首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Variable angle spectroscopic ellipsometry (VASE) in the wavelength range from 245 to 1680 nm has been applied to determine the optical properties of the recently developed electron donor α,ω-bis-dicyanovinylene-sexithiophene (DCV6T), an efficient absorber material in organic solar cells (OSCs). To ensure uniqueness of the evaluation results interference enhanced substrates are used and comparison to simple native silicon substrates is presented. Similar as applied in OSC, DCV6T was deposited both as a pure single layer as well as in a mixed heterojunction with C60. For both cases, the in-plane refractive indices and extinction coefficients were higher than the out-of-plane ones, revealing that the DCV6T molecules in the films are preferentially horizontally oriented. This rough indication was further quantified by the so called molecular orientation parameter. Moreover, it is shown that annealing initiates molecular reorganization of the films, which leads to a higher birefringence and more defined horizontal orientation in the single layer. However, in the mixed layer annealing seems to reduce anisotropy. These effects and the consequences for the performance of organic solar cells are discussed.  相似文献   

2.
We report that the molecular orientation of a disk-shaped Pt(II) complex dopant in organic thin films is linearly proportional to the orientation of the host molecules. We ascribe this relationship to the parallel alignment of the Pt complex with the host molecules induced by a π-π interaction. This would be caused by their planar and conjugated structure, indicating that the intermolecular interaction and steric effect play an important role. This finding can be applied to obtain a horizontal emitter orientation, resulting in highly efficient OLEDs based on Pt(II) complexes.  相似文献   

3.
Photoconductivity, photoluminescence (PL), and thermally stimulated luminescence of photoconductive poly-N-epoxypropylcarbazole and poly-N-vinylcarbazole films and non-photoconductive polyvinylbutyral, polyvinyl alcohol, polystyrene, and polyethylene films doped with cationic, anionic, and neutral dyes are studied. It is found that the PL of cationic dyes in photoconductive polymer films is enhanced in comparison to nonphotoconductive ones. The PL enhancement correlates with an increase in photoconductivity, with the quenching effect of an external electric field on the PL intensity, and with an increase in the intensity of the recombination luminescence. It is assumed that this enhancement is related to the presence of predimer traps for holes in the vicinity of dye ions in the films of carbazolyl-containing polymers. A model describing the trap formation upon the photoexcitation of holes into predimer states is suggested.  相似文献   

4.
The results of experimental studies of the copper-doped hydrogenated amorphous carbon films by scanning tunneling microscopy and spectroscopy are reported. These results are indicative of the effect of spatial ordering of nanostructures in thin films based on carbon and copper. Geometric parameters of nanostructures were measured. In the context of the Simmons model, the work function was estimated to be equal to ? ~0.05 eV. Oscillations in differential conductance with a period in a voltage of ΔV=200–400 mV were detected in tunneling contacts of Ir with the films. The origin of the observed oscillations is discussed.  相似文献   

5.
The electrical behavior of devices based on highly crystalline thin films of organic semiconductors is inherently anisotropic. Thin film optimization requires simple and accessible means to characterize the orientation of the constituent crystals. The standard polarized light microscopy (PLM) provides a contrast between different crystallites but fails to distinguish crystals with relative orientation of 90°. In this paper, we discuss two methods that enable the unambiguous identification of crystal orientation in thin films of optically anisotropic materials: PLM with a full-wave retardation plate and differential interference contrast (DIC). The latter is standard on most microscopes and delivers images with high contrast and good color balance.As an illustration, we use DIC to extract the optical properties of highly crystalline thin films of three high-performance organic semiconductors: rubrene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT). Building on the relation between optical properties and crystal orientation, we demonstrate how DIC characterizes the in-plane crystal orientation of these thin films. This leads to the identification of the fast growth direction of the crystal front.  相似文献   

6.
《Organic Electronics》2014,15(2):577-581
The magnetic field effects of photoluminescence (MPL) from rubrene doped organic films were recorded at different temperatures. The measured line shapes were attributed to the field modification on the rate constant of thermally activated singlet exciton fission which occurred between the doped rubrene molecules. And its amplitude exhibited a nonlinear dependence on the averaged intermolecular distance. Such an observation implies that the intermolecular coupling (IMC) which is modulated by changing the intermolecular distance is able to significantly affect the intensity of fission process. Therefore, investigating the variation of singlet fission with different strength of IMC could be an important means to study the dynamics of fission process. Our work reveals the importance of IMC factor which needs to be considered for the design of efficient singlet fission-sensitized organic photovoltaic devices.  相似文献   

