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Conjugated polymers present a compelling option for thermoelectric applications due to their low working temperatures, good compatibility with solution-processing techniques, and high potential for scalability. However, the inherently low electrical conductivities of the pristine conjugated polymers necessitate improvements via doping methods. Doping effectively enhances the electrical conductivity by increasing the charge concentration and mobility within the conjugated polymer matrix. Hence, the present study investigates the compatibility between a ferric chloride (FeCl3) dopant and four distinct conjugated polymers and evaluates the effects of the dopant/polymer combination on the thermoelectric properties of the material. First, the influence of backbone engineering is investigated via a comparison between 4-(3′,4′-difluoro-3,3′′-bis(2-hexyldecyl)-5′′-methyl-[2,2′:5′,2′′-terthiophen]-5-yl)-7-methylbenzo[c][1,2,5]thiadiazole (PC16BTF) and 4-(3,3′′-bis(2-hexyldecyl)-5′′-methyl-[2,2′:5′,2′′-terthiophen]-5-yl)-7-methylbenzo[c][1,2,5]thiadiazole (PC16BTH). These polymers differ in that PC16BTF incorporates two fluorine-atom substituents on the thiophene ring, while PC16BTH contains hydrogen atoms in these positions. Then, the effects of various side-chain lengths are investigated by comparing the abovementioned PC16BTH with both 4-(3,3′′-bis(2-butyloctyl)-5′′-methyl-[2,2′:5′,2′′-terthiophen]-5-yl)-7-methylbenzo[c][1,2,5]thiadiazole (PC12BTH) and 4-methyl-7-(5′′-methyl-3,3′′-bis(2-octyldodecyl)-[2,2′:5′,2′′-terthiophen]-5-yl)benzo[c][1,2,5]thiadiazole (PC20BTH). The FeCl3 dopant was selected for its suitable size and charge transfer capability, which significantly influence the thermoelectric performance of each conjugated polymer. As a result, PC16BTH exhibits the highest power factor (PF) of 22.4 μW m−1 K−2 due to its moderate side-chain length and relatively high doping efficiency. Thus, the present study provides valuable insights into suitable strategies for improving the compatibility between dopants and polymers, thereby offering a promising avenue for further enhancing the thermoelectric performance of doped conjugated polymers. [ABSTRACT FROM AUTHOR]

The ternary strategy can be used to optimize the light harvesting, energy level alignment, and blend morphology of organic photovoltaics (OPVs). Therefore, herein four non-fullerene acceptors (NFAs), INDCDTT-b16 (1), INFDCDTT-b16 (2), INClDCDTT-b16 (3) and INBrDCDTT-b16 (4), featuring dicyclopentadithienothiophene (DCDTT) as the core with soluble branched alkyl side chains with indanone (IN), and its fluoro-(INF), chloro-(INCl) and bromo-(INBr) derivatives as an electron-accepting end group, have been rationally designed and synthesized from simple and readily available starting materials for PM6:Y6-based ternary OPVs. The thermal, optical and electrochemical properties of 1–4 have been studied extensively. Following optimization, the power conversion efficiency (PCE) increased from 15.26% for the PM6:Y6 based OPV to 16.27% for the PM6:Y6:INDCDTT-b16 (1) based OPV. In contrast, ternary OPVs based on NFAs 2, 3, and 4 exhibited PCEs of 14.58%, 15.11%, and 15.14%, respectively. Through tapping-mode atomic force microscopy and grazing-incidence wide-angle X-ray scattering analysis, we confirmed that the introduction of NFAs into PM6:Y6 binary blend films/devices enables adjustment of the blend morphology, leading to improvements in carrier mobility, bimolecular/trap-assisted suppressed recombination, and charge collection. This study demonstrates that our NFA molecular design strategy and further addition of INDCDTT-b16 (1) as a guest acceptor are effective for the construction of high-performance OPVs. [ABSTRACT FROM AUTHOR]

Photothermoelectric (PTE) materials have gained significant attention as a promising avenue for converting light into electricity. Herein, the PTE properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are enhanced by introducing black phosphorus nanosheets (BP NSs) modified with silver nanoparticles (Ag@BP). Under 100 mW cm−2 illumination, the resulting PEDOT:PSS/Ag@BP nanocomposite film (P_Ag@BP) exhibits an output voltage of 528.4 μV compared to 300.9 μV for the PEDOT:PSS film. This is attributed to (i) the enhanced photothermal performance of P_Ag@BP, which generates a temperature difference of 18 °C under 100 mW cm−2 illumination compared to 10 °C for the PEDOT:PSS film and (ii) the enhanced thermoelectric performance of P_Ag@BP, with an increased power factor of 107.2 μW m−1 K−2 compared to 32.9 μW m−1 K−2 for the PEDOT:PSS film. Moreover, a photothermoelectric generator (PTEG) consisting of 36 legs of P_Ag@BP exhibits an open circuit voltage of 16.1 mV, a short circuit current of 47.9 μA, and an output power of 192.6 nW under 120 mW cm−2 illumination. Furthermore, when the PTEG is worn on the forearm and exposed to sunlight, it generates an output voltage of 9.2 mV, thus showcasing its potential application in wearable energy harvesting devices. [ABSTRACT FROM AUTHOR]

