Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Dopants”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Tuning Thermal Stability through Dopant Size in Chemically Doped DPP–Thiophene Polymers

Molecular doping of conjugated polymers (CPs) is a key strategy for improving the performance of organic electronics devices, particularly thermoelectrics. Doped donor–acceptor (D–A) conjugated polymers, characterized by a tunable energy gap between the Fermi level and the transport band, show great promise in achieving high electrical conductivity (σ) while preserving a favorable Seebeck coefficient (S). Despite the promising performance enhancement of chemically doped D–A polymers, their thermal stability remains largely underexplored, a crucial consideration for the long-term operation of organic thermoelectric devices. In this study, we investigated the dopant size-dependent thermal stability of a diketopyrrolopyrrole-thiophene (DPP-T) D–A copolymer, utilizing two p-dopants: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) and Mo(tfd-CO 2 Me) 3 . Temperature-dependent UV–vis–NIR spectroscopy revealed that DPP-T/F 4 TCNQ is more prone to dedoping under a high temperature thermal stress than DPP-T/Mo(tfd-CO 2 Me) 3 . Although the F 4 TCNQ doped polymer shows higher initial in-plane conductivity than its Mo(tfd-CO 2 Me) 3 counterpart, it undergoes a conductivity loss of more than an order of magnitude after annealing at 120 °C for 30 min. In contrast, the in-plane conductivity of DPP-T/Mo(tfd-CO 2 Me) 3 remains stable under the same thermal conditions. Thermogravimetric analysis ruled out dopant sublimation as a primary contributor to dedoping, leading us to attribute the conductivity loss in F 4 TCNQ-doped DPP-T to dopant phase separation and migration. This observation was further confirmed by X-ray scattering studies and nanoscale infrared microscopy and spectroscopy studies. This work could provide further insights into the thermal stability of doped conjugated polymers and suggests that incorporating bulkier dopants is an effective strategy to enhance the thermal robustness of doped DPP-type systems.

Conjugated polymers↗
DOE OSTI2023

Diffusion of Brønsted acidic dopants in conjugated polymers

Many semiconductor devices (e.g., light emitting diodes and photovoltaics) utilize heterojunctions of doped and undoped layers or depend on gradients of electronic doping to control charge transport. Understanding of the formation and stability of gradients in doping requires an understanding of diffusion of dopants and the complex changes in polymer properties that arise during doping. Conjugated polymers can be electrically doped by strong acids, but the details of the reaction mechanism and subsequent stability are not understood. Here, we show a clear kinetic isotope effect in the doping of thin films of poly(3-hexylthiophene) (P3HT) by bis(trifluoromethane)sulfonimide (HTFSI) from solution indicating that this doping process is limited by proton transfer to the polymer. Complementary X-ray photoelectron spectroscopy and dynamic secondary ion mass spectrometry (DSIMS) depth profiling of dopant concentrations show definitive evidence of dopant enrichment at the P3HT surface. These surface-limited concentration profiles suggest that diffusivity of dopants vary inversely with dopant concentration due to doping-induced changes to the structure of the conjugated polymer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

High-compression implosions based on high density carbon ablator using modified drive and capsule dopant profiles

