Regioregular Poly 3-hexylthiophene Research Articles

Low voltage driven P3HT/PS phototransistor for ultra-high power efficiency UV sensing

This study explores the physical properties and electrical characteristics of a regioregular poly 3-hexylthiophene (rr-P3HT) semiconductor blended with the polymer insulator polystyrene. Given the high operating voltage required by conventional P3HT transistors, we employed a hybrid dielectric layer, combining plasma-reacted metal oxide with a polymer pre-layer (AlOx/PMMA and HfOx/PMMA), to reduce the operating voltage of P3HT transistors. As a result, an operating voltage lower than −5 V for the blended sample was achieved. The structural, morphological, and electrical properties of the prepared blended sample were investigated using XRD, AFM, XPS, UV–Visible spectroscopy, Raman spectroscopy, and I–V characteristics. The blended sample exhibits improved crystalline ordering and an extended effective conjugation length, accompanied by an increased formation of dendritic P3HT fibrils that enhance UV absorption. PS captures generated electrons, effectively delaying their recombination with generated holes in P3HT. This leads to heightened UV responsivity in P3HT/PS transistors. The key discovery of this study is the ultra-low power consumption UV sensing device. The blended sample, illuminated with a UV intensity of 550 μW/cm2, exhibited the highest sensitivity of 194.5, nearly 60 times higher than that of pristine P3HT. Consequently, our investigated device shows promise for applications in visible-blind sunlight or environmental monitoring systems, given its ultra-high-power efficiency.

Improved charge transport ability of polymer solar cells by using NPB/MoO3 as anode buffer layer

Efficient polymer solar cells were fabricated with regioregular poly 3-hexylthiophene (P3HT):(6,6)-phenyl C61 butyric acid methyl ester (PCBM)) as active layer and molybdenum trioxide (MoO3) and (N,N′-diphenyl)-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) as buffer layers. The results of transient photocurrent and electrochemical impedance spectrometry of device indicate that the insertion of NPB layer between the active layer and MoO3 layer is critical to the enhanced performance. It can effectively prevent charge recombination at the interface of MoO3 hole extraction layer, reduce interfacial resistance due to the formation of Ohmic contact and enhance the exciton dissociation because of the newly formed NPB/PCBM dissociation interface. The optimized thickness of NPB layer is 5 nm, resulting in maximized power conversion efficiency (PCE) of 3.94% under AM1.5G 100 mW cm−2 illumination.

Charge carrier transport and recombination in disordered materials

In this brief review the methods for investigation of charge carrier transport and recombination in thin layers of disordered materials and the obtained results are discussed. The method of charge carrier extraction by linearly increasing voltage (CELIV) is useful for the determination of mobility, bulk conductivity and density of equilibrium charge carriers. The extraction of photogenerated charge carriers (photo-CELIV) allows one to independently investigate relaxation of both the mobility and density of photogenerated charge carriers. The extraction of injected charge carriers (i-CELIV) is effective for the independent investigation of transport peculiarities of both injected holes and electrons in bulk heterojunctions. For the investigation of charge carrier recombination we proposed integral time-of-flight (TOF) and double-injection (DI) current transient methods. The methods allowed us to obtain the following significant results: to determine the reason of the conductivity dependence on electric field strength and temperature in the amorphous and microcrystalline hydrogenated silicon and π-conjugated polymers, the time dependent Langevin recombination, the impact of morphology on charge carrier mobility, the reason of reduced Langevin recombination in RR-PHT (regioregular poly(3-hexylthiophene))/PCBM (1-(3-methoxycarbonyl)propyl-1phenyl-[6,6]-methanofullerene) bulk heterojunction structures – 2D Langevin recombination; and to evaluate that the mobility of holes is predetermined by off-diagonal dispersion in poly-PbO.

Characterization of semicrystalline polymers after nanoimprint by spectroscopic ellipsometry

Semicrystalline Reg-P3HT (regio-regular poly-3-hexylthiophene) is a promising material for organic electronics. It features relatively high charge mobility and enables easy preparation because of its solubility. Due to its high optical and electrical anisotropy, the size, number and orientation of the ordered domains are important for applications. To control these properties without limitation from crystalline domains existing after spin coating, thermal nanoimprint is performed beyond the melting point. The state of the art of measurement to analyze the complex morphology is X-ray diffraction (XRD). We address an alternative measurement method to characterize the material by its optical properties, spectroscopic ellipsometry. It provides information on the degree of order from the typical fingerprint absorption spectrum. In addition, when the material is modeled as a uniaxial layer, an anisotropy factor can be derived. The results obtained from spectroscopic ellipsometry are in accordance with those from XRD. In particular, spectroscopic ellipsometry is able to distinguish between order along the backbone and order in π–π stacking direction, which is important with respect to conductivity.

