Christopher Robert McNeill

This work focuses on the influence of the electron-withdrawing character of acceptor units on both the molecular and macroscopic properties of thiophene (T)-bridged push-pull donor–π–acceptor chromophores with tetrahydroquinoline (TQ) as donor.

The application of cycloparaphenylene (CPP) macrocycles in organic photovoltaics has remained largely unexplored despite their unique three‐dimensional (3D) topologies. Herein, we expand the functional scope of CPPs by covalently integrating a carbon‐nanohoop scaffold with Y‐series electron acceptors to develop a novel 3D trimeric acceptor, CPP‐3Y. Distinct from conventional planar molecules, CPP‐3Y combines radially oriented π‐conjugation, a continuously curved π‐surface, and sterically hindered 3D topology, resulting in strong aggregation with low crystallinity. When introduced as a third component into the D18:L8‐BO‐X binary system, CPP‐3Y preferentially associates with the L8‐BO‐X‐rich acceptor phase, resulting in large fibrillar structures in blended thin films. This narrows the energetic tail‐state distribution, suppresses trap‐assisted and non‐radiative recombination, and enables more balanced charge transport. Consequently, D18:L8‐BO‐X:CPP‐3Y ternary OSCs achieve a PCE of 20.62%, outperforming binary devices (19.90%). They also retain over 80% of their initial efficiency after 964 h at 70 °C, whereas the binary devices fall below this level after 432 h. This work demonstrates that cyclic electron acceptors with 3D configurations and strong aggregation can act as morphological regulators to tune the phase separation of photoactive layers and hence realize high PCEs in OSCs.

The application of cycloparaphenylene (CPP) macrocycles in organic photovoltaics has remained largely unexplored despite their unique three‐dimensional (3D) topologies. Herein, we expand the functional scope of CPPs by covalently integrating a carbon‐nanohoop scaffold with Y‐series electron acceptors to develop a novel 3D trimeric acceptor, CPP‐3Y. Distinct from conventional planar molecules, CPP‐3Y combines radially oriented π‐conjugation, a continuously curved π‐surface, and sterically hindered 3D topology, resulting in strong aggregation with low crystallinity. When introduced as a third component into the D18:L8‐BO‐X binary system, CPP‐3Y preferentially associates with the L8‐BO‐X‐rich acceptor phase, resulting in large fibrillar structures in blended thin films. This narrows the energetic tail‐state distribution, suppresses trap‐assisted and non‐radiative recombination, and enables more balanced charge transport. Consequently, D18:L8‐BO‐X:CPP‐3Y ternary OSCs achieve a PCE of 20.62%, outperforming binary devices (19.90%). They also retain over 80% of their initial efficiency after 964 h at 70 °C, whereas the binary devices fall below this level after 432 h. This work demonstrates that cyclic electron acceptors with 3D configurations and strong aggregation can act as morphological regulators to tune the phase separation of photoactive layers and hence realize high PCEs in OSCs.

Polycyclic aromatic hydrocarbons (PAHs) are an interesting class of organic semiconducting material (OSM) due to their notable optoelectronic properties. However, their widespread use in organic electronics is often limited by their poor solubility, vacuum processes, and high cost. Herein, we report two series of PAHs integrated OSMs (DPPPy-C10-AN, DPPPy-C10-FA, and DPPPy-C10-DPB-FA; DPPPy-C-Si-AN, DPPPy-C-Si-FA, and DPPPy-C-Si-DPB-FA) in which alkyl/siloxane-appended pyridine-flanked diketopyrrolopyrrole is π-conjugated to acenaphthene (AN), fluoranthene (FA), and diphenylbenzo-fluoranthene (DPB-FA), respectively. Although both series of PAHs integrated OSMs showed sufficient solubility in common organic solvents, the siloxane derivatives exhibited superior solubility compared to the alkyl counterparts. Upon varying the PAHs (from AN to FA and further to DPB-FA) on OSMs, only marginal variations were observed in the optical properties, band gaps, and frontier energy level values. In contrast, GIWAXS results revealed substantial changes in the crystalline properties of thin films. Importantly, AN- and FA-based molecules demonstrated enhanced crystallinity compared to DPB-FA molecules. Furthermore, DPPPy-C-Si-AN:SEBS and DPPPy-C-Si-FA:SEBS stretchable blends showed ordered orientation compared to DPPPy-C10-AN:SEBS and DPPPy-C10-FA:SEBS. DPPPy-C10-DPB-FA:SEBS and DPPPy-C-Si-DPB-FA:SEBS blends exhibited poorer orientation compared to the pristine or other molecules. Organic field-effect transistors based on DPPPy-C-Si-FA displayed the highest electron mobility of 28 × 10–3 cm2 V–1 s–1 among all the molecules and their elastomeric blends.

