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.

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.

Abstract Fused filament fabrication (FFF) 3D printing provides an accessible route to fabricating retrievable photocatalytic architectures with tunable geometry and composition. Here, we address the limited recoverability and reusability of conventional powder-based photocatalysts by translating a metal-free semiconductor catalyst to 3D printed electrodes. Graphitic carbon nitride (g-C3N4) was functionalized with carbonized polydopamine (cPDA) to create a modified photocatalyst with improved photophysical behavior, consistent, more effective charge separation, and longer-lived photoexcited states, which correlates with enhanced photocatalytic activity. The optimized formulation was compounded into an extrudable PLA-based composite filament and printed into electrodes containing either g-C3N4 or g-C3N4/cPDA. The printed g-C3N4/cPDA electrodes show enhanced photocatalytic rhodamine B degradation under simulated sunlight compared with unmodified printed electrodes. In contrast to suspended powders, the electrodes enable straightforward retrieval, improved operational stability, and reuse without postseparation steps. Furthermore, we demonstrate that electrode performance can be increased by scaling the surface area, highlighting geometry as a simple handle for upscaling. This work demonstrates the potential of photocatalytic 3D printed electrodes made from abundant materials via low-energy processing as a scalable and sustainable route for wastewater treatment.

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.

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.

Ligand engineering is an effective method to reduce defects in perovskite solar cells (PSCs) and to enhance efficiency. Likewise, enhancing device stability through ligand engineering is currently emerging as a key focus to suppress the bidirectional migration of halides and silver ions, which otherwise can cause irreversible chemical corrosion to the electrode and perovskite layer. Here, triphenylphosphine oxide (TPPO) is demonstrated to improve the long-term operational stability of PSCs when introduced at the interface between the perovskite and the electron transport layer (ETL). TPPO effectively eliminates uncoordinated Pb2+ and thus reduces surface defects. Accordingly, the target solar cell yields a hero power conversion efficiency (PCE) of 26.01% and a maximum open-circuit voltage (VOC) of 1.23 V, representing the minimum voltage deficit (0.32 V) reported for methylammonium-free (MA-free) PSCs. Moreover, long-term operational analysis reveals that the bidirectional migration of halides and silver ions is significantly suppressed, resulting in enhanced device stability. TPPO-modified PSCs retain 90% of the initial PCE after 1200 hours of operation in maximum power point tracking. Ligand engineering with TPPO marks a significant advancement in enhancing the stability of PSCs and is fully compatible to upscaling scenarios.

Template-assisted crystal engineering provides a powerful strategy for constructing ordered networks tailored to organic electronic applications. We introduce a solution-based strategy to fabricate crystalline needle-like arrays of charge-transfer complexes (CTCs) between electron-donating benzo(ghi)perylene (BP) and electron-accepting TCNQ. Well-defined square-crystals of BP polymorphs were employed as templates for the spatially controlled anisotropic growth of CTC needle-like arrays. By tuning concentration and deposition rates, we modulated BP crystal dimensions and hence controlled the growth of needle-networks mimicking the template spatial scale. In solution, these free-standing flexible meshes were detached from the BPs and redeposited onto variable substrates, while the BP templates remain undissolved, enabling repeated fabrication cycles. CTC formation induces an electronic redistribution with thermally reversible modulation of characteristic electronic states. Such transformation modifies the BP luminescence character: while bare BP exhibits a strong green emission, it is quenched in the presence of TCNQ and replaced by a weaker blueish CTC emission, establishing a charge-transfer-mediated photonic response. Our study provides a combination of crystal engineering with microspectroscopic insights offering a highly sensitive handle for elucidating charge redistribution and modulation of electronic states in CTC upon external stimuli.

