Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive

doi:10.21203/rs.3.rs-5136690/v1

Download PDF

Article

Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive

https://doi.org/10.21203/rs.3.rs-5136690/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Nucleating agents are widely recognized for their ability to refine the solid-state morphology and microstructure of semi-crystalline polymers, significantly influencing their physicochemical properties. This study presents a simple yet effective strategy to dramatically improve the thermoelectric properties of semi-crystalline polymer films. By blending less than 1 wt% of the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA) into Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14), we induce a controlled modulation of crystallization behavior, resulting in optimized microstructures with reduced structural disorder and improved charge carrier mobility. Systematic analysis of varying PDA concentrations identifies an optimal loading of 0.9 wt%, which yields a remarkable 45% increase in crystallinity relative to pristine PBTTT films. Under optimized doping conditions, the doped PBTTT-C14 film with 0.9 wt% PDA exhibits an exceptional electrical conductivity of 1800 S cm⁻¹ and an optimal power factor of 150 µW m^− 1 K^− 2, representing 105% and 384% improvements, respectively, over the doped pristine PBTTT-C14 film. These enhancements are primarily due to the synergistic effects of polymer chain extension and reduction of grain boundary size, which together mitigate grain boundary resistance and improve charge transport efficiency. Furthermore, the study elucidates the role of ion exchange doping in maintaining a high density of charge carriers without compromising the crystalline structure introduced by PDA. This research not only deepens the understanding of polymer thermoelectrics but also sets the stage for the development of innovative materials that could transform energy conversion technologies and polymer-based electronic devices.

Physical sciences/Materials science/Soft materials/Polymers

Physical sciences/Materials science/Materials for energy and catalysis/Thermoelectrics

In the quest for sustainable energy solutions, semiconductor polymers have garnered significant attention as viable materials for flexible thermoelectric applications¹. Their inherent low thermal conductivity, combined with attributes such as processability, lightness, flexibility, and environmental compatibility^2,3, make them ideal candidates for energy conversion technologies. Over the past decade, concerted efforts have propelled the power factors of thermoelectric polymers to hundreds or even thousands of µW m^− 1 K^− 2.⁴ Despite these advancements, polymer-based materials still lag behind their inorganic counterparts, such as PbSe crystals, which boast a record power factor of approximately 10,000 µW m^− 1 K^− 2 and average zT of 1.5 at 300 K⁵. Recent progress⁶ has seen the development of polymer films with periodic heterogeneous structures, achieving a power factor of 347 µW m^− 1 K^− 2 at 298 K and a peak zT of approximately 1.28 at 368 K. This achievement underscore the potential of organic semiconductor polymers for efficient energy conversion. However, a significant performance gap remains, necessitating strategic advancements to enhance the thermoelectric performance of semiconductor polymers by refining their microstructure.

The efficiency of thermoelectric materials, as quantified by the figure of merit \(\:zT=\frac{{S}^{2}\sigma\:}{\kappa\:}\), hinges on optimizing electrical conductivity (σ) and the Seebeck coefficient (S) in conjunction with thermal conductivity (κ). The inherently low κ in conducting polymers places emphasis on the power factor (\(\:{PF=S}^{2}\sigma\:\)), directing research towards enhancing σ and S simultaneously. Achieving this, however, is challenging due to the inverse relationship between σ and S with increased charge density (n). A promising approach involves improving mobility while maintaining constant carrier concentration, thereby circumventing the inherent trade-off between σ and S^7,8.

For conjugated polymers, increasing crystallinity is a key strategy to enhance carrier mobility, as it promotes long-range order and facilitates efficient charge transport⁹. This approach has been successfully applied in the development of high-performance thermoelectric polymers, particularly in semicrystalline polymers derived from polythiophenes and donor-acceptor (D-A) copolymers³. These materials exhibit high crystallinity, which enables efficient charge transport and high power factors through meticulous molecular design^10,11. However, validating these molecular designs can be time-consuming and labor-intensive due to the complexities involved in polymer synthesis.

To address these challenges, alternative approaches such as polymer chain alignment have emerged. By reimagining solution processing techniques, researchers have achieved significant improvements in thermoelectric performance^3,12,13. For example, a record power factor of 2900 µW m^− 1 K^− 2 was achieved in a polythiophene system through mechanical rubbing to align polymer chains¹⁴. Yet, this alignment tactic introduces anisotropic transport in polymer films, complicating the design of thermoelectric devices for real-world applications. Moreover, high crystallinity along the chain alignment direction often leads to increased thermal conductivity, which can diminish thermoelectric efficiency as dictated by the Wiedemann-Franz law¹⁵. Given these challenges, exploring alternative yet simple methods to create systems with superior crystallinity for polymer thermoelectrics is of significant interest.

Nucleating agents are widely employed in traditional polymer industry to control crystallization kinetics and optimize the solid-state microstructures of bulk polymers¹⁶. These agents, including macromolecular additives like carbon nanotubes¹⁷, graphene¹⁸, and thiophene-containing copolymers¹⁹, have been effectively used to modify crystallization processes and improve the morphology of thin films, thereby enhancing targeted properties. More recently, supramolecular nucleating agents²⁰ have emerged as transformative additives, capable of dissolving uniformly in polymer melts at high temperatures and self-assembling into structured nanoarchitectures upon cooling. These agents can significantly enhance carrier mobilities in semicrystalline polymers like P3DDT²¹ and P3HT²² by up to 40-fold. Integrating such additives into doped semicrystalline polymers could be a promising approach to enhance their thermoelectric properties. However, several challenges remain, particularly whether the addition of nucleating agents will improve crystallinity and if the enhanced crystallinity introduced by the nucleating agent can be preserved during doping without compromising doping efficiency. To advance high-performance thermoelectric polymers using this strategy, it is essential to gain a comprehensive understanding of the interaction between nucleating agents and chemical doping, particularly its impact on microstructural evolution and charge transport within the nucleating agent-integrated polymer system.

