We observed the Raman spectra of carriers, positive polarons and bipolarons, generated in a poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) film by FeCl3 vapor doping. Electrical conductivity and Raman measurements indicate that the dominant carriers in the conducting state were bipolarons. We identified positive polarons and bipolarons generated in an ionic-liquid-gated transistor (ILGT) fabricated with PBTTT-C14 as an active semiconductor and an ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [BMIM][TFSI] as a gate dielectric using Raman spectroscopy. The relationship between the source−drain current (ID) at a constant source−drain voltage (VD) and the gate voltage (VG) was measured. ID increased above −VG = 1.1 V and showed a maximum at −VG = 2.0 V. Positive polarons were formed at the initial stage of electrochemical doping (−VG = 0.8 V). As ID increased, positive bipolarons were formed. Above VG = −2.0 V, bipolarons were dominant. The charge density (n), the doping level (x), and the mobility of the bipolarons were calculated from the electrochemical measurements. The highest mobility (μ) of bipolarons was 0.72 cm2 V−1 s−1 at x = 110 mol%/repeating unit (−VG = 2.0 V), whereas the highest μ of polarons was 4.6 × 10−4 cm2 V−1 s−1 at x = 10 mol%.

We studied the carriers generated in regioregular poly(3-hexylthiophene) (P3HT) upon FeCl3 vapor and solution doping using visible/near-infrared (VIS/NIR) absorption, infrared (IR), and Raman spectroscopy. Upon doping with an FeCl3 solution in air, the main carriers that were generated were positive polarons. Upon doping with FeCl3 vapor, positive polarons also formed initially, but at higher doping levels, positive bipolarons formed with the concomitant disappearance of the positive polarons. The Raman and IR spectra of the positive bipolarons and the positive polarons were obtained. Raman spectroscopy is very useful for characterizing positive polarons and bipolarons. The Raman results indicated that the positive bipolarons were converted to polarons upon heating to 85 °C, indicating that the positive bipolarons formed a metastable state. The temporal changes in the electrical conductivity of a P3HT film upon doping with FeCl3 vapor were measured. The conductivity reached a maximum and then decreased by 2 orders of magnitude. This result suggests that the mobility of the polarons is approximately 100 times as high as that of the bipolarons.

The changes in intensity of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-11 were measured as a function of a cyclic external electric field of 1.4 MV/cm. The infrared bands assigned to the NH stretching, amide I, NH-vicinal, and CO-vicinal CH2 scissoring modes showed butterfly-shaped hysteresis loops that are characteristic of ferroelectrics; however, the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes are small and showed no butterfly-shaped hysteresis loops. These results indicate that the amide groups are inverted, while the methylene groups are not inverted under the external electric field. We propose a new molecular mechanism that explains the ferroelectric properties of nylon-11. Only the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds; these two states form a nearly double-minimum potential.

We have observed the Raman spectrum of an operating phosphorescent organic light-emitting diode fabricated with bis(2-(2′-benzothienyl)-pyridinato-N,C3′)iridium(acetylacetonate) (Btp2Ir(acac)) as a phosphorescent emitter with excitation at 532 nm. All of the observed bands have been attributed to Btp2Ir(acac) because of the resonance Raman effect. We have determined the temperature of the emitting layer containing Btp2Ir(acac) from the ratio of the anti-Stokes to Stokes Raman bands of the 283-cm−1 vibrational mode attributed to Btp2Ir(acac). The temperature of the emitting layer is estimated to be 89 ± 8 °C at a current density of 400 A/m2.We have measured the temperature of the emitting layer containing phosphor Btp2Ir(acac) in a operating phosphorescent light-emitting diode from resonance Raman spectroscopy.

Voltage-induced infrared absorption spectra from the top- and bottom-contact field-effect transistors fabricated with n-Si, SiO2, and poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) as a gate electrode, an insulator, and a semiconductor, respectively, have been measured in a transmission–absorption configuration by the FT-IR difference-spectrum method. The observed voltage-induced infrared bands have been attributed to positive carriers (polarons) injected into the MEH-PPV layer by the application of minus gate bias. The cross section of the doping-induced 1510-cm−1 band has been obtained to be 7.7 × 10−17 cm2 for the MEH-PPV films doped electrochemically with ClO4−. The observed intensities of the voltage-induced 1510-cm−1 band have been converted to carrier sheet densities by this cross section. The carrier sheet density induced by field effect shows a saturation effect as the gate voltage increases for the top- and bottom-contact devices. The number of carriers injected in the top-contact device is larger than that in the bottom-contact device.