Laser-driven inertial fusion experiments have, for the first time, achieved a target gain greater than unity in a laboratory setting [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)]. Despite this breakthrough, the burn-up fraction remains limited to about one-fourth of ideal estimates due to insufficient areal density, highlighting the potential for greater gains through enhanced compression. In our previous work, we demonstrated record-high compression of stagnated fuel in indirectly driven implosions using high-density carbon ablators. This was achieved by combining a continuous ramped pulse drive with a modified ablator dopant profile, which reduced mixing at the fuel–ablator interface and improved stability [Tommasini et al., Phys. Rev. Res. 5, L042034 (2023)]. Based on this foundation, the study presented here investigates the limits of compression achievable by combining the continuous ramped pulse drive with different dopant profiles to further minimize unstable interfaces and gradient discontinuities, thereby reducing fuel–ablator mixing. Our results demonstrate that the continuous ramped pulse consistently outperforms designs based on 3-shock drive pulses across all ablator profiles studied, with compression showing only a relatively modest dependence on dopant configurations that reduce the number of interfaces or eliminate discontinuities in the dopant gradient profile. Sub-scale experiments using the continuous ramped pulse achieved compression levels exceeding those of full-scale “HyE” implosions [Kritcher et al., Phys. Plasmas 28, 072706 (2021)] at similar adiabat, anticipating significant performance gains with increased scale, as supported by models and simulations. These findings underscore the critical role of the continuous ramped pulse in reducing mix and achieving improved compression. They also provide a foundation for future large-scale experiments to test the continuous ramped pulse design on deuterium–tritium fuel in the burn-wave propagation regime, leveraging the most effective combinations of continuous ramped pulse and dopant profiles identified in this study.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Dopant Compensation within the Intrinsic Poly-Si Isolation Region in Poly-Si/SiOx Passivated IBC Si Solar Cells

We report on the effect of dopant compensation within intrinsic poly-Si regions between p- and n-type fingers of poly-Si/SiOx passivated interdigitated back contact (IBC) solar cells using intrinsic poly-Si as the isolation region between the doped poly-Si fingers. First, we show that dopants from the doped fingers contaminate the intrinsic gap, resulting in doping of the entire intrinsic gap and overlap of the dopant tails from each finger. Next, we show that despite this doping across the gap, shunting between the doped fingers does not occur. We show that this is a result of trap-assisted compensation creating a highly resistive intrinsic region, preventing shunt. We simulate shunt resistance across the gap based on local carrier concentration and deep trap density. We show that trap defects within the poly-Si enhance compensation between the dopant tails. We experimentally confirm these predictions by scanning spreading resistance microscopy of the gap showing ~20 um domain with resistivity ~10^7 ..omega.. cm. Additionally, Kelvin probe force microscopy are compared to finite element simulations which result in the same approximate shape for potential profile, indicating diode behavior across the isolation region. These results demonstrate the powerful effect that trap defects have within the poly-Si isolation region and suggest that precision patterning is not as essential as once thought.

dopant compensation↗
DOE OSTI2026

Dopant adsorption as a function of bulk concentration at a near 42º (100) twist grain boundary in SrTiO3

The enrichment of grain boundaries with dopant atoms is of critical importance for the macroscopic physical properties of materials. In thermodynamic equilibrium the Gibbs adsorption isotherm relates grain boundary excess of dopant atoms, their chemical potential in the adjacent bulk, and the respective interface energy. This study has used bicrystals with a near 42º (100) twist grain boundary in SrTiO3 to demonstrate that different kinetic pathways of Fe dopant atom additions converge towards comparable grain boundary configurations. Despite differences in bulk chemical potentials remarkably similar grain boundary excess quantities were observed. The experimental results indicate the general experimental feasibility to establish quantitative relationships between variations of grain boundary energy, interfacial excess, and overall dopant concentration. Improved experimental counting statistics are needed to distinguish solute interface excess as a function of bulk chemical potential.

Hahn, William [University of California, Davis]↗
DOE OSTI2021

Thermal stability of dopants in boron carbide

Undoped (B 4 C), B rich (B 5.5 C), and B/Si co-doped (Si-B 6.5 C) boron carbides were annealed at 500 °C for up to 21 days to investigate the thermal stability of primary dopants, B and Si. Structural changes associated with dedoping were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The stable phase B 4 C showed no microstructural or lattice parameter changes. Similarly, lattice parameters of B 5.5 C remained constant, suggesting that B dopant is stable at the given conditions. However, the shortened lattice parameters and reduced Si content of Si-B 6.5 C over the annealing time indicated that Si dopant was in a metastable state at the annealing temperature. Consequently, Si dedoping led to an increase in amorphization (a loss of local crystalline order) which degrades the ballistic performance of boron carbide. The insight highlights the importance of Si dopant in boron carbide and suggests that rapid processing may be necessary to retain more silicon for better performance.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of Ni Dopant on Furan Activation over Mo 2 C Surface: Insights from First-Principles-Based Microkinetic Modeling

