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Abstract The orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution‐processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large‐area oriented p‐type SCP films. Here, UFTM can be used to prepare high‐performance n‐type SCP films of P(NDI2OD‐T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD‐T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2OD‐T2) floating films are uniaxially aligned with edge‐on orientation, whereas the spin‐coated films are isotropic with face‐on orientation. Notably, the floating films of P(NDI2OD‐T2) prepared with solvent blending have higher electron mobility with ambipolar‐like device characteristics and high threshold voltage (VTH) of ≈25 V. Finally, using the one‐step immersion process, the introduction of an interlayer of hexa(ethylene glycol)‐dithiol between the source/drain contacts and P(NDI2OD‐T2) film results in a drastic improvement in device, giving unipolar n‐channel transistor characteristics with a VTH of ≈0 V, on/off ratio of >105, and mobility reliability factor of almost 100%.

Herein, the hole transport in a quinoxaline– thiophene based conjugated polymer (PTQ1) mixed with an insulating polystyrene (PS) was studied by macroscopic and local current density voltage characteristics measurements. As a result, we found that the hole conductivity in PTQ1:PS blends increases as the weight ratio of PTQ1 is reduced down to 20 wt%. This is mainly ascribed to increases in mobility because the charge carrier density would be constant in the insulating PS matrix. With decreasing PTQ1 weight ratio in the blends, the absorption bandwidth of PTQ1 and additional emission due to excimer decreased, suggesting that interchain interactions are suppressed. By measuring the temperature-dependent conductivity, we also found that the activation energy for the hole conductivity is smaller in PTQ1:PS blends than in PTQ1 neat films. These findings suggest that trap sites decrease because of the suppressed interaction between PTQ1 chains in blend films. We also measured conductive atomic force microscope images of the blend films to clarify the local conductive property. For PTQ1 neat films, a low conductive image was observed over the entire film. For PTQ1:PS blends, on the other hand, many highly conductive spots were locally found. We thus conclude that the dilution of PTQ1 chains in the PS matrix leads to a lower formation of trap sites, resulting in more conductive transport in PTQ1:PS blends than in PTQ1 neat films. [ABSTRACT FROM AUTHOR]

The charge-transport characteristics of phase-separated blend films of poly(3-hexylthiophene) (P3HT; electron donor) and poly[2,7-(9,9-didodecylfluorene)-alt-5,5-(4',7'-bis(2-thienyl)-2',1',3'-benzothiadiazole)] (PF12TBT; electron acceptor) were visualized by conductive atomic force microscopy (C-AFM). The C-AFM hole-current images clearly showed two phases: an electrically conductive region assigned to the P3HT-rich donor domain and a nonconductive region assigned to the PF12TBT-rich acceptor domain. The hole current in the conductive region was small compared with that of a neat P3HT film with similar thickness, indicating that the P3HT-rich domain contained a large fraction of PF12TBT as a minor component. Thermal annealing initially increased the hole current throughout the P3HT-rich domain because of reorganization of the P3HT chains from their as-cast configurations. Further annealing increased the hole current mainly in the middle of the P3HT-rich domain, but it decreased the hole current in the boundary areas close to the PF12TBT-rich domain owing to the presence of an intermixed region with a gradient of the P3HT/PF12TBT composition ratio. After annealing at temperatures above the glass-transition point of PF12TBT, the widths of the intermixed regions decreased to ∼30 nm as phase separation proceeded with decomposition of the intermixed region. Such variations in the intermixed region, which were electrically resolved by the C-AFM, accounted for the temperature dependence of the photovoltaic properties of P3HT/PF12TBT blend solar cells. [ABSTRACT FROM AUTHOR]

We have fabricated ternary blend solar cells by incorporating a wide-bandgap molecule, tris[4-(5-dicyanomethylidenemethyl-2-thienyl)phenyl]amine (TDCV-TPA), into a binary blend of a low-bandgap polymer, poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (PTQ1), and afullerene derivative (PCBM) in order to enhance exciton generation and hence charge generation in the visible region. The ternary blend solar cells exhibited large external quantum efficiency (EQE) in the visible range as well as in the near-IR range. As a result, the short-circuit current density (JSC) was improved by more than 20%. [ABSTRACT FROM AUTHOR]

Intermoiety electronic interactions in the singlet and triplet excimer states of triply bridged 3.3.n(3,6,9)carbazolophanes (3.3.nCz, n3−6) were studied by emission and transient absorption measurements. In these 3.3.nCz molecules, the dihedral angle and the separation distance rbetween fully overlapped two carbazole rings change systematically from nearly parallel (n3, r3.35 Å) to oblique (n6, r4.03 Å). In rigid glass at 77 K, 3.3.nCz (n3, 4) (r< 4 Å) exhibited red-shifted and structureless excimer fluorescence and phosphorescence while 3.3.nCz (n5, 6) (r> 4 Å) exhibited monomer-like vibrational fluorescence and phosphorescence. In solution at 130 K, all 3.3.nCz molecules exhibited an excimeric fluorescence band while 3.3.5Cz still exhibited monomer-like phosphorescence. Transient absorption spectra measured at 294 K exhibited local excitation and charge-transfer bands for all 3.3.nCz molecules in the excited singlet and triplet states, suggesting that not only singlet but also triplet excimers of carbazole are formed at room temperature. Furthermore, the singlet−triplet energy gap decreased with the decrease in n, suggesting that electrons are effectively delocalized over the two carbazole moieties. These findings showed that both singlet and triplet excimers of carbazole are formed with a separation distance shorter than about 4 Å and are most stable in the parallel-sandwich structure and that the configurational mixing between exciton resonance and charge resonance states plays an essential role in the formation of singlet and triplet excimers of carbazole. [ABSTRACT FROM AUTHOR]

The incorporation of silicon phthalocyanine bis(trihexylsilyloxide) (SiPc) dye in hybrid solar cells based on blends of poly(3-hexylthiophene) and zinc oxide (P3HT/ZnO) increased the short-circuit current density by 65% as compared to that of P3HT/ZnO binary hybrid solar cell and hence improved the overall power conversion efficiency under AM1.5G illumination. Furthermore, the enhanced external quantum efficiency peaks demonstrated that SiPc molecules serve as a lightharvesting photosensitizer as well as an energy funnel for P3HT excitons at the P3HT/ZnO interface. [ABSTRACT FROM AUTHOR]

CH3NH3PbI3 thin films were formed with various deposition rates of PbI2 first layer using a sequential vacuum evaporation method (SVE) to understand the formation behavior. Under low PbI2 deposition rates with 1 and 3 Å s−1, the thin films did not form the hybrid perovskite structure. Over the 6 Å s−1 deposition rate, the perovskite structure is observed with the remaining PbI2 and an intermediate phase together. In the 10 Å s−1, the intermediate phase is increased, and the CH3NH2 molecular defect is observed. The hybrid perovskite thin film formed by SVE is confirmed with tiny grains and CH3NH2-incorporated intermediate state. [ABSTRACT FROM AUTHOR]