Bilayered organic field-effect transistors were fabricated by successive vapor-depositions of 1,4-bis{5-[4-(trifluoromethyl)phenyl]thiophene-2-yl}benzene (AC5-CF3) and 5,5″-bis(4-biphenylyl)-2,2′:5′,2″-terthiophene (BP3T). With decreasing thickness of the n-type AC5-CF3 film in contact with the dielectric layer, ambipolar characteristics were improved under both positive and negative gate biases. Two types of asymmetric source/drain electrodes were prepared by either obliquely shadowed lamination or mask-shifted depositions of AlLi and Au. The latter method in which the device was characterized without exposure to air after the electrode deposition of AlLi resulted in remarkable improvement of ambipolarity and reduction of leak currents. Finally, optimized ambipolar mobilities of μe = 5.00 × 10−2 and μh = 1.56 × 10−2 cm2 V−1 s−1) were obtained with 5-nm-thick AC5-CF3 and 30-nm-thick BP3T.Graphical abstractHighlights► Bilayered organic field-effect transistors were fabricated by vapor-deposition. ► n- and p-type thiophene/phenylene co-oligomer derivatives were used. ► Well-balanced ambipolar characteristics were obtained by thinning the n-type layer. ► Fabrication of asymmetric electrodes was improved for device performances.

Light-emitting field-effect transistors with a liquid crystalline polymer of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) were investigated under alternating current (AC) gate operations. Bottom-contact/top-gate devices were fabricated with indium-tin-oxide (ITO) source/drain electrodes, a poly(methyl methacrylate) dielectric and a gold gate electrode. The crystalline F8T2 film exhibited ambipolar characteristics with electron and hole mobilities of 1.8 × 10−3 and 2.5 × 10−3 cm2/V s, respectively, although the threshold voltage was considerably higher for electron injection. By applying square-wave voltages to the gate, light emission was obtained at the both edges of the source and drain electrodes by alternating injection of opposite carriers even when the source and drain were grounded. The light intensity was enhanced in the channel region by biasing the source negative while biasing the drain positive where the holes injected from the drain were transported to recombine with the electrons injected at the source edge.Graphical abstractHighlights► Organic field-effect transistors were fabricated with a liquid crystalline polymer. ► Ambipolar characteristics were obtained with the bottom-contact/top-gate structure. ► Light emission was observed from the device under AC-gate operations. ► Alternate carrier injections occurred at the source and drain electrode edges. ► Time responses of light emission were explained by the recombination mechanism.

Thin film waveguides of polyphenylenevinylene were formed on a distributed feedback resonator. Light emission under pulsed optical pumping was measured as a function of excitation wavelengths. A distributed feedback lasing appeared constantly at 635 nm. In addition, an emission peak due to stimulated resonant Raman scattering emerged and its peak position shifted according to the excitation wavelength. When the latter peak just overlapped with the former one, the emission intensity was enhanced and its peak width and background noise by amplified spontaneous emission were reduced. The coupling of Raman scattering with the feedback mode would be a useful technology for development of a plastic laser.

A new side electron emission device (SEED) was fabricated with carbon nanofiber/aluminum (CNF/Al) composites prepared by the elastomer precursor method. In the SEED, a cross-sectional side face of the CNF/Al composite plate was perpendicularly placed onto an anode surface by inserting an insulating spacer. Above a certain threshold voltage in a vacuum, field electrons were obtained from the side face of the composite emitter. With increasing content of CNFs in the composite, the threshold voltage decreased and emission currents increased. The current of ~ 8 μA was kept stable up to 93 h under a continuous application of 1 kV. This improved stability as compared to a conventional field emission device was attributed to a reduced damage of CNFs in the SEED structure.

Photoluminescence (PL) based on Förster energy transfer between p-sexiphenyl (p-6P) and 5,5′-bis(4-phenylyl)-2,2′-bithiophene (BP2T) was investigated for their coevaporated and laminated thin films. In the former films, fluorescence quenching of the p-6P was accompanied by appearance of BP2T fluorescence, which indicated existence of the energy transfer between the donors and the acceptors. The latter films were fabricated by successive depositions of p-6P, MgF2 and BP2T in which the thickness of the MgF2 spacer was varied. The energy-transferred acceptor fluorescence was suppressed by the spacer thicker than the Förster distance (∼10 nm).

Ambipolar organic field effect transistors with heterojunction structures have been fabricated using a biphenyl-capped thiophene oligomer (BP2T) and a naphthalene derivative (GS1b) for p-type and n-type organic semiconductors, respectively. Asymmetric electrode structures with Au source and Al–Li drain resulted in better performances than that of a symmetric device due to improved electron injection by the low work-function drain metal.

Photoluminescence dynamics based on Förster energy transfer between 2,5-bis(4-biphenylyl)thiophene (BP1T) and 5,5ʺʺ′-diphenyl-2,2′:5′,2ʺ:5ʺ,2ʺ′:5ʺ′,2ʺʺ:5ʺʺ,2ʺʺ′-sexithiophene (P6T) were investigated for their co-evaporated and laminated thin films. In the former film, the blue fluorescence of the BP1T donor was thoroughly quenched by 0.06 mol% of the P6T acceptor based on the Förster energy transfer, resulting in white luminescence. From time-decay measurements of the donor fluorescence, the Förster radius was determined to be 3.4-3.9 nm. The laminated films were fabricated by successive depositions of BP1T, MgF2 and P6T in which the thickness of the MgF2 spacer was varied. The energy transfer from the BP1T to P6T layer was controlled by the MgF2 thickness.