Aligned conjugated polymer nanowires for enhanced performance in organic transistors and neuromorphic devices

Abstract

Conjugated semiconducting polymers have emerged as attractive materials for flexible and solution-processable electronics. However, their relatively low charge transport performance remains a key limitation for practical applications. To overcome this issue, we introduce a novel patterning strategy employing a polydimethylsiloxane (PDMS) mold to fabricate highly aligned PBTTT-C₁₄ nanowires for advanced organic transistor applications. The formation of nanowires is facilitated by evaporation-induced solute accumulation at the mold edges, resulting in localized polymer deposition and crystallization. This approach enables the creation of well-defined nanowire structures with minimal residual polymer. Comprehensive characterization using optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV–visible spectroscopy, and X-ray diffraction (XRD) confirms significant molecular alignment within the fabricated films. The distinct nanowire geometry markedly enhances electrolyte accessibility and interaction, substantially boosting device performance. Consequently, organic electrochemical transistors utilizing these nanowires exhibit notably high transconductance and superior retention capabilities. Furthermore, synaptic devices based on the nanowire structure demonstrate markedly improved functional characteristics. Our findings highlight the potential of directionally aligned nanowire structures for next-generation multifunctional organic electronic devices, particularly those targeting ionic and neuromorphic applications.

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Introduction

Solution-processable conjugated polymers have emerged as essential materials for flexible, cost-effective organic electronics. Their inherent mechanical flexibility and compatibility with large-area manufacturing methods render them highly appealing for a variety of applications, including organic transistors, sensors, and neuromorphic devices. Nevertheless, their comparatively modest charge transport properties—often attributed to disordered molecular packing—have constrained their utility in advanced electronic applications. Given that charge transport predominantly occurs along polymer backbones, enhancing molecular alignment has historically been a critical strategy for improving electrical performance, particularly in switching devices such as organic field-effect transistors (OFETs).^1–6

While increasing charge carrier mobility remains a pivotal objective, there is an emerging imperative to broaden the functionalities of conjugated polymers beyond OFETs. In particular, organic electrochemical transistors (OECTs) and neuromorphic synaptic devices have garnered significant interest as promising platforms that exploit both electronic and ionic transport mechanisms.^7–13 These devices operate fundamentally differently, relying on volumetric ion injection and dynamic charge modulation at the electrolyte–semiconductor interface. Consequently, the geometry and interfacial accessibility of the active layer become crucial factors in optimizing transconductance, signal retention, and synaptic plasticity. However, conventional polymer thin-films typically exhibit limited ion accessibility due to densely packed molecular structures and restricted surface exposure.

To address these limitations, the fabrication of conjugated polymer nanowires has emerged as a promising approach. Laterally confined nanowire structures not only promote chain alignment but also provide an exposed surface geometry that is inherently favorable for ion transport and interaction with electrolytes. This makes nanowires especially suitable for enhancing the performance of ionic and neuromorphic devices. Moreover, spatially controlled nanowire arrays help suppress parasitic current pathways and facilitate dense device integration. Notably, Li et al. demonstrated that externally engineered pinning of capillary bridges between a grooved template and a substrate can direct polymer assembly during solvent evaporation, enabling high-resolution patterning with sub-100 nm features.¹⁴ Such approaches highlight the potential of geometry-controlled solution processing for enhancing both morphological control and functional performance.^14–17

In this work, we present a solvent evaporation-assisted patterning strategy for fabricating PBTTT-C₁₄ nanowires via soft lithographic imprinting. During solvent evaporation, evaporation-induced solute accumulation at the mold edge guides the formation of edge-localized nanowire arrays with minimal residual material. The resulting structures were characterized by optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV–visible spectroscopy, and X-ray diffraction (XRD), confirming their nanowire morphology and crystalline structure. While the electrical performance in OFETs remains comparable to that of spin-coated films, the nanowire-based devices demonstrate significantly enhanced transconductance and long-term memory (LTM) characteristics in OECT and synaptic operation, owing to their geometry-driven ion accessibility. These findings underscore the importance of structural design for electrolyte-interfacing polymer devices and highlight nanowire patterning as a viable platform for advancing organic ionic and neuromorphic electronics.

