The organic films of vanadyl-phthalocyanine (VOPc) compounds showed weak epitaxy growth (WEG) behavior on thin ordered para-sexiphenyl (p-6P) layer with high substrate temperature. The WEG of VOPc molecules standing up on the p-6P layer leaded to high in-plane orientation and their layer-by-layer growth behavior. In consequence, high quality VOPc films were obtained, which were consisted of lamellar crystals. Organic field-effect transistors with VOPc∕p-6P films as active layers realized high mobility of above 1cm2∕Vs. This result indicated that nonplanar compounds can obtain a device performance better than planar compounds, therefore, it may provide a rule to find disklike organic semiconductor materials.

The relationship between the performance characteristics of organic field‐effect transistors (OFETs) with 2,5‐bis(4‐biphenylyl)bithiophene/copper hexadecafluorophthalocyanine (BP2T/F16CuPc) heterojunctions and the thickness of the BP2T bottom layer is investigated. Three operating modes (n‐channel, ambipolar, and p‐channel) are obtained by varying the thickness of the organic semiconductor layer. The changes in operating mode are attributable to the morphology of the film and the heterojunction effect, which also leads to an evolution of the field‐effect mobility with increasing film thickness. In BP2T/F16CuPc heterojunctions the mobile charge carriers accumulate at both sides of the heterojunction interface, with an accumulation layer thickness of ca. 10 nm. High field‐effect mobility values can be achieved in continuous and flat films that exhibit the heterojunction effect.

Organic thin-film transistors (OTFTs) have attracted much attention because of their potential application in low-cost, flexible, and large-area electronics. [1,2] High-performance n-type semiconductors are an essential component in OTFT applications, such as ambipolar transistors and complementary metal-oxide-semiconductor (CMOS) circuits. [3][4][5] However, although various high-performance n-type organic semiconducting materials have been reported, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] most of them can only deliver OTFT devices that have to operate in vacuum or under an inert atmosphere, and only a few of them, that is, hexadecahalogenated metal phthalocyanine [21,22] and perylene and naphthalene diimides with electron-withdrawing groups, [9,13,14] have been claimed to allow fabrication of devices that are relatively stable in air.Owing to their high mobility, great stability, and ease of preparation metal phthalocyanine (MPc) derivatives have become one of the most important classes of organic semiconductors for OTFTs since the first demonstration of high-performance OTFTs with electron or hole mobilities over 0.01 cm 2 V À1 s À1

A series of donor−acceptor low-bandgap conjugated polymers, i.e., PT n BT (n = 2−6), composed of alternating oligothiophene (OTh) and 2,1,3-benzothiadiazole (BT) units were synthesized by Stille cross-coupling polymerization. The number of thiophene rings in OTh units, that is n, was tuned from 2 to 6. All these polymers display two absorption bands in both solutions and films with absorption maxima depending on n. From solution to film, absorption spectra of the polymers exhibit a noticeable red shift. Both high- and low-energy absorption bands of PT5BT and PT6BT films locate in the visible region, which are at 468 and 662 nm for PT5BT and 494 and 657 nm for PT6BT. Consequently, their absorption spectra cover the region between 400 and 800 nm, and their optical bandgaps are 1.56 and 1.52 eV, respectively, which renders them “black” polymers. Moreover, PT5BT and PT6BT can form highly ordered thin films with field-effect mobilities up to 2.46 × 10−2 and 1.40 × 10−2 cm2 V−1 s−1, respectively. Bulk-heterojunction polymer solar cells (PSCs) fabricated with these polymers as the donor materials and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) as the acceptor material exhibited power conversion efficiencies (PCEs) of 0.93−2.23%. PSCs based on the high-mobility “black” polymer PT6BT showed the best device performance with a PCE of 2.23%. Our results provide a rational strategy for design and synthesis of high-mobility low-bandgap conjugated polymers with broad absorption range.

We have measured the current as a function of gate charge Q in superconducting Coulomb blockade electrometers with charging energies E, &&A, the superconducting gap. We find a large pair current which exhibits a clear transition from 2e to e periodicity at about 250 mK. To explain our data, we propose an equilibrium model in which the current is due entirely to Cooper pairs. The periodicity change results from rapid shifts in the instantaneous etfective Q, caused by Iluctuations in quasiparticle number.We find good agreement, and predict the loss of 2e periodic current for large E,.PACS numbers: 73.40. Rw, 73.40.6k, 74.50.+r A Coulomb-blockade electrometer can be thought of as a very small conducting island which is weakly coupled to the external world by means of two tunnel junctions. The device also has a capacitively coupled gate electrode, with capacitance Cg, which allows the island's potential to be altered by application of a voltage Vg. To ensure that the coupling is weak, and therefore that the number of electrons on the island is well defined, each junction must have a normal state tunneling resistance R"&h/4e and the total island capacitance C~must be small enough that the elementary charging energy E, =e /2Cs is much greater than kqT, where T is the temperature. To use the electrometer, one applies a fixed voltage V across the series junctions (see inset to Fig. 1), and measures the current I passing through the island as a function of the gate charge Q=CgVg. The device characteristics are well understood when the island and leads are normal metal; current arises from the discrete tunneling of electrons onto the island and is periodic in Q with periodicity e [1,2]. The e periodicity in the normal state arises from the simple fact that the current is carried by individual electrons. Naively, one would expect a superconducting device to show a 2e periodicity because the current should then be carried by Cooper pairs. However, in several previous studies where 2e periodicity was expected, only eperiodic behavior was found [3][4][5]. Recently, 2e periodicity has been reported for entirely superconducting electrometers (SSS) [5][6][7][8], as well as electrometers in which the island is superconducting and the leads are normal (NSN) [9][10][11][12]. Tuominen et al. [6] found the current to be 2e periodic below -300 mK, and explained the crossover to e periodicity above that temperature in terms of the disappearance of a parity-dependent free energy. Although their explanation gives the correct transition temperature, the complexity of their I(g) curves makes it di%cult to interpret the crossover in detail. I n this Letter, we present detailed measurements and discussion of the 2e to e periodicity transition in two SSS electrometers. In a notable departure from previously reported work, our data are taken on devices with E, ((h"and show remarkably simple features that we explain using an equilibrium theory which incorporates E, and Q as well Island 0--:10

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Single-crystal-like organic heterojunction films of copper phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F16CuPc) were fabricated by weak-epitaxy-growth method. The intrinsic properties of organic heterojunction were revealed through threshold voltage shift of field-effect transistors and measurement of single-crystal-like diodes. At both sides of the heterojunction interface 40 nm thick charge accumulation layers formed, which showed that the long carriers’ diffusion length is due to the high crystallinity and low density of deep bulk traps of single-crystal-like films. This also indicated the electronic properties of organic heterojunction can be adjusted by controlling the growth condition.

Air-stable n-type field effect transistors were fabricated with an axially oxygen substituted metal phthalocyanine, tin (IV) phthalocyanine oxide (SnOPc), as active layers. The SnOPc thin films showed highly crystallinity on modified dielectric layer, and the electron field-effect mobility reached 0.44cm2V−1s−1. After storage in air for 32days, the mobility and on/off ratio did not obviously change. The above results also indicated that it is an effective approach of seeking n-type semiconductor by incorporating the appropriate metal connected with electron-withdrawing group into π-π conjugated system.