5‐Hexyl‐5′′‐hexynyl‐2,2′:5′,2′′‐terthiophene exhibits the smectic E phase below 200 °C and does not crystallize when it is cooled to ?100 °C. Between 200 and ?100 °C, non‐dispersive transport is observed for holes and electrons with time‐of‐flight spectroscopy. Over the entire temperature range, the electron mobility is approximately twice as high as that of the hole. The hole and electron transport characteristics in the smectic phase below 0 °C are explained by the Gaussian disorder model, which was proposed for amorphous organic semiconductors. The disorder parameters, σ and Σ, are almost the same for holes and electrons. However, the pre‐exponential parameter μ0 for the electron is twice as large as that for the hole, which can be attributed to the difference in the extension of the LUMO of the molecules. The energetic disorder σ is primarily determined by the disorder in the orientation of the permanent dipoles of liquid crystal molecules. 相似文献
Two diketopyrrolopyrrole (DPP)‐based donor–acceptor (D–A) conjugated molecules, DPP‐F and DPP‐2F, which contain E‐(1,2‐difluorovinyl) moieties, are reported. The LUMO energies of DPP‐F and DPP‐2F were estimated to be ?3.49 and ?3.70 eV, respectively, based on their redox potentials and absorption spectral data; these values were clearly lowered because of the incorporation of electron‐withdrawing E‐(1,2‐difluorovinyl) moieties. Organic field‐effect transistors (OFETs) with thin films of DPP‐F and DPP‐2F were successfully fabricated with conventional techniques. Based on the respective transfer and output characteristics measured in an inert atmosphere, thin films of DPP‐2F display ambipolar semiconducting behavior with hole and electron mobilities reaching 0.42 and 0.80 cm2 V?1 s?1, respectively. The as‐prepared OFET of DPP‐2F already shows high hole and electron mobilities that are not influenced remarkably by thermal annealing. For thin films of DPP‐F, only p‐type semiconducting behavior was observed in both an inert atmosphere and air, and the hole mobility increased to 0.1 cm2 V?1 s?1 after thermal annealing. XRD and AFM studies were performed with thin films of DPP‐F and DPP‐2F after annealing at different temperatures. 相似文献
Mesoporous barium titanate (BT) thin films are synthesized by a surfactant‐assisted sol–gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (Tc) of the mesoporous BT reaches approximately 470 °C. 相似文献
The morphology of micro‐ and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium‐tin‐oxide‐coated glass is presented for the extended 1‐alkyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnC1im][Ntf2]; n=1–8) series, and the results show the nanostructuration of ILs. The use of in‐vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films. 相似文献
Dye‐sensitized solar cells (DSCs) with nanotubular TiO2 electrodes of varying thicknesses are compared to DSCs based on conventional nanoparticulate electrodes. Despite the higher degree of order in one‐dimensional nanotubular electrodes, electron transport times and diffusion coefficients, determined under short‐circuit conditions, are comparable to those of nanoparticulate electrodes. The quasi‐Fermi level, however, is much lower in the nanotubes, suggesting a lower concentration of conduction band electrons. This provides evidence for a much higher diffusion coefficient for conduction band electrons in nanotubes than in nanoparticulate films. The electron lifetime and the diffusion length are significantly longer in nanotubular TiO2 electrodes than in nanoparticulate films. Nanotubular electrodes have a trap distribution that differs significantly from nanoparticulate electrodes; they possess relatively deeper traps and have a characteristic energy of the exponential distribution that is more than two times that of nanoparticulate electrodes.相似文献
A quinoidal small‐molecule semiconductor QDPPBTT was synthesized. Organic thin‐film transistor (OTFT) devices based on QDPPBTT showed an electron mobility as high as 0.13 cm2 V?1 s?1 and Ion/Ioff ratio of 106 under ambient conditions. We suggested that 2D extended π‐conjugation and quinoid‐enhancing effect had an important role in electron mobility and stability of n‐type FET devices, which might be a good strategy in designing new material systems. 相似文献
Organic field‐effect transistors incorporating planar π‐conjugated metal‐free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H2(OX)] (H2OX=etioporphyrin‐I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H2TBP=tetra‐(n‐butyl)porphyrin) as determined by single crystal X‐ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field‐effect transistors (FETs) made from thin films of all these metal‐free macrocycles and their metal derivatives show a p‐type semiconductor behavior with a charge mobility (μ) ranging from 10?6 to 10?1 cm2 V?1 s?1. Annealing the as‐deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2×10?1 cm2 V?1 s?1, which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field‐effect transistors made from thin films of metal‐free macrocycles (except tetra‐(n‐propyl)porphycene) have significantly lower μ values (3.0×10?6–3.7×10?5 cm2 V?1 s?1). 相似文献