Experimental section

Materials and polymer solution preparation

PBTTT-C₁₄ (>99% purity) was purchased from Sigma-Aldrich and used without further purification. 1,2,3,4-Tetrahydronaphthalene (Tetralin, 99%) was also obtained from Sigma-Aldrich and used as the solvent. The polymer was dissolved in Tetralin and stirred at 170 °C under nitrogen atmosphere until a clear and homogeneous solution was obtained.

Nanowire fabrication

A 0.1 μl of the conjugated-polymer solution was drop-cast onto pre-cleaned substrates inside a nitrogen-filled glovebox. A contact-mode polydimethylsiloxane (PDMS) mold bearing the groove pattern (Fig. S1) was gently laminated onto the wet droplet to guide pattern formation during solvent evaporation. After complete drying, the films were thermally annealed at 160 °C for 90 min to enhance molecular alignment and crystallinity. The mold was then lifted off, yielding arrays of aligned nanowires.

Device fabrication

Bottom-gate/bottom-contact structural OFETs and OECTs were fabricated on heavily doped silicon substrates with a 100 nm thermally grown SiO₂ dielectric layer. Source and drain electrodes composed of Au/Ti (50 nm/10 nm) were deposited using a thermal evaporator through a metal shadow mask. For OECTs, the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) was carefully dispensed onto the polymer channel using a micropipette to serve as the electrolyte-gating.^18–20

Electrical characterization

The electrical performance of the OFET and OECT devices was evaluated using a semiconductor probe station equipped with a Keithley 4200A and 2636B source-measure unit. Output and transfer characteristics were recorded under ambient conditions. Carrier mobilities were extracted using standard models in the saturation regime for OFETs.

Optical and structural characterization

Surface morphologies of the polymer nanowires and reference films were examined using optical microscopy (OM; Olympus BX53M), atomic force microscope (AFM; NX-10, Park Systems) and field-emission scanning electron microscopy (FE-SEM; JEOL JSM6700F). Crystallinity and molecular orientation were analyzed using X-ray diffraction (XRD; Rigaku Ultima IV diffractometer) with Cu Kα radiation (λ = 1.5406 Å). Optical absorption characteristics were measured by UV–visible–near-infrared (UV-vis-NIR) spectroscopy (JASCO V-670 spectrophotometer).

Results and discussion

The fabrication of PBTTT-C₁₄ nanowires in this study was accomplished using a solvent-guided soft lithographic imprinting method with Tetralin as the solvent. A 0.1 wt% PBTTT-C₁₄ solution was dispensed onto a SiO₂/Si substrate inside a nitrogen-filled glovebox, after which a flexible PDMS mold bearing groove patterns was gently laminated onto the wet film without applying external pressure. The sequential process is illustrated in Fig. 1. As shown in Fig. 1a, a 0.1 μl of PBTTT-C₁₄ solution is deposited onto the substrate surface. Upon gentle placement of the patterned PDMS mold (Fig. 1b), the solution spreads within the groove structure due to surface wetting. As solvent evaporation proceeds at room temperature (Fig. 1c), the liquid meniscus retracts toward the groove walls, leading to lateral solute transport and the formation of capillary bridges at the edge of each groove.^17,21 The groove geometry acts as a pinning site for the contact line, anchoring the liquid front and inducing directional solute accumulation. The inset of Fig. 1c presents a cross-sectional schematic of the proposed mechanism: solvent evaporation drives migration of polymer chains toward the mold–substrate interface while suppressing deposition beneath the ridge regions.¹⁴ Further details of the edge-accumulation mechanism are provided in the SI. As a result, crystallization occurs selectively along the groove edges, leaving no residual film between adjacent features. After solvent removal, a post-anneal at 170 °C for 90 min increases the crystallinity of the patterned structures. Finally, the mold is lifted off (Fig. 1d), revealing a uniform array of PBTTT-C₁₄ nanowires aligned parallel to the groove direction.

Fig. 1 The fabrication process of polymer nanowires on a substrate. (a) Dispensing of PBTTT-C₁₄ polymer solution onto a SiO₂/Si substrate (inset: chemical structure of PBTTT-C₁₄). (b) Conformal lamination of a PDMS stamp with a topographically patterned surface onto the polymer droplet under mild pressure. (c) Under constant pressure, solvent gradually evaporates during drying at room temperature, inducing directional migration of solute toward the sidewalls of the topographic features. Subsequent thermal annealing at 160 °C for 90 minutes enhances crystallinity and alignment (inset: cross-sectional illustration showing polymer solution filling the patterned structures, where solvent evaporation induces solute migration and accumulation at the pattern corners). (d) Removal of the PDMS stamp, resulting in well-aligned PBTTT-C₁₄ nanowire arrays on the substrate.