In the present study, we focus on Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), a thiophene-based semiconducting polymer renowned for its ordered microstructures and high charge carrier mobility²³, as a foundational model system. We simply blend PBTTT-C14 with the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA), targeting enhanced charge transport and thermoelectric properties. PBTTT's resilience to sequential doping allows it to maintain a high degree of structural order at high doping levels²⁴, making it an ideal platform to explore the intricate interplay between structural morphology, charge transport, and thermoelectric performance. Our findings reveal that PDA markedly optimizes the crystallization behavior of PBTTT-C14, as substantiated by techniques like differential scanning calorimetry (DSC), atomic force microscopy (AFM) and grazing incidence wide-angle X-ray scattering (GIWAXS). The subsequent doping via the ion exchange (IEx) method amplifies these traits, leading to notable advancements in the electrical conductivity and thermoelectric properties.

Notably, incorporating just 0.9 wt% PDA into PBTTT-C14 films minimizes structural disorder, demonstrating remarkable resilience to IEx doping, and achieving a high electrical conductivity of 1800 S cm^− 1 alongside a maximum power factor approximating 150 µW m^− 1 K^− 2, surpassing that of doped, pristine PBTTT-C14 films (σ_max ~ 878 S cm^− 1 and PF_max ~ 31 µW m^− 1 K^− 2). We provide a comprehensive analysis of the mechanisms underlying this significant enhancement in charge transport and thermoelectric performance, drawing upon optical spectroscopy, thermal analysis, microstructural characterization, and transport measurements. This study highlights the strategic integration of nucleating agents as a simple approach to advance thermoelectric polymers, potentially revolutionizing the field of polymer-based thermoelectric materials for advanced scientific applications.

2.1. Incorporating A Nucleating Agent to Achieve Enhanced Crystallinity in Pristine PBTTT-C14 Films

As highlighted earlier, the key objective of this study is to systematically regulate the crystallinity of a model semicrystalline polymer, specifically PBTTT-C14, to elucidate the complex relationship between microstructure, morphology, charge carrier transport, and thermoelectric performance, particularly under chemical doping conditions. Prior to the sequential IEx doping process, we firstly fine-tune the crystallinity of pristine polymer films, which are spin-coated from blending solutions with varying concentrations of the nucleating agent (Fig. 1a; and see Experimental Section for details). We selected PDA, a supramolecular nucleating agent known for its remarkable ability to enhance the crystallinity of chemically similar polymer, such as Poly(3-hexylthiophene) (P3HT), with just 0.1 wt% loading²⁰. Impressively, PDA significantly improves the crystallinity and crystalline domain size of PBTTT-C14, as corroborated by DSC, GIWAXS, and AFM. The results of these characterizations are discussed in detail below.

We conducted a series of DSC experiments on PBTTT-C14/PDA blended samples, varying additive concentrations ranging from 0 wt% to 3.4 wt%, to probe the impact of nucleating agents on the crystallization kinetics of the polymer. All samples exhibit two primary thermal transitions (Fig. 1b): a low-temperature transition (Transition I) occurring below 100 ℃, and a high-temperature transition (Transition II) centered around 220 ℃, which is characteristic of PBTTT's thermal behavior²⁵. The effect of nucleating agents on Transition I is less pronounced, as indicated by the cooling curves in Fig. 1b. Notably, the calorimetric peak corresponding to Transition II exhibits distinct variations with increasing PDA concentrations. Therefore, our further investigations focus on film samples annealed above the T_c of Transition II, specifically the ribbon phase regime.

The addition of PDA progressively raises the crystallization temperature (T_c) of PBTTT-C14, reaching 226.33 ℃ at a 0.9 wt% concentration, an increase of 3.04 ℃. Beyond this concentration, higher PDA loadings resulted in a decline in T_c. This initial shift in T_c to higher temperatures at low additive loadings, up to 0.9 wt%, suggests heterogeneous nucleation, which enhances the polymer's crystallization capacity²⁰. The substantial improvement in crystallinity for these blended samples is directly evidenced by the increase in the enthalpy of crystallization (ΔH), a parameter proportional to the degree of crystallinity²⁶. Specifically, the sample with 0.9 wt% PDA exhibited a ΔH peak of 16.69 J/g at transition II (Fig. 1c), representing a 45% increase compared to pristine PBTTT films. However, at higher PDA concentrations, the degree of crystallinity declined, as evident by notable reductions in both T_c and ΔH. This reduction in crystallinity can be attributed to the overloading of the nucleating agent. Overuse of nucleating agents might lead to an excessively high nucleation rate, resulting in the formation of numerous small and imperfect crystalline grains. This high nucleation rate impedes further crystal growth, ultimately leading to a decrease in overall crystallinity²⁷.

GIWAXS analysis was employed to investigate the evolution of crystalline order in pristine PBTTT-C14 and PBTTT-C14/PDA blended films across various nucleating agent concentrations. Both pristine and blended films exhibit high crystallinity, characterized by four orders of (h00) diffraction peaks along the q_z axis, representing the lamellar stacking direction, and two additional peaks at 1.45 Å⁻¹ and 1.71 Å⁻¹ on the q_xy axis, corresponding to the polymer backbone and π-stacking orientation, respectively (Fig. 1d-f; and Figure S1 in the Supporting Information). Overall, the 2D GIWAXS scattering patterns reveal a remarkable similarity between the samples, with enhanced diffraction intensities along the in-plane q_xy directions for the film containing 0.9 wt% of the nucleating agent. To further explore the molecular stacking behavior upon the incoporation of the nucleating agent, we analyzed the 1D line-cut scattering profiles (Figure S1) and extracted crystallographic parameters, summarized in Table S1. For the film with 0.9 wt% PDA, no notable changes in paracrystallinity (g_π−π) and higher coherence length (L_c) were observed. These observations suggest that while there is a significant enhancement in crystallinity, the molecular stacking behavior of PBTTT-C14 is largely preserved up to an optimal concentration of PDA.