Doped polythiophene (PT)-based semiconductors are of significant interest in the field of organic electronics, and are designed for novel thermoelectric applications based on their remarkable electrical properties, ease of processing, and tunable molecular structures. In the present study, the effects of the vinyl linkers in the PTs are systematically investigated in order to understand the interdependence of the structural properties, thin film morphologies, and thermoelectric performance. In particular, the soluble poly(thienylene vinylene) (PTV)-based conjugated polymer, poly[3,4-bis(2-ethylhexyl)thienylene vinylene] (P3,4EHTV), is synthesized via halogen-free and transition metal-free polymerization, and compared with the often-studied poly[3-(ethylhexyl)thiophene] (P3EHT) analogue. In addition, the thermoelectric properties of these two PT films doped with tris(pentafluorophenyl)borane (B(C6F5)3, BCF) are characterized. Furthermore, the bipolaron states of the doped P3,4EHTV are retrieved via detailed ultra violet-visible-near infrared (UV-vis-NIR) and electron paramagnetic resonance (EPR) spectral analyses. Systematic microstructural characterizations reveal that the introduction of vinyl groups into the conjugated polymer backbone results in good miscibility with the BCF dopant, along with enhanced doping efficiency, thereby providing the appropriate sites for accommodating the dopant without disrupting the original chain packing and charge transport channels. The maximum power factor (PF) is measured as 1.47 μW m−1 K−2 for the BCF-doped P3,4EHTV with a molar ratio of 20%, due to the high electrical conductivity (σ) of 0.34 S cm−1, which is ten-fold higher than that of the P3EHT (0.17 μW m−1 K−2). The present study therefore provides a suitable methodology for the realization of doped polymers with good host-dopant miscibility, compatible morphologies, and undisrupted microstructural packing in order to favor an increased power factor by introducing vinylene linkers into the main chains of PTs. [ABSTRACT FROM AUTHOR]

The chemical design of side chains and the physical control of molecular aggregation on conjugated polymer semiconductors have been demonstrated to be effective strategies for achieving efficient doping and charge transport in preparing doped conjugated polymer thermoelectric devices. Herein, our study introduces a unique approach for regulating the doping efficiencies and the thermoelectric properties of polymers, which involves manipulating the hydrophilicity and asymmetric side chain engineering. From isoindigo–bithiophene (IID–T2) donor–acceptor conjugated polymers, three polymers named P(Si–Si), P(Si–O), and P(Si–F) with the symmetric carbosilane side chains, asymmetric carbosilane/oligoether, and carbosilane/semifluorinated side chains, respectively, attached on the IID rings are investigated for their FeCl3-doped thermoelectric films. It is found that the morphological structures and molecular packing can be controlled by altering the hydrophilicity and asymmetricity of side chain substituents. The doped P(Si–O) from the asymmetric side chain with oligoether moieties exhibits the maximum power factor of 23.4 μW m−1 K−2, which is attributed to the high doping efficiency of the polymers due to the intercalation of dopant molecules in the polymer side chains (without chain orientation disruption) while maintaining the charge transport percolation morphologies. The poor affinity between the semifluorinated side chains in P(Si–F) and dopants results in aggregation morphologies with low thermoelectric performance. These findings suggest that the combined asymmetric and hydrophilic side chains in conjugated polymers can effectively facilitate their miscibility with dopants for improving thermoelectric properties. [ABSTRACT FROM AUTHOR]

The conjugated polymer PEDOT:PSS and the related hybrid systems undoubtedly possess a high electrical conductivity and a reasonable Seebeck coefficient, showing potential for thermoelectric applications due to the feasibility of modulating their degree of doping by partially extracting the PSS section. Herein, the combination of PEDOT:PSS, with four ionic liquids (XMIM BF4) having cations of various alkyl chain lengths (methyl, ethyl, butyl, and hexyl denote X = M, E, B, and H, respectively) and the same tetrafluoroborate BF4 anion, was studied to optimize the thermoelectricity. It was found that the introduction of ionic liquids with small-(MMIM BF4) and large-sized cations (HMIM BF4) into the PEDOT:PSS film contributes to an improved Seebeck coefficient and conductivity, respectively. The obtained PEDOT:PSS/MMIM BF4 hybrids display a remarkably enhanced thermoelectric performance with the highest power factor of 86.3 μW m−1 K−2 measured at 313 K. The maximum output power of the robust 7-leg thermoelectric module reaches 10.4 nW for a temperature gradient of 14.0 K. It also exhibits excellent environmental stability with less than 10% variation in resistance for 28 days at room temperature without encapsulation and excellent mechanical flexibility under 500 bending cycles, respectively. A prototype wearable thermoelectric generator installed on the human wrist generates a thermovoltage of ∼0.74 mV with a 4.3 K temperature difference relative to the colder surroundings. Our finding highlights the importance of the rational selection of ionic liquids for enhancing the thermoelectric properties of a PEDOT:PSS film and indicates its potential for use in power generators. [ABSTRACT FROM AUTHOR]