The success of the patterning process can be directly observed through optical microscopy. Fig. 2a shows bright-field and polarized optical images of the resulting nanowire arrays. The alternating light and dark contrast under polarized light confirms the uniaxial alignment of the polymer chains, and the regular spacing between features verifies the fidelity of the patterning process. The formation of highly aligned, residue-free PBTTT-C₁₄ nanowires demonstrates the effectiveness of this evaporation-driven confinement method in producing structurally defined polymer architectures. The morphological and crystalline properties of the PBTTT-C₁₄ nanowires were systematically investigated using a combination of OM, FE-SEM, AFM, UV–visible spectroscopy, and XRD, as shown in Fig. 2. Fig. 2a presents bright-field (top) and polarized optical microscopy (bottom) images of the nanowire arrays at ×100 magnification. The bright-field image reveals a uniform, parallel alignment of the nanowires over a large area, reflecting the high pattern fidelity achieved through capillary-bridge-assisted self-assembly. Under polarized light, the nanowires exhibit strong birefringence, indicating molecular alignment along the wire axis. The anisotropic optical response suggests that PBTTT-C₁₄ wires are oriented parallel to the pattern direction.¹⁴

Fig. 2 Morphological and structural characterization of PBTTT-C₁₄ nanowires. (a) OM images of PBTTT-C₁₄ nanowires under bright-field and polarized optical microscopy images of PBTTT-C₁₄ nanowires at ×100 magnifications. Top: bright-field; bottom: polarized. (b) SEM image of the nanowires. (c) AFM phase image visualizing contrast between nanowires and the substrate. (d) 3D AFM image representing the topography of the nanowire array. (e) UV–vis absorption spectra comparing PBTTT-C₁₄ in solution, spin-coated film, drop-cast film, and nanowire form. (f) XRD spectra of a spin-coated PBTTT-C₁₄ film. (g) XRD spectra of PBTTT-C₁₄ nanowires.

SEM imaging (Fig. 2b) further confirms the well-defined nanowire morphology with sharp contrast between the wires and the substrate. The magnified inset shows that the spacing and width of the nanowires are consistent, indicating reproducible pattern transfer. In addition, AFM phase imaging (Fig. 2c) clearly reveals the contrast between the nanowire domains and the bare substrate. The nanowires are arranged in a well-ordered, parallel fashion, with uniform spacing throughout the observed area. Importantly, no noticeable residual polymer is observed between adjacent wires, confirming the selective deposition mechanism induced by solvent-guided confinement. This spatial isolation reflects the high pattern fidelity of the process and supports the interpretation that solute migration and crystallization were effectively restricted to the groove-pinned regions. The corresponding 3D topographic AFM image (Fig. 2d) further confirms the periodic structure of the nanowires and their spatial separation. The well-defined wire edges and flat substrate background indicate that polymer deposition was cleanly confined to the patterned regions, without overflow or bridging between features.

The UV–visible absorption spectrum of the PBTTT-C₁₄ nanowire sample (Fig. 2e) provides insight into its molecular aggregation and packing behavior. Compared to the drop-cast film, the nanowire sample exhibits a noticeable blue shift in the absorption peak, suggesting reduced interchain aggregation and a more uniform distribution of polymer chains within the patterned geometry. The broad and red-shifted spectrum observed in the drop-cast film typically reflects uncontrolled chain packing and excessive aggregation, which are minimized in the confined nanowire structure.^14,22,23

Notably, the nanowire spectrum is red-shifted relative to the solution-state spectrum, indicating that the polymer chains still interact through π–π stacking in the solid state. This confirms that the nanowires are not amorphous or disordered but maintain a degree of crystalline order.²⁴ The spectral position and shape of the nanowire sample closely resemble those of the spin-coated film, suggesting that their overall crystallinity is comparable. These results indicate that while the nanowire fabrication process effectively reduces aggregation and improves spatial uniformity, it does not compromise molecular ordering. Instead, it achieves a balanced state of alignment and crystallinity, comparable to that of conventional films, but with the added advantage of structural confinement. This supports the suitability of nanowire architectures for applications requiring both optical consistency and controlled morphology.