3D printing of conductive structures via fused deposition modelling has emerged as a mainstream manufacturing technique for electrochemical devices owing to the affordability and availability of thermoplastic-carbon-based filaments. On the current market, the existing filaments are limited in terms of their electrical conductivity and functionality. To address this, the development of multi-material filaments incorporating additional functional materials along with conductive carbons strategically produces 3D-printed electrodes with enhanced functionalities. In parallel, filament fabrication allows for precise control over the material composition and properties, such as chemical, thermal, and mechanical properties of the filament. In this work, we explored the fabrication of a multi-material filament combining photocatalytic carbon nitride, C3N4, and conductive carbon nanotubes, CNTs. Our C3N4-CNTs electrodes 3D-printed from it outperformed CNTs electrodes in hydrogen evolution and photocatalytic degradation of an organic dye. Our findings suggest that multi-material filaments may transcend the current filament-extrusion printing technique and expand its potential beyond electrochemistry.

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.

A growing interest towards all-organic electronics emphasized the importance of interfaces between the functional components of such devices. In particular, the interaction between the dielectric and semiconductor plays a critical role in device functionality, with strong dependency of charge carrier accumulation and mobility on semiconductor molecular arrangement. We report on the beneficial adsorption conformation with a nearly upright standing molecular orientation of a 2-tridecyl-[1]benzothieno[3,2-b][1]benzothiophene (C13-BTBT) semiconductor monolayer deposited on Langmuir-Blodgett-prepared polymethyl methacrylate (PMMA) dielectric films. Such an alignment favors a smooth transfer of charge carriers due to the optimal orbital overlap between π-conjugated BTBT units. Atomistic insights into the C13-BTBT/PMMA system through molecular dynamics revealed an advantageous direct contact of the charge-transporting BTBT unit with PMMA, while the alkyl chain is pointing outwards. Compared to non-alkylated BTBT, we demonstrate a 43% lower stiffness for surface-exposed alkyl chains of a C13-BTBT monolayer, as determined by force-distance analysis, highlighting the advantage for flexible device applications. These insights open new perspectives for further engineering of advanced interfaces, paving the way for innovations in efficient carbon-based electronics.

Three-dimensional/two-dimensional (3D/2D) heterojunctions in perovskite solar cells exhibit excellent optoelectronic properties and enhanced stability under mild ageing conditions. However, their performance degrades drastically under harsh ageing conditions. This study reveals the intrinsic instability of mono-ammonium based 2D perovskites (2D-mono) under photo-thermal ageing, which decompose into PbI2 and metallic lead (Pb0). The structural collapse promotes vacancy formation and facilitates iodide migration to the anode. As a result, it triggers a redox reaction that reduces the transport layer's mobility and doping concentration, leading to a significant increase in series resistance. Compared to mono-ammonium-2D structure, di-ammonium-2D (2D-di) based interfaces demonstrate superior structural stability and effectively block iodide migration into the transporting layer. However, blocking-induced uneven iodide distribution leads to interstitial defect formation in the 3D layer, exacerbating non-radiative recombination. To address it, we propose a strategical method by incorporating 2D-di in the 3D bulk instead of on the top surface, which effectively confines mobile ions within the grain and suppresses cation phase segregation. This optimization yields stable perovskite solar cells with an extrapolated operational T80 lifetime exceeding 560 hours under harsh conditions (85 degrees C and 2-sun illumination). Three-dimensional/two-dimensional (3D/2D) heterojunctions in perovskite solar cells exhibit excellent optoelectronic properties and enhanced stability under mild ageing conditions.

Perovskite-based tandem solar cells stand at the forefront of photovoltaic innovation due to their exceptional performance and cost-effective fabrication. This study focuses on minimizing energy losses within a 1.80 eV perovskite sub-cell. We demonstrate that the surface treatment of perovskite with binary guanidinium bromide and 4-fluorophenylammonium iodide synergistically reduces defect densities and adjusts interfacial energy-level alignment. The enhanced passivation effect and the formation of a surface dipole significantly reduce nonradiative recombination and transport losses, leading to a notable increase in the open-circuit voltage and fill factor product, thereby achieving an impressive power conversion efficiency (PCE) of 19.0%. The reproducibility of these findings is confirmed by consistent results across different laboratories. Furthermore, integration with a narrow-band-gap perovskite yields an all-perovskite tandem device with a PCE of 27.2%. This comprehensive understanding of the pivotal role of spacer cations in surface treatment significantly advances the pathway toward efficient perovskite photovoltaics.

