P3HT Films Research Articles

Resonant Soft X-ray Scattering Reveals the Distribution of Dopants in Semicrystalline Conjugated Polymers.

The distribution of counterions and dopants within electrically doped semicrystalline conjugated polymers, such as poly(3-hexylthiophene-2,5-diyl) (P3HT), plays a pivotal role in charge transport. The distribution of counterions in doped films of P3HT with controlled crystallinity was examined using polarized resonant soft X-ray scattering (P-RSoXS). The changes in scattering of doped P3HT films containing trifluoromethanesulfonimide (TFSI-) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ•-) as counterions to the charge carriers revealed distinct differences in their nanostructure. The scattering anisotropy of P-RSoXS from doped blends of P3HT was examined as a function of the soft X-ray absorption edge and found to vary systematically with the composition of crystalline and amorphous domains and by the identity of the counterion. A computational methodology was developed and used to simulate the soft X-ray scattering as a function of morphology and molecular orientation of the counterions. Modeling of the P-RSoXS at N and F K-edges was consistent with a structure where the conjugated plane of F4TCNQ•- aligns perpendicularly to that of the P3HT backbone in ordered domains. In contrast, TFSI- was distributed more uniformly between domains with no significant molecular alignment. The approach developed here demonstrates the capabilities of P-RSoXS in identifying orientation, structural, and compositional distributions within doped conjugated polymers using a computational workflow that is broadly extendable to other soft matter systems.

Impact of Irreversible Adsorption on Molecular Ordering and Charge Transport in Poly(3-hexylthiophene) Thin Films on Solid Substrates.

We investigate the irreversible adsorption of poly(3-hexylthiophene) (P3HT) polymer thin films on silicon dioxide/silicon (SiO2/Si) substrates during thermal annealing at a temperature below the melting temperature (Tm) but far above the glass transition temperature (Tg), i.e., Tg ≪ T = 170 °C < Tm, and its effect on their crystalline ordering and charge transport properties. It was found that short-time annealing enhances the molecular ordering of P3HT films, while prolonged thermal annealing gradually disrupts the crystalline structures and reduces the overall crystallinity of the film. Concurrently, thermal annealing at this temperature facilitates the slow irreversible adsorption of P3HT chains at the polymer-solid interface, resulting in the formation of a 1.7 Rg-thick (∼18 nm thick) adsorbed layer on SiO2/Si substrates that is fully amorphous and contains a large fraction of loosely adsorbed chains. We postulate that such irreversible adsorption is responsible for the reduced crystalline packing of P3HT at the polymer-solid interface at Tg ≪ T < Tm, which further disrupts the molecular ordering of the entire 46 nm thick P3HT film by a long-range perturbation effect. Electrical measurements using an organic field-effect transistor (OFET) device reveal that the enhanced charge carrier mobility of P3HT films correlates with an optimized annealing time at Tg ≪ T < Tm, which achieves a balance between maximizing molecular ordering and minimizing the impact of irreversible chain adsorption. These findings provide new insights into the underlying mechanism of thermal annealing in tailoring the structure and property of conjugated polymer thin films prepared on solid substrates.

Solution-processed NO2 gas sensor based on poly(3-hexylthiophene)-doped PbS quantum dots operable at room temperature

The global industrial development and increase in the number of transportation vehicles, such as automobiles and ships, have led to a steady increase in the issues related to greenhouse gas emissions. NO2 is a greenhouse gas emitted in large quantities from automobiles and factories, and its emission is unavoidable in the modern world. Therefore, a sensor capable of precise detection of NO2 is required. The most commonly reported types of NO2 sensors are those based on metal oxides. However, their operation at room temperature is impossible owing to their high-temperature operating characteristics, and therefore, a heater must be designed inside or installed outside the sensor for heating. Meanwhile, NO2 sensors based on PbS quantum dots (QDs) are advantageous as they can operate at room temperature and can be easily manufactured through a solution process rather than a complicated semiconductor process. Herein, a NO2 sensor was fabricated by doping PbS QDs with poly(3-hexylthiophene) (P3HT). The as-developed sensor exhibited high responsivity to 100–0.4-ppm NO2 gas with a resolution of 200 ppb owing to the stability of the thin film and high hole mobility of P3HT.

