting P-CND by shedding light onto differences relative to nano-aggregates of phenazine (PNZ NA ), which served as reference. In particular, chemical as well as electrochemical reduction of PNZ NA initiated a reaction cascade that affords the primary reduction intermediate, that is, the reduced and protonated (PNZ-H)⋅. In accordance with existing literature, the final product of a bimolecular disproportionation was 5,10-dihydrophenazine (PNZ-H 2 ). Reducing P-CND also resulted in the formation of (PNZ-H)⋅. But, no evidence for a subsequent bimolecular disproportionation was gathered. Instead, (PNZ-H)⋅ as an integrative part of P-CND was found to be actively involved in a H 2 generation reaction. A more than twofold increase in efficiency compared to PNZ NA under identical conditions was the consequence.

We report a deposition pathway for barium titanate (BTO) onto hydrophobically coated cobalt ferrite (CFO) nanoparticles, resulting in the formation of magnetoelectric core-shell nanoparticles. Our strategy utilizes a bimetallic Ba and Ti oleate (BTOle) precursor, which hydrophobically interacts with dimethyl-dioctadecyl-ammonium bromide (DDAB)-stabilized CFO particles during an interfacial phase transfer step. Thermal post-treatment yields a crystalline structure comprising distinguishable BTO and CFO phases, with BTO adopting a distorted cubic to tetragonal crystal phase. Magnetoelectric characterization yields a millivolt voltage-range output associated with the mechanical coupling between the piezoelectric and magnetostrictive phases. This method circumvents traditional sol-gel limitations and phase transfer hurdles, offering a streamlined route for fabricating magnetoelectric nanoparticles. Our results suggest magnetoelectric particles are suitable for incorporation in wireless actuation technologies.

Atomic-level control of solution-processed hybrid halide perovskites is achieved experimentally by solution atomic layer deposition (sALD). This method transfers the surface chemical principles of gas-phase ALD (gALD) to precursors dissolved in the liquid phase. Circumventing limitations associated with precursor volatility, sALD broadens the portfolio of reaction chemistries usable and material classes accessible. We establish its applicability to depositing ultrathin films of ionic semiconductors by developing an sALD procedure for the most prominent halide perovskite, methylammonium triiodoplumbate (CH3NH3PbI3, 'MAPI'). The process saturates upon precursor dosage variation to self-limiting growth typical for ALD, as analyzed by ex-situ and in-situ techniques. sALD-deposited MAPI is highly pure, stoichiometric, and polycrystalline. When MAPI films are prepared in congruent pairs by sALD and by a state-of-the-art spin-coating method, sALD-grown films clearly outperform their spin-coated counterparts in terms of charge carrier lifetimes and stability. They exhibit high carrier mobility and yield functional light absorbing layers in solar cells.

Understanding and controlling crystal growth mechanisms are essential for advancing materials development for optoelectronic applications. By controlling the morphology of the material, ultrathin transistors, flexible devices, surface-sensitive sensors, and the charge density wave phenomenon become realizable. Here, we report a solution-based synthesis of BaTiS3 nanostructures using tetrakis(dimethylamido)titanium, N,N'-diethylthiourea, and either barium bis(trimethylsilyl)amide (Ba[N(SiMe3)2]2) or barium iodide (BaI2) in oleylamine. The choice of barium precursor critically influences the morphology and crystal phase of the target material: Ba[N(SiMe3)2]2 yields ellipsoids that evolve into nanorods, while BaI2 produces two-dimensional (2D) nanoribbons, both in a nonperovskite hexagonal phase. Density functional theory calculations reveal that iodide ions selectively block specific crystal facets during growth, driving the formation of anisotropic nanoribbons. In situ mass spectrometry was employed to analyze gaseous species during synthesis, providing insights into the distinct growth mechanisms driven by precursor chemistry. X-ray diffraction patterns of the nanoribbons display sharp, periodic low 2 theta reflections, indicative of superlattice formation, which can be tuned by varying ligand chain lengths, which enables formation of metamaterials and photonic crystals by precisely controlling the supercrystal periodicity. Establishing a robust synthetic method using widely available precursors and equipment is a key step forward in applying this material in advanced devices. This study highlights the role of precursor selection and surface chemistry in controlling the growth and assembly of BaTiS3 nanostructures, offering a pathway for designing advanced 2D materials for optoelectronic applications.

Perovskite oxides like barium titanate (BaTiO3) exhibit desirable properties: notably high dielectric constants, piezoelectricity, and ferroelectricity, thereby enabling more advanced electronic devices and actuators. There are numerous synthesis procedures for BaTiO3, among which, nanoparticle syntheses are versatile and well-studied. However, colloidal organometallic synthesis is less commonly employed for this material despite offering processing advantages like facile compositional control and customizable surface chemistry. Here, an organometallic synthesis route is explored to produce colloidally stable BaTiO3 nanoparticles with oleyl alkoxide ligands. Subsequently, we further develop ligand exchange procedures with X-type ligands using KOH and oxalic acid to produce colloidal inks applicable for solution-processed nanocrystalline films for dielectrics in devices for which there is still a need for better nanoscale control. The BaTiO3 nanoparticles and films were characterized using X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and density functional theory (DFT), to understand their properties and to develop processes for device applications.