The morphological changes in the polymer films due to the addition of PDA were examined using AFM. The height image in Fig. 1g shows that the pristine PBTTT-C14 thin film, annealed at 260 ℃, exhibits uniform ribbons-like structures with an average width of 53.18 nm, a characteristic feature of films annealed from a smectic, liquid crystalline phase (Transition II)²⁸. These ribbons consist of crystalline domains that maintain a smectic chain arrangement, typically comprising multiple chain-extended or chain-folded polymer chains, depending on the degree of chain alignment in the solid state²⁹. Upon the initial incorporation of PDA, the ribbon structure was preserved, with the ribbon width increasing by 62%, from 53 nm in the pristine film to 86 nm at 0.9 wt% nucleating agent, indicating a tendency for aggregation. However, at a higher PDA concentration of 3.4 wt%, the ribbon width decreased to 42 nm. This transformation is accompanied by the gradual blurring of the nanofibrillar structure, suggesting a loss of long-range fiber periodicity (Fig. 1i; and Figure S3 in the Supporting Information). These observations imply that the addition of PDA at low concentrations (up to 0.9 wt%) enhances the degree of crystallinity and promotes the growth of individual ribbons, which is crucial for improving both structural order and charge transport. The observation of enlarged crystalline domains (ribbons) coupled with narrower grain boundaries at an optimal PDA loading suggests that the PBTTT-C14/PDA blended system may serve as a viable platform for subsequent doping and thermoelectric property investigations. Such a highly ordered microstructural morphology is anticipated to facilitate both efficient intradomain and interdomain charge transport.

2.2. Preserving Superior Structural Order in PBTTT-C14/PDA Blended Films upon Ion Exchange Doping

Chemical doping plays a pivotal role in modulating the electronic and thermoelectric properties of polymer semiconductors, effectively adjusting the energy level and optimizing the charge concentration n.¹¹ However, achieving optimal thermoelectric conversion in a polymer system often necessitates a charge concentration n surpassing 10¹⁹ cm^− 3, which may significantly disturb the molecular packing within the neat polymer matrix, potentially compromising the high carrier mobility µ derived from its high crystalline order³⁰. To harness the enhanced crystallinity of PBTTT-C14 films induced by the nucleating agent for enhancing thermoelectric performance, we adopted a newly developed IEx doping method. This doping technique has exhibited remarkable efficacy in achieving doping concentrations exceeding 10²⁰ cm^− 3, while imparting minimal or even positive effects on the microstructure and morphology of the polymer films. This preservation of superior structural order is critical for maintaining efficient charge transport. The successful achievement of efficient doping and preservation of superior structural order in PBTTT-C14/PDA blended films was confirmed through spectroscopic, GIWAXS, and AFM characterizations (Fig. 2 and Figure S2, S4 in the Supporting Information).

The extent of doping in all polymer films, with varying PDA concentrations, both before and after IEx doping, was evaluated using Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) spectroscopy. For all the blended films studied, the neutral π-π^* band centered around 550 nm exhibited nearly complete bleaching (Fig. 2a; and Figure S5 in the Supporting Information), a trend consistent with the pristine PBTTT film (Figure S5). Simultaneously, two broad absorption bands, labelled P1 and P2, appeared at wavelengths > 2000 nm and around 800 nm, respectively. These absorption bands are indicative of polaron or multi-polaron states, as commonly observed in highly doped PBTTT films^24,31. These UV-Vis-NIR absorption profiles suggest the blended films obtained at high doping levels comparable to those of pristine PBTTT-C14, with a doping concentration around 10²¹ cm^− 3, corresponding to roughly one charge per monomer unit. This high carrier density, confirmed for both pristine and blended systems, is further validated by Hall effect analysis presented in Section 4 of the Supporting Information.

Fourier Transform Infrared Spectroscopy (FT-IR) was employed to investigate the degree of polaron delocalization in doped films (Fig. 2b). Polaron delocalization can be effectively assessed by examining polaron-induced absorption features in the mid-infrared (mid-IR) region^32,33. Upon doping, the P1 band peaks around 1800 cm^− 1 with a weak shoulder below 1500 cm^− 1, corresponding to intrachain and interchain transitions, respectively³². Additionally, a number of narrow peaks are superimposed between 400 cm^− 1 and 1475 cm^− 1, which are typically interpreted as infrared active vibrational modes (IRAVs). The intensity of the IRAVs is an indicator of the extent of polaron delocalization along the polymer chains and between chains. The more intense the IRAVs, the greater the degree of polaron delocalization³⁴. In the FT-IR spectra of the doped blended films, the pronounced IRAV peaks suggest that a high level of polaron delocalization was achieved via ion exchange doping, similar to that observed in pristine PBTTT-C14 films^35,36.

GIWAXS characterization was employed to examine the microstructural changes in both pristine PBTTT-C14 and PBTTT-C14/PDA blended films after IEx doping. As depicted in the 2D diffraction patterns in Fig. 2d-f, all doped films retain their lamellar packing, featuring an edge-on orientation of the polymer backbone and considerable long-range crystallinity. Both the well-ordered out-of-plane peaks (h00) and in-plane stacking peaks remain clearly visible, resembling their undoped counterparts. Upon IEx doping, the lamellar spacing notably expands for both the pristine and blended films, for instance, from 20.937 Å to 26.449 Å for the 0.9 wt% blended sample. This expansion suggests that the counterions predominantly integrate into the alkyl side-chain regions, consistent with previous findings on semicrystalline polythiophenes^36–38. Interestingly, a reduction in the π-π stacking distance is observed across all samples: in the pristine film, this distance decreases from 3.601 Å to 3.526 Å (Fig. 2d; and Table S2 in the Supporting Information), while in the 0.9 wt% and 3.4 wt% blended films, it reduces from 3.646 Å to 3.516 Å and from 3.654 Å to 3.524 Å, respectively (Fig. 2e-f; and Table S2 in the Supporting Information). This reduction can be attributed to the strengthening of polaronic coupling between chains, facilitated by the IEx doping process³⁶. Furthermore, all three films display a ~ 10% decrease in paracrystallinity parameter (g_π−π) compared to their undoped states, suggesting that ion exchange doping effectively enhances structural order without causing discernible disruption, even in the presence of nucleating agent additives (Table S2 in the Supporting Information). The high electrical conductivities of both the pristine and blended systems, with σ_max ranging from 878 to 1800 S cm^− 1, are strongly correlated with reduced paracrystalline disorder, in line with previous findings in high-mobility semicrystalline polymers and donor-acceptor copolymers³⁶.