Self‐doped conjugated polyelectrolytes (S‐CPEs) with high electrical conductivity and stable self‐doping, without the use of external dopants, are reported. Two types of soluble copolymers with different levels of self‐doping were synthesized. The degree of self‐doping was precisely controlled by varying the amount of self‐dopable monomer units, 3HOTS ⁻ [TMA ⁺ ] or 3HOT‐[SO ₃ H], over a wide compositional range. These units were copolymerized with a non‐self‐dopable monomer, 3MEEET. Compared to S‐CPEs bearing tetramethylammonium sulfonate side chains, the corresponding S‐CPEs containing free sulfonic acid groups (SO ₃ ⁻ H ⁺ ) show additional self‐acid doping, which results in higher self‐doping levels. As the fraction of self‐dopable repeating units increases, both S‐CPE series show stronger polaron absorption, as evidenced by ultraviolet–visible–near‐infrared (UV–vis‐NIR) spectroscopy, alongside a decrease in barrier to hole injection. Spectroscopic data enabled us to propose the underlying self‐doping mechanism. The degree of self‐doping is found to strongly influence organic electrochemical transistor (OECT) performance, especially the threshold voltage ( V _T ), which can be precisely tuned from −0.6 to +0.1 V. Additional studies examine morphology, crystal orientation, swelling in electrolytes under applied bias, volumetric capacitance, and cytotoxicity. Overall, this copolymer approach enables precise control of charge carrier concentration and conductivity of soluble semiconductor polymers for different applications.

Single‐component organic solar cells (SCOSCs) based on double‐cable conjugated polymers offer unparalleled morphological stability compared to bulk‐heterojunction systems, but their efficiencies are severely bottlenecked by rapid geminate recombination. While the intrinsic donor–acceptor proximity in these polymers generates ultralong‐lived charge‐transfer (CT) states (>5 ns), these “cold” carriers are traditionally viewed as an energetic trap. Here, we report a thermodynamic strategy that converts this extended temporal window into a resource for thermally activated charge extraction. By engineering an interfacial energy ladder using a D18 polymer layer with a precise 0.02 eV highest occupied molecular orbital (HOMO) offset, we demonstrate that long‐lived holes can be thermally promoted and selectively harvested. This active energy management mechanism successfully outcompetes non‐radiative recombination loss, simultaneously elevating the open‐circuit voltage, short‐circuit current, and fill factor. Consequently, the optimized devices achieve a record‐breaking power conversion efficiency of 15.65%. This work establishes a new paradigm for organic photovoltaics: demonstrating that long‐lived excited states, previously considered a fundamental limitation, can be strategically harnessed as a thermal activation reservoir to overcome thermodynamic recombination losses.

Single‐component organic solar cells (SCOSCs) based on double‐cable conjugated polymers offer unparalleled morphological stability compared to bulk‐heterojunction systems, but their efficiencies are severely bottlenecked by rapid geminate recombination. While the intrinsic donor–acceptor proximity in these polymers generates ultralong‐lived charge‐transfer (CT) states (>5 ns), these “cold” carriers are traditionally viewed as an energetic trap. Here, we report a thermodynamic strategy that converts this extended temporal window into a resource for thermally activated charge extraction. By engineering an interfacial energy ladder using a D18 polymer layer with a precise 0.02 eV highest occupied molecular orbital (HOMO) offset, we demonstrate that long‐lived holes can be thermally promoted and selectively harvested. This active energy management mechanism successfully outcompetes non‐radiative recombination loss, simultaneously elevating the open‐circuit voltage, short‐circuit current, and fill factor. Consequently, the optimized devices achieve a record‐breaking power conversion efficiency of 15.65%. This work establishes a new paradigm for organic photovoltaics: demonstrating that long‐lived excited states, previously considered a fundamental limitation, can be strategically harnessed as a thermal activation reservoir to overcome thermodynamic recombination losses.