Here, the role of Ni dopant in a molybdenum carbide (Mo 2 C) catalyst for butadiene and propyne production from furan is investigated by using a Mo 2 C(001) surface model and first-principles-based microkinetic modeling (MKM). A reaction mechanism including 18 reaction steps is generated to compute the turnover frequency (TOF) of butadiene and propyne from furan gas. The butadiene production is dominant with the TOF being 3-6 orders of magnitude higher than the TOF of propyne on a bare Mo 2 C surface due to an active C-O bond scission reaction compared to C-C bond cleavage reaction. The exothermic binding of ring-opened furan (CHCHCHCHO*) inhibits the activity of a bare Mo 2 C surface for butadiene and propyne production. Calculations predict that Mo 2 C surface modification with a Ni dopant energetically destabilizes the adsorption of CHCHCHCHO*, which facilitates the formation of butadiene and propyne. In the presence of Ni dopants on a Mo 2 C(001) surface, the selectivity toward the butadiene formation is decreased compared to propyne due to relatively favorable C-C bond scission as opposed to the C-O bond scission. This first-principles-based study provides mechanistic and kinetic insights into the role of dopants in cost-efficient Mo 2 C catalysts during the vapor phase conversion of furan to gaseous products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Understanding the dopant induced effects on SFX-MeOTAD for perovskite solar cells: a spectroscopic and computational investigation

SFX-MeOTAD [2,2',7,7'-tetrakis(N,N-di(4-methoxyphenyl)amino)-spiro-(fluorene-9,9'-xanthene)] (also known as X60) has emerged as a cost-effective alternative to the ubiquitous, but excessively-expensive, spiro-MeOTAD hole transport material (HTM) in perovskite solar cells. Using its pre-oxidised dicationic salt, SFX-(TFSI) 2 , a controlled concentration dependent conductivity tuning of this HTM without the requirement of air (oxygen) exposure has been carried out. This study details the modifications in the optical and electrical properties of this low cost HTM as a function of the concentration of the dicationic salt (0–100 mol%) using UV-vis absorption and electrical conductivity measurements. X-ray absorption and photoelectron spectroscopy investigations have been carried out to elucidate the role of the dicationic salt in the enhanced electronic properties of SFX-MeOTAD. By incorporating the dicationic SFX-(TFSI) 2 it has been shown that the conductivity of SFX-MeOTAD increased by 4 orders of magnitude from 2.55 × 10 –8 S cm –1 to 9.4 × 10 –4 S cm –1 when using an optimal dopant concentration of 20.5 mol%. The degree of oxidation of SFX-MeOTAD was determined through UV-vis absorption and consolidated using the computational calculations. The XPS study reveals that doping SFX-MeOTAD with SFX(TFSI) 2 not only results in the oxidation of the HTM but also leads to a variation in the local chemistry around carbon and nitrogen which directly influences the conductivity of the doped films. NEXAFS studies indicate that doping enhances the aromatic nature of the molecule initially but increasing the dopant concentration further affects the aromaticity and possibly the π stacking, similar to the trend seen in dopant concentration dependent conductivity of the SFX-MeOTAD films. These findings have implications on the choice of dopant concentration and counterions more generally for triarylamine based HTMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Molecular dopants: Tools to control the electronic structure of metal halide perovskite interfaces

In the standard configurations of metal halide perovskite solar cell, the active layer, or absorber, follows a p-i-n or n-i-p electronic structure that is designed to enhance the separation and extraction of photo-induced charge carriers. The control of the Fermi level position across the film, between electron and hole transport layers, is therefore of paramount importance. Direct localized doping in metal halide perovskites being still elusive, the design of n-i-p and p-i-n structures has so far relied predominantly on surface and interface doping of the perovskite as well as on the control of the work function of the substrate and transport layers on which, or between which, the absorber is being placed. We provide here a short review of that work, emphasizing the fundamental studies of electronic structure performed on systems modified with organic molecular dopants. The review starts with a justification for the effectiveness of interface doping, based on the ability to move the Fermi level across the gap of the perovskite. We then review work done on the deposition of molecular oxidants and reductants on perovskite surfaces, including the mitigation of the surface states, and the impact of these dopants on energy level alignment with substrate and charge transport layers. The second part of the review focuses on the use of molecular dopants to either modify the work function of electron or hole transport layers to establish the boundary conditions for a p-i-n or n-i-p structure, or to enhance the conductivity of these layers in order to facilitate charge carrier extraction. Final considerations are also given on recent work on bulk doping of the perovskite layer with molecular dopants.

14 SOLAR ENERGY↗
DOE OSTI2024

Understanding electronic structure tunability by metal dopants for promoting MgB 2 hydrogenation

Hydrogen is a promising energy carrier, but its onboard application is limited by the need for compact, low-pressure storage solutions. Solid-state complex metal hydride systems, such as MgB 2 /Mg(BH 4 ) 2 , offer high storage capacities but suffer from sluggish kinetics and poor reversibility. One avenue for improving reactivity is to introduce metal dopants to alter electronic and atomic properties, but the role of these chemical additives remains poorly understood, particularly for the hydrogenation reaction. In this work, we used density functional theory calculations on model MgB 2 systems to rationalize the potential role of metal dopants in destabilizing B–B bonding within the MgB 2 lattice. We carried out detailed electronic structure analyses for 28 different metal dopant adatoms to identify properties that contribute to a dopant’s efficacy. Based on the simulation results, we propose that an intermediate ionic and covalent character of the bonds between adatoms and B atoms is desirable for facilitating charge redistribution, disrupting the B–B bond network, and promoting H 2 dissociation and H atom chemisorption on MgB 2 .

08 HYDROGEN↗
DOE OSTI2024

Dissolution of Mg-enriched defects in implanted GaN and increased p-type dopant activation

Annealing Mg-implanted homoepitaxial GaN at temperatures above 1400 °C eliminates the formation of inversion domains and leads to improved dopant activation efficiency. Extended defects, in the form of inversion domains, contain electrically inactive Mg after post-implantation annealing at temperatures as high as 1300 °C (one GPa N 2 overpressure), which results in a low dopant activation efficiency. Triple-axis x-ray data reveal that implant-induced strain is fully relieved after annealing at 1300 °C for 10 min, indicating that strain-inducing point defects formed during implantation have reconfigured and inversion domains are formed. However, annealing at temperatures of 1400–1500 °C (one GPa N 2 overpressure) eliminates the presence of the inversion domains. While residual defects, such as dislocation loops, still exist after annealing at and above 1400 °C, chemical analysis at multiple dislocation loops shows no sign of Mg segregation. Meanwhile, an overall decreasing trend in the dislocation loop density is observed after annealing at the higher temperatures and longer times. Additionally, once inversion domains are formed and the samples are cooled to room temperature, they are shown to dissolve with subsequent annealing above 1400 °C. While such defects have been observed before, the important finding that such defects can be dissolved with a short, higher temperature step is key. Earlier work [Breckenridge et al., J. Appl. Phys. Lett. 118, 022101 (2021)] addressing electrical measurements of these types of samples showed that annealing at 1400 °C leads to a dopant activation efficiency that is an order of magnitude higher than that observed at 1300 °C. In conclusion, this work complements earlier work by identifying the inversion domains, which incorporate Mg, and points to the benefits, in terms of defect density and p-type dopant activation, of using higher temperature (>1400 °C) annealing cycles to activate Mg in GaN, even if the Mg-containing inversion domains had been formed during lower temperature annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dopant levels in large nanocrystals using stochastic optimally tuned range-separated hybrid density functional theory

In this work, we apply a stochastic version of an optimally tuned range-separated hybrid functional to provide insight on the electronic properties of P- and B- doped Si nanocrystals of experimentally relevant sizes. We show that we can use the range-separation parameter for undoped systems to calculate accurate results for dopant activation energies. We apply this strategy for tuning functionals to study doped nanocrystals up to 2.5 nm in diameter at the hybrid functional level. In this confinement regime, the P- and B- dopants have large activation energies and have strongly localized states that lie deep within the energy gaps. Structural relaxation plays a greater role for B-substituted dopants and contributes to the increase in activation energy when the B dopant is near the nanocrystal surface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Electronegative metal dopants improve switching variability in Al 2 ⁢O 3 resistive switching devices

Resistive random-access memories are promising for nonvolatile memory and brain-inspired computing applications. High variability and low yield of these devices are key drawbacks hindering reliable training of physical neural networks. In this paper, we show that doping an oxide electrolyte, Al 2 ⁢O 3 , with electronegative metals makes resistive switching significantly more reproducible, surpassing the reproducibility requirements for obtaining reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. Throughout this work, we validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of Al 2 ⁢O 3 and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Transition metal elements as donor dopants in CdO

CdO has been shown to achieve a high electron concentration N (> 10 21 cm -3 ) and at the same time a high mobility μ (> 100cm 2 /V s) when doped with conventional shallow dopants (In or Ga), and consequently making it a transparent conducting oxide with very low resistivity ρ <10 -4 $\Omega$ cm. In this work, the properties of CdO thin films doped with a series of transition metal elements (CdO:TM) with partially filled 3d and 4d shells, including Sc, Ti, V, Cr, Fe, Y, Mo, and W, were investigated. We find that doping with these TM elements can effectively increase the N in CdO to a maximum N (N max ) of ~(7-12)×10 20 cm -3 with a dopant concentration x max of 4-7 %. However, unlike CdO:In, the μ of CdO:TM films drops rapidly from > 100 to < 10cm 2 /Vs as the dopant concentration x increases, so that they can only achieve a minimum ρ of ~ (1-2) × 10 -4 $\Omega$ cm, ~ a factor of 2-3 higher than that in CdO:In. As a result, free-carrier absorption and plasma reflection effects limit their optical transparency to <1200 nm. For most 3d TM dopants, a qualitatively higher d-donor level E d,donor gives rise to higher E F,max or a higher N max . Although at low x, the optical band gap E opt of CdO:TM follows the calculated values due to free-carrier effects, as x increases, E opt values are significantly higher than the calculated values. This is believed to be an effect of the anticrossing interaction of the localized d-levels and the extended CdO conduction-band (CB) states, giving rise to a lower occupied E - and an upper unoccupied E + subband. In conclusion, the restructured CBs have much flatter dispersion, which also results in a much higher effective mass $m^{\star}_{e}$, hence it can also explain the much lower μ of CdO:TM films with high N.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synchrotron X-ray metrology of dopant distribution and oxidation state in high pressure CVD grown TM 2+ :ZnSe optical fibers

High pressure chemical vapor deposition (HPCVD) has shown to be a promising method for producing Cr 2+ :ZnSe and Fe 2+ :ZnSe mid-IR optical fiber lasers. The oxidation state of the dopants and their spatial homogeneity are critical for the characterization of effective fiber laser performance; however, this is challenging for small fiber cores and small doping concentrations. We demonstrate using synchrotron micro X-ray fluorescence (XRF) mapping to study the distribution of the dopants throughout the fiber cross-sections. Furthermore, we study the local chemical environment of these unique fiber structures using micro X-ray near edge absorption spectroscopy (XANES). Our study reveals that transition metal doped ZnSe deposited using HPCVD has nanoscale dopant aggregation although the material is chemically identical to the commercially produced diffusion doped laser crystals, as indicated by the presence +2 oxidation state of the dopants. This work demonstrates the power of synchrotron-based X-ray techniques for use as metrology tools for improving the performance of laser materials in fiber geometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effect of Magnesium Dopant on the Grain Boundary Stability of Nanocrystalline Aluminum Powders during Cryomilling

In this investigation, pure aluminum (Al) powders were cryomilled with and without magnesium dopants to study (a) the effect of cryomilling time on the crystallite size and (b) the effect of magnesium dopant on Al to achieve grain boundary stability. The cryomilling process was carried out using liquid nitrogen for different durations. The characterization of the cryomilled powders was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to understand the particle morphology, crystallite size, and elemental composition. The results demonstrated that the size of the crystallites in both Al and Mg-doped Al powders reduces as the cryomilling duration increases. The results also indicated that the preferential segregation of Mg dopant at the grain boundaries of Al provides stability to the cryomilled powders at elevated temperatures. This article discusses the mechanism for the changes in crystallite size and the effect of the Mg dopant on the grain boundary stability in Al powders.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Using Preformed Meisenheimer Complexes as Dopants for n-Type Organic Thermoelectrics with High Seebeck Coefficients and Power Factors

A pre-formed Meisenheimer complex of a naphthalenediimide (NDI) with tetrabutylammonium fluoride (TBAF) is obtained in a simple way by mixing dibrominated 4,9-dibromo-2,7-bis(2-octyldodecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone and TBAF in solution and used as a dopant for n-type organic thermoelectrics. Additionally, two n-type polymers PNDIClTVT and PBDOPVTT are synthesized, n-doped, and characterized as conductive and thermoelectric materials. PNDIClTVT doped with NDI-TBAF presents a high σ value of 0.20 S cm –1 , a Seebeck coefficient (S) of -1854 µV K –1 , and a power factor (PF) of 67 µW m –1 K –2 , among the highest reported PF in solution-processed conjugated n-type polymer thermoelectrics. Using 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine and NDI-TBAF as co-dopants, PNDIClTVT has a PF > 35 µW m –1 K –2 ; while for PBDOPVTT σ = 0.75 S cm –1 and PF = 58 µW m –1 K –2 . In this study it is found that an ionic adduct together with a neutral dopant improves the performance of n-type organic thermoelectrics leading to an enhanced power factor, and more generally, the role of such an adduct in polymer doping is also elucidated.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Solution–Doped Donor–Acceptor Copolymers Based on Diketopyrrolopyrrole and 3, 3'–Bis (2–(2–(2–Methoxyethoxy) Ethoxy) ethoxy)–2, 2'–Bithiophene Exhibiting Outstanding Thermoelectric Power Factors with p –Dopants

The design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large-area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3-dihydrothieno[3,4-b][1,4]dioxine (EDOT), thieno[3,2-b]thiophene (TT), and 3, 3'-bis (2-(2-(2-methoxyethoxy) ethoxy) ethoxy)-2, 2'-bithiophene (MEET) are investigated as side-chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F 4 TCNQ), CF3SO3H, and the synthesized dopant Cp(CN) 3 -(COOMe) 3 , differing in geometry and electron affinity. The DPP-EDOT-based polymer containing MEET as side-chains exhibits the highest conductivity (σ) ≈700 S cm–1 in this series with the acidic dopant (CF 3 SO 3 H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen-based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm–1 and power factor up to 300 µW m –1 K –2 . The mechanism of conductivity is predominantly electronic, as validated by time-dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. Furthermore, these materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM-EDS) and x-ray diffraction, provides insight into the solid-state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant.

36 MATERIALS SCIENCE↗