It is important to note the differences in charge transport and thermoelectric properties between the pristine and blended systems. In particular, the doped 0.9 wt% blended system achieves a conductivity of approximately 1800 S cm^− 1 and an exceptional thermoelectric power factor of about 150 µW m^− 1 K^− 2 (as disscussed in Section 2.3 and 2.4). These remarable enhancements cannot be solely attributed to molecular packing, as there are no significant differences in paracrystallinity and coherence length between doped pristine PBTTT film and 0.9 wt% blended film (Table S2 in Supporting Information). Instead, the enhanced thermoelectric performance in the blended systems can be primarily linked to a notable increase in crystallinity, as demonstrated through detailed microstructural and morphological analyses of the undoped counterparts.

In conclusion, the GIWAXS analysis reveals that the counterions primarily occupy the side-chain regions, while IEx doping enhances backbone planarization, promoting efficient charge transport in all doped films—especially in the 0.9 wt% PBTTT-C14/PDA blended system. Overall, the introduction of the nucleating agent into PBTTT-C14 does not significantly interfere with the IEx doping process, enabling highly effective doping while maintaining or even improving the superior crystalline order.

2.3. Thermoelectric Properties of Ion Exchange Doped PBTTT-C14/PDA Blended Films

We now turn our attention to the thermoelectric performance of the ion exchange (IEx) doped PBTTT-C14/PDA blended films. As shown in Figs. 3a and 3b, the electrical conductivity (σ) and Seebeck coefficient (S) of these doped polymers exhibit distinct trends as a function of PDA concentration, ranging from 0 wt% to 3.4 wt%.

Specifically, Fig. 3a shows a significant increase in electrical conductivity, reaching a peak value of 1178 S cm^− 1 at 0.9 wt% PDA loading with a doping concentration of 3 mM. This represents an 85% enhancement compared to the conductivity of the doped pristine PBTTT-C14 film under the same doping conditions. This improvement is consistent with the crystallinity evolution with PDA concentration, as discussed in Section 2.1. Notably, the Seebeck coefficient follows a similar trend, decoupling from the electrical conductivity. The doped 0.9 wt% blended film exhibits a maximum Seebeck coefficient of approximately 36 µV K^− 1, which is 148% higher than that of the doped pristine film. As a result, the power factor (PF) of the doped 0.9 wt% blended film attains an impressive 150 µW m^− 1 K^− 2, representing a remarkable 1011% improvement over the pristine film at an equivalent doping concentration, as shown in Fig. 3c.

The inset of Fig. 3c further emphasizes the competitive advantage of our IEx doped 0.9 wt% blended system when compared to other unaligned benchmark systems, achieved through morphology control³⁹, doping engineering^40,41. Remarkably, this optimal performance is on par with a recently developed highly oriented PBTTT system⁴², which, despite requiring complex processing techniques—such as controlled tie chain incorporation through polymer blending coupled with large-scale alignment—results in notable charge transport anisotropy. The simultaneous increase in both σ and S, leading to a substantial enhancement in the PF with the appropriate PDA additive loading, is unprecedented. The detailed mechanisms underlying this phenomenon are elaborated in Section 2.4.

To further fine-tune the thermoelectric performance of the 0.9 wt% blended system, we optimized the S and σ as a function of doping concentration. For comparison, the same experiment was performed on a pristine PBTTT-C14 system to better understand the impact of PDA additives on thermoelectric properties. As shown in Fig. 3d, the electrical conductivity initially increases with rising doping concentration, peaking at approximately 7 mM for the doped 0.9 wt% blended system. At this concentration, the blended film achieves an electrical conductivity of 1800 S cm^− 1, more than double the maximum conductivity of 878 S cm^− 1 observed in the doped pristine system at a doping concentration of 12.5 mM. In terms of the Seebeck coefficient, both the blended and pristine systems exhibit a comparable downward trend with increasing doping concentration. Consequently, the calculated power factors are presented in Fig. 3f. Notably, the ion exchange doped PBTTT-C14/PDA blended films reach a significantly higher maximum power factor of 150 µW m^− 1 K^− 2, far surpassing the 31 µW m^− 1 K^− 2 achieved by the doped pristine counterpart.

These findings underscore the promising potential of nucleating agent additive engineering in significantly enhancing the thermoelectric performance of high-performance semicrystalline conjugated polymers. A comparative analysis of the thermoelectric properties between blended and pristine systems reveals that the remarkable PF achieved by the IEx doped PBTTT-C14/PDA blend (0.9 wt%) is primarily driven by its exceptional charge transport properties. To further investigate, we explored the charge transport physics to uncover the fundamental mechanisms by which the nucleating agent facilitates improved charge transport in the doped PBTTT systems.

2.4. Mechanisms Underlying the Remarkable Enhancement in Charge Transport and Thermoelectric Performance of IEx Doped PBTTT-C14/PDA Blended Films

Charge transport measurements are essential for characterizing transport parameters in semiconducting materials, allowing for the correlation between microscopic spatial and energetic distributions through microstructural characterization and charge transport models⁴³. For doped polymer semiconductors, temperature-dependent measurements of electrical conductivity, the Seebeck coefficient, and the Hall coefficient provide insight into the dominant transport mechanisms—whether they involve localization (hopping-like) or delocalization (metal-like)—that govern electronic transport^44–46. In this study, we applied this experimental framework to investigate how the incorporation of a nucleating agent additive affects charge transport physics and the microstructural characteristics of PBTTT-C14 films subjected to sequential ion exchange doping.

Figure 4a depicts the temperature (T) dependence of electrical conductivity for both pristine and blended films doped at a concentration of 5 mM, highlighting the significant effect of PDA concentration. Across all systems the temperature dependence of conductivity reflects that of high conductivity PBTTT, characterized by a plateau or slight decrease above 250 K, particularly prominent in the 0.9 wt% blended system. The appearance of a conductivity peak suggests a shift toward metallic conduction rather than thermally activated hopping conduction, especially at grain boundaries⁴². To quantify the thermal activation energy (E_a) governing each sample's conductivity, we applied the Arrhenius equation (see Supporting Information Section 5). The E_a, which reflects energetic disorder within integer charge transfer complex (ICTC) states⁴⁷, decreases from 3.25 meV in pristine PBTTT to 2.67 meV at 0.9 wt% PDA loading, where conductivity peaks (Fig. 4b, upper panel). This minimal E_a in the 0.9 wt% blended sample signifies the lowest energetic disorder, which can be attributed to optimal crystallinity and structural ordering (Sections 2.1 & 2.3). As a result, the 0.9 wt% blended film achieves a peak charge carrier mobility of 2.92 cm² V^− 1 s^− 1, confirmed by Hall effect measurements (Fig. 4e).