Achieving optimal morphology and long-term stability in organic solar cells (OSCs) remains challenging because the donor–acceptor crystallization sequence is often poorly coordinated during solution processing. Here, we develop a supramolecular crystallization seeding strategy by introducing a hydroxyl-terminated, highly crystalline acceptor (Y–OH) into the D18/L8-BO system. By engineering a hierarchical thermodynamic compatibility gradient (χD18/Y–OH > χL8-BO/Y–OH > χD18/L8-BO), Y–OH becomes interface-active and exhibits an interfacial distribution tendency in the multicomponent film. In situ UV–vis measurements reveal that Y–OH undergoes early stage ordering on a time scale closer to the donor, thereby participating in the initial morphology evolution and steering the subsequent organization of L8-BO into a refined interpenetrating fibrillar network with reduced fibril diameters. This morphology simultaneously promotes efficient exciton harvesting/charge generation and enables balanced charge transport, leading to concurrent enhancements in short-circuit current density (JSC) and fill factor (FF). As a result, the optimized ternary devices deliver a PCE of 20.90% (vs 20.05% for the binary control). Moreover, hydroxyl-enabled supramolecular interactions provide noncovalent anchoring that retards thermally driven morphology relaxation, allowing the devices to retain ≈83% of their initial efficiency after 900 h at 65 °C. This work highlights supramolecular crystallization seeding as an effective design principle for simultaneously improving efficiency and thermal stability in OSCs.

This study reveals how the morphology of organic mixed ionic-electronic conductors (OMIECs) controls the mixed ionic-electronic transport of organic electrochemical transistors (OECTs). Two p-type OMIECs with oligoethylene glycol (OEG) side chains, namely P3MEEET and P3MEEMT, are blended with polystyrene (PS) to produce laterally phase-separated morphologies. By varying the ratio between OMIEC and PS, distinct morphologies are created via nucleation and growth and via spinodal decomposition. Furthermore, porous films are fabricated through the selective dissolution of PS, providing a direct comparison between blend and porous structures on OECT performance. In blends, the reduced ion injection area significantly enhances the mobility (μ) and figure of merit (μC^*). Due to the hydrophilic nature of the OMIECs, adding pores to the films does not have a positive effect on signal amplification but improves ion storage via side injection and increases the effective volumetric capacitance (C^*). Comparing the two OMIECs studied, porous samples based on P3MEEMT experience a greater benefit from electrolyte side injection. Both blend and porous samples are characterized using a range of techniques, including spectroelectrochemistry (SEC), atomic force microscopy (AFM), scanning transmission X-ray microscopy (STXM), quartz crystal microbalance (QCM), along with ex situ and in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) to unravel the mechanism of the mixed ionic-electronic transport from both an ionic and electronic perspective.

The thermal transitions of organic semiconductors have important implications for morphological and thermomechanical properties of electronic devices. Here we show that in situ UV–vis spectroscopy coupled with automated data analysis is a facile tool to determine the numerous thermal transitions that can exist in organic semiconductor thin films. Thermal transitions are automatically identified through employing linear segment detection of the semilogarithmic normalized deviation metric (NDM) as well as the spectral changes using piecewise linear regression. Furthermore, by comparing the in situ UV–vis with other thermal measurement methods we observe the temperature dependent absorbance can be used to discern the type of thermal transitions including liquid crystal transitions, glass transitions, and melting temperatures. This approach is used to characterize five well‐known conjugated polymers and a small molecule semiconductor, each with distinct thermal phase behavior, where we show good agreement with other thermal characterization methods. Thus, the method we introduce, which we refer to as A utomated T hermal transition identification using L inear regression analysis of the A bsorbance S pectra (ATLAS), is shown to be an effective and simple screening tool to identify multiple thermal transitions in thin films. This is a high‐throughput thermal analysis approach that will assist in advancing structure‐morphology‐function relations in organic electronics.