The ability to effectively transfer photoexcited electrons and holes is an important endeavor toward achieving high‐efficiency solar energy conversion. Now, a simple yet robust acid‐treatment strategy is used to judiciously create an amorphous TiO2 buffer layer intimately situated on the anatase TiO2 surface as an electron‐transport layer (ETL) for efficient electron transport. The facile acid treatment is capable of weakening the bonding of zigzag octahedral chains in anatase TiO2, thereby shortening staggered octahedron chains to form an amorphous buffer layer on the anatase TiO2 surface. Such amorphous TiO2‐coated ETL possesses an increased electron density owing to the presence of oxygen vacancies, leading to efficient electron transfer from perovskite to TiO2. Compared to pristine TiO2‐based devices, the perovskite solar cells (PSCs) with acid‐treated TiO2 ETL exhibit an enhanced short‐circuit current and power conversion efficiency. 相似文献
DTfBT‐Th3, a new conjugated polymer based on dithienobenzothiadiazole and terthiophene, possesses a bandgap of ≈1.86 eV and a HOMO level of −5.27 eV. Due to strong interchain aggregation, DTfBT‐Th3 can not be well dissolved in chlorobenzene (CB) and o‐dichlorobenzene (DCB) at room temperature (RT), but the polymer can be processed from hot CB and DCB solutions of ≈100 °C. In CB, with a lower solvation ability, a certain polymer chain aggregation can be preserved, even in hot solution. DTfBT‐Th3 displays a field‐effect hole mobility of 0.55 cm2 V−1 s−1 when fabricated from hot CB solution, which is higher than that of the device processed from hot DCB (0.16 cm2 V−1 s−1). In DTfBT‐Th3‐based polymer solar cells, a good power conversion efficiency from 5.37% to 6.67% can be achieved with 150−300 nm thick active layers casted from hot CB solution, while the highest efficiency for hot DCB‐processed solar cells is only 5.07%. The results demonstrate that using a solvent with a lower solvation ability, as a “wet control” process, is beneficial to preserve strong interchain aggregation of a conjugated polymer during solution processing, showing great potential to improve its performances in optoelectronic devices.
The development of selenophene‐flanked DPP (SeDPP) based copolymers, especially for the ambipolar ones, lags behind other aromatic group flanked DPP‐based polymers. Herein, we report two new ambipolar SeDPP‐based conjugated polymers. One is the alternating polymer PSeDPPFT with normal SeDPP and 3,4‐difluorothiophene units. The other is PSeFDFT , in which the electron acceptor unit is replaced by a new SeDPP derivative, referred as to half‐fused SeDPP. The more planar structure of half‐fused SeDPP endows the backbone of PSeFDFT with good rigidity and planarity. Both polymers exhibit ambipolar transporting properties in air. The PSeFDFT based field‐effect transistors (FETs) display higher and more balanced ambipolar properties with μhave of 0.27 cm2·V–1·s–1, μeave of 0.18 cm2·V–1·s–1, and μhave/μeave of 1.5 than those of PSeDPPFT (μhave = 0.11 cm2·V–1·s–1, μeave = 0.042 cm2·V–1·s–1, and μh/μe = 2.6). This is attributed to the more planar structure, lower LUMO level, higher HOMO level, and better interchain packing orientations of PSeFDFT by comparing with PSeDPPFT . Therefore, a new molecular design strategy to modulate the hole and electron transporting properties is proposed for conjugated D‐A polymers. 相似文献
We report the synthesis, characterization, and optical and electrochemical properties of two structurally similar coumarin dyes ( C1 and C2 ). These dyes have been deployed as sensitizers in TiO2 nanoparticles and thin films, and the effect of molecular structure on interfacial electron‐transfer dynamics has been studied. Steady‐state optical absorption, emission, and time‐resolved emission studies on both C1 and C2 , varying the polarity of the solvent and the solution pH, suggest that both photoexcited dyes exist in a locally excited (LE) state in solvents of low polarity. In highly polar solvents, however, C1 exists in an intramolecular charge‐transfer (ICT) state, whereas C2 exists in both ICT and twisted intramolecular charge‐transfer (TICT) states, their populations depending on the degree of polarity of the solvent and the pH of the solution. We have employed femtosecond transient absorption spectroscopy to monitor the charge‐transfer dynamics in C1 ‐ and C2 ‐sensitized TiO2 nanoparticles and thin films. Electron injection has been confirmed by direct detection of electrons in the conduction band of TiO2 nanoparticles and of radical cations of the dyes in the visible and near‐IR regions of the transient absorption spectra. Electron injection in both the C1 /TiO2 and C2 /TiO2 systems has been found to be pulse‐width limited (<100 fs); however, back‐electron‐transfer (BET) dynamics has been found to be slower in the C2 /TiO2 system than in the C1 /TiO2 system. The involvement of TICT states in C2 is solely responsible for the higher electron injection yield as well as the slower BET process compared to those in the C1 /TiO2 system. Further pH‐dependent experiments on C1 ‐ and C2 ‐sensitized TiO2 thin films have corroborated the participation of the TICT state in the slower BET process in the C2 /TiO2 system. 相似文献