Additionally, by fitting the Seebeck coefficient-conductivity (S-σ) data using the Kang-Snyder model⁴⁸ (see the Supporting Information Section 6 for more details), we derived the energy barrier for charge percolation between ordered domains, denoted as W_γ. Unlike E_a, which provides insights into the overall transport mechanism encompassing both intra- and inter-domain transport, W_γ specifically offers insights into inter-domain transport, providing a macroscopic perspective on conductivity across crystalline regions^48,49. W_γ follows a trend similar to E_a (Fig. 4b, bottom panel), reaching its minimum at intermediate PDA concentrations before slightly increasing at higher concentrations, likely due to decreased overall crystallinity from excessive PDA loadings, as observed in DSC, GIWAXS, and AFM data discussed earlier. Notably, the decreasing ratio of W_γ to E_a with increasing PDA concentration (Fig. 4c) suggests that inter-domain energetic disorder plays a diminished role in limiting conductivity and carrier mobility.

To further investigate the synergistic impact of nucleating agent additive engineering and IEx doping on the charge transport properties of PBTTT-C14, we conducted comparative analyses of the S-σ relationship (Fig. 4d) across varying doping concentrations for both pristine and 0.9 wt% blended systems. By applying the Kang-Snyder model to the S-σ relationship, we observe that a single parameter set (s and σ_E0) inadequately describes the entire conductivity range (See the Supporting Information Section 6 for more details). Notably, both systems exhibit a distinct change in charge transport characteristics around 200 S cm^− 1, transitioning from s = 3 to s = 1 with increasing conductivity. This transition is generally indicative of an insulator-to-metal transition occurring in semicrystalline polymer systems, particularly when carrier densities exceed 10²¹ cm^{− 3 40,50}.

In both the 's = 3' and 's = 1' regimes, the 0.9 wt% blended system demonstrates notably higher σ_E0 values, specifically 0.03 S cm^− 1 and 120 S cm^− 1, respectively, which are approximately more than 2 times greater than those of the pristine system. Since σ_E0 acts as a weighted mobility factor tied to intrinsic carrier mobility^49,51, this observation highlight the enhanced charge transport capability of the doped 0.9 wt% blended system. This superiority is further evidenced by the consistently higher Hall mobility measurements across the entire conductivity spectrum (Fig. 4e). Consequently, the 0.9 wt% blended system exhibits significantly improved electrical conductivity for a given Seebeck coefficient, resulting in a substantially higher PF.

A comprehensive correlation analysis between transport measurements and microstructural characterization data allowed us to formulate a physical model (Fig. 4f) that elucidates the mechanism behind the enhanced charge transport properties induced by the nucleating agent additive. Upon incorporating an optimal concentration (0.9 wt%) of PDA, PBTTT-C14 films experience a significant increase in crystallinity, as demonstrated by DSC analysis. This increase is accompanied by improved structural order at the grain boundaries without disrupting the crystalline lattices within the domains. The polymer chain extension, supported by AFM and GIWAXS characterizations, contributes to this enhanced structural order. Such improvements are preserved, and in some cases intensified, across a broad range of carrier concentrations through ion exchange doping (Section 2.2).

Recent experimental and theoretical investigations have underscored structural disorder, rather than Coulombic trapping, as the primary determinant limiting charge transport in doped polymers, especially at high doping levels^24,52. This explains the superior carrier mobility of the doped 0.9 wt% blended system, which achieves substantially higher electrical conductivities compared to the unblended system when sufficient charge densities are introduced. Specifically, the chain extension reduces grain boundary sizes and promotes the formation of tie chains that bridge adjacent crystalline domains by clustering together. This enables charge carriers to traverse domains without relying on interchain hopping through disordered regions. This dual effect—grain boundary size reduction and tie chain formation—significantly alleviates energetic disorder at grain boundaries, as evidenced by the substantial decreases in the activation energies E_a and the transport energy barriers W_γ. The macroscopic resistance of the 0.9 wt% system is therefore reduced, with grain boundary resistance often being a major limiting factor for conductivity in many polymer semiconductors^42,53. Additionally, the enhanced crystalline order within domains after IEx doping, indicated by reduced g_π−π values, fosters intradomain charge transport, promoting two-dimensional charge carrier delocalization. This further reduces the overall energetic disorder and lowers E_a.

This synergistic improvement in both intra- and inter-domain charge transport, stemming from nucleating agent additive engineering and ion-exchange doping, results in a record-high electrical conductivity of approximately 1800 S cm^− 1 and an outstanding thermoelectric performance, with a PF of 150 µW m^− 1 K^− 2 for PBTTT-C14 films.

In summary, we propose a straightforward yet highly effective conceptual approach that utilizes nucleating agents to precisely control the crystallization behavior of semicrystalline polymer semiconductors, thus thermoelectric performance. This method presents a clear pathway to enhance charge transport and achieve outstanding thermoelectric performance by increasing the degree of crystallinity without compromising the molecular packing order, while also improving electrical connectivity within doped polymer films. Through meticulous assessment of microstructural evolution driven by nucleating agents and IEx doping, we identified 0.9 wt% as the optimal PDA loading for achieving superior structural ordering. Remarkably, this ordering remains robust, even slightly improving after doping. As a result, structural disorder is minimized, and charge carrier mobility is maximized in highly doped PBTTT-C14 films, leading to exceptional transport properties, including a Hall mobility of up to 2.92 cm² V^− 1 s^− 1, electrical conductivity reaching 1800 S cm^− 1, and a power factor close to 150 µW m^− 1 K^− 2. Our approach breaks through the conventional barriers limiting the thermoelectric performance of polymer semiconductors by significantly boosting conductivity without reducing the Seebeck coefficient. This enhancement is primarily due to the reduction in grain boundary size facilitated by nucleating agent engineering, coupled with a modest increase in crystalline order within domains, further amplified by IEx doping. Importantly, this methodology holds broad applicability across various semicrystalline polymers, potentially driving significant advances in fast charge transport in highly doped conjugated polymers, ultimately contributing to the development of high-performance thermoelectric materials for next-generation organic electronics.