7.
The influence of charge transfer from organic molecules to transition metal oxide on molecular orientation characteristics of N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) was investigated. Absorption peaks originating from neutral and cationic states of α-NPD increased in absorbance when α-NPD was deposited on metal oxides (MoO2, MoO3, and WO3). Photoluminescence from this α-NPD was directional normal to the film plane. These results indicate that α-NPD is horizontally oriented near the metal oxide surfaces so that charge transfer from α-NPD to metal oxide occurs efficiently. Such horizontal orientation of α-NPD enhanced current density of hole-only α-NPD devices because of improvement of wave function overlap and charge transfer degree at the metal oxide/α-NPD interface.  相似文献   

8.
Features of electrical conductivity and photoconductivity of polyvinylbutyral films containing porous silicon nanoparticles and similar films doped with cationic and anionic polymethine dyes are studied. Sensitization of the photoelectric effect by dyes with different ionicities in films is explained by the possible photogeneration of holes and electrons from dye molecules and the intrinsic bipolar conductivity of porous silicon nanoparticles. It is assumed that the electronic conductivity in porous silicon nanoparticles is higher in comparison with p-type conductivity.  相似文献   

9.
The authors investigate a relationship between substrate transfer speeds during vacuum vapor deposition and orientation characteristics of organic molecules. Results show that rod-shaped molecules of alpha-sexithiophene (α-6T) are oriented in a substrate transfer direction and an absorption dichroic ratio of 1.44 is obtained from the oriented α-6T molecule film when a high substrate transfer speed of 4 m s−1 is used. By combining the substrate transfer technique with homoepitaxial growth of α-6T molecules on a rubbed surface, the absorption dichroic ratio further increases to 4.29. Polarized electroluminescence (EL) characteristics are investigated using rod-shaped molecules of 4,4′-bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi) as a light-emitting hole-transport layer. An EL dichroic ratio of 2.12 is obtained due to an orientation of DPAVBi molecules caused by combining two techniques.  相似文献   

10.
Pure nickel and gold thin films were vacuum-deposited on (111) silicon single crystals. When Ni/Au/Si or Au/Ni/Si samples were heated to about 550° insitu, hexagonal or deformed hexagonal shaped crystallites were formed on the silicon substrates. The composition of these crystallites was determined by using x-ray diffraction, scanning elec-tron microscopy and scanning Auger microprobe methods. The crystallites were identified as NiSi2. The crystal-lites on the (111) silicon plane parallel to the surface appeared as regular hexagons while the inclined crystal-lites resembled trapezia. The results of Auger spectra and in-depth composition profiles for Ni, Au, and Si showed that the NiSi2 crystallites are islands in a matrix of Au-Si eutectic. Work supported by the Materials Research Division of the National Science Foundation  相似文献   

11.
Amorphous Teflon®, deposited by spin-coating and thermal evaporation, has been studied as a low dielectric constant insulator for high performance interconnects. Since it is difficult to deposit a film on amorphous Teflon because of its inert chemical bonds, plasma etching and Zonyl FSN® fluorosurfactant are used to improve the adhesion of photoresist to amorphous Teflon. Plasma etching is shown to increase surface roughness and change chemical bonds of the amorphous Teflon, resulting in improved adhesion of metals and SiO2 to amorphous Teflon. While amorphous Teflon cannot be etched by wet chemicals, etching the films in Ar, O2, or CF4/O2 plasma is very effective.  相似文献   

12.
We report on transparent and flexible amorphous In–Zn–Al–O (a-IZAO) films prepared by roll-to-roll (RTR) sputtering for use as anodes in acidic buffer free flexible organic solar cells (FOSCs). The presence of Zn and Al structural stabilizers in the In2O3 matrix produced a completely amorphous structure with the high optical transmittance of 89.25% and the low resistivity of 2.123 × 10−3 Ω-cm, as well as the high work function of 5.14 eV, making the a-IZAO films suitable for use as flexible anodes for FOSCs. In addition, the a-IZAO films showed no change in resistance (ΔR) during outer and inner bending fatigue tests due to their good mechanical flexibility. Relative to the power conversion efficiency (1.944%) of a PEDOT:PSS-based FOSCs, a FOSC fabricated by using an a-IZAO anode and without the use of acidic PEDOT:PSS buffer showed greater power conversion efficiency (2.509%), owing to the absence of interfacial reactions between the acidic PEDOT:PSS and the a-IZAO anode.  相似文献   

13.
Switching and memory effects in amorphous chalcogenide thin films   总被引:1,自引:0,他引:1  
The performance of threshold- and memory-switching devices is discussed. The threshold devices were prepared by vacuum deposition from the Ge-As-Te-Si system and exhibited threshold voltages over a wide range from less than 2.0 V to greater than 50 V. Lifetimes of the order of 106-108switching operations before failure were obtained and the operation of the threshold device with a capacitative load was demonstrated. Memory-switching devices were prepared from the Ge-As-Te system. The bistable operation is discussed and it is concluded that the bistable impedance states are due to the presence, or absence, of a crystalline filament between the electrodes. Typical pulse levels required to produce the transition between the impedance states were 2 × 10-2A for 5 × 10-3s and 5 × 10-2A for 5 × 10-6s. The devices possess fairly stable characteristics and currently have lifetimes of 102- 103operations before failure; this is expected to improve with device development.  相似文献   