To further evaluate the crystallinity of the PBTTT-C₁₄ nanowire sample, XRD analysis was performed and compared to that of a spin-coated film (Fig. 2f, g, and Table 1). The spin-coated film exhibits multiple higher-order diffraction peaks ((100), (200), (300), and (400)), indicating a well-ordered lamellar structure across the sample.²⁵ In contrast, the nanowire sample shows a relatively weaker diffraction intensity and fewer observable peaks. This difference may arise from the confined alignment of polymer chains near the mold sidewalls, resulting in a reduced proportion of well-ordered domains across the entire sample volume. Despite the lower overall diffraction intensity, the full width at half maximum (FWHM) of the (100) peak is narrower in the nanowire sample (0.0059 Å⁻¹) than in the spin-coated film (0.0151 Å⁻¹), which corresponds to an increased coherence length from 374.3 Å to 1063.0 Å. This implies that the crystalline domains in the nanowire sample are larger and more continuous, reflecting improved local ordering. These results also indicate that nanowire confinement does not diminish the intrinsic crystallinity of the polymer chains; rather, it promotes more extended crystalline regions within the aligned areas, albeit localized. The nanowire architecture thus offers an effective strategy to enhance order at the molecular level while enabling structural control via spatial confinement.

Table 1 Summary of XRD analysis parameters for PBTTT spin-coated film and NW samples

	(100) peak
	q (Å^−1)	d-Spacing (Å)	FWHM (Å^−1)	Coherence length (Å)
PBTTT-C14 film	0.4173	15.06	0.0151	374.3
PBTTT-C14 NW	0.3289	19.40	0.0059	1063.0

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The electrical performance of PBTTT-C₁₄-based OFETs was comparatively evaluated using spin-coated films and nanowire-structured channels, as shown in Fig. 3 and Table 2. All devices were fabricated in a bottom-gate, bottom-contact architecture with a channel length of 10 μm. Despite their similar materials, the geometric configuration of the active layer significantly influenced device behavior. The spin-coated device exhibited an on/off current ratio (I_on/I_off) of 2.42 × 10³ and a threshold voltage (V_th) of −7.8 V, with a calculated field-effect mobility of 1.12 × 10⁻⁴ cm² V⁻¹ s⁻¹. In contrast, the nanowire-based OFET showed a higher I_on/I_off ratio (1.07 × 10⁵) and a more positive shift threshold voltage (−2.8 V), also achieved an improved mobility of 1.72 × 10⁻² cm² V⁻¹ s⁻¹, exceeding 100 times that of its spin-coated counterpart. The mobility was extracted from the transfer curves in the saturation regime using the gradual approximation of FET equation:²⁶

Table 2 Electrical performance of PBTTT-C₁₄ OFETs according to film and NW structures

OSC	W/L^a	V DS ^b (V)	μ (cm^2 V^−1 s^−1)	V th ^d (V)	I on/Ioff ^e
a Channel width/channel length. b Drain voltage. c Charge carrier mobility of OFETs. d Threshold voltage. e On/off current ratio.
PBTTT-C14 film	250	−30	6.94 × 10^−3	−1.7	8.48 × 10^5
PBTTT-C14 NW	24.8	−30	1.72 × 10^−2	−2.8	1.07 × 10^5

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Fig. 3 Comparison of organic field-effect transistor (OFET) characteristics using PBTTT-C₁₄ in film and nanowire geometries. (a) Schematic illustration of the OFET architecture employing a spin-coated PBTTT-C₁₄ film as the channel layer. (b) Schematic illustration of the OFET architecture employing aligned PBTTT-C₁₄ nanowires as the channel layer. (c) Transfer characteristics of the film-based OFET measured at V_DS = −10 V, −20 V, −30 V. (d) Output characteristics of the film-based OFET. (e) Transfer characteristics of the nanowire-based OFET measured at V_DS = −10 V, −20 V, −30 V. (f) Output characteristics of the nanowire-based OFET.