Sample Preparation:

Materials

Poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) was purchased from Sigma-Aldrich. N,N'-(1,4-phenylene)diisonicotinamide (PDA, > 97% purity), acetonitrile (ACN, > 99.9% purity, water content < 30 ppm), and 1,2-dichlorobenzene (DCB, > 98% purity, water content < 50 ppm) were sourced from Adamas. Iron(III) chloride (FeCl₃, > 99.99% purity) and 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide (BMP-TFSI, > 99% purity, water content < 0.04%) were obtained from Aladdin. All reagents were used as received, without further purification.

Blend solution preparation

PBTTT-C14 was dissolved in DCB at a concentration of 10 g/L, with heating to 110°C and stirring for 2 hours, followed by filtration through a 0.22 µm PTFE membrane. PDA was dispersed in DCB at 1 g/L with 2 hours of stirring. Defined volumes of PBTTT-C14 and PDA solutions were mixed, and the mixture was heated and stirred at 110°C for an additional hour.

Dopant solution preparation

BMP-TFSI solutions were prepared in ACN at concentrations of 250, 500, 750, 1000, and 1500 mM, and FeCl₃ solutions were prepared in ACN at concentrations of 2.5, 5, 7.5, 10, and 15 mM. Dopant mixtures were obtained by combining appropriate volumes of BMP-TFSI and FeCl₃ solutions (e.g., 250 mM BMP-TFSI solution with 2.5 mM FeCl₃ solution can be configured to produce a 0.25 mM mixed dopant solution). The mixed dopant solution concentration was set to 0.25, 0.5, 0.75, 1, 3, 5, 7, 10, 12.5 mM. The FeCl₃ solutions were freshly prepared before use. All solutions were prepared in an argon-filled glove box (< 1 ppm H₂O and O₂).

Thin film preparation: The solutions were spin-coated onto preheated substrates at 1500 rpm for 60 seconds using preheated pipettes. Following deposition, films were annealed at 260°C for 20 minutes and cooled at a controlled rate of 2°C/min to room temperature to promote the formation of a ribbon phase. For doping, 150 µL cm^− 2 of dopant solution was applied to the films, left for 60 seconds, and then the excess solution was removed by spin-coating at 7000 rpm for 60 seconds. Afterward, the films were rinsed with acetonitrile to eliminate residual dopants. For electrical measurements, a protective layer of Cytop was spin-coated onto the films using a diluted Cytop solution (Cytop:solvent = 1:2) at 2000 rpm for 60 seconds. All procedures were carried out in an argon-filled glove box.

Sample Preparation for Characterization:

Electrical and seebeck measurements

Samples were fabricated on 13 mm × 6 mm glass substrates with 10 nm-thick gold electrodes (1.5 mm wide).

Hall effect measurements

Samples were prepared on 10 mm × 10 mm glass substrates with 2 mm × 2 mm gold electrodes deposited at the corners.

GIWAXS samples

Prepared on 10 mm × 10 mm silicon substrates.

UV-Vis and FTIR samples

Prepared on glass substrates of comparable dimensions.

Characterization Methods:

Differential scanning calorimentry (DSC)

PBTTT-C14/PDA samples were analyzed using a TA Discovery25 under nitrogen. Samples were annealed at 280°C for 5 minutes and cooled at 10°C/min to -80°C.

Conductivity and Seebeck Coefficient Measurements

Conductivity and Seebeck coefficient were measured using a ULVAC-RIKO ZEM-3 system under helium. Film thickness was determined by AFM (Bruker Dimension Icon), and conductivity was measured via the four-probe method. Seebeck coefficients were obtained through the linear fitting of ΔV vs. ΔT.

Ultraviolet-Visible-Near Infrared Spectroscopy (UV-Vis-NIR)

Spectra were recorded using a Lambda365 instrument over a range of 250–2500 nm with 2 nm intervals. Substrate background spectra were collected separately as the baseline.

Fourier-transform infrared spectroscopy (FTIR): FTIR spectra were obtained on a Bruker Vertex 70 spectrometer over the 400–4000 cm^− 1 range, with a 4 cm^− 1 interval. Atomic force microscopy (AFM): Tapping-mode AFM was conducted on a Bruker Dimension Icon system to characterize the surface morphology. The ribbon width was determined by averaging measurements from at least thirty randomly selected ribbons.

Grazing incidence wide angle X-ray scattering (GIWAXS)

Measurements were performed using the Xenocs Xeuss 3.0 system with an 8.04 keV X-ray source and an EIGER2 detector positioned 80 mm from the sample. Data were recorded with a 0.18° incident angle and analyzed using GIWAXS-Tools software. Coherence length and paracrystallinity were calculated using convolution Gaussian and Lorentzian fittings⁵⁴ (see Section 1 in the Supporting Information for more details).

Hall effect Measurement

Hall measurements were performed on an ET9000 Hall instrument modified with the reverse field reciprocity theorem^55–57. The setup included Keithley 6220, 2182A, and 6485 instruments, achieving 10 fA current and 1 nV voltage resolutions. Measurements were conducted with a 1000 nA current and a magnetic field of 18 kG. Film thicknesses were measured by AFM.

ACKNOWLEDGMENT

We acknowledge support from the National Natural Science Foundation of China (52273029, 52203022), Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China (2021ZZ119), the Pilot Project of Fujian Province (2022H0037), Fuzhou Technology Innovation Platform (2022-P-020), Natural Science Foundation of Fujian Province for Distinguished Young Scholars (2023J06045), and Fujian– CAS joint STS Project (2023T3064). C.C. acknowledges support from the Hunan Provincial Natural Science Foundation of China (2022JJ40547), and the University of Defense Technology Research Project (ZK22-15).