The defects at the interface and grain boundaries of perovskite films downgrade the performance of perovskite solar cells (PSCs) dramatically. Hence, improving perovskite film quality is essential for the achievement of high-performance solar cells. Herein, three new dicyclopentadithienothiophene (DCDTT)-based non-fullerene acceptors (NFAs) IN-DCDTT (1), INCl-DCDTT (2), and INBr-DCDTT (3) are developed as a promising platform for organic–inorganic hybrid perovskite solar cells to achieve simple preparation, high efficiency, and good stability. SEM and XRD data indicate that, with the addition of chlorinated NFA 2 in the active layer preparation, perovskite hybrid films exhibit larger grain sizes and higher crystallinity than pristine perovskite films. As shown by EDS and IR, all the non-fullerene acceptors (compounds 1–3) with functional carbonyl (C＝O) and cyano (C≡N) groups have good interaction with undercoordinated Pb atoms and passivate the trap states in the perovskite films. Time-resolved photoluminescence reveals that the molecule INCl-DCDTT (2) facilitates efficient hole extraction. Consequently, solar cells based on 2−perovskite hybrid films yield an excellent power conversion efficiency of 21.39% with an FF of 0.82, a Jsc of 23.71 mA cm−2, and a Voc of 1.10 V, which represents a significant improvement as compared to a PCE of 17% obtained for the control device. Meanwhile, devices based on IN-DCDTT (1) and INBr-DCDTT (3)−perovskite hybrid films also show enhanced performance with a slightly lower PCE of 19.21% and 20.59%, respectively than cells based on 2−perovskite hybrid films. The cost-effective chlorinated INCl-DCDTT (2) and brominated INBr-DCDTT (3) organic small molecules were successfully used as donor passivation agents to improve the photovoltaic performance of Pb-based PSCs. Furthermore, compound 1–3 derived PSC devices also exhibit excellent long-term stability enhancement. In particular, a device based on INCl-DCDTT (2) treated perovskite retains ∼90% of the initial PCE after 63 days in a glove box as compared to that (55%) of the control device. This simple surface treatment, by the addition of new NFAs, provides a new strategy to simultaneously passivate surface defects and enhance charge transport at the device interface. [ABSTRACT FROM AUTHOR]

Two tetrathioalkyl-substituted bithiophene-based small molecule quinoids (TSBTQs) having different chain lengths (thio-hexyl and -decyl) are synthesized and applied as an n-type active component in organic field effect transistors (OFETs). The resulting two TSBTQs exhibit good solubility in various organic solvents and LUMO levels below −4.0 eV. The theoretical DFT calculation supported by single crystal structures confirms the π-conjugated backbone planarity due to the S(thiophene)⋯S(alkyl) non-covalent interaction. Optimized TSBQT-10 OFETs exhibit an electron mobility of 0.18 cm2 V−1 s−1, which is higher than that of TSBTQ-6 (0.09 cm2 V−1 s−1). The reliability of the OFETs under representative environmental and operational conditions is also determined. The effects of side chains including their lengths and contribution to the main chain π-system coplanarity presented here demonstrate an efficient method to manipulate the charge carrier mobility of the quinoidal organic semiconductors. [ABSTRACT FROM AUTHOR]

This paper reports a UV-sensing organic field-effect phototransistor with a stacked pentacene channel and a doped aggregation-enhanced emission (AIE)-fluorescent electret for potential applications, such as photomemory storage and photodetectors. It is found that the emission of the photoirradiated doped electret (PA-SMX and PI-SMX) layer can be manipulated at various doping levels, which can be further absorbed by the photoactive pentacene channel. These photogenerated excitons can be separated, and the electrons can be trapped into the electret layer in the presence of gate voltage bias. Therefore, the photoinduced programming and electric field-driven erasing effects of the designed memory device based on doped electrets exhibit optimal photomemory performance with a memory window (MW) of 37.2 V and a reliable retention time over 10 000 s with good cyclic endurance. The photodetection can also be modulated by the illumination power intensity, which reflects a photosensitivity (S) of 1.92 × 106 and a photoresponsivity (R) of 45 A W−1 for organic phototransistors with the PI-SM5 doped electret at a photoexcitation intensity of 720 μW cm−2 at 365 nm. The photoresponse following the change in the threshold voltage and photocurrent correlate well with the spectroscopic results and provide further understanding and optimization of organic phototransistor memory devices. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a pair of pentafluorosulfanylated styrenic polymers and their subsequent application in nonvolatile organic field-effect transistor (OFET) memory devices are reported. The unusual pentafluorosulfanyl (SF5) functional group is unique in that it possesses a strong dipole moment that arises from both inductive and resonance effects but is at the same time highly hydrophobic. This intriguing chemical moiety also presents steric bulk that is comparable to a tert-butyl group. Exploiting these intrinsic physicochemical properties, the use of pentafluorosulfanylated styrenic polymers as the electret layer of nonvolatile OFET-based memory devices is reported. Aside from being the first examples of SF5-functionalized styrenic polymers, the reported materials also display excellent thermal stability, moderately large memory windows and retention times, and stable reversibilities spanning multiple PGM/ERS cycles. [ABSTRACT FROM AUTHOR]