The exceptional performance of nanowire-based devices, particularly the observed enhancement in charge carrier mobility, can be attributed to the directional alignment and geometrically confined structure of the active layer. This unique morphology effectively minimizes structural defects and facilitates efficient in-plane charge transport.^26,27 Further supporting this, the high on/off ratio and a significant positive shift in threshold voltage unequivocally indicate that the formation of nanowire channels enables more facile charge transport. These interpretations are strongly corroborated by the transfer characteristics presented in Fig. 3a and c. In direct contrast to spin-coating based OFETs, nanowire OFETs exhibit a turn-on voltage remarkably close to 0 V and demonstrate superior off-current efficiency owing to significantly lower leakage currents. Upon full channel formation, as evidenced by the output curves (Fig. 3b and d), nanowire-based devices display clearly-defined saturation behavior, a stark improvement over the spin-coated devices, which show notably lower current values and signs of performance degradation. This distinct behavior in nanowire devices underscores the efficient charge injection and transport facilitated by the nanowire morphology across the entire operational voltage range. Collectively, these results demonstrate that nanowire patterning leads to a substantial improvement in charge carrier mobility by optimizing charge efficiency through precise geometric alignment. This highlights the critical dual influence of both the charge transport pathway and the device fabrication morphology in achieving high-performance organic electronic devices.

The OECT performance of PBTTT-C₁₄ was systematically evaluated using both spin-coated film and patterned nanowire geometries. The schematics in Fig. 4a and d illustrate the interaction between the ionic liquid electrolyte and the organic semiconductor channel in each configuration. In the nanowire device, the electrolyte interfaces with the channel from multiple directions, whereas in the film, contact is largely limited to the top surface. This difference in interface geometry plays a critical role in determining ionic accessibility and gating efficiency.^8,28 Such enhanced accessibility has also been reported in systems utilizing ion exchange gels, which further facilitate volumetric ion penetration and transconductance improvement.²⁹ The nanowire channel has a thickness of 80 nm, which is comparable to or smaller than the Debye screening length of typical ionic liquids. The Debye length defines how deeply electric fields—and thus mobile ions—can penetrate into the bulk of the semiconductor.^8,12,30 When the channel thickness is smaller than or similar to this characteristic length, the electrolyte ions are capable of reaching the entire volume of the channel. This enables uniform and volumetric electrochemical doping, rather than being confined only to the surface layer, as is often the case in thicker or planar films.⁸ In contrast, spin-coated films may possess similar thicknesses, but their continuous planar geometry results in limited surface exposure, hindering lateral ion diffusion. The nanowire's three-dimensional geometry, with electrolyte accessibility from both sides and along its entire length, greatly enhances the rate and depth of ion injection.

Fig. 4 Comparison of organic electrochemical transistor (OECT) characteristics using PBTTT-C₁₄ in film and nanowire. (a) Schematic illustration of the OECT architecture employing a PBTTT-C₁₄ film as the channel layer. (b) Transfer characteristics and transconductance of the film-based OECT measured at V_DS = −0.3 V. (c) Output characteristics of the film-based OECT. (d) Schematic illustration of the OECT architecture employing aligned PBTTT-C₁₄ nanowires as the channel layer. (e) Transfer characteristics and transconductance of the nanowire-based OECT measured at V_DS = −0.3 V. (f) Output characteristics of the nanowire-based OECT.

The electrical data reflect these geometric advantages. The transconductance (g_m)—which quantifies the rate of drain current change with respect to gate voltage—is calculated using the standard OECT relation:⁸

Here, μ is the charge carrier mobility, C* is the volumetric capacitance, and d is the channel thickness (80 nm for nanowire).