Russ B, Glaudell A, Urban JJ, Chabinyc ML, Segalman RA (2016) Organic thermoelectric materials for energy harvesting and temperature control. Nat Rev Mater 1
Wang SH, Zuo GZ, Kim J, Sirringhaus H (2022) Progress of Conjugated Polymers as Emerging Thermoelectric Materials. Prog Polym Sci 129:101548. 10.1016/j.progpolymsci.2022.101548
Tang JH, Pai YH, Liang ZQ (2022) Strategic Insights into Semiconducting Polymer Thermoelectrics by Leveraging Molecular Structures and Chemical Doping. Acs Energy Lett 7:4299–4324. 10.1021/acsenergylett.2c02119
Vijayakumar V et al (2019) Bringing Conducting Polymers to High Order: Toward Conductivities beyond 10⁵ S cm^-1 and Thermoelectric Power Factors of 2 mW m^-1 K^-2. Adv Energy Mater 9:201900266. 10.1002/aenm.201900266
Liu DR et al (2023) Lattice plainification advances highly effective SnSe crystalline thermoelectrics. Science 380:841–846. 10.1126/science.adg7196
Wang DY et al (2024) Multi-heterojunctioned plastics with high thermoelectric figure of merit. Nature 632:528. 10.1038/s41586-024-07724-2
Petsagkourakis I et al (2018) Correlating the Seebeck coefficient of thermoelectric polymer thin films to their charge transport mechanism. Org Electron 52:335–341. 10.1016/j.orgel.2017.11.018
Sun PJ et al (2015) Large Seebeck effect by charge-mobility engineering. Nat Commun 6:7475. 10.1038/ncomms8475
Yao ZF, Wang JY, Pei J (2023) Controlling morphology and microstructure of conjugated polymers via solution-state aggregation. Prog Polym Sci 136:101626. 10.1016/j.progpolymsci.2022.101626
Zhang FJ, Di CA (2020) Exploring Thermoelectric Materials from High Mobility Organic Semiconductors. Chem Mater 32:2688–2702. 10.1021/acs.chemmater.0c00229
Peterson KA, Thomas EM, Chabinyc ML (2020) 50 Thermoelectric Properties of Semiconducting Polymers. Annual Review of Materials Research, Vol 50, 551–574, 10.1146/annurev-matsci-082219-024716 (2020)
Guchait S, Zhong Y, Brinkmann M (2023) High-Temperature Rubbing: An Effective Method to Fabricate Large-Scale Aligned Semiconducting and Conducting Polymer Films for Applications in Organic Electronics. Macromolecules 56:6733–6757. 10.1021/acs.macromol.3c01073
Deng L, Chen GM (2021) Recent progress in tuning polymer oriented microstructures for enhanced thermoelectric performance. Nano Energy 80:105448. 10.1016/j.nanoen.2020.105448
Durand P et al (2022) Single Ether-Based Side Chains in Conjugated Polymers: Toward Power Factors of 2.9 mW m^-1 K^-2. Adv Energy Mater 12:2103049. 10.1002/aenm.202103049
Shi W, Shuai Z, Wang D (2017) Tuning Thermal Transport in Chain-Oriented Conducting Polymers for Enhanced Thermoelectric Efficiency: A Computational Study. Adv Funct Mater 27:1702847. 10.1002/adfm.201702847
Seven KM, Cogen JM, Gilchrist JF (2016) Nucleating Agents for High-Density Polyethylene-A Review. Polym Eng Sci 56:541–554. 10.1002/pen.24278
Kim SH, Jeong S, Kim D, Son CY, Cho K (2023) Effects of Connecting Polymer Structure and Morphology at Inter-Tube Junctions on the Thermoelectric Properties of Conjugated Polymer/Carbon Nanotube Composites. Adv Electron Mater 9:202201293. 10.1002/aelm.202201293
Acevedo-Cartagena DE et al (2015) Selective Nucleation of Poly(3-hexyl thiophene) Nanofibers on Multilayer Graphene Substrates. Acs Macro Lett 4:483–487. 10.1021/acsmacrolett.5b00038
Deribew D et al (2013) Crystallization-Driven Enhancement in Photovoltaic Performance through Block Copolymer Incorporation into P3HT:PCBM Blends. Macromolecules 46:3015–3024. 10.1021/ma302128h
Wenzel FA et al (2022) Highly Efficient Supramolecular Nucleating Agents for Poly(3-hexylthiophene). Macromolecules 55:2861–2871. 10.1021/acs.macromol.1c02283
Treat ND et al (2013) Microstructure formation in molecular and polymer semiconductors assisted by nucleation agents. Nat Mater 12:628–633. 10.1038/Nmat3655
Yuan N, Huo H (2016) 2,3,4-bis(p-methylbenzylidene sorbitol) accelerates crystallization and improves hole mobility of poly(3-hexylthiophene). Nanatechnol 27 1:06LT01. 10.1088/0957-4484/27/6/06LT01
Kang K et al (2019) Investigation of the thermoelectric response in conducting polymers doped by solid-state diffusion. Mater Today Phys 8:112–122. https://doi.org/10.1016/j.mtphys.2019.02.004
Chen C et al (2023) Observation of Weak Counterion Size Dependence of Thermoelectric Transport in Ion Exchange Doped Conducting Polymers Across a Wide Range of Conductivities. Adv Energy Mater 13:202202797. 10.1002/aenm.202202797
Pirela V, Müller AJ, Martín J (2024) Crystallization kinetics of semiconducting poly(2,5-bis(3-alkylthiophen-2-yl)-thieno-[3,2-b]thiophene) (PBTTT) from its different liquid phases. J Mater Chem C 12:4005–4012. 10.1039/D3TC03850E
Snyder CR et al (2014) Quantifying Crystallinity in High Molar Mass Poly(3-hexylthiophene). Macromolecules 47:3942–3950. 10.1021/ma500136d
Schultz JM, Polymer Crystallization (2002) The Development of Crystalline Order in Thermoplastic Polymers. J Am Chem Soc 124:7251–7252. 10.1021/ja015359h
DeLongchamp DM et al (2009) Controlling the Orientation of Terraced Nanoscale Ribbons of a Poly(thiophene) Semiconductor. ACS Nano 3:780–787
Greco C, Melnyk A, Kremer K, Andrienko D, Daoulas KC (2019) Generic Model for Lamellar Self-Assembly in Conjugated Polymers: Linking Mesoscopic Morphology and Charge Transport in P3HT. Macromolecules 52:968–981. 10.1021/acs.macromol.8b01863