Effects of conjugated polymer on the magnetotransport properties in La0.7Sr0.3MnO3 ferromagnetic electrodes

Magnetotransport of La0.7Sr0.3MnO3 (LSMO)/regioregular poly3-hexylthiophene (rr-P3HT) interfaces were studied at 5–300 K to gain insight of spin transport in polymer coated LSMO. LSMO films on SrTiO3 (STO), MgO, and quartz substrates were characterized in pristine state, after depositing rr-P3HT and after removing rr-P3HT. Application and removal of rr-P3HT caused the disappearance of colossal magneto resistance and the emerging of low-field magnetoresistance (LFMR) in STO/LSMO, while the same treatment on MgO and quartz showed only a large LMFR signal with no significant changes during application and removal of rr-P3HT. This result signifies that epitaxial thin films of LSMO do not maintain their transport characteristics when coated with organic semiconductors, posing a limitation for efficient spin polarized injection at such interfaces.

All-Atom Molecular Dynamics Simulation of Temperature Effects on the Structural, Thermodynamic, and Packing Properties of the Pure Amorphous and Pure Crystalline Phases of Regioregular P3HT

Molecular dynamics simulations have been carried out to probe chain self-organization and structure in regioregular poly-3-hexylthiophene (Rr-P3HT). Taking into account recent experimental findings that provide evidence for a semicrystalline ordering in P3HT where crystalline lamellae are periodically separated by interlamellar amorphous zones, we have separately simulated the pure crystalline and the pure amorphous phases of Rr-P3HT, and studied the dependence of their conformational and configurational properties on temperature (from 225 to 600 K). All simulations have been carried out with the very accurate, all-atom Dreiding force-field. In the pure crystalline phase, the system is found to adopt a noninterdigitated and tilted structure irrespective of temperature and chain molecular weight (Mw) consistent with the results of XRD measurements and other theoretical works. Increasing the temperature did not seem to dramatically affect the interchain distance inside the crystal. Temperature therefore sho...

Poly(3-hexylthiophene) and hexafluoro-2-propanol-substituted polysiloxane based OFETs as a sensor for explosive vapor detection

The organic field effect transistors (OFETs) with regioregular poly 3-hexylthiophene (rr-P3HT) and hexafluoro-2-propanol-substituted polysiloxane (SXFA) as an organic layer, have been used for detection of explosive vapors with excellent sensitivity of less than 70 ppt for 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and less than 100 ppt for 2,4,6-trinitrotoluene (TNT). The sensor response (% change in saturation current) was found to be 125 ± 10% for TNT and 90 ± 10% for RDX. It was also observed that the incorporation of Cu II tetraphenylporphyrin (CuTPP) into rr-P3HT/SXFA matrix resulted in an improved selectivity for the vapors of nitro based analytes (TNT, RDX and DNB) as compared to the vapors of non explosive oxidizing agents such as nitrobenzene (NB), benzoquinone (BQ) and benzophenone (BP). This is attributed to the increased binding of the vapors containing nitro compound to the thin films due to the presence of CuTTP. Spin coated thin films were further characterized by Atomic Force Microscopy (AFM) and Electrostatic Force Microscopy (EFM).

High performance organic phototransistor based on regioregular poly(3-hexylthiophene)

We fabricated solution processed organic phototransistors (OPT) by dropcasting regioregular poly 3-hexylthiophene (P3HT) from three different solvents:p-xylene, dichlorobenzene and chloroform. The best performance was obtained for films drop-casted fromp-xylene with a maximumphotosensitivity (P) of 3.8 × 103 andresponsivity (R) of 250 A W − 1 under white light illumination. For films deposited from dichlorobenzene and chloroform the values ofP were 1.1 × 103 and 30, respectively,while the values of R were 150 and 35, respectively. The maximum responsivity value reported hereis at least one order of magnitude higher than that of previously reportedsolution processed OPT devices. By analyzing the absorption spectra ofdifferent films, we conclude that the better device performance of OPT fromp-xylene is due to better crystallinity of P3HT. Demonstration of high performance OPTs isa significant step forward in integrating these devices in various optoelectroniccircuits.

Electrical characterization of single-walled carbon nanotubes in organic solar cells by Kelvin probe force microscopy

The electrical role (donor or acceptor) of single-walled carbon nanotubes (SWCNTs) in organic solar cells remains controversial in the literature. Using Kelvin probe force microscopy (KPFM) to investigate SWCNTs on regioregular poly 3-hexylthiophene (P3HT) film as well as on P3HT and methanofullerene blended film, we have observed that photoinduced holes transport from active layer to SWCNTs, which indicates that SWCNTs work as donor materials. Moreover, KPFM study of SWCNTs on P3HT film reveals that the relatively low power conversion efficiency of P3HT/SWCNTs solar cells is attributed to deficient photoexcited carrier transport between P3HT and SWCNTs because of inefficient exciton dissociation.