Based on this equation, the extracted μC* value for the nanowire device is 15.04 F cm⁻¹ V⁻¹ s⁻¹, which is over six times greater than that of the film device (2.28 F cm⁻¹ V⁻¹ s⁻¹). Additionally, the nanowire device exhibits a higher I_on/I_off ratio (6.9 × 10⁵vs. 5.7 × 10⁴) and a more negative threshold voltage (−0.92 V vs. −0.54 V) (Table 3). Importantly, μC* was obtained from g_m ≈ (Wd/L)μC*|(V_GS − V_th)| using the measured W, L, and d for each device; thus thickness-dependent geometric factors are already normalized and cannot alone account for the six-fold gain. Moreover, because the nanowires and films have comparable d (≈80 nm, near the Debye length), the persistence of the μC* enhancement underscores a geometry-enabled, volumetric-doping origin. The steeper output characteristics (Fig. 4f) further support more complete gate charge compensation in nanowires. Finally, electrode–channel contact effects are expected to be minor in electrolyte-gated operation, where high carrier densities suppress injection barriers; our devices share identical metallization and exhibit linear low-bias I–V behavior, indicating channel-limited transport.³¹ Taken together, these results show that the superior OECT metrics of the nanowire architecture arise predominantly from geometry-driven ionic accessibility and complete volumetric doping, with channel-thickness optimization playing a supportive role and contact resistance contributing minimally.

Table 3 Electrical performance of PBTTT-C₁₄ OECTs according to film and NW structures

Devices	W/L^a	μC*^b [F cm^−1 V^−1 s^−1]	V th ^c [V]	I on/Ioff ^d
a Channel width/channel length. b Product of average charge carrier mobility and volumetric capacitance. c Threshold voltage. d On/off current ratio.
PBTTT-C14 film	250	2.28	−0.54	5.7 × 10^4
PBTTT-C14 NW	24.8	15.04	−0.92	3.6 × 10^4

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The synaptic characteristics of PBTTT-C₁₄-based devices were investigated under identical ionic gating conditions, comparing spin-coated film and nanowire geometries. As shown in Fig. 5, three stimulus modes—pulse count, voltage sweep, and pulse width modulation—were employed to assess the dynamic response of each device in terms of excitatory post-synaptic current (EPSC). All measurements were performed under consistent electrolyte conditions and gate/drain biases to isolate geometric effects. In the pulse count mode (Fig. 5b), both devices were stimulated with 10 identical pulses (−1.0 V), and their cumulative EPSC responses were recorded. The nanowire device exhibited a steeper and more pronounced increase in EPSC, indicating more effective ion accumulation and retention within the channel. This can be attributed to the nanowire's large surface area and full exposure to the electrolyte, which facilitate efficient ionic exchange during each pulse. In the voltage sweep mode (Fig. 5c), where the pulse amplitude was varied from −0.1 V to −1.0 V in −0.1 V steps, the nanowire again demonstrated superior sensitivity and larger current modulation. The continuous and monotonic rise in EPSC with increasing pulse amplitude reflects strong ionic coupling and a linear doping response across the nanowire channel. In the pulse width modulation mode (Fig. 5d), where pulse duration ranged from 0.1 to 1.0 seconds, the nanowire device maintained consistent EPSC amplification as the stimulation time increased. This behavior suggests that the channel remains accessible to ions over extended timeframes, without saturation or recombination loss—further evidence of its volumetric gating capacity.³¹ Finally, in the long-term memory (LTM) test (Fig. 5e), the nanowire device retained a significantly larger portion of its EPSC signal after the stimulus ended, compared to the spin-coated film. This indicates enhanced retention characteristics likely resulting from deeper, more stable electrochemical doping within the nanowire structure.³² Collectively, these results confirm that nanowire geometry provides a robust platform for synaptic transistors. Its directional alignment, structural openness, and ionic permeability together enable more responsive, stronger, and longer-lasting neuromorphic behavior compared to planar films-without requiring chemical modification or external doping is not merely due to the choice of material, but arises from geometry-driven electrochemical accessibility. Structural openness, thin-channel design, and complete volumetric doping together provide a decisive advantage for high-performance ion-gated organic transistors.

Fig. 5 Synaptic behavior of PBTTT-C₁₄ nanowire-based OECT devices. (a) EPSC responses under pulse count mode with 10 presynaptic spikes at a fixed pulse intensity of −1.0 V. (b) LTM behavior of the nanowire-based OECT, demonstrating sustained EPSC retention over time. (c) EPSC responses under pulse width sweep mode with pulse durations ranging from 0.1 to 1.0 s at a constant voltage. (d) EPSC responses under voltage sweep mode with pulse amplitudes ranging from −0.1 to −1.0 V in steps of −0.1 V.