Zhao WR, Ding JM, Zou Y, Di CA, Zhu DB (2020) Chemical doping of organic semiconductors for thermoelectric applications. Chem Soc Rev 49:7210–7228. 10.1039/d0cs00204f
Balooch Qarai M, Ghosh R, Hestand NJ, Spano FC (2023) Multipolaron Complexes in Conducting Polymers: The Importance of Hole-Hole Repulsion in Charge Delocalization. J Phys Chem C 127:6414–6424. 10.1021/acs.jpcc.3c00289
Ghosh R, Spano FC (2020) Excitons and Polarons in Organic Materials. Acc Chem Res 53:2201–2211. 10.1021/acs.accounts.0c00349
Moulé AJ et al (2022) Quantifying Polaron Mole Fractions and Interpreting Spectral Changes in Molecularly Doped Conjugated Polymers. Adv Electron Mater 8:202100888. 10.1002/aelm.202100888
Qarai MB, Ghosh R, Spano FC (2021) Understanding Bipolarons in Conjugated Polymers Using a Multiparticle Holstein Approach. J Phys Chem C 125:24487–24497. 10.1021/acs.jpcc.1c06767
Yamashita Y et al (2019) Efficient molecular doping of polymeric semiconductors driven by anion exchange. Nature 572:634–638. 10.1038/s41586-019-1504-9
Jacobs IE et al (2022) High-Efficiency Ion-Exchange Doping of Conducting Polymers. Adv Mater 34:202102988. 10.1002/adma.202102988
Ishii M, Yamashita Y, Watanabe S, Ariga K, Takeya J (2023) Doping of molecular semiconductors through proton-coupled electron transfer. Nature 622:285–291. 10.1038/s41586-023-06504-8
Wang S et al (2024) Enhancing the Thermoelectric Properties of Conjugated Polymers by Suppressing Dopant-Induced Disorder. Adv Mater 36:202314062. 10.1002/adma.202314062
Patel SN et al (2017) Morphology controls the thermoelectric power factor of a doped semiconducting polymer. Sci Adv 3:1700434. 10.1126/sciadv.1700434
Kim J, Ju D, Kim S, Cho K (2024) Disorder-Controlled Efficient Doping of Conjugated Polymers for High-Performance Organic Thermoelectrics. Adv Funct Mater 34:202309156. 10.1002/adfm.202309156
Patel SN, Glaudell AM, Kiefer D, Chabinyc ML (2016) Increasing the Thermoelectric Power Factor of a Semiconducting Polymer by Doping from the Vapor Phase. Acs Macro Lett 5:268–272
Zhu W et al (2024) Enhancing the Conductivity and Thermoelectric Performance of Semicrystalline Conducting Polymers Through Controlled Tie Chain Incorporation. Adv Mater 36:2310480. 10.1002/adma.202310480
Oberhofer H, Reuter K, Blumberger J (2017) Charge Transport in Molecular Materials: An Assessment of Computational Methods. Chem Rev 117:10319–10357. 10.1021/acs.chemrev.7b00086
Gregory SA et al (2021) Quantifying charge carrier localization in chemically doped semiconducting polymers. Nat Mater 20:1414–1421. 10.1038/s41563-021-01008-0
Gregory SA et al (2023) Quantifying Charge Carrier Localization in PBTTT Using Thermoelectric and Spectroscopic Techniques. J Phys Chem C 127:12206–12217. 10.1021/acs.jpcc.3c01152
Scheunemann D et al (2022) Charge transport in doped conjugated polymers for organic thermoelectrics. Chem Phys Reviews 3:021309. 10.1063/5.0080820
Schwarze M et al (2019) Molecular parameters responsible for thermally activated transport in doped organic semiconductors. Nat Mater 18:242–248. 10.1038/s41563-018-0277-0
Kang SD, Snyder GJ (2017) Charge-transport model for conducting polymers. Nat Mater 16:252–257
Lu K et al (2024) Molecular Doping-Driven Modulation of Domain Charge Transport Elevates Thermoelectric Performance in Polar Polythiophene. ACS Mater Lett 6:4351–4359. 10.1021/acsmaterialslett.4c01056
Tanaka H et al (2020) Thermoelectric properties of a semicrystalline polymer doped beyond the insulator-to-metal transition by electrolyte gating. Sci Adv 6:eaay8065. 10.1126/sciadv.aay8065
Lin Y et al (2020) Graphene/Strontium Titanate: Approaching Single Crystal-Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering. Adv Funct Mater 30:201910079. 10.1002/adfm.201910079
Jacobs IE et al (2022) Structural and Dynamic Disorder, Not Ionic Trapping, Controls Charge Transport in Highly Doped Conducting Polymers. J Am Chem Soc 144:3005–3019. 10.1021/jacs.1c10651
Noriega R et al (2013) A general relationship between disorder, aggregation and charge transport in conjugated polymers. Nat Mater 12:1038–1044. 10.1038/nmat3722
Rivnay J, Noriega R, Kline RJ, Salleo A, Toney MF (2011) Quantitative analysis of lattice disorder and crystallite size in organic semiconductor thin films. Phys Rev B 84:045203. 10.1103/PhysRevB.84.045203
Chen HY et al (2024) High-Entropy Cubic Pseudo-Ternary Ag₂(S, Se, Te) Materials With Excellent Ductility and Thermoelectric Performance. Adv Energy Mater 14:202303473. 10.1002/aenm.202303473
Deng SH et al (2024) High-Performance and Ecofriendly Organic Thermoelectrics Enabled by N-Type Polythiophene Derivatives with Doping-Induced Molecular Order. Adv Mater 36:202309679. 10.1002/adma.202309679
Ke ZF et al (2024) Controlled Dedoping and Redoping of N-Doped Poly(benzodifurandione) (n-PBDF). Adv Funct Mater 34:202400255. 10.1002/adfm.202400255

There is NO Competing Interest.

SI.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive

Status:

Version 1

Abstract

Figures

1. Introduction

2. Results and Discussion

2.1. Incorporating A Nucleating Agent to Achieve Enhanced Crystallinity in Pristine PBTTT-C14 Films

2.2. Preserving Superior Structural Order in PBTTT-C14/PDA Blended Films upon Ion Exchange Doping

2.3. Thermoelectric Properties of Ion Exchange Doped PBTTT-C14/PDA Blended Films

3. Conclusion

4. Experimental Section

Declarations

ACKNOWLEDGMENT

References

Additional Declarations

Supplementary Files

Status:

Version 1