A Practical Approach for the Preparation of Regioregular Poly(3-hexylthiophene)

Scheme 1. Preparation of monomer Polythiophenes have been intensively studied over the last three decades. And major studies have been focused on poly 3-alkylthiophene especially poly 3-hexylthiophene (P3HT), which has shown very unique properties in conducting polymer applications. Of these, the most notable property is electrical conductivity, which is contributed to the delocalization of πelectrons through overlap of π-orbitals. In addition to this, since it is very soluble in normal organic solvents, a good processability has been observed. In general, preparation of P3HT could be achieved by either chemical or electrochemical method. For electrochemical polymerization including FeCl3 catalyzed polymerization, a potential was applied to a solution containing monomer and electrolyte. Chemical synthesis was performed by metal-mediated polymerization of monohalogenated and/or dihalogenated thiophene derivatives under appropriate conditions. An advantage in chemical polymerization over electrochemical method is that this method generally affords a highly regioregular polymer in excellent yields. Since regioregularity of P3HT is a critical element for the application of this polymer, a lot of different procedures have been developed especially in chemical synthetic methods. Generally accepted methods include metal (Ni) catalyzed self-condensation of thienyl organozinc and thienyl Grignard reagents. A big breakthrough for the preparation of regioregular P3HT has been reported by Rieke and McCullough, separately. From these works, high regioregular (> 98%) head-to-tail P3HT has been achieved with reasonable molecular weight. As mentioned above, 2,5-dibromo-3-alkylthiophenes have been extensively used as a monomer in the chemical synthetic method. However, only a few examples of using 2-bromo-5iodo-3-alkylthiopenes have been appeared in the chemical method. Recently, Knochel and co-workers introduced the application of commercially available and relative cheap zinc powder to organic synthesis. This work prompted us immediately to study the possibility of using zinc powder in the preparation of P3HT. To this end, 2-bromo-5-iodo-3-alkylthiopene could be the most proper candidate since zinc dust showed excellent insertion reactivity to carbon-iodine bond. Here, we wish to report the first result obtained from the application of the activated zinc dust to the preparation of regioregular P3HT.

Effects of semiconducting and metallic single-walled carbon nanotubes on performance of bulk heterojunction organic solar cells

This letter reports that the performance of organic solar cells made from blended films of regioregular poly 3-hexylthiophene and methanofullerene can be boosted by introducing single-walled carbon nanotubes (SWCNTs) into the active layer at low concentration. However, the performance degrades at higher SWCNTs concentration. The intensity dependent photocurrent measurement shows that the decreased performance at higher concentration of SWCNTs is attributed to bimolecular recombination in the presence of metallic SWCNTs. Meanwhile, it has been found that the increased performance at low concentration of SWCNTs is due to the increased carrier mobility as semiconducting SWCNTs provide lower resistance pathways.

Effect of polymer processing on spin magnetoresistance in organic structures

Results from studies of spin dependent transport in the hole transporting organic semiconductor regioregular poly 3-hexylthiophene (RR-P3HT) are reported. The organic spin valves were grown on glass, with the structure Fe50Co50∕RR-P3HT∕Ni81Fe19. RR-P3HT was cast from five different solvents with different boiling points; 1,2,4 trichlorobenzene, toluene, xylene, chloroform, and chlorobenzene. Magnetoresistance measurements were carried out at room temperature. Spin dependent transport was only observed when toluene, xylene, and annealed 1,2,4 trichlorobenzene were used as solvents. Results are interpreted on the basis of differences in the RR-P3HT morphology induced by different solvents under fixed processing conditions.

PV and magnetic field effects in poly(3-hexylthiophene)-fullerene cells doped with phthalocyanine soluble derivative

An attempt was made to widen the photosensitivity spectral range of poly(3-hexylthiophene)-fullerene blend by adding an extra electron donor — a newly synthesized soluble phthalocyanine derivative (SnClPc) having the electron absorption band at 708 nm. As the electron acceptor, home-synthesised di(ethoxycarbonyl) methano-fullerene carboxylate (C 61 (CO 2 Et) 2 ) was used, and as the hole transporter — the regioregular poly 3-hexylthiophene (P3HT). The sandwich-type samples were prepared on an ITO glass substrate by coating it with a 30–50 nm thick PEDOT:PSS layer followed by a ~100 nm thick P3HT:C 61 (CO 2 Et) 2 :SnClPc blend. For the top electrodes In or Au were used. Spectral dependences of the PV effect and of the influence of external magnetic field (0–3000 Oe) on it were studied in the 370–1000 nm spectral range in vacuum of ~10 -6 Torr. Significant photosensitivity of the blend was observed in the 370–800 nm spectral range. However, the short-circuit photocurrent quantum efficiency evaluated for absorbed light was found to be 4 times higher for illumination in the P3HT absorption band as compared with that in the SnClPc band. The observed magnetic field effect shows that the low IPCE values may be explained by the space charge formation in the samples, leading to a strong geminate recombination of CP states.