We note that the patterned channels occupy only a fraction of the available area, which may constrain the maximum on-current achievable by a single stripe and raises concerns regarding scalability to finer features, where identical rheological self-assembly cannot necessarily be assumed. Such limitations should be regarded not as intrinsic but as architectural constraints, which can be mitigated through strategies that preserve the demonstrated crystallinity: (i) parallelization of nanowires to increase the effective channel width, (ii) interdigitated source/drain architectures to multiply the active edge length, and (iii) duty-cycle optimization (ridge : gap ratio) at the experimentally validated feature scale. Additional process-level optimizations—including solvent composition, evaporation kinetics, mold-edge geometry, and multi-pass coating—further enhance semiconductor coverage without necessitating extrapolation to sub-feature dimensions. These approaches enable recovery of array-level on-current while maintaining nanoscale order. In addition, the value proposition is strongly application-dependent. For wearable biointerfaces and neuromorphic primitives, key performance metrics such as low-voltage transconductance, stable volumetric doping, analog tunability, and reliable retention and linearity of weight updates are decisive; in these contexts, the nanowire morphology can provide system-level advantages that outweigh partial coverage penalties. Moreover, the presented strategy is broadly transferable to planar, high-mobility donor–acceptor copolymers, where nanoscale confinement and directional alignment can simultaneously reinforce electronic anisotropy and charge–ion coupling.^33,34

Overall, this study demonstrates that structural engineering of the active layer specifically through nanowire patterning offers a powerful route to enhance the performance of organic electronic and neuromorphic devices.^8,14,32 The inherent nanowire morphology not only leads to a substantial improvement in OFET characteristics attributable to its elevated crystallinity over spin-coated films but also critically enables volumetric and highly accessible ion transport, thereby providing clear advantages for OECT device operation and mimicking synaptic behavior. The geometry-driven enhancement is achieved without chemical doping or material modification, highlighting the effectiveness of nanoscale confinement and directional alignment in optimizing charge–ion coupling. Integrating morphological control with electrochemical functionality thus provides a generalizable design pathway—readily extendable to planar, high-mobility D–A copolymers—for wearable bio-interfaces requiring low-voltage, high-g_m transduction, while also charting a medium-term route toward neuromorphic chips that exploit uniform, volumetric ion-driven weight updates alongside rapid electronic transport.

Conclusion

In this study, we investigated the impact of nanowire patterning on the electrical and synaptic behavior of conjugated polymer-based devices using PBTTT-C₁₄ as the active material. Patterned nanowires demonstrate significantly enhanced field-effect mobility compared to spin-coated films, attributed to their improved crystallinity. Furthermore, they exhibit more pronounced advantages in OECT performance and synaptic responses. These improvements are attributed to the nanowire's geometry, which allows volumetric ion penetration and enhanced electrochemical modulation across the entire channel. The nanowire-based OECTs showed significantly higher transconductance, on/off ratios, and more efficient gate control, while synaptic devices demonstrated stronger and more sustained EPSC under various stimulation conditions. Notably, these enhancements were achieved without altering the chemical composition of the polymer or introducing additional dopants, underscoring the effectiveness of morphology-driven optimization. These findings highlight the importance of geometric design in the development of high-performance organic devices, particularly those requiring mixed ionic-electronic transport. The ability to tune charge–ion interactions through nanoscale structural engineering opens promising pathways for future neuromorphic electronics, bio-interfaces, and electrolyte-gated transistor technologies.

Author contributions

W. Jeong and J. Yoon contributed equally to this work. The manuscript was written with contributions from all the authors. The authors have approved the final version of the manuscript.

Conflicts of interest

The authors declare no conflict of interest.

Data availability

All data supporting the findings of this study are available within the article and its supplementary information (SI). Supplementary information: horizontal and vertical geometrical characterization of the PDMS mold, edge-accumulation mechanism and process parameters, and definition of effective channel width and device metric calculation. See DOI: https://doi.org/10.1039/d5nr03612g.

Acknowledgements

This research was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIT) (RS-2022-NR071808, RS-2023-00213534, and 2021R1A2C1007212). This work was also partially supported by the Korea Basic Science Institute (National Research Facilities and Equipment Center) grant funded by the Ministry of Education (2022R1A6C101B738). Dr Y. Kim acknowledges support from the 2024 Postdoctoral Fellowship Program funded by the Pukyong National University Industry–University Cooperation Foundation.

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Footnote

† These authors contributed equally to this work.

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