Solution-processed micro-ribbon shaped organic semiconductors and high k hybrid gate dielectric were fabricated for low-voltage-driven organic phototransistors, which integrate the photodetection and memory properties within one single device. [ABSTRACT FROM AUTHOR]

Three new organic semiconductors with alkyl chain-substituted tetrathienoacene (TTAR) as the central core and both ends capped with thiophene (DT-TTAR), thienothiophene (DTT-TTAR) and dithienothiophene (DDTT-TTAR) have been synthesized and characterized for organic field effect transistor (OFET) applications. A hole mobility of 0.81 cm2 V−1 s−1 was achieved for the DDTT-TTAR film, which represents the highest mobility yet found for a solution-processable p-type TTAR-based small molecular semiconductors. [ABSTRACT FROM AUTHOR]

We report the morphology and field effect transistor (FET) characteristics of aligned electrospun nanofibers prepared from poly(3-hexylthiophene) (P3HT)–graphene composites. The graphene flakes were more uniformly distributed in the nanofibers compared with spin-coated films, leading to different FET characteristics. The geometrical confinement from electrospun nanofibers resulted in enhanced π–π molecular packing with highly ordered orientation and reduced the grain boundaries under strong stretching forces, thereby increasing carrier mobility. The graphene behaved as an electrically conducting bridge between the P3HT domains in the composites, and thus the FET mobility generally increased as the graphene composition increased. Remarkably, the ES-PG4 FET had the highest hole mobility of 1.82 cm2 V−1 s−1 and a moderately high ION/IOFF of 5.88 × 104, which also exhibited good environmental stability for its transfer characteristics. The experimental results indicated that semiconducting composites based one-dimensional nanofiber devices offer advantages over conventional spin-coated thin films and provide a simple strategy for producing high-performance FET devices. [ABSTRACT FROM AUTHOR]

We report on the fabrication of low-voltage operating pentacene-based organic thin film transistors (OTFTs), composed of a high k gate dielectric made from titanium–silicon oxide/organic hybrid materials covered with a long alkyl chain having a phosphonic binding group. [ABSTRACT FROM AUTHOR]

We report the nonvolatile memory characteristics of organic field effect transistors (OFETs) using one-dimensional aligned electrospun (ES) nanofibers of semiconducting poly(9,9-dioctyl-fluorene-co-bithiophene) (F8T2). The effects of the nanofiber diameter associated with the polymer chain orientation on the charge transport and storage ability were explored. The OFET devices using the F8T2 ES nanofibers exhibited a large average memory window of ∼30 V, an on–off ratio of 102–103 and a hole mobility of 10−4 to 10−2 cm2 V−1 s−1. The write, erase and read processes of the memory device were performed by voltages across the nanofiber channels for at least 100 cycles and could be stabilized for at least 1000 s. The reversible hysteresis characteristics were attributed to the shallow trapping in the ordered/disordered domains of the F8T2 nanofibers from the in situ grazing incidence wide angle X-ray scattering (GIWAXS) analysis. Our results suggest that the semiconducting ES nanofibers could have potential applications for high performance OFET-based nonvolatile organic memory devices. [ABSTRACT FROM AUTHOR]

A conjugated poly(fluorene-thiophene) donor and a tethered phenanthro[9,10-d]imidazole acceptor (PFT-PI) was used as the active layer in flexible nonvolatile resistor memory devices with low threshold voltages (±2 V), low switching powers (∼100 μW cm(-2)), large ON/OFF memory windows (10(4)), good retention (>10(4) s) and excellent endurance against electric and mechanical stimulus.

Bistable resistive switching characteristics obtained using a supramolecular hybrid route to hydrogen-bonded block copolymers (BCP) and graphene oxide (GO) as charge storage materials are reported for write-once-read-many-times (WORM) memory devices., (This journal is © The Royal Society of Chemistry 2012)