Cover Picture: Tuning the Dimensions of C60-Based Needlelike Crystals in Blended Thin Films (Adv. Funct. Mater. 6/2006)

A new ordered structure of the C60 derivative PCBM is obtained in thin films based on the blend PCBM:P3HT, as detailed by Swinnen, Manca, and co-workers on p. 760. Needlelike crystalline PCBM structures, whose dimensions and spatial distribution ca be tuned by adjusting the blend ratio and annealing conditions, are formed. In typical solar-cell applications of these blended films, these results indicate that during long-term operation under normal conditions (50–70 °C) morphology changes and a decrease in cell performance could occur. A new ordered structure of the C60 derivative PCBM ([6-6]-phenyl C61-butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3-hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as-obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix.

Tuning the Dimensions of C60-Based Needlelike Crystals in Blended Thin Films

A new ordered structure of the C60 derivative PCBM ([6-6]-phenyl C61-butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3-hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as-obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix.

Increase in the Mobility of Photogenerated Positive Charge Carriers in Polythiophene

We report the increase in the mobility of charge carriers in regioregular poly 3-hexyl thiophene (RR-P3HT) films by mixing them with tetracyanoethylene (TCNE), which is examined by in situ time-resolved microwave conductivity (TRMC) and transient optical spectroscopy (TOS). TCNE acts not only as an electron acceptor which increases the number of charge carriers on photoexposure but also as a functional additive which enhances the mobility of the charge carriers. This conclusion was deduced from the results of fluorescence quenching, transient optical absorption and photobleaching, and comparison of the TRMC signal with the TOS signal. The combination of the TRMC and TOS techniques represents a comprehensive and fully experimental approach to the determination of the intrinsic carrier mobility in conjugated polymers.

Effects of FeCl3 doping on polymer-based thin film transistors

Polymer-based thin film transistors (PTFTs) were fabricated on glass substrates with anodized Al2O3 as gate insulators. RR-P3HT (regioregular poly–3-hexylthiophene) and MEH-PPV [poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)] were respectively used as semiconducting active layers for the transistors. A two orders of magnitude increase in field effect mobility (from 7.2×10−4 cm2/V s to 7.4×10−2 cm2/V s) deduced from electrical data of transistors fabricated using FeCl3 doped RR-P3HT was observed. This increase is believed to be mainly due to a large reduction in contact resistance (from 108 Ω to 103 Ω) to the source and drain Au contacts. The conductivity of RR-P3HT was found to increase only slightly with the doping. For MEH-PPV, doping with FeCl3 also decreased its contact resistance. However, it (4 GΩ) was still much larger than the channel (polymer) resistance (1 MΩ), leading to a slight improvement in its field effect mobility. Theoretically, contacts between Au and P3HT should have very small energy barrier heights (<0.2 eV) for hole injection. We believe that a negative vacuum level shift introduced by metal to organic interfacial dipoles might be the origin of this large energy barrier, as well as to large contact resistance.

Electronic structure of thiophenes and phtalocyanines

The results of x-ray fluorescence measurements of thiophenes [regioregular poly 3-hexylthiophene (P3HT) and {alpha},{omega}-dihexylquaterthiophene (DH{alpha}4T)] and phtalocyanines [copper phtalocyanine (CuPc) and copper hexadecafluorophtalocyanine (F{sub 16}CuPc)] are presented. Experimental carbon, nitrogen, fluorine K{alpha} and sulphur, copper L{sub 2,3} x-ray emission spectra are compared with ultraviolet photoemission spectroscopy spectra and deMon density-functional theory calculations of model molecules. We find that the carbon K{alpha} emission is almost identical for P3HT and DH{alpha}4T. This indicates that the electronic structure of the {pi} system is not affected by the presence of the side group. The ratio of emission intensities of the Cu L{sub 2} to Cu L{sub 3} intensities is found to be smaller by a factor of 2 for CuPc and F{sub 16}CuPc than it is for pure metal. This demonstrates the strong covalency in phalocyanines.