Formamidinium (FA)-based perovskites exhibit significant potential for highly efficient photovoltaics due to their promising optoelectronic properties and optimal bandgap. However, the undesired inactive phase arises from multiple crystal nucleation pathways formed by various intermediate phases during the film formation process, persistently accompanying it. FA-based perovskites frequently struggle to form uniform, highly crystalline films. This challenge complicates the development of reliable and highly reproducible crystallization processes for perovskites and the establishment of guidelines for controlling the alpha-phase formation. In this work, we investigate the role of poly(acrylonitril-co-methyl acrylate) (PAM) to simultaneously control nucleation and subsequent alpha-phase crystallization. This successfully demonstrates the regulation of oriented crystal growth through the creation of a PAM-PbI2 intermediate. Ultimately, PAM-modified p-i-n architecture devices obtain a promising power conversion efficiency (PCE) of 25.30%, with V-OC (1.211 V), achieving 95% of the detailed balance limit. Additionally, PAM-modified devices maintain >= 90% of the initial efficiency for 1000 h under 1 sun and 65 degrees C operation.

Realizing efficient and stable organic solar cells (OSCs) via all-solution processing requires the design of tailored charge extraction interfaces. Herein, we demonstrate a substantially different interface concept for OSC that is based on a low-temperature processed mesoscopic hole transporting layer (HTL) derived from partially covered organic nanoparticles (NPs) in the n-i-p structure. The mesoscopic interface is further doped in a second coating step with an organic salt dopant, BCF-Li. The interactions among the dopant, the solvent for sequential doping, and the semiconductor layer are surprisingly complex. The mesoscopic interface is necessary to evenly wet the semiconductor and prevent the aggregation of the dopant. At the same time, the sequential process reduces the excess acceptor at the interface. Both processes together are necessary to generate an efficiently doped interface for low-Ohmic-charge extraction and stable contacts. Devices with fully solution-processed mesoscopic interfaces show a superb shelf lifetime of over 22000 h without encapsulation and a long-term operational stability under 1 sun illumination for 2000 h (T80). Flexible devices bypass 1000 bending cycles with negligible degradation. Mesoscopic doped interfaces are demonstrated as an alternative to PEDOT:PSS as well as PEDOT related interface concepts for nonfullerene acceptors (NFA) in the n-i-p architecture.

Most interface materials for organic solar cells (OSCs) were originally optimized for fullerene-based systems and are now being adapted for non-fullerene acceptor (NFA) based solar cells. This reliance on established interface materials results in a limited choice of interface materials for NFA based OSCs. For vacuum processed organic devices, the concept of doped interface materials is exceptionally successful, but has not yet been translated to modern NFA based devices due to solution processing constraints requiring orthogonal solubility. Herein, we report a novel concept for the development of solution-processed HTL in inverted n-i-p architecture OSCs using doped organic nanoparticles (D-NPs), overcoming solvent compatibility limitations and enabling scalable pro-duction processes. We demonstrate that the functional key interface properties of D-NPs HTLs can be tailored independently over a wide regime. Specifically, conductivity and work function can be optimized separately by varying the dopant concentration and the material system. By using D-NPs as HTL in the n-i-p architecture, power conversion efficiencies (PCE) of over 12 % are achieved for PM6:Y6 based devices. The D-NPs HTL concept is successfully applied to a variety of organic semiconductors used in photovoltaics and opens a new class of tailorable interface materials for solution-processed HTL materials.

Advances in organic materials manufacturing have enabled the creation of electronic devices using solution-processing techniques by employing soluble materials with high conductivity grade. In this exploratory study, the use of micro-contact for poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer ink deposition as high-quality structured electrodes for organic field-effect transistors (OFETs) in top-contact geometry is demonstrated. The optimized OFET's solution-processed fabrication is a promising strategy to be realized in the simple, cost-effective roll-to-roll manufacturing processes. The electrical performance of the fabricated devices is comparable to transistors with gold electrodes prepared via vacuum deposition, and even exceeding the values of the charge carriers' mobilities and featuring lower contact resistance (R-c), due to lower charge-carrier injection barrier for carbon-based organic electrodes. An addition of multi-walled carbon nanotubes to the PEDOT:PSS decreases R-c even further, changing the work function for better energy alignment with semiconductor materials.