14.
通过化学溶液沉积法制备的BiFeO3-BaTiO3薄膜在室温下能够同时显现铁电性和铁磁性。在600℃至700℃的条件下,以Pt/TiOx/SiO2/Si为载体,能够成功得到钙钛矿单相0.7BiFeO3-0.3BaTiO3薄膜。随着结晶温度上升,晶粒持续增长,最终在700℃时到达更高的结晶度。由于0.7BiFeO3-0.3BaTiO3薄膜的绝缘电阻较低,它所显现的极化(P)-电场(E)磁滞回线较弱。尽管如此,在0.7BiFeO3-0.3BaTiO3薄膜铁的位置上添加锰,高作用场的漏电流有效地减少,最终铁电性质得到了提高。在室温下,添加了摩尔分数5%的锰的0.7BiFeO3-0.3BaTiO3薄膜同时显现铁电极化和铁磁磁化磁滞回线。  相似文献   

15.
非晶含氢碳膜(amorphous ydmgenated arbon a-C:H films)在力学、热学、电学、化学、光学等方面具有优异的性能,被广泛应用于诸多领域,有巨大的应用前景。随着a-C:H薄膜制备技术的进一步完善,在此基础上的改性材料又引起了人们的注意。氮掺杂类金刚石薄膜(a-C:H:N)近年来成为人们研究的  相似文献   

16.
Excess noise measurements have been carried out on either sputtered a-Si or sputtered a-Si:H thin films, at 300 K and in the absence of light. The dependence of excess noise amplitude on hydrogen partial pressure in the sputtering chamber during the film growth has been studied. Investigations of 1/f noise in B-doped a-Si:H thin films have also been carried out. The results of this study show that1/f noise can be correlated to both the hydrogen content in a-Si:H films and to the doping of the films. The noise is explained in terms of fluctuations in the number of gap states due to thermally activated configurational changes involving hydrogenated bonds and dangling bonds.  相似文献   

17.
Relaxation of electrical defects in amorphous barium titanate thin films was studied by the thermally stimulated current (TSC) technique. We were able to detect at least three relaxation peaks in the TSC spectra. One is associated with activation energy of 0.65 eV and is possibly related to electronic trap levels below the conduction band. Another one is associated with activation energy close to 1 eV corresponding to the migration of positively charged oxygen vacancies within the films.  相似文献   

18.
The diffusion of a chromium bottom contact has been studied through thin 10-nm amorphous silicon film. The concentration of the diffused impurity has been analyzed by an X-ray photon spectroscopy technique and the diffusion coefficient was estimated. Diffusion annealing was carried out in vacuum (10?6 mTorr), the temperature was kept at 400°C, and the annealing time was varied from 0 to 300 min. The authors propose that diffusion of chromium in thin hydrogenated amorphous film is limited by silicide formation at the metal-silicon interface.  相似文献   

19.
Optical and electrical properties have been measured for amorphous SiC films prepared by rf sputtering in a pure Ar atmosphere with a sintered 6H-SiC target. The absorption edge E0 determined from the relation of αhΝ = B(hΝ-E0)2 ranged from 1.45 to 1.80 eV depending on the film thickness and the substrate temperature. The room temperature electrical conductivity is in the range of 5.4×10−11 and 1.4×10−5 Ω−1cm−1. The absorption edge decreases and the conductivity increases with increasing film thickness. The absorption edge shifts to shorter wavelengths (blue shift) and the conductivity decreases during annealing below 400‡C for 60 min, whereas the absorption edge shifts to the longer wavelength side (red shift) and the conductivity increases during annealing at 800‡C It is proposed that the two annealing processes cause structural changes in amorphous SiC films, one of which involves removal of defects or voids while the other involves rearrangement or rebonding of the component atoms.  相似文献   

20.
Boron carbide films were grown using glow discharge decomposition of C2B10H12 powder sublimation products. The film composition found as a-B0.52C0.48:H using nuclear reaction and infrared spectroscopy techniques was shown to depend weakly on the discharge gas (Ar or He) and the substrate temperature (20–100°C). The optical band gap was found to be about 3.8 eV; the resistivity varied from 106 to 105 Ω cm as the substrate temperature increased. Weak photoluminescence with a peak at 475 nm indicates that there is an acceptor level in the band gap which correlates with the conduction activation energy.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号