Correlation of dopant solution on doping mechanism and performance of F4TCNQ‐doped P3HT

AbstractUnderstanding the doping mechanism between the dopants and the conjugated polymers (CPs) is crucial for efficiently utilizing the doping process in a controllable manner. In this work, we doped the poly(3‐hexylthiophene) (P3HT) films with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) from a chlorobenzene/acetonitrile (CB/AN) solvent blend and pure AN solvent by using the common sequential doping method. We found that the dissolution ability of the dopant solvent to P3HT and the concentration of the dopant solution were two critical factors to determine the doping process (solution doping or sequential doping) and the doping region (the amorphous or the crystalline phase). When the concentration of the dopant solution was low, solution doping was dominant in the P3HT film doped with F4TCNQ CB/AN solution, and the amorphous regions were doped in the P3HT film doped with F4TCNQ AN solution. With the increase of the dopant solution concentration, the ratio of ordered integer charge transfer (ICT) species, which formed from sequentially doped crystalline domains in the P3HT precast film, increased. Based on the above doping mechanism, a P3HT film with good electrical and tensile performance could be constructed by doping from F4TCNQ CB/AN solution with a relatively low concentration. Our work indicates that the dissolution or swelling ability of the dopant solvent to CP is an important factor in determining not only the doping mechanism but also the electrical and mechanical performances of doped CP films.

Photoelectronic synaptic transistors with tuneable synaptic plasticity based on films of P3HT with ordered polymer chains

We show that the properties of photoelectronic synaptic transistors based on films with aligned P3HT polymer chains can be tuned by varying the orientations of the polymer chains with respect to the electrodes. The electrical responses corresponding to displays of synaptic plasticity are studied using a range of electrical and optical stimulation. It is shown that the orientation significantly modulates the properties, demonstrating that the orientation of the polymer film with respect to the electrodes enables a tuning of the synaptic plasticity.

Poly(3‐hexylthiophene) film coated on plastic substrate as an organic photoanode for water oxidation/oxygen evolution with light illumination

AbstractPoly(3‐hexylthiophene) (P3HT) film was applied as a photoanode on an electron‐extracting layer‐coated upon a current‐collecting plastic substrate. The film soaked in an aqueous solution (pH 12) exhibited an enhanced anodic current with light illumination, and the photocurrent density (J) reached almost 100 μA/cm2 for its wound cylinder, which was accompanied by oxygen bubble evolution. The light ON/OFF response, light‐intensity proportion, and wavelength‐dependency of the J value supported the photo‐electrolytic function of the P3HT film. The hole‐injection efficiency of the film estimated for water oxidation using a solution involving a sacrificial reagent, was relatively high in the range of 46%–86%. Although an apparent activation energy of 39 kJ/mol for the electrolytic water oxidation in the dark suggested a chemical but catalytic pathway for the film anode, the temperature independence of the photocurrent indicated direct hole‐injection into water or hydroxide ions. The photoanode performance of the P3HT film for water oxidation was discussed in relation to the energy diagram including the highest occupied molecular orbital level.

Structural optimization of ion storage layer for highly stable electrochromic devices based on polythiophene derivative films

Due to their rich color, fast switching speed and high coloration efficiency, polymer-based electrochromic devices (ECDs) have broad application prospects in various fields such as smart windows, anti-glare rearview mirrors, displays and adaptive camouflage. However, the preparation of highly stable polymer-based ECDs is still a great challenge. Herein, we present a simple and efficient strategy to construct the poly (3,4-ethylenedioxythiophene) (PEDOT)-multi-walled carbon nanotubes (MWCNTs) composite film or PEDOT/MWCNTs bilayer film, which serves as ion storage layer. The ECDs are assembled with poly (3-hexylthiophene) (P3HT) as EC layer due to its good EC behavior. The P3HT film was prepared by potentiostatic deposition, and the PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films were obtained by spray-coating technology. We investigated the structure, morphology and electrochemical performance of P3HT, PEDOT, PEDOT-MWCNTs and PEDOT/MWCNTs films, and EC properties of devices. The results indicate that the rough and porous P3HT film consists of many nanoparticles. Compared with PEDOT-MWCNTs composite film, the PEDOT/MWCNTs film is more loose and porous, where PEDOT nanoparticles and some PEDOT nanosheets are coated on a three-dimensional skeleton film of MWCNTs. These films possess good electrochemical performance. The ECD based on P3HT and PEDOT/MWCNTs films achieves an optical contrast of 38 % and coloration efficiency of 375 cm2/C, exhibiting good cyclic stability (retaining 92 % of initial optical contrast after 2000 cycles). Its coloration time and bleaching time are 0.60 and 1.83 s, respectively. This study suggests that structural optimization of ion storage layer might be a facile strategy for fabricating highly stable polymer-based ECDs.

Bidirectional Voltage Regulation for Integrated Photovoltachromic Device Based on P3HT-Electrochromic Unit and Perovskite/Organic Tandem Solar Cells.

Integrated electrochromic devices powered by photovoltaic cells have evoked a lot of interest due to their promising commercial prospects. However, their application has been restricted by the voltage adaption between the self-powered voltage and the color-changing threshold voltage (Vt). Herein, a strategy of bidirectional voltage regulating is proposed to develop a novel stand-alone integrated photovoltachromic device (I-PVCD), which integrates perovskite/organic tandem solar cells (P/O-TSCs) to drive color-changing process of conjugated poly(3-hexylthiophene) (P3HT) films. To lower the driving-voltage of electrochromic layer, C60 is introduced to decrease the onset oxidation potential of P3HT film, and thus leading to a reduced Vt of 0.70V benefiting from the enhanced highest occupied molecular orbital level and decreased charge transfer resistance from 67.46 to 49.89 Ω. Simultaneously, PBDB-T is utilized as the hole transport layer in the interconnecting layer of CsPbI2Br/PTB7-Th:IEICO-4F P/O-TSC to improve its open-circuit voltage (Voc) to 1.85V. Under their synergetic merits, a I-PVCD with a wider self-adaptive voltage range is achieved. This device can undergo fast and reversible chromic transition from beautiful magenta to transparent only under the solar radiation, and demonstrates a coloration efficiency of 351.90 cm2 C-1 and a switching time of 2 s besides its excellent operating reliability.

Using Bulky Dodecaborane-Based Dopants to Produce Mobile Charge Carriers in Amorphous Semiconducting Polymers.

Conjugated polymers are a versatile class of electronic materials featured in a variety of next-generation electronic devices. The utility of such polymers is contingent in large part on their electrical conductivity, which depends both on the density of charge carriers (polarons) and on the carrier mobility. Carrier mobility, in turn, is largely controlled by the separation between the polarons and dopant counterions, as counterions can produce Coulombic traps. In previous work, we showed that large dopants based on dodecaborane (DDB) clusters were able to reduce Coulombic binding and thus increase carrier mobility in regioregular (RR) poly(3-hexylthiophene-2,5-diyl) (P3HT). Here, we use a DDB-based dopant to study the effects of polaron-counterion separation in chemically doped regiorandom (RRa) P3HT, which is highly amorphous. X-ray scattering shows that the DDB dopants, despite their large size, can partially order the RRa P3HT during doping and produce a doped polymer crystal structure similar to that of DDB-doped RR P3HT; Alternating Field (AC) Hall measurements also confirm a similar hole mobility. We also show that use of the large DDB dopants successfully reduces Coulombic binding of polarons and counterions in amorphous polymer regions, resulting in a 77% doping efficiency in RRa P3HT films. The DDB dopants are able to produce RRa P3HT films with a 4.92 S/cm conductivity, a value that is ∼200× higher than that achieved with 3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the traditional dopant molecule. These results show that tailoring dopants to produce mobile carriers in both the amorphous and semicrystalline regions of conjugated polymers is an effective strategy for increasing achievable polymer conductivities, particularly in low-cost polymers with random regiochemistry. The results also emphasize the importance of dopant size and shape for producing Coulombically unbound, mobile polarons capable of electrical conduction in less-ordered materials.

Molecularly doped polythiophene film as an efficient photocathode for oxygen reduction to hydrogen peroxide

AbstractThe molecularly doped poly(3-hexylthiophene) (P3HT) was used for the first time as a photocathode for reducing oxygen to H2O2. For this purpose, a P3HT film was doped with hexaazatriphenylenehexacarbonitrile, which increased the oxygen reduction current at an applied negative potential in the dark. Visible light illumination of the doped P3HT film significantly facilitated the oxygen reduction with a high current density and shifted the onset potential beyond the reaction equilibrium potential. The oxygen reduction performance of the doped P3HT film is discussed in relation to the energy level diagram. Graphical abstract

Tuning the order of poly(3-alkylthiophene) derivatives ultrathin films through side-chain polarity: From a short-range ordered monolayer to a highly crystalline bilayer

In order to pave the way for the formation of ultrathin electronically conductive organic films, we explored the structure and morphology of polythiophene derivatives in situ on the water surface. By changing the side chain end-group of poly(3-hexylthiophene) (P3HT) from methyl to carboxylic acid potassium salt, we showed that the film structure is drastically changed from a highly ordered bilayer to a short-range organized monolayer. Using a comprehensive experimental approach from macroscopic length scale to molecular organization as well as simulations of diffraction patterns, the detailed structure of the crystalline P3HT bilayer was determined. Some similarities with the structure measured on thicker films deposited on solid substrates were evidenced such as the π-stacking distance, the interlayer spacing, and the edge-on conformation. Some differences were also pointed out, in particular the in-plane packing along the polymer backbones and the shift of the upper monolayer with respect to the bottom one in this direction. Such observations highlighted the influence of both the forced two-dimensional confinement and the nature of the substrate (water) on the P3HT film structure. The presence of a carboxylic acid potassium salt at the end of the side chain induced completely different behavior. Indeed, high pressures were necessary to observe a π-stacking of the thiophene units, but only short-range, and although the polymer keeps a monolayer organization independently of the pressure, a deep change in the polymer conformation was evidenced with the pressure.

Crystal Structure Control of the Energetics of Chemical Doping in Rub-Aligned P3HT Films

Crystal Structure Control of the Energetics of Chemical Doping in Rub-Aligned P3HT Films

Exploring response time and synaptic plasticity in P3HT ion-gated transistors for neuromorphic computing: impact of P3HT molecular weight and film thickness

Response time and plasticity of P3HT-IGTs can be controlled by engineering input stimuli, P3HT molecular weight and channel thickness.

Characterization of nanoscale morphology and mechanical properties of conjugated polymer thin films dynamically exposed to a secondary solvent

Solution processing techniques are often used to enhance intra and interchain order in semiconducting conjugated polymer thin films used in the active layer of organic optoelectronic devices. While there has been extensive research into the impact of solution processing on the local structural and electronic properties of these films, the nanomechanical properties of the films are less well understood and are challenging to characterize. We investigate the nanomechanical properties of conjugated polymer thin films arising from solution processing techniques. Our study relies on dynamic secondary solvent dripping to induce subtle changes to the film morphology. We examine thin films of P3HT, PCDTBT, PTB7, and PBDB-T-SF conjugated polymers, commonly used in organic photovoltaics, with the bimodal amplitude modulation-frequency modulation (AM-FM) imaging mode of the atomic force microscopy (AFM) viscoelastic method to probe their local physical and mechanical properties. We find that Young's Modulus data measured by AM-FM AFM can detect additional changes in film properties not discernible by other commonly used bulk thin-film characterization techniques. For PBDB-T-SF, we detect an increase in molecular order that is not noticable by UV–visible absorption spectroscopy, X-ray diffraction or nanoindentation. PCDTBT, the most amorphous of the polymers studied, shows no changes in absorption or X-ray diffraction data, yet clear changes in Young's Modulus were detected by AFM. On the other hand, increases in P3HT order that occurred due to dynamic secondary solvent dripping are detected in both the bulk and AFM measurements. Our study demonstrates the applicability of nanomechanical measurements for characterizing local structural variations in conjugated polymer films. This work is relevant to ongoing efforts to control and understand the complex structure-property-processing relationships of conjugated polymer thin films.

Effect of drying behavior-induced self-organization process on the morphology and electronic properties of conjugated polymer films

In this study, the morphology and electronic properties of semiconducting polymer films were investigated in relation to a different drying behavior induced by the spinning time variation. Morphology changes related to the decreased spinning time were evaluated for p-type (P3HT, PQT-12) and n-type (N2200, PDBPyBT) polymer films fabricated at different preparation conditions. Based on the improved morphology, OFET devices were fabricated showing a 2.5 times carrier mobility increase (0.044 ± 0.012 cm2V−1s−1 for 3 s spin to 0.018 ± 0.011 cm2V−1s−1 for 30 s spin) for P3HT films, and 3 times improvement (0.088 ± 0.023 cm2V−1s−1 for 50 s to 0.28 ± 0.017 cm2V−1s−1 for 5 s) for N2200 films. For short spinning times, the slow drying of residual solvent allowed for the self-organization of polymer chains improving the crystallinity of polymer films. The presented approach synergizes the benefits of the spin coating method, like highly controlled film uniformity and thickness, with improved film morphology provided by other methods, like drop casting, or dip-coating.

Nanoparticles of poly(3-hexylthiophene): Toward a solvent-independent performance of electrochromic films

Nanoparticles of poly(3-hexylthiophene), P3HT(NP), uniquely enable the preparation of stable dispersions in environmentally-friendly media and thus offer a sustainable liquid phase fabrication of electrochromic device structures. In this work, we assess the electrochromic performance of P3HT(NP) films spray-coated from either tetrahydrofuran (THF)-water or chloroform (CHCl3)-ethanol dispersions on ITO substrates. The nanoparticle films exhibit consistent and reproducible high optical contrast values of around 50 %, t90-switching speeds of about 0.45 s and a cycling stability of approximately 200 cycles for a 20 % performance retention, independent of the solvent being used. Conversely, non-nanostructured P3HT films spray-coated from THF or CHCl3 reveal a strong solvent dependent variability in their electrochromic behavior presenting low optical contrast, high switching speeds and fast degradation rates in the case of CHCl3. The solvent independent electrochromic characteristics of P3HT nanoparticle films is related to a consistent availability of accessible electroactive sites provided by a homogeneous porous P3HT network structure formed on the underlying substrate, as probed by SEM and profilometric studies. Our findings reveal that the use of nanoparticles of P3HT and its environmentally benign liquid phase processing, a concept which is extendable to other electrochromic polymers, opens a sustainable pathway toward the large-area fabrication of electrochromic device structures with favorable and consistent performance parameters.

Ion effects on salt-in-water electrolyte gated polymer electrochemical transistors

Aqueous electrolyte-gated polymer transistors attracted intensive attention in the field of implantable bionics and biochemical sensors due to their simple fabrication process, low operating voltage, and biocompatibility of salt-in-water. In these devices, under gate bias, the free cations and anions in the water solution gate will drift toward the gate electrode or electrolyte/active layer interface, respectively. Under high enough bias, some ions might insert into the active layer and dope the polymer in electrochemical transistors. Therefore, the ions play a crucial role in the salt-in-water electrolyte-gated polymer electrochemical transistors. In this work, the poly (3-hexylthiophene-2, 5-diyl) (P3HT) electrochemical transistors based on different cations and anions contained in the aqueous electrolytes were characterized. The various measurements imply that the larger perchlorate ions can penetrate the P3HT film much more heavily than the smaller chloride ions and the electrochemical bulk doping occurs in the perchlorate devices while the chloride devices involve surface doping. This is why the perchlorate ions can electrochemically dope the P3HT film more heavily than the chloride ions, leading to the larger transconductance and switching ratio. The various anions show different electrochemical doping processes, leading to various electrical hysteresis characteristics. In addition, the cations can affect the doping relaxation process for the electrochemical transistors. Both cation and anion effects on the device performance and doping/dedoping processes have been investigated in this work.

Enhancing the Molecular Order and Vertical Component Distribution of the P3HT/O-IDTBR System during Layer-by-Layer Processing.

The molecular order and vertical component distribution are critical to enhance the charge transport in layer-by-layer (LbL) processed active layer. However, the excessive inter-diffusion between donor and acceptor layers during LbL processing irrepressibly reduces their ordered packing. Herein, a novel tactic to optimize the molecular order and vertical morphology of the active layer through suppressing the deep penetration of (5Z,5'Z)-5,5'-((7,7'-(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6 -b']dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene)) bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR) to poly(3-hexylthiophene) (P3HT) film during LbL processing is proposed. This is enabled by inducing the formation of P3HT nanofibers through ultraviolet (UV) irradiation and solution aging. During the LbL processing, these nanofibers with high crystallinity reduce the damage of O-IDTBR solution to P3HT film and restrict the penetration of O-IDTBR into P3HT matrix. As a result, the P3HT nanofibers are preserved and the degree of vertical phase separation is enlarged in the LbL-processed film. Meanwhile, the molecular order of both components is enhanced. The resulting morphology that featured as intertwined P3HT nanofibers/O-IDTBR network efficiently promotes charge transport and extraction, boosting the power conversion efficiency (PCE) of the devices from 6.70±0.12% to 7.71±0.10%.

Synthesis and characterization of thin films of P3HT − G/MoS2 nanocomposites in photodetectors applications

Synthesis and characterization of thin films of P3HT − G/MoS2 nanocomposites in photodetectors applications

Enhancing the Performance of Organic Phototransistors Based on Oriented Floating Films of P3HT Assisted by Al-Island Deposition.

The fabrication of high-performance Organic Phototransistors (OPTs) by depositing Al-islands atop Poly(3-hexylthiophene) (P3HT) thin film coated using the unidirectional floating-film transfer method (UFTM) has been realized. Further, the effect of Al-island thickness on the OPTs' performance has been intensively investigated using X-ray photoelectron spectroscopy, X-ray Diffraction, Atomic force microscopy and UV-Vis spectroscopy analysis. Under the optimized conditions, OPTs' mobility and on-off ratio were found to be 2 × 10-2 cm2 V-1 s-1 and 3 × 104, respectively. Further, the device exhibited high photosensitivity of 105, responsivity of 339 A/W, detectivity of 3 × 1014 Jones, and external quantum efficiency of 7.8 × 103% when illuminated with a 525 nm LED laser (